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Webb and Hubble telescopes affirm Universe’s expansion rate, puzzle persists

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A face-on spiral galaxy with four spiral arms that curve outward in a counterclockwise direction. The spiral arms are filled with young, blue stars and peppered with purplish star-forming regions that appear as small blobs. The middle of the galaxy is much brighter and more yellowish, and has a distinct narrow linear bar angled from 11 o’clock to 5 o’clock. Dozens of red background galaxies are scattered across the image. The background of space is black.

Webb and Hubble telescopes affirm Universe’s expansion rate, puzzle persists

Webb measurements shed new light on a decade-long mystery.

The rate at which the Universe is expanding, known as the Hubble constant, is one of the fundamental parameters for understanding the evolution and ultimate fate of the cosmos. However, a persistent difference, called the Hubble Tension, is seen between the value of the constant measured with a wide range of independent distance indicators and its value predicted from the afterglow of the Big Bang. The NASA/ESA/CSA James Webb Space Telescope has confirmed that the Hubble Space Telescope’s keen eye was right all along, erasing any lingering doubt about Hubble’s measurements.

One of the scientific justifications for building the NASA/ESA Hubble Space Telescope was to use its observing power to provide an exact value for the expansion rate of the Universe. Prior to Hubble’s launch in 1990, observations from ground-based telescopes yielded huge uncertainties. Depending on the values deduced for the expansion rate, the Universe could be anywhere between 10 and 20 billion years old. Over the past 34 years Hubble has shrunk this measurement to an accuracy of less than one percent, splitting the difference with an age value of 13.8 billion years. This has been accomplished by refining the so-called ‘cosmic distance ladder’ by measuring important milepost markers known as Cepheid variable stars.

A horizontal two-panel image of pixelated, black-and-white star fields. The left image is labelled Webb Near-IR and has a few dozen points of light of varying brightness. At the centre of the image, one bright point is circled. The right image is labelled Hubble Near-IR and has more indistinct, blurry patches whose overall brightness is similar to the more defined regions in the left image. At the centre, a light grey pixel is circled.
At the centre of these side-by-side images is a special class of star used as a milepost marker for measuring the Universe’s rate of expansion — a Cepheid variable star. The two images are very pixelated because each is a very zoomed-in view of a distant galaxy. Each of the pixels represents one or more stars. The image from the James Webb Space Telescope is significantly sharper at near-infrared wavelengths than Hubble (which is primarily a visible-ultraviolet light telescope). By reducing the clutter with Webb’s crisper vision, the Cepheid stands out more clearly, eliminating any potential confusion. Webb was used to look at a sample of Cepheids and confirmed the accuracy of the previous Hubble observations that are fundamental to precisely measuring the Universe’s expansion rate and age.
Credit: NASA, ESA, CSA, STScI, A. Riess (JHU/STScI)

However, the Hubble value does not agree with other measurements that imply that the Universe was expanding faster after the Big Bang. These observations were made by the ESA Planck satellite’s mapping of the cosmic microwave background radiation — a blueprint for how the Universe would evolve structure after it cooled down from the Big Bang.

The simple solution to the dilemma would be to say that maybe the Hubble observations are wrong, as a rresult of some inaccuracy creeping into its measurements of the deep-space yardsticks. Then along came the James Webb Space Telescope, enabling astronomers to crosscheck Hubble’s results. Webb’s infrared views of Cepheids agreed with Hubble’s optical-light data. Webb confirmed that the Hubble telescope’s keen eye was right all along, erasing any lingering doubt about Hubble’s measurements.

The bottom line is that the so-called Hubble Tension between what happens in the nearby Universe compared to the early Universe’s expansion remains a nagging puzzle for cosmologists. There may be something woven into the fabric of space that we don’t yet understand.

Does resolving this discrepancy require new physics? Or is it a result of measurement errors between the two different methods used to determine the rate of expansion of space?

Hubble and Webb have now tag-teamed to produce definitive measurements, furthering the case that something else — not measurement errors — is influencing the expansion rate.

“With measurement errors negated, what remains is the real and exciting possibility that we have misunderstood the Universe,” 

said Adam Riess, a physicist at Johns Hopkins University in Baltimore. Riess holds a Nobel Prize for co-discovering the fact that the Universe’s expansion is accelerating, owing to a mysterious phenomenon now called ‘dark energy’.

As a crosscheck, an initial Webb observation in 2023 confirmed that Hubble’s measurements of the expanding Universe were accurate. However, hoping to relieve the Hubble Tension, some scientists speculated that unseen errors in the measurement may grow and become visible as we look deeper into the Universe. In particular, stellar crowding could affect brightness measurements of more distant stars in a systematic way.

The SH0ES (Supernova H0 for the Equation of State of Dark Energy) team, led by Riess, obtained additional observations with Webb of objects that are critical cosmic milepost markers, known as Cepheid variable stars, which can now be correlated with the Hubble data.

“We’ve now spanned the whole range of what Hubble observed, and we can rule out a measurement error as the cause of the Hubble Tension with very high confidence,” Riess said.

The team’s first few Webb observations in 2023 were successful in showing Hubble was on the right track in firmly establishing the fidelity of the first rungs of the so-called cosmic distance ladder.

Astronomers use various methods to measure relative distances in the Universe, depending upon the object being observed. Collectively these techniques are known as the cosmic distance ladder — each rung or measurement technique relies upon the previous step for calibration.

But some astronomers suggested that, moving outward along the ‘second rung’, the cosmic distance ladder might get shaky if the Cepheid measurements become less accurate with distance. Such inaccuracies could occur because the light of a Cepheid could blend with that of an adjacent star — an effect that could become more pronounced with distance as stars crowd together on the sky and become harder to distinguish from one another.

The observational challenge is that past Hubble images of these more distant Cepheid variables look more huddled and overlapping with neighbouring stars at ever greater distances between us and their host galaxies, requiring careful accounting for this effect. Intervening dust further complicates the certainty of the measurements in visible light. Webb slices through the dust and naturally isolates the Cepheids from neighbouring stars because its vision is sharper than Hubble’s at infrared wavelengths.

“Combining Webb and Hubble gives us the best of both worlds. We find that the Hubble measurements remain reliable as we climb farther along the cosmic distance ladder,” said Riess.

A face-on spiral galaxy with four spiral arms that curve outward in a counterclockwise direction. The spiral arms are filled with young, blue stars and peppered with purplish star-forming regions that appear as small blobs. The middle of the galaxy is much brighter and more yellowish, and has a distinct narrow linear bar angled from 11 o’clock to 5 o’clock. Dozens of red background galaxies are scattered across the image. The background of space is black.
This image of NGC 5468, a galaxy located about 130 million light-years from Earth, combines data from the Hubble and James Webb space telescopes. This is the most distant galaxy in which Hubble has identified Cepheid variable stars. These are important milepost markers for measuring the expansion rate of the Universe. The distance calculated from Cepheids has been cross-correlated with a Type Ia supernova in the galaxy. Type Ia supernovae are so bright they are used to measure cosmic distances far beyond the range of the Cepheids, extending measurements of the Universe’s expansion rate deeper into space.
Credit: NASA, ESA, CSA, STScI, A. Riess (JHU/STScI)

The new Webb observations include five host galaxies of eight Type Ia supernovae containing a total of 1000 Cepheids, and reach out to the farthest galaxy where Cepheids have been well measured — NGC 5468, at a distance of 130 million light-years. 

“This spans the full range where we made measurements with Hubble. So, we’ve gone to the end of the second rung of the cosmic distance ladder,”

said co-author Gagandeep Anand of the Space Telescope Science Institute in Baltimore, which operates the Webb and Hubble Telescopes for NASA.

Together, Hubble’s and Webb’s confirmation of the Hubble Tension sets up other observatories to possibly settle the mystery, including NASA’s upcoming Nancy Grace Roman Space Telescope and ESA’s recently launched Euclid mission.

At present it’s as though the distance ladder observed by Hubble and Webb has firmly set an anchor point on one shoreline of a river, and the afterglow of the Big Bang observed by Planck from the beginning of the Universe is set firmly on the other side. How the Universe’s expansion was changing in the billions of years between these two endpoints has yet to be directly observed.

“We need to find out if we are missing something on how to connect the beginning of the Universe and the present day,” said Riess.

These findings were published in the 6 February 2024 issue of The Astrophysical Journal Letters.

 

Press release from ESA Webb.

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Webb peers into the tendrils of NGC 604

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Webb NGC 604 At the centre of the image is a nebula on the black background of space. The nebula is composed of clumpy, red, filamentary clouds. At the centre-right of the red clouds is a large cavernous bubble, and at the centre of the bubble there is an opaque blue glow with speckles of stars. At the edges of the bubble, the dust is white. There are several other smaller cavernous bubbles at the top of the nebula. There are also some smaller, red stars and a few disc-shaped galaxies scattered about the image.

Two new images from the NASA/ESA/CSA James Webb Space Telescope’s NIRCam (Near-Infrared Camera) and MIRI (Mid-Infrared Instrument) showcase the star-forming region NGC 604, located in the Triangulum Galaxy (M33), 2.73 million light-years away from Earth. In these images, cavernous bubbles and stretched-out filaments of gas etch a more detailed and complete tapestry of star birth than seen in the past.

Sheltered among NGC 604’s dusty envelopes of gas are more than 200 of the hottest, most massive kinds of stars, all in the early stages of their lives. These types of stars are known as B-types and O-types, the latter of which can be more than 100 times the mass of our own Sun. It’s quite rare to find this concentration of them in the nearby Universe. In fact, there’s no similar region within our own Milky Way galaxy.

This concentration of massive stars, combined with its relatively close distance, means NGC 604 gives astronomers an opportunity to study these objects at a fascinating time early in their life.

At the centre of the image is a nebula on the black background of space. The nebula is composed of clumpy, red, filamentary clouds. At the centre-right of the red clouds is a large cavernous bubble, and at the centre of the bubble there is an opaque blue glow with speckles of stars. At the edges of the bubble, the dust is white. There are several other smaller cavernous bubbles at the top of the nebula. There are also some smaller, red stars and a few disc-shaped galaxies scattered about the image.
This image from the NASA/ESA/CSA James Webb Space Telescope’s NIRCam (Near-Infrared Camera) of star-forming region NGC 604 shows how stellar winds from bright, hot young stars carve out cavities in surrounding gas and dust.
The bright orange streaks in this image signify the presence of carbon-based molecules known as polycyclic aromatic hydrocarbons, or PAHs. As you travel further from the immediate cavities of dust where the star is forming, the deeper red signifies molecular hydrogen. This cooler gas is a prime environment for star formation. Ionised hydrogen from ultraviolet radiation appears as a white and blue ghostly glow.
NGC 604 is located in the Triangulum Galaxy (M33), 2.73 million light-years away from Earth. It provides an opportunity for astronomers to study a high concentration of very young, massive stars in a nearby region.
Credit: NASA, ESA, CSA, STScI

In Webb’s near-infrared NIRCam image, the most noticeable features are tendrils and clumps of emission that appear bright red, extending out from areas that look like clearings, or large bubbles in the nebula. Stellar winds from the brightest and hottest young stars have carved out these cavities, while ultraviolet radiation ionises the surrounding gas. This ionised hydrogen appears as a white and blue ghostly glow.

The bright orange streaks in the Webb near-infrared image signify the presence of carbon-based molecules known as polycyclic aromatic hydrocarbons, or PAHs. This material plays an important role in the interstellar medium and the formation of stars and planets, but its origin is a mystery. As you travel further from the immediate clearings of dust, the deeper red signifies molecular hydrogen. This cooler gas is a prime environment for star formation.

Webb’s exquisite resolution also provides insights into features that previously appeared unrelated to the main cloud. For example, in Webb’s image, there are two bright, young stars carving out holes in dust above the central nebula, connected through diffuse red gas. In visible-light imaging from the NASA/ESA Hubble Space Telescope, these appeared as separate splotches.

At the centre of the image is a nebula on the black background of space. The nebula is composed of wispy filaments of light blue clouds. At the centre-right of the blue clouds is a large cavernous bubble. The bottom left edge of this cavernous bubble is filled with hues of pink and white gas. Hundreds of dim stars fill the area surrounding the nebula.
This image from the NASA/ESA/CSA James Webb Space Telescope’s MIRI (Mid-Infrared Instrument) of star-forming region NGC 604 shows how large clouds of cooler gas and dust glow at mid-infrared wavelengths. This region is a hotbed of star formation and home to more than 200 of the hottest, most massive kinds of stars, all in the early stages of their lives.
In the MIRI view of NGC 604, there are noticeably fewer stars than Webb’s NIRCam image. This is because hot stars emit much less light at these wavelengths. Some of the stars seen in this image are red supergiants — stars that are cool but very large, hundreds of times the diameter of our Sun. The blue tendrils of material signify the presence of polycyclic aromatic hydrocarbons, or PAHs.
Credit: NASA, ESA, CSA, STScI

Webb’s view in mid-infrared wavelengths also illustrates a new perspective on the diverse and dynamic activity of this region. In the MIRI view of NGC 604, there are noticeably fewer stars. This is because hot stars emit much less light at these wavelengths, while the larger clouds of cooler gas and dust glow. Some of the stars seen in this image from the surrounding galaxy are red supergiants — stars that are cool but very large, hundreds of times the diameter of our Sun. Additionally, some of the background galaxies that appeared in the NIRCam image also fade. In the MIRI image, the blue tendrils of material signify the presence of PAHs.

NGC 604 is estimated to be around 3.5 million years old. The cloud of glowing gases extends to some 1300 light-years across.

At the centre of the image is a nebula on the black background of space. The nebula is composed of clumpy, red, filamentary clouds. At the centre-right of the red clouds is a large cavernous bubble, and at the centre of the bubble there is an opaque blue glow with speckles of stars. At the edges of the bubble, the dust is white. There are several other smaller cavernous bubbles at the top of the nebula. There are also some smaller, red stars and a few disc-shaped galaxies scattered about the image.
This image from the NASA/ESA/CSA James Webb Space Telescope’s NIRCam (Near-Infrared Camera) of star-forming region NGC 604 shows how stellar winds from bright, hot young stars carve out cavities in surrounding gas and dust.
The bright orange streaks in this image signify the presence of carbon-based molecules known as polycyclic aromatic hydrocarbons, or PAHs. As you travel further from the immediate cavities of dust where the star is forming, the deeper red signifies molecular hydrogen. This cooler gas is a prime environment for star formation. Ionised hydrogen from ultraviolet radiation appears as a white and blue ghostly glow.
NGC 604 is located in the Triangulum Galaxy (M33), 2.73 million light-years away from Earth. It provides an opportunity for astronomers to study a high concentration of very young, massive stars in a nearby region.
Credit: NASA, ESA, CSA, STScI

Press release from ESA Webb.

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Webb unlocks secrets of GN-z11, one of the most distant galaxies ever seen

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A rectangular image shows thousands of galaxies of various shapes and colours on the black background of space. The pullout features a galaxy labelled GN-z11, seen as a fuzzy yellow dot. Above it is another galaxy, seen as a fuzzy red oval. To the left of the small box, a scale bar is labelled 60 arcseconds. It extends about one tenth of the way across the image. Below the image, a list of NIRCam filters show what colours were used to make the image. Filters shown in blue are F090W, F115W, and F150W. Filters shown in green are F200W, F277W, and F335M. Filters shown in red are F356W, F410M, and F444W.

Webb unlocks secrets of GN-z11, one of the most distant galaxies ever seen

Looking deep into space and time, two teams using the NASA/ESA/CSA James Webb Space Telescope have studied the exceptionally luminous galaxy GN-z11, which existed when our 13.8 billion-year-old Universe was only about 430 million years old.

A rectangular image with thousands of galaxies of various shapes and colours on the black background of space. Some are noticeably spirals, either face-on or edge-on, while others are blobby ellipticals. Many are too small to discern any structure. One prominent foreground star at top centre features Webb’s signature eight-point diffraction spikes.
This image from Webb’s NIRCam (Near-Infrared Camera) instrument shows a portion of the GOODS-North field of galaxies.
Credit: NASA, ESA, CSA, B. Robertson (UC Santa Cruz), B. Johnson (CfA), S. Tacchella (Cambridge), M. Rieke (University of Arizona), D. Eisenstein (CfA)

Delivering on its promise to transform our understanding of the early Universe, the James Webb Space Telescope is probing galaxies near the dawn of time. One of these is the exceptionally luminous galaxy GN-z11, which existed when the Universe was just a tiny fraction of its current age. Initially detected with the NASA/ESA Hubble Space Telescope, it is one of the youngest and most distant galaxies ever observed, and it is also one of the most enigmatic. Why is it so bright? Webb appears to have found the answer.

A team studying GN-z11 with Webb found the first clear evidence that the galaxy is hosting a central, supermassive black hole that is rapidly accreting matter. Their finding makes this the most distant active supermassive black hole spotted to date.

“We found extremely dense gas that is common in the vicinity of supermassive black holes accreting gas,” explained principal investigator Roberto Maiolino of the Cavendish Laboratory and the Kavli Institute of Cosmology at the University of Cambridge in the United Kingdom. “These were the first clear signatures that GN-z11 is hosting a black hole that is gobbling matter.”

Using Webb, the team also found indications of ionised chemical elements typically observed near accreting supermassive black holes. Additionally, they discovered that the galaxy is expelling a very powerful wind. Such high-velocity winds are typically driven by processes associated with vigorously accreting supermassive black holes.

“Webb’s NIRCam (Near-Infrared Camera) has revealed an extended component, tracing the host galaxy, and a central, compact source whose colours are consistent with those of an accretion disc surrounding a black hole,” said investigator Hannah Übler, also of the Cavendish Laboratory and the Kavli Institute.

Together, this evidence shows that GN-z11 hosts a two-million-solar-mass, supermassive black hole in a very active phase of consuming matter, which is why it’s so luminous.

A second team, also led by Maiolino, used Webb’s NIRSpec (Near-Infrared Spectrograph) to find a gaseous clump of helium in the halo surrounding GN-z11.

“The fact that we don’t see anything else beyond helium suggests that this clump must be fairly pristine,” said Maiolino. “This is something that was expected by theory and simulations in the vicinity of particularly massive galaxies from these epochs — that there should be pockets of pristine gas surviving in the halo, and these may collapse and form Population III star clusters.”

A graphic labelled Galaxy GN-z11, Pristine Gas Clump Near GN-z11. The graphic is divided into two sections. The top half of the graphic features a rectangular image of a field of galaxies with two pullouts, the second of them labelled Helium Two Detected. The bottom half shows a single line graph.
This two-part graphic shows evidence of a gaseous clump of helium in the halo surrounding the galaxy GN-z11. In the top portion, at the far right, a small box identifies GN-z11 in a field of galaxies. The middle box shows a zoomed-in image of the galaxy. The box at the far left displays a map of the helium gas in the halo of GN-z11, including a clump that does not appear in the infrared colours shown in the middle panel. In the lower half of the graphic, a spectrum shows the distinct ‘fingerprint’ of helium in the halo. The full spectrum shows no evidence of other elements and so suggests that the helium clump must be fairly pristine, made almost entirely of hydrogen and helium gas left over from the Big Bang, without much contamination from heavier elements produced by stars. Theory and simulations in the vicinity of particularly massive galaxies from these epochs predict that there should be pockets of pristine gas surviving in the halo, and these may collapse and form Population III star clusters.
Credit: NASA, ESA, CSA, Ralf Crawford (STScI)

Finding the so far unseen Population III stars [1] — the first generation of stars formed almost entirely from hydrogen and helium — is one of the most important goals of modern astrophysics. These stars are expected to be very massive, very luminous, and very hot. Their signature would be the presence of ionised helium and the absence of chemical elements heavier than helium.

The formation of the first stars and galaxies marks a fundamental shift in cosmic history, during which the Universe evolved from a dark and relatively simple state into the highly structured and complex environment we see today.

In future Webb observations, Maiolino, Übler, and their team will explore GN-z11 in greater depth, and they hope to strengthen the case for the Population III stars that may be forming in its halo.

The research on the pristine gas clump in GN-z11’s halo has been accepted for publication in Astronomy & Astrophysics. The results of the study of GN-z11’s black hole were published in the journal Nature on 17 January 2024. The data was obtained as part of the JWST Advanced Deep Extragalactic Survey (JADES), a joint project between the NIRCam and NIRSpec teams.

A rectangular image with thousands of galaxies of various shapes and colours on the black background of space. Some are noticeably spirals, either face-on or edge-on, while others are blobby ellipticals. Many are too small to discern any structure. One prominent foreground star at top centre features Webb’s signature eight-point diffraction spikes. At lower right, a small region is highlighted with a white box. Vertical lines extend upward like a cone to the bottom corners of a larger box at upper right, showing a zoomed-in version of the highlighted area. The pullout features a galaxy labelled GN-z11, seen as a fuzzy yellow dot. Above it is another galaxy, seen as a fuzzy red oval.
This image from Webb’s NIRCam (Near-Infrared Camera) instrument shows a portion of the GOODS-North field of galaxies. At the lower right, a pullout highlights the galaxy GN-z11, which is seen at a time just 430 million years after the Big Bang. The image reveals an extended component, tracing the GN-z11 host galaxy, and a central, compact source whose colours are consistent with those of an accretion disc surrounding a black hole.
Credit: NASA, ESA, CSA, B. Robertson (UC Santa Cruz), B. Johnson (CfA), S. Tacchella (Cambridge), M. Rieke (University of Arizona), D. Eisenstein (CfA)

Notes

[1] The name Population III arose because astronomers had already classified the stars of the Milky Way as Population I (stars like the Sun, which are rich in heavier elements) and Population II (older stars with a low heavy-element content, found in the Milky Way bulge and halo, and in globular star clusters).

A rectangular image shows thousands of galaxies of various shapes and colours on the black background of space. The pullout features a galaxy labelled GN-z11, seen as a fuzzy yellow dot. Above it is another galaxy, seen as a fuzzy red oval. To the left of the small box, a scale bar is labelled 60 arcseconds. It extends about one tenth of the way across the image. Below the image, a list of NIRCam filters show what colours were used to make the image. Filters shown in blue are F090W, F115W, and F150W. Filters shown in green are F200W, F277W, and F335M. Filters shown in red are F356W, F410M, and F444W.
This image of the GOODS-North field, captured by Webb’s Near-Infrared Camera (NIRCam), shows compass arrows, a scale bar, and a colour key for reference.
The north and east compass arrows show the orientation of the image on the sky. Note that the relationship between north and east on the sky (as seen from below) is flipped relative to direction arrows on a map of the ground (as seen from above).
The scale bar is labelled in angular distance on the sky, where one arcsecond is one 3600th of a degree. The scale bar is 60 arcseconds long.
This image shows invisible near-infrared wavelengths of light that have been translated into visible-light colours. The colour key shows which NIRCam filters were used when collecting the light. The colour of each filter name is the visible light colour used to represent the infrared light that passes through that filter.
Credit: NASA, ESA, CSA, B. Robertson (UC Santa Cruz), B. Johnson (CfA), S. Tacchella (Cambridge), M. Rieke (University of Arizona), D. Eisenstein (CfA)

Press release from ESA Webb.

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Webb finds dwarf galaxies reionised the Universe

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small galaxies reionised the Universe A crowded galaxy field on a black background, with one large star dominating the image just right of center. Three areas are concentrated with larger white hazy blobs on the left, lower right, and upper right above the single star. Scattered between these areas are many smaller sources of light; some also have a hazy white glow, while many other are red or orange.

Webb finds dwarf galaxies reionised the Universe

Using the unprecedented capabilities of the NASA/ESA/CSA James Webb Space Telescope, an international team of scientists have obtained the first spectroscopic observations of the faintest galaxies during the first billion years of the Universe. These findings help answer a longstanding question for astronomers: what sources caused the reionisation of the Universe? These news results have effectively demonstrated that small dwarf galaxies are the likely producers of prodigious amounts of energetic radiation.

Researching the evolution of the early Universe is an important aspect of modern astronomy. Much remains to be understood about the time in the Universe’s early history known as the era of reionisation [1]. It was a period of darkness without any stars or galaxies, filled with a dense fog of hydrogen gas, until the first stars ionised the gas around them and light began to travel through. Astronomers have spent decades trying to identify the sources that emitted radiation powerful enough to gradually clear away this hydrogen fog that blanketed the early Universe.

The Ultradeep NIRSpec and NIRCam ObserVations before the Epoch of Reionization (UNCOVER) programme (#2561) consists of both imaging and spectroscopic observations of the lensing cluster Abell 2744. An international team of astronomers used gravitational lensing by this target, also known as Pandora’s Cluster, to investigate the sources of the Universe’s period of reionisation. Gravitational lensing [2] magnifies and distorts the appearance of distant galaxies, so they look very different from those in the foreground. The galaxy cluster ‘lens’ is so massive that it warps the fabric of space itself, so much so that light from distant galaxies that passes through the warped space also takes on a warped appearance. The magnification effect allowed the team to study very distant sources of light beyond Abell 2744, revealing eight extremely faint galaxies that would otherwise be undetectable, even to Webb.

The team found that these faint galaxies are immense producers of ionising radiation, at levels that are four times larger than what was previously assumed. This means that most of the photons that reionised the Universe likely came from these dwarf galaxies.

“This discovery unveils the crucial role played by ultra-faint galaxies in the early Universe’s evolution,” said team member Iryna Chemerynska of the Institut d’Astrophysique de Paris in France. “They produce ionising photons that transform neutral hydrogen into ionised plasma during cosmic reionisation. It highlights the importance of understanding low-mass galaxies in shaping the Universe’s history.”

“These cosmic powerhouses collectively emit more than enough energy to get the job done,” added team leader Hakim Atek, Institut d’Astrophysique de Paris, CNRS, Sorbonne Université, France, and lead author of the paper describing this result. “Despite their tiny size, these low-mass galaxies are prolific producers of energetic radiation, and their abundance during this period is so substantial that their collective influence can transform the entire state of the Universe.”

To arrive at this conclusion, the team first combined ultra-deep Webb imaging data with ancillary imaging of Abell 2744 from the NASA/ESA Hubble Space Telescope in order to select extremely faint galaxy candidates in the epoch of reionisation. This was followed by spectroscopy with Webb’s Near-InfraRed Spectrograph (NIRSpec). The instrument’s Multi-Shutter Assembly was used to obtain multi-object spectroscopy of these faint galaxies. This is the first time scientists have robustly measured the number density of these faint galaxies, and they have successfully confirmed that they are the most abundant population during the epoch of reionisation. This also marks the first time that the ionising power of these galaxies has been measured, enabling the astronomers to determine that they are producing sufficient energetic radiation to ionise the early Universe.

“The incredible sensitivity of NIRSpec combined with the gravitational amplification provided by Abell 2744 enabled us to identify and study these galaxies from the first billion years of the Universe in detail, despite their being over 100 times fainter than our own Milky Way,” continued Atek.

In an upcoming Webb observing programme, termed GLIMPSE, scientists will obtain the deepest observations ever on the sky. By targeting another galaxy cluster, named Abell S1063, even fainter galaxies during the epoch of reionisation will be identified in order to verify whether this population is representative of the large-scale distribution of galaxies. As these new results are based on observations obtained in one field, the team notes that the ionising properties of faint galaxies can appear differently if they reside in over-dense regions. Additional observations in an independent field will therefore provide further insights to help verify these conclusions. The GLIMPSE observations will also help astronomers probe the period known as Cosmic Dawn, when the Universe was only a few million years old, to develop our understanding of the emergence of the first galaxies.

These results have been published today in the journal Nature.

small galaxies reionised the Universe A crowded galaxy field on a black background, with one large star dominating the image just right of center. Three areas are concentrated with larger white hazy blobs on the left, lower right, and upper right above the single star. Scattered between these areas are many smaller sources of light; some also have a hazy white glow, while many other are red or orange.
Webb finds dwarf galaxies reionised the Universe. Astronomers estimate 50 000 sources of near-infrared light are represented in this image from the NASA/ESA/CSA James Webb Space Telescope. Their light has travelled through various distances to reach the telescope’s detectors, representing the vastness of space in a single image. A foreground star in our own galaxy, to the right of the image centre, displays Webb’s distinctive diffraction spikes. Bright white sources surrounded by a hazy glow are the galaxies of Pandora’s Cluster, a conglomeration of already-massive clusters of galaxies coming together to form a mega cluster. The concentration of mass is so great that the fabric of spacetime is warped by gravity, creating a natural, super-magnifying glass called a ‘gravitational lens’ that astronomers can use to see very distant sources of light beyond the cluster that would otherwise be undetectable, even to Webb.
These lensed sources appear red in the image, and often as elongated arcs distorted by the gravitational lens. Many of these are galaxies from the early Universe, with their contents magnified and stretched out for astronomers to study.
Credit: NASA, ESA, CSA, I. Labbe (Swinburne University of Technology), R. Bezanson (University of Pittsburgh), A. Pagan (STScI)

Notes

[1] Theory predicts that the first stars were 30 to 300 times as massive as our Sun and millions of times as bright, burning for only a few million years before exploding as supernovae. The energetic ultraviolet light from these first stars was capable of splitting hydrogen atoms back into electrons and protons (or ionising them). This era, from the end of the dark ages to when the Universe was around a billion years old, is known as the epoch of reionisation. This is the period when most of the neutral hydrogen was reionised by the increasing radiation from the first massive stars. Reionisation is an important phenomenon in our Universe’s history as it presents one of the few means by which we can (indirectly) study these earliest stars and galaxies.

[2] Gravitational lensing occurs when a massive celestial body — such as a galaxy cluster — causes a sufficient curvature of spacetime for the path of light around it to be visibly bent, as if by a lens. The body causing the light to curve is accordingly called a gravitational lens. According to Einstein’s general theory of relativity, time and space are fused together in a quantity known as spacetime. Within this theory, massive objects cause spacetime to curve, and gravity is simply the curvature of spacetime. As light travels through spacetime, the theory predicts that the path taken by the light will also be curved by an object’s mass. Gravitational lensing is a dramatic and observable example of Einstein’s theory in action. Extremely massive celestial bodies such as galaxy clusters cause spacetime to be significantly curved. In other words, they act as gravitational lenses. When light from a more distant light source passes by a gravitational lens, the path of the light is curved, and a distorted image of the distant object results.

 

Press release from ESA Webb.

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Webb finds evidence for a neutron star at heart of SN 1987A, a young supernova remnant

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neutron star SN 1987A A graphic with three images, each of a glowing, ring-shaped nebula. The left side shows a large, full-colour image of the nebula and its surroundings, labelled “NIRCam”. A rectangle in the centre of the nebula is highlighted and two images of this area are pulled out to the right. Both are shown in shades of orange. The top one is labelled “MIRI MRS Argon II” and the bottom one “NIRSpec IFU Argon VI.

Webb finds evidence for a neutron star at heart of SN 1987A, a young supernova remnant

The NASA/ESA/CSA James Webb Space Telescope has found the best evidence yet for emission from a neutron star at the site of SN 1987A, a recently observed supernova. The supernova, known as SN 1987A, occurred 160 000 light-years from Earth in the Large Magellanic Cloud. SN 1987A was a type II supernova [1] that was observed on Earth in 1987, the first supernova that was visible to the naked eye since 1604 — before the advent of telescopes. It has thus offered the astronomical community a rare opportunity to study the evolution of a supernova and what was left behind, from the very beginning. SN 1987A was a core-collapse supernova, meaning the compacted remains at its core are expected to have formed either a neutron star or a black hole. Evidence for such a compact object has long been sought, and whilst indirect evidence for the presence of a neutron star has previously been found, this is the first time that the effects of high energy emission from the young neutron star has been detected.

Astronomy typically involves the study of processes that take place over at least tens of thousands of years: far longer than all of human recorded history. Supernovae — the explosive final death throes of some massive stars — blast out within hours, and the brightness of the explosion peaks within a few months. The remains of the exploding star will continue to evolve at a rapid rate over the following decades. Thus, supernovae offer a very rare opportunity for astronomers to study a key astronomical process in real time. The supernova SN 1987A was first observed on Earth in February 1987 and its brightness peaked in May that year (although its distance from Earth means that the supernova event actually took place about 160 000 years before). It was the first supernova that could be seen with the naked eye since Kepler’s Supernova was observed in 1604.

About two hours prior to the visible observation of SN 1987A, three observatories around the world observed a burst of neutrinos lasting only a few seconds [2]. Shortly after, visible light from SN 1987A was observed. The two different observations were linked to the same supernova event, and provided important evidence to inform the theory of how core-collapse supernovae take place. This theory included the supposition that this type of supernova would form a neutron star or a black hole. Astronomers have searched for evidence for one or other of these compact objects [3] at the centre of the expanding remnant material ever since. Indirect evidence for the presence of a neutron star at the centre of the remnant has been found in the past few years, and observations of much older supernova remnants — such as the Crab Nebula — confirm that neutron stars are found in many supernova remnants. However, no direct evidence of a neutron star in the aftermath of SN 1987A (or any other such recent supernova explosion) had been observed, until now.

Claes Fransson of Stockholm University, and the lead author on this study, explains: “From theoretical models of SN 1987A, the 10-second burst of neutrinos observed just before the supernova implied that a neutron star or black hole was formed in the explosion. But we have not observed any compelling signature of such a newborn object from any supernova explosion. With JWST, we have now found direct evidence for emission triggered by the newborn compact object, most likely a neutron star.”

Webb began science observations in July 2022, and the Webb observations behind this work were taken on 16 July, making the SN 1987A remnant one the first objects observed by Webb. The team used the Medium Resolution Spectrograph (MRS) mode of Webb’s MIRI instrument, which the members of the same team helped to develop. The MRS is a type of instrument known as an Integral Field Unit (IFU). IFUs are fascinating instruments that are able to image an object and take a spectrum of it at the same time. An IFU forms a spectrum at each pixel, allowing observers to see spectroscopic differences across the object. Analysis of the Doppler shift [4] of each spectrum also permits the evaluation of the velocity at each position. Spectral analysis of the results showed a strong signal due to ionised argon from the centre of the ejected material that surrounds the original site of SN 1987A. Subsequent observations using the other IFU, NIRSpec (Near Infrared Spectrograph) at shorter wavelengths, the team found even more heavily ionised [5] chemical species, particularly five times ionised argon (meaning argon atoms that have lost five of their 18 electrons). Such ions require highly energetic photons to form, and those photons have to come from somewhere.

“To create these ions that we observed in the ejecta, it was clear that there had to be a source of high-energy radiation in the centre of the SN 1987A remnant,” Fransson said. “In the paper we discuss different possibilities, finding that only a few scenarios are likely, and all of these involve a newly born neutron star.” 

More observations are planned this year, with Webb and ground-based telescopes. The research team hopes ongoing study will provide more clarity about exactly what is happening in the heart of the SN 1987A remnant. These observations will hopefully stimulate the development of more detailed models [6], ultimately enabling astronomers to better understand not just SN 1987A, but all core-collapse supernovae.

A graphic with three images, each of a glowing, ring-shaped nebula. The left side shows a large, full-colour image of the nebula and its surroundings, labelled “NIRCam”. A rectangle in the centre of the nebula is highlighted and two images of this area are pulled out to the right. Both are shown in shades of orange. The top one is labelled “MIRI MRS Argon II” and the bottom one “NIRSpec IFU Argon VI.
The NASA/ESA/CSA James Webb Space Telescope has observed the best evidence yet for emission from a neutron star at the site of 1987A, a well-known and recently-observed supernova. The supernova, known as SN 1987A, occurred 160 000 light-years from Earth in the Large Magellanic Cloud.
LEFT: Webb’s 2023 NIRCam (Near-Infrared Camera) image of SN 1987A that highlights the object’s central structure, expanding with several thousands km/s. The blue region is the densest part of the clumpy ejecta, containing heavy elements like carbon, oxygen, magnesium and iron, as well as dust. The bright ‘ring of pearls’ is the result of the collision of the ejecta with a ring of gas ejected about 20 000 years before the explosion. Now spots are found even exterior to the ring, with diffuse emission surrounding it. These are the locations of supernova shocks hitting more exterior material from the progenitor star. The outer ejecta is now illuminated by X-rays from the collision, while the inner ejecta is powered mainly by radioactivity and a putative compact object.
RIGHT: An international team of astronomers has now used two of Webb’s instruments to study the emissions from the core of SN 1987A. The top image features the data from Webb’s MRS (Medium Resolution Spectrograph) mode of the MIRI instrument (Mid-InfraRed Instrument). The bottom image depicts data from Webb’s NIRSpec (Near Infrared Spectrograph) at shorter wavelengths. Spectral analysis of the MIRI results showed a strong signal due to ionised argon from the centre of the ejected material that surrounds the original site of SN 1987A. The NIRSpec data found even more heavily ionised chemical species, particularly five times ionised argon (meaning argon atoms that have lost five of their 18 electrons). Weak lines of ionised sulphur were also detected with MIRI. This indicated to the science team that there is a source of high-energy radiation in the centre of the SN 1987A remnant, illuminating an almost point-like region in the centre. The most likely source is believed to be a newly born neutron star.
Credit: NASA, ESA, CSA, STScI, and C. Fransson (Stockholm University), M. Matsuura (Cardiff University), M. J. Barlow (University College London), P. J. Kavanagh (Maynooth University), J. Larsson (KTH Royal Institute of Technology)

Notes

[1] Type II supernovae are distinguishable from Type Ia supernovae by the presence of hydrogen in their spectra. They typically result from the core-collapse of a dying massive star with 8–25 times the mass of our Sun. Core-collapse supernovae derive their energy from gravitational potential energy and create and release far more neutrinos than the other mechanism that causes supernovae (nuclear runaway in certain binary star systems). About 99.6 % of the energy is released as neutrinos, while most the rest comes out as kinetic energy and only a tiny fraction as light. Still, they can be as bright as whole galaxy.

[2] Neutrinos are a chargeless type of subatomic particle. They are extremely low in mass (about 500 000 times less massive than an electron). They interact very weakly with other matter, making them extremely challenging to detect. They are produced in abundance in core-collapse supernovae, hence the association between the observed blast of neutrinos and SN 1987A.

[3] Compact objects in astronomy are extremely dense stellar remnants, including white dwarfs, neutron stars and black holes. The core of a neutron star is so dense that a single teaspoon of the neutron material there would weigh over three billion tons.

[4] The Doppler shift of light occurs when light is stretched or compressed, either due to the velocity of a light source relative to an observer, or due to the expansion or compression of spacetime itself. In this case, the light from the supernova is notably Doppler shifted by the very high velocities of the ejecta from the supernova explosion.

[5] Ionisation occurs when an atom or a molecule gains or loses electrons, giving it an overall electric charge. This typically happens as a result of either collisions with other particles, or the presence of so-called ionising radiation, such as X-rays and some ultraviolet radiation.

[6] Models are simplified theoretical representations of the behaviour of objects or systems, that allow scientists to predict and explain observations. They might be built on mathematical, chemical and physical principles. In astronomy, as with all sciences, both models and observations are used to develop and refine our understanding of how things work.

 

Press release from ESA Webb.

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Tridentinosaurus antiquus, the oldest fossil reptile from the Alps is, in part, an historical forgery

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Tridentinosaurus antiquus was discovered in the Italian alps in 1931 and was thought to be an important specimen for understanding early reptile evolution - but has now been found to be, in part a forgery. Its body outline, appearing dark against the surrounding rock, was initially interpreted as preserved soft tissues but is now known to be paint. Credits: Dr Valentina Rossi

Mystery solved: Tridentinosaurus antiquus, the oldest fossil reptile from the Alps is, in part, an historical forgery

Palaeontological analysis shows renowned fossil thought to show soft tissue preservation is in fact just paint

A 280-million-year-old fossil that has baffled researchers for decades has been shown to be, in part, a forgery following new examination of the remnants.

The discovery has led the team led by Dr Valentina Rossi of University College Cork, Ireland (UCC) to urge caution in how the fossil is used in future research.

Tridentinosaurus antiquus was discovered in the Italian alps in 1931 and was thought to be an important specimen for understanding early reptile evolution.

Its body outline, appearing dark against the surrounding rock, was initially interpreted as preserved soft tissues. This led to its classification as a member of the reptile group Protorosauria.

Tridentinosaurus antiquus was discovered in the Italian alps in 1931 and was thought to be an important specimen for understanding early reptile evolution - but has now been found to be, in part a forgery. Its body outline, appearing dark against the surrounding rock, was initially interpreted as preserved soft tissues but is now known to be paint. Credits: Dr Valentina Rossi
Tridentinosaurus antiquus was discovered in the Italian alps in 1931 and was thought to be an important specimen for understanding early reptile evolution – but has now been found to be, in part a forgery. Its body outline, appearing dark against the surrounding rock, was initially interpreted as preserved soft tissues but is now known to be paint. Credits: Dr Valentina Rossi

However, this new research, published in the scientific journal Palaeontology, reveals that the fossil renowned for its remarkable preservation is mostly just black paint on a carved lizard-shaped rock surface.

The purported fossilised skin had been celebrated in articles and books but never studied in detail. The somewhat strange preservation of the fossil had left many experts uncertain about what group of reptiles this strange lizard-like animal belonged to and more generally its geological history.

Dr Rossi, of UCC’s School of Biological, Earth and Environmental Sciences, said:

“Fossil soft tissues are rare, but when found in a fossil they can reveal important biological information, for instance, the external colouration, internal anatomy and physiology.”

“The answer to all our questions was right in front of us, we had to study this fossil specimen in details to reveal its secrets – even those that perhaps we did not want to know”.

Dr Valentina Rossi with an image of Tridentinosaurus antiquus. The fossil, discovered in the Italian alps in 1931, was thought to be an important specimen for understanding early reptile evolution - but has now been found to be, in part a forgery. Its body outline, appearing dark against the surrounding rock, was initially interpreted as preserved soft tissues but is now known to be paint. Credits: Zixiao Yang
Dr Valentina Rossi with an image of Tridentinosaurus antiquus. The fossil, discovered in the Italian alps in 1931, was thought to be an important specimen for understanding early reptile evolution – but has now been found to be, in part a forgery. Its body outline, appearing dark against the surrounding rock, was initially interpreted as preserved soft tissues but is now known to be paint. Credits: Zixiao Yang

The microscopic analysis showed that the texture and composition of the material did not match that of genuine fossilised soft tissues.

Preliminary investigation using UV photography revealed that the entirety of the specimen was treated with some sort of coating material. Coating fossils with varnishes and/or lacquers was the norm in the past and sometimes is still necessary to preserve a fossil specimen in museum cabinets and exhibits. The team was hoping that beneath the coating layer, the original soft tissues were still in good condition to extract meaningful palaeobiological information.

The findings indicate that the body outline of Tridentinosaurus antiquus was artificially created, likely to enhance the appearance of the fossil. This deception misled previous researchers, and now caution is being urged when using this specimen in future studies.

The team behind this research includes contributors based in Italy at the University of Padua, Museum of Nature South Tyrol, and the Museo delle Scienze in Trento.

Co-author Prof Evelyn Kustatscher, coordinator of the project “Living with the supervolcano”, funded by the Autonomous Province of Bolzano said:

“The peculiar preservation of Tridentinosaurus had puzzled experts for decades. Now, it all makes sense. What it was described as carbonized skin, is just paint”.

However all not all is lost, and the fossil is not a complete fake. The bones of the hindlimbs, in particular, the femurs seem genuine, although poorly preserved. Moreover, the new analyses have shown the presence of tiny bony scales called osteoderms – like the scales of crocodiles – on what perhaps was the back of the animal.

This study is an example of how modern analytical palaeontology and rigorous scientific methods can resolve an almost century-old palaeontological enigma.

Bibliographic information:

Forged soft tissues revealed in the oldest fossil reptile from the early Permian of the Alps, Palaeontology (16-Feb-2024), DOI: 10.1111/pala.12690

Press release from University College Cork

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The Complete Library of Charles Darwin revealed for the first time

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Oil painting by Victor Eustaphieff of Darwin in his study at Down House with one of his bookcases that made up his extensive personal library reflected in the mirror.Reproduced with kind permission by State Darwin Museum, Moscow

The Complete Library of Charles Darwin revealed for the first time

Charles Darwin – arguably the most influential man of science in history, accumulated a vast personal library throughout his working life. Until now, 85 per cent of its contents were unknown or unpublished.

Oil painting by Victor Eustaphieff of Darwin in his study at Down House with one of his bookcases that made up his extensive personal library reflected in the mirror.Reproduced with kind permission by State Darwin Museum, Moscow
Oil painting by Victor Eustaphieff of Darwin in his study at Down House with one of his bookcases that made up his extensive personal library reflected in the mirror.Reproduced with kind permission by State Darwin Museum, Moscow

This year, coinciding with Darwin’s 215th birthday, The Complete Work of Charles Darwin Online, the scholarly project helmed by Dr John van Wyhe at the National University of Singapore (NUS) Department of Biological Sciences, has released an online 300-page catalogue detailing Darwin’s complete personal library, with 7,400 titles across 13,000 volumes and items including books, pamphlets and journals. Previous lists only had 15 per cent of his whole collection. Darwin’s library has also been virtually re-assembled with 9,300 links to copies of the works freely available online.

“This unprecedentedly detailed view of Darwin’s complete library allows one to appreciate more than ever that he was not an isolated figure working alone but an expert of his time building on the sophisticated science and studies and other knowledge of thousands of people. Indeed, the size and range of works in the library makes manifest the extraordinary extent of Darwin’s research into the work of others,” said Dr van Wyhe.

Discovering Darwin’s complete library

After his death in 1882, much of Darwin’s library was preserved and catalogued, but many other items were dispersed or lost, and details of the vast majority of the contents have never been published until now. For many years, scholars have referred to Darwin’s library as containing 1,480 books, based on those that survive in the two main collections, the University of Cambridge and Down House.

Two historic images, a photograph (left) and an etching (right), are here combined to show the bookcases in his study.Reproduced with kind permission by Darwin Online
Two historic images, a photograph (left) and an etching (right), are here combined to show the bookcases in his study.Reproduced with kind permission by Darwin Online

Over 18 years the Darwin Online project has identified thousands of Darwin’s obscure references in his own catalogues and lists of items such as pamphlets and journals that were originally in his library. Each reference required its own detective story to discover the publications that Darwin had hurriedly recorded. In addition, missing details such as author, date or the source of clippings in thousands of records from older catalogues have been identified for the first time.

A major source of information that helped to reveal the original contents is the 426-page handwritten “Catalogue of the Library of Charles Darwin”, compiled from 1875. Painstaking comparison of its abbreviated entries revealed 440 unknown titles that were originally in the library. An inventory of his home made after his death recorded 2,065 bound books and an unknown number of unbound volumes and pamphlets. In the drawing room, 133 titles and 289 volumes of mostly unscientific literature were recorded. Amazingly, the legacy duty valuer estimated that the “Scientific Library that is books relating to Science” was worth only 30 pounds and 12 shillings [about £2,000 today] Indeed, all the books were valued at only66 pounds and 10 shillings [about £4,400 today]. Today any book that belonged to Darwin is worth a great deal to collectors.

Other sources of information that helped to build Darwin’s complete library were lists of pamphlets, Darwin’s reading notebooks, Emma Darwin’s diaries, the Catalogue of books given to the Cambridge Botany School in 1908 and the 30 volumes of the Darwin Correspondence. Items that still exist but were never included in the lists of Darwin’s library include his unbound materials at Cambridge University Library, books now in other institutional collections, private collections and books sold at auctions over the past 130 years. Combining these and many other sources of evidence allowed Darwin’s library to be reconstructed.

For example, Darwin’s copy of an 1826 article by the ornithologist John James Audubon: ‘Account of the habits of the Turkey Buzzard (Vultura aura), particularly with the view of exploding the opinion generally entertained of its extraordinary power of smelling’ was sold in 1975. Darwin had investigated this point during the voyage of the Beagle and recorded reading a critic of Audubon in the lost Galapagos notebook. In 2019, a copy of Elizabeth Gaskell’s 1880 novel Wives and daughters appeared at auction. A note in it records: “This book was a great favourite of Charles Darwin’s and the last book to be read aloud to him.”

Understanding Darwin’s library

Most of the works in Darwin’s library are, unsurprisingly, on scientific subjects, especially biology and geology. Yet, the library also included works on farming, animal breeding and behaviour, geographical distribution, philosophy, psychology, religion, and other topics that interested Darwin, such as art, history, travel and language. Most of the works are in English, but almost half are in other languages, especially German, French and Italian as well as Dutch, Danish, Spanish, Swedish and Latin.

The frontispiece of the Principles of Geology, volume 1 by Charles Lyell, a book from which Darwin drew inspiration to explain how species change over time
The frontispiece of the Principles of Geology, volume 1 by Charles Lyell, a book from which Darwin drew inspiration to explain how species change over time

Some of the hundreds of books not previously known to be in Darwin’s library include Sun Pictures, a 1872 coffee table book showcasing photographs of artworks. Another book that the we did not know that the Darwins purchased was a copy of the popular science book on gorillas that was all the rage just after Origin of species was published: Paul Du Chaillu’s Explorations and adventures in equatorial Africa. Of the thousands of shorter items were also found in Darwin’s library, such as an issue of a German scientific periodical sent to him in 1877 that contained the first published photographs of bacteria and another article amusingly entitled The hateful or Colorado grasshopper. In his complete library, Darwin’s eclectic sources are there for all to see.

An issue of a German scientific periodical was sent to Darwin in 1877 that contained the first published photographs of bacteria
An issue of a German scientific periodical was sent to Darwin in 1877 that contained the first published photographs of bacteria

Click to view The Complete Library of Charles Darwin: http://darwin-online.org.uk/Complete_Library_of_Charles_Darwin.html

Click to view Introduction to the Library by John van Wyhe

 

Press release from the National University of Singapore.

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Webb depicts staggering structure in 19 nearby spiral galaxies

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19 Nineteen Webb images of face-on spiral galaxies are combined in a mosaic, some within squares, and others horizontal or vertical rectangles. Galaxies’ spiral arms appear in shades of orange, and many of their centres have light blue hazes.

Webb depicts staggering structure in 19 nearby spiral galaxies

A new treasure trove of images from the NASA/ESA/CSA James Webb Space Telescope showcases near- and mid-infrared portraits of 19 face-on spiral galaxies. This new set of exquisite images show stars, gas, and dust on the smallest scales ever observed beyond our own galaxy. Teams of researchers are studying these images to uncover the origins of these intricate structures. The research community’s collective analysis will ultimately inform theorists’ simulations, and advance our understanding of star formation and the evolution of spiral galaxies.

19 Nineteen Webb images of face-on spiral galaxies are combined in a mosaic, some within squares, and others horizontal or vertical rectangles. Galaxies’ spiral arms appear in shades of orange, and many of their centres have light blue hazes.
This collection of 19 face-on spiral galaxies from the NASA/ESA/CSA James Webb Space Telescope in near- and mid-infrared light is at once overwhelming and awe-inspiring. Webb’s NIRCam (Near-Infrared Camera) captured millions of stars in these images. Older stars appear blue here, and are clustered at the galaxies’ cores. The telescope’s MIRI (Mid-Infrared Instrument) observations highlight glowing dust, showing where it exists around and between stars – appearing in shades of red and orange. Stars that haven’t yet fully formed and are encased in gas and dust appear bright red.
Webb’s high-resolution images are the first to show large, spherical shells in the gas and dust in such exquisite detail. These holes may have been created by stars that exploded and carved out giant regions in the interstellar material.
Another eye-catching detail? Several galaxy cores are awash in pink-and-red diffraction spikes. These are clear signs that these galaxies may have central active supermassive black holes or central star clusters.
These spiral galaxies are Webb’s first big batch of contributions to the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) program, that includes existing images and data from the NASA/ESA Hubble Space Telescope, the Very Large Telescope’s Multi-Unit Spectroscopic Explorer (MUSE), and the Atacama Large Millimetre/submillimetre Array (ALMA). With Webb’s images, researchers can now examine these galaxies in ultraviolet, visible, infrared, and radio light.
Credit: NASA, ESA, CSA, STScI, J. Lee (STScI), T. Williams (Oxford), PHANGS Team, E. Wheatley (STScI)

If you follow each of the galaxy’s clearly defined arms, which are brimming with stars, to their centres, there may be old star clusters and – sometimes – active supermassive black holes. Only the James Webb Space Telescope can deliver highly detailed scenes of nearby galaxies in a combination of near- and mid-infrared light – and a set of these images were publicly released today.

These Webb images are part of a large, long-standing project, the Physics at High Angular resolution in Nearby GalaxieS (PHANGS) programme, which is supported by more than 150 astronomers worldwide. Before Webb took these images, PHANGS was already brimming with data from the NASA/ESA Hubble Space Telescope, the Very Large Telescope’s Multi-Unit Spectroscopic Explorer, and the Atacama Large Millimetre/submillimetre Array, including observations in ultraviolet, visible, and radio light. Webb’s near- and mid-infrared contributions have provided several new puzzle pieces.

Webb’s NIRCam (Near-Infrared Camera) captured millions of stars in these images, which sparkle in blue tones. Some stars are spread throughout the spiral arms, but others are clumped tightly together in star clusters.

The telescope’s MIRI (Mid-Infrared Instrument) data highlights glowing dust, showing us where it exists behind, around, and between stars. It also spotlights stars that haven’t yet fully formed – they are still encased in the gas and dust that feed their growth, like bright red seeds at the tips of dusty peaks.

To the amazement of astronomers, Webb’s images also show large, spherical shells in the gas and dust that may have been created by exploded stars.

The spiral arms’ extended regions of gas also reveal details in red and orange. Astronomers study the spacing of these features to learn how a galaxy distributes its gas and dust. These structures will provide key insights about how galaxies build, maintain, and shut off star formation.

Evidence shows that galaxies grow from inside out – star formation begins at galaxies’ cores and spreads along their arms, spiralling away from the centre. The farther a star is from the galaxy’s core, the more likely it is to be younger. In contrast, the areas near the cores that look lit by a blue spotlight are populations of older stars. The galaxy cores that are awash in pink-and-red diffraction spikes may indicate an active supermassive black hole or saturation from bright star clusters toward the centre.

There are many avenues of research that scientists can begin to pursue with the combined PHANGS data, but the unprecedented number of stars Webb resolved are a great place to begin. In addition to immediately releasing these images, the PHANGS team has also released the largest catalogue to date of roughly 100 000 star clusters.

 

Press release from ESA Webb.

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Hubble finds water vapour in the atmosphere of GJ 9827d, a small exoplanet

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Exoplanet GJ 9827d (artist’s concept) water vapour atmosphere Occupying the upper half of this illustration is a foreground exoplanet, partly in shadow, with subtle blue and white atmospheric features along the crescent closest to the star. The planet appears above a red dwarf star, which is represented by a smaller reddish-white, mottled globe at the bottom left. Two other planets in this system are to the left and right of the red dwarf star. The planet to the star’s left is tiny, appears fully lit, and is closest to the star. The second planet is slightly larger, but appears farther away, about midway between the star and the foreground exoplanet. It is in shadow, with only the crescent facing the star bathed in light.

Hubble finds water vapour in the atmosphere of GJ 9827d, a small exoplanet

Astronomers using the NASA/ESA Hubble Space Telescope observed the smallest exoplanet where water vapour has been detected in its atmosphere, GJ 9827d. At only approximately twice Earth’s diameter, the planet GJ 9827d could be an example of potential planets with water-rich atmospheres elsewhere in our galaxy.

“This would be the first time that we can directly show through an atmospheric detection that these planets with water-rich atmospheres can actually exist around other stars,” said team member Björn Benneke of the Université de Montréal. “This is an important step toward determining the prevalence and diversity of atmospheres on rocky planets.”

However, it remains too early to tell whether Hubble spectroscopically measured a small amount of water vapour in a puffy hydrogen-rich atmosphere, or if the planet’s atmosphere is mostly made of water, left behind after a primaeval hydrogen/helium atmosphere evapourated under stellar radiation.

“Our observing programme was designed specifically with the goal of not only detecting the molecules in the planet’s atmosphere, but of actually looking specifically for water vapour. Either result would be exciting, whether water vapour is dominant or just a tiny species in a hydrogen-dominant atmosphere,” said the science paper’s lead author, Pierre-Alexis Roy of the Université de Montréal.

“Until now, we had not been able to directly detect the atmosphere of such a small planet. And we’re slowly getting into this regime now,” added Benneke. “At some point, as we study smaller planets, there must be a transition where there’s no more hydrogen on these small worlds, and they have atmospheres more like Venus (which is dominated by carbon dioxide).”

Because the planet is as hot as Venus at roughly 425 degrees Celsius, it definitely would be an inhospitable, steamy world if the atmosphere were predominantly water vapour.

At present the team is left with two possibilities. The planet is still clinging to a hydrogen-rich envelope laced with water, making it a mini-Neptune. Alternatively, it could be a warmer version of Jupiter’s moon Europa, which has twice as much water as Earth beneath its crust. 

“The planet GJ 9827d could be half water, half rock. And there would be a lot of water vapour on top of some smaller rocky body,” said Benneke.

If the planet has a residual water-rich atmosphere, then it must have formed farther away from its host star, where the temperature is cold and water is available in the form of ice, than its present location. In this scenario, the planet would have then migrated closer to the star and received more radiation. The hydrogen was then heated and escaped, or is still in the process of escaping, the planet’s weak gravity. The alternative theory is that the planet formed close to the hot star, with a trace of water in its atmosphere.

The Hubble programme observed the planet during 11 transits — events in which the planet crossed in front of its star — that were spaced out over three years. During transits, starlight is filtered through the planet’s atmosphere and carries the spectral fingerprint of water molecules. If there are clouds on the planet, they are low enough in the atmosphere that they don’t completely hide Hubble’s view of the atmosphere, and Hubble is able to probe water vapour above the clouds.

Hubble’s discovery opens the door to studying the planet in more detail. It’s a good target for the NASA/ESA/CSA James Webb Space Telescope to do infrared spectroscopy to look for other atmospheric molecules.

GJ 9827d was discovered by NASA’s Kepler Space Telescope in 2017. It completes an orbit around a red dwarf star every 6.2 days. The star, GJ 9827, lies 97 light-years from Earth in the constellation Pisces.

Occupying the upper half of this illustration is a foreground exoplanet, partly in shadow, with subtle blue and white atmospheric features along the crescent closest to the star. The planet appears above a red dwarf star, which is represented by a smaller reddish-white, mottled globe at the bottom left. Two other planets in this system are to the left and right of the red dwarf star. The planet to the star’s left is tiny, appears fully lit, and is closest to the star. The second planet is slightly larger, but appears farther away, about midway between the star and the foreground exoplanet. It is in shadow, with only the crescent facing the star bathed in light.
This is an artist’s conception of the exoplanet GJ 9827d, the smallest exoplanet where water vapour has been detected in its atmosphere. The planet could be an example of potential planets with water-rich atmospheres elsewhere in our galaxy. It is a rocky world, only about twice Earth’s diameter. It orbits the red dwarf star GJ 9827. Two inner planets in the system are on the left. The background stars are plotted as they would be seen to the unaided eye looking back toward our Sun, which itself is too faint to be seen. The blue star at upper right is Regulus, the yellow star at bottom centre is Denebola, and the blue star at bottom right is Spica. The constellation Leo is on the left, and Virgo is on the right. Both constellations are distorted from our Earth-bound view from 97 light-years away.
Credit: NASA, ESA, Leah Hustak and Ralf Crawford (STScI)

Press release from ESA Hubble.

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Astronomy

Galaxy mergers are the solution to the early Universe mystery concerning the Lyman-α emission

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Galaxy mergers Lyman-α emission A graphic with three images. The top image, labelled “CEERS survey”, shows many square images of stars and galaxies, stitched together according to their locations in the sky. One square is highlighted, and a cutout on the bottom left shows it enlarged, labelled “Webb/ NIRCam”. A tiny spot is shown zoomed-in to the right, labelled “EGSY8p7” with a scale marker of “0.5 arcsec”. Here it can be seen that the spot is three neighbouring galaxies, appearing as coloured blobs with bright, distinct cores.

Webb reveals that galaxy mergers are the solution to the early Universe mystery concerning the Lyman-α emission

One of the key missions of the NASA/ESA/CSA James Webb Space Telescope is to probe the early Universe. Now, the unmatched resolution and sensitivity of Webb’s NIRCam instrument have revealed, for the first time, what lies in the local environment of galaxies in the very early Universe. This has solved one of the most puzzling mysteries in astronomy — why astronomers detect light from hydrogen atoms which should have been entirely blocked by the pristine gas that formed after the Big-Bang. These new Webb observations have found small, faint objects surrounding the very galaxies that show the ‘inexplicable’ hydrogen emission. In conjunction with state-of-the-art simulations of galaxies in the early Universe, the observations have shown that the chaotic merging of these neighbouring galaxies is the source of this hydrogen emission.

A close-in view of three neighbouring galaxies. They appear as coloured blobs with bright, distinct cores. The image is mostly black, with a few unrelated galaxies visible nearby.
This image shows the galaxy EGSY8p7, a bright galaxy in the early Universe where light emission is seen from, among other things, excited hydrogen atoms — Lyman-α emission. Webb’s high sensitivity picks out this distant galaxy along with its two companion galaxies, where previous observations saw only one larger galaxy in its place.
This discovery of a cluster of interacting galaxies sheds light on the mystery of why the hydrogen emission from EGSY8p7, shrouded in neutral gas formed after the Big Bang, should be visible at all. Astronomers have concluded that the intense star-forming activity within these interacting galaxies energised hydrogen emission and cleared swathes of gas from their surroundings, allowing the unexpected hydrogen emission to escape.
This close-up view of EGSY8p7 has been newly processed, making use of NIRCam data captured with seven different near-infrared filters.
Credit: ESA/Webb, NASA & CSA, C. Witten, M. Zamani (ESA/Webb)

Light travels at a finite speed (300 000 kilometres per second), which means that the further away a galaxy is, the longer it has taken the light from it to reach our Solar System. As a result, not only do observations of the most distant galaxies probe the far reaches of the Universe, but they also allow us to study the Universe as it was in the past. In order to study the very early Universe, astronomers require exceptionally powerful telescopes that are capable of observing very distant — and therefore very faint — galaxies. One of Webb’s key capabilities is its ability to observe those very distant galaxies, and hence to probe the early history of the Universe. An international team of astronomers have put Webb’s amazing capacity to excellent use in solving a long-standing mystery in astronomy.

The very earliest galaxies were sites of vigorous and active star formation, and as such were rich sources of a type of light emitted by hydrogen atoms called Lyman-α emission [1]. However, during the epoch of reionisation [2] an immense amount of neutral hydrogen gas surrounded these areas of active star formation (also known as stellar nurseries). Furthermore, the space between galaxies was filled by more of this neutral gas than is the case today. The gas can very effectively absorb and scatter this kind of hydrogen emission [3], so astronomers have long predicted that the abundant Lyman-α emission released in the very early Universe should not be observable today. This theory has not always stood up to scrutiny, however, as examples of very early hydrogen emission have previously been observed by astronomers. This has presented a mystery: how is it that this hydrogen emission — that should have long since been absorbed or scattered — is being observed? Researcher at the University of Cambridge and principal investigator on the new study Callum Witten elaborates:

“One of the most puzzling issues that previous observations presented was the detection of light from hydrogen atoms in the very early Universe, which should have been entirely blocked by the pristine neutral gas that was formed after the Big-Bang. Many hypotheses have previously been suggested to explain the great escape of this ‘inexplicable’ emission.”

A graphic with three images. The top image, labelled “CEERS survey”, shows many square images of stars and galaxies, stitched together according to their locations in the sky. One square is highlighted, and a cutout on the bottom left shows it enlarged, labelled “Webb/ NIRCam”. A tiny spot is shown zoomed-in to the right, labelled “EGSY8p7” with a scale marker of “0.5 arcsec”. Here it can be seen that the spot is three neighbouring galaxies, appearing as coloured blobs with bright, distinct cores.
This image shows the galaxy EGSY8p7, a bright galaxy in the early Universe where light emission is seen from, among other things, excited hydrogen atoms — Lyman-α emission. The galaxy was identified in a field of young galaxies studied by Webb in the CEERS survey. In the bottom two panels, Webb’s high sensitivity picks out this distant galaxy along with its two companion galaxies, where previous observations saw only one larger galaxy in its place.
This discovery of a cluster of interacting galaxies sheds light on the mystery of why the hydrogen emission from EGSY8p7, shrouded in neutral gas formed after the Big Bang, should be visible at all. Astronomers have concluded that the intense star-forming activity within these interacting galaxies energised hydrogen emission and cleared swathes of gas from their surroundings, allowing the unexpected hydrogen emission to escape.
This graphic is assembled from multiple images captured by Webb’s NIRCam instrument as part of the CEERS survey. The close-up view of EGSY8p7 was newly processed for this image, making use of NIRCam data captured with seven different near-infrared filters.
Credit: ESA/Webb, NASA & CSA, S. Finkelstein (UT Austin), M. Bagley (UT Austin), R. Larson (UT Austin), A. Pagan (STScI), C. Witten, M. Zamani (ESA/Webb)

The team’s breakthrough came thanks to Webb’s extraordinary combination of angular resolution and sensitivity. The observations with Webb’s NIRCam instrument were able to resolve smaller, fainter galaxies that surround the bright galaxies from which the ‘inexplicable’ hydrogen emission had been detected. In other words, the surroundings of these galaxies appear to be a much busier place than we previously thought, filled with small, faint galaxies. Crucially, these smaller galaxies were interacting and merging with one another, and Webb has revealed that galaxy mergers play an important role in explaining the mystery emission from the earliest galaxies. Sergio Martin-Alvarez, team member from Stanford University, adds:

“Where Hubble was seeing only a large galaxy, Webb sees a cluster of smaller interacting galaxies, and this revelation has had a huge impact on our understanding of the unexpected hydrogen emission from some of the first galaxies.”

The team then used state-of-the-art computer simulations to explore the physical processes that might explain their results. They found that the rapid build-up of stellar mass through galaxy mergers both drove strong hydrogen emission and facilitated the escape of that radiation via channels cleared of the abundant neutral gas. So the high merger rate of the previously unobserved smaller galaxies presented a compelling solution to the long-standing puzzle of the ‘inexplicable’ early hydrogen emission.

The team are planning follow up observations with galaxies at various stages of merging, in order to continue to develop their understanding of how the hydrogen emission is ejected from these changing systems. Ultimately, this will enable them to improve our understanding of galaxy evolution.

These findings have been published today in Nature Astronomy.

Notes

[1] Lyman-α emission is light emitted at a wavelength of 121.567 nanometres when the electron in an excited hydrogen atom drops from an excited state in the n = 2 orbital down to its ground state n = 1 (the lowest energy state the atom can have). Quantum physics dictates that electrons can only exist in very specific energy states, and this means that certain energy transitions — such as when the electron in a hydrogen atom drops from orbital n = 2 to n = 1 — can be identified by the wavelength of the light emitted during that transition. Lyman-α emission is important in many branches of astronomy, partly because hydrogen is so abundant in the Universe, and also because hydrogen is typically excited by energetic processes such as ongoing active star formation. Accordingly, Lyman-α emission can be used as a sign that active star formation is taking place.

[2] The epoch of reionisation was a very early stage in the Universe’s history that took place after recombination (the first stage following the Big Bang). During recombination, the Universe cooled enough that electrons and protons began to combine to form neutral hydrogen atoms. During reionisation, denser clouds of gas started to form, creating stars and eventually entire galaxies whose light gradually reionised the hydrogen gas..

[3] Neutral hydrogen gas is made of hydrogen atoms that are in the lowest energy state they can be, each with their electron in orbital n = 1. Since the light emitted by a hydrogen atom during Lyman-α emission carries the energy of the atomic transition from orbital n = 2 down to n = 1, when it strikes a neutral hydrogen atom, it has exactly the right amount of energy to ionise the atom and take its electron up to the next available orbital. This means the neutral gas absorbs and blocks Lyman-α emission very easily.

 

 

Press release from ESA Webb.

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