Webb discovers methane, carbon dioxide in atmosphere of K2-18 b
A new investigation by an international team of astronomers using data from the NASA/ESA/CSA James Webb Space Telescope into K2-18 b, an exoplanet 8.6 times as massive as Earth, has revealed the presence of carbon-bearing molecules including methane and carbon dioxide. The discovery adds to recent studies suggesting that K2-18 b could be a Hycean exoplanet, one which has the potential to possess a hydrogen-rich atmosphere and a water ocean-covered surface.
This artist’s concept shows what exoplanet K2-18 b could look like based on science data. K2-18 b, an exoplanet 8.6 times as massive as Earth, orbits the cool dwarf star K2-18 in the habitable zone and lies 120 light-years from Earth. A new investigation with the NASA/ESA/CSA James Webb Space Telescope into K2-18 b has revealed the presence of carbon-bearing molecules including methane and carbon dioxide. The abundance of methane and carbon dioxide, and shortage of ammonia, support the hypothesis that there may be an ocean underneath a hydrogen-rich atmosphere in K2-18 b. Credit: NASA, CSA, ESA, J. Olmstead (STScI), N. Madhusudhan (Cambridge University)
The first insight into the atmospheric properties of this habitable-zone exoplanet came from observations with the NASA/ESA Hubble Space Telescope, which prompted further studies that have since changed our understanding of the system.
K2-18 b orbits the cool dwarf star K2-18 in the habitable zone and lies 120 light-years from Earth in the constellation Leo. Exoplanets such as K2-18 b, which have sizes between those of Earth and Neptune, are unlike anything in our Solar System. This lack of equivalent nearby planets means that these ‘sub-Neptunes’ are poorly understood, and the nature of their atmospheres is a matter of active debate among astronomers. Exoplanets such as K2-18 b, which have sizes between those of Earth and Neptune, are unlike anything in our Solar System. This lack of analogous nearby planets means that these ‘sub-Neptunes’ are poorly understood and the nature of their atmospheres is a matter of active debate between astronomers. The suggestion that the sub-Neptune K2-18 b could be a Hycean exoplanet is intriguing, as some astronomers believe that these worlds are promising environments to search for evidence for life on exoplanets.
“Our findings underscore the importance of considering diverse habitable environments in the search for life elsewhere,”
explained Nikku Madhusudhan, an astronomer at the University of Cambridge and lead author of the paper announcing these results.
“Traditionally, the search for life on exoplanets has focused primarily on smaller rocky planets, but the larger Hycean worlds are significantly more conducive to atmospheric observations.“
The abundance of methane and carbon dioxide, and shortage of ammonia, support the hypothesis that there may be an ocean underneath a hydrogen-rich atmosphere on K2-18 b. These initial Webb observations also provided a possible detection of a molecule called dimethyl sulphide (DMS). On Earth, this is only produced by life. The bulk of the DMS in Earth’s atmosphere is emitted from phytoplankton in marine environments.
The inference of DMS is less robust and requires further validation.
“Upcoming Webb observations should be able to confirm if DMS is indeed present in the atmosphere of K2-18 b at significant levels,” explained Madhusudhan.
While K2-18 b lies in the habitable zone and is now known to harbour carbon-bearing molecules, this does not necessarily mean that the planet can support life. The planet’s large size — with a radius 2.6 times the radius of Earth — means that the planet’s interior likely contains a large mantle of high-pressure ice, like Neptune, but with a thinner hydrogen-rich atmosphere and an ocean surface. Hycean worlds are predicted to have oceans of water. However, it is also possible that the ocean is too hot to be habitable or be liquid.
“Although this kind of planet does not exist in our solar system, sub-Neptunes are the most common type of planet known so far in the galaxy,” explained team member Subhajit Sarkar of Cardiff University. “We have obtained the most detailed spectrum of a habitable-zone sub-Neptune to date, and this allowed us to work out the molecules that exist in its atmosphere.”
Characterising the atmospheres of exoplanets like K2-18 b — meaning identifying their gases and physical conditions — is a very active area in astronomy. However, these planets are outshone — literally — by the glare of their much larger parent stars, which makes exploring exoplanet atmospheres particularly challenging.
The team sidestepped this challenge by analysing light from K2-18 b’s parent star as it passed through the exoplanet’s atmosphere. K2-18 b is a transiting exoplanet, meaning that we can detect a drop in brightness as it passes across the face of its host star. This is how the exoplanet was first discovered. This means that during transits a tiny fraction of starlight will pass through the exoplanet’s atmosphere before reaching telescopes like Webb. The starlight’s passage through the exoplanet atmosphere leaves traces that astronomers can piece together to determine the gases of the exoplanet’s atmosphere.
“This result was only possible because of the extended wavelength range and unprecedented sensitivity of Webb, which enabled robust detection of spectral features with just two transits,” continued Madhusudhan. “For comparison, one transit observation with Webb provided comparable precision to eight observations with Hubble conducted over a few years and in a relatively narrow wavelength range.”
“These results are the product of just two observations of K2-18 b, with many more on the way,” explained team member Savvas Constantinou of the University of Cambridge. “This means our work here is but an early demonstration of what Webb can observe in habitable-zone exoplanets.”
The team now intends to conduct follow-up research with the telescope’s Mid-InfraRed Instrument (MIRI) spectrograph that they hope will further validate their findings and provide new insights into the environmental conditions on K2-18 b.
“Our ultimate goal is the identification of life on a habitable exoplanet, which would transform our understanding of our place in the Universe,” concluded Madhusudhan. “Our findings are a promising step towards a deeper understanding of Hycean worlds in this quest.”
Spectrum of K2-18 b, obtained with Webb’s NIRISS (Near-Infrared Imager and Slitless Spectrograph) and NIRSpec (Near-Infrared Spectrograph), displays an abundance of methane and carbon dioxide in the exoplanet’s atmosphere, as well as a possible detection of a molecule called dimethyl sulfide (DMS). The detection of methane and carbon dioxide, and shortage of ammonia, are consistent with the presence of an ocean underneath a hydrogen-rich atmosphere in K2-18 b. K2-18 b, 8.6 times as massive as Earth, orbits the cool dwarf star K2-18 in the habitable zone and lies 120 light-years from Earth. Credit: NASA, CSA, ESA, J. Olmstead (STScI), N. Madhusudhan (Cambridge University)
The team’s results are accepted for publication in The Astrophysical Journal Letters.
Notes
[1] The Habitable Zone is the region around a star where the conditions could potentially be suitable to sustain life on a planet within this region, for example allowing the presence of liquid water on its surface.
Researchers using the NASA/ESA/CSA James Webb Space Telescope are getting their first look at star formation, gas, and dust in nearby galaxies with unprecedented resolution at infrared wavelengths. The data have enabled an initial collection of 21 research papers which provide new insight into how some of the smallest-scale processes in the Universe — the beginnings of star formation — impact the evolution of the largest objects in our cosmos: galaxies.
The largest survey of nearby galaxies in Webb’s first year of science operations is being carried out by the Physics at High Angular resolution in Nearby Galaxies (PHANGS) collaboration, involving more than 100 researchers from around the globe. The Webb observations are led by Janice Lee, Gemini Observatory chief scientist at the US National Science Foundation’s NOIRLab and an affiliate astronomer at the University of Arizona in Tucson.
The team is studying a diverse sample of 19 spiral galaxies, and in Webb’s first few months of science operations, observations have been made of five of those targets — M74, NGC 7496, IC 5332, NGC 1365, and NGC 1433. The results are already astounding astronomers.
Webb Reveals Intricate Networks of Gas and Dust in Nearby Galaxies. This image taken by the NASA/ESA/CSA James Webb Space Telescope shows one of a total of 19 galaxies targeted for study by the Physics at High Angular resolution in Nearby Galaxies (PHANGS) collaboration. Nearby barred spiral galaxy NGC 1433 takes on a completely new look when observed by Webb’s Mid-Infrared Instrument (MIRI).NGC 1433’s spiral arms are littered with evidence of extremely young stars releasing energy and, in some cases, blowing out the gas and dust of the interstellar medium they plough into. Areas that once appeared dark and dim in optical imaging light up under Webb’s infrared eye, as clumps of dust and gas in the interstellar medium absorb the light from forming stars and emit it back out in the infrared.Webb’s image of NGC1433 is a dramatic display of the role that dynamic processes within the forming stars, dust, and gas play in the larger structure of an entire galaxy.At the centre of the galaxy, a tight, bright core featuring a unique double ring structure shines in exquisite detail, revealed by Webb’s extreme resolution. In this case, that double ring is actually tightly wrapped spiral arms that wind into an oval shape along the galaxy’s bar axis.NGC 1433 is classified as a Seyfert galaxy, a galaxy relatively close to Earth that has a bright, active core. The brightness and lack of dust in the MIRI image of NGC 1433 could hint at a recent merger or even collision with another galaxy.In the image of NGC 1433, blue, green, and red were assigned to Webb’s MIRI data at 7.7, 10 and 11.3, and 21 microns (the F770W, F1000W and F1130W, and F2100W filters, respectively).MIRI was contributed by ESA and NASA, with the instrument designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) and NASA’s Jet Propulsion Laboratory, in partnership with the University of Arizona.Credit:NASA, ESA, CSA, and J. Lee (NOIRLab), A. Pagan (STScI)
Webb Reveals Intricate Networks of Gas and Dust in Nearby Galaxies. This image of the nearby galaxy NGC 1433, captured by Webb’s Mid-Infrared Instrument (MIRI) shows compass arrows, scale bar, and color 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). At the lower right is a scale bar labeled 7,000 light-years, 30 arcseconds. The length of the scale bar is approximately one-fifth the total width of the image. Below the image is a color key showing which MIRI filters were used to create the image and which visible-light color is assigned to each filter. In the image of NGC 1433, blue, green, and red were assigned to Webb’s MIRI data at 7.7, 10 and 11.3, and 21 microns (the F770W, F1000W and F1130W, and F2100W filters, respectively).This image taken by the NASA/ESA/CSA James Webb Space Telescope shows one of a total of 19 galaxies targeted for study by the Physics at High Angular resolution in Nearby Galaxies (PHANGS) collaboration. Nearby barred spiral galaxy NGC 1433 takes on a completely new look when observed by Webb’s Mid-Infrared Instrument (MIRI).NGC 1433’s spiral arms are littered with evidence of extremely young stars releasing energy and, in some cases, blowing out the gas and dust of the interstellar medium they plough into. Areas that once appeared dark and dim in optical imaging light up under Webb’s infrared eye, as clumps of dust and gas in the interstellar medium absorb the light from forming stars and emit it back out in the infrared.Webb’s image of NGC1433 is a dramatic display of the role that dynamic processes within the forming stars, dust, and gas play in the larger structure of an entire galaxy.At the centre of the galaxy, a tight, bright core featuring a unique double ring structure shines in exquisite detail, revealed by Webb’s extreme resolution. In this case, that double ring is actually tightly wrapped spiral arms that wind into an oval shape along the galaxy’s bar axis.NGC 1433 is classified as a Seyfert galaxy, a galaxy relatively close to Earth that has a bright, active core. The brightness and lack of dust in the MIRI image of NGC 1433 could hint at a recent merger or even collision with another galaxy.MIRI was contributed by ESA and NASA, with the instrument designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) and NASA’s Jet Propulsion Laboratory, in partnership with the University of Arizona.Credit:NASA, ESA, CSA, and J. Lee (NOIRLab), A. Pagan (STScI)
Webb Reveals Intricate Networks of Gas and Dust in Nearby Galaxies. Scientists are getting their first look with the NASA/ESA/CSA James Webb Space Telescope’s powerful resolution at how the formation of young stars influences the evolution of nearby galaxies. The spiral arms of NGC 7496, one of a total of 19 galaxies targeted for study by the Physics at High Angular resolution in Nearby Galaxies (PHANGS) collaboration, are filled with cavernous bubbles and shells overlapping one another in this image from Webb’s Mid-Infrared Instrument (MIRI). These filaments and hollow cavities are evidence of young stars releasing energy and, in some cases, blowing out the gas and dust of the interstellar medium they plough into.Until Webb’s high resolution at infrared wavelengths came along, stars at the earliest point of their lifecycle in nearby galaxies like NGC 7496 remained obscured by gas and dust. Webb’s specific wavelength coverage (7.7 and 11.3 microns), allows for the detection of polycyclic aromatic hydrocarbons, which play a critical role in the formation of stars and planets. In Webb’s MIRI image, these are mostly found within the main dust lanes in the spiral arms.In their analysis of the new data from Webb, scientists were able to identify nearly 60 new, undiscovered embedded cluster candidates in NGC 7496. These newly identified clusters could be among the youngest stars in the entire galaxy.At the centre of NGC 7496, a barred spiral galaxy, is an active galactic nucleus (AGN). An AGN is a supermassive black hole that is emitting jets and winds. The AGN glows brightly at the centre of this Webb image. Additionally, Webb’s extreme sensitivity also picks up various background galaxies,far distant from NGC 7496, which appear green or red in some instances.NGC 7496 lies over 24 million light-years away from Earth in the constellation Grus.In this image of NGC 7496, blue, green, and red were assigned to Webb’s MIRI data at 7.7, 10 and 11.3, and 21 microns (the F770W, F1000W and F1130W, and F2100W filters, respectively).MIRI was contributed by ESA and NASA, with the instrument designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) and NASA’s Jet Propulsion Laboratory, in partnership with the University of Arizona.Credit:NASA, ESA, CSA, and J. Lee (NOIRLab), A. Pagan (STScI)
Webb Reveals Intricate Networks of Gas and Dust in Nearby Galaxies. This image of the nearby galaxy NGC 1433, captured by Webb’s Mid-Infrared Instrument (MIRI) shows compass arrows, scale bar, and color 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). At the lower right is a scale bar labeled 3,500 light-years, 30 arcseconds. The length of the scale bar is approximately one-fifth the total width of the image. Below the image is a color key showing which MIRI filters were used to create the image and which visible-light color is assigned to each filter. In this image of NGC 7496, blue, green, and red were assigned to Webb’s MIRI data at 7.7, 10 and 11.3, and 21 microns (the F770W, F1000W and F1130W, and F2100W filters, respectively).Scientists are getting their first look with the NASA/ESA/CSA James Webb Space Telescope’s powerful resolution at how the formation of young stars influences the evolution of nearby galaxies. The spiral arms of NGC 7496, one of a total of 19 galaxies targeted for study by the Physics at High Angular resolution in Nearby Galaxies (PHANGS) collaboration, are filled with cavernous bubbles and shells overlapping one another in this image from Webb’s Mid-Infrared Instrument (MIRI). These filaments and hollow cavities are evidence of young stars releasing energy and, in some cases, blowing out the gas and dust of the interstellar medium they plough into.Until Webb’s high resolution at infrared wavelengths came along, stars at the earliest point of their lifecycle in nearby galaxies like NGC 7496 remained obscured by gas and dust. Webb’s specific wavelength coverage (7.7 and 11.3 microns), allows for the detection of polycyclic aromatic hydrocarbons, which play a critical role in the formation of stars and planets. In Webb’s MIRI image, these are mostly found within the main dust lanes in the spiral arms.In their analysis of the new data from Webb, scientists were able to identify nearly 60 new, undiscovered embedded cluster candidates in NGC 7496. These newly identified clusters could be among the youngest stars in the entire galaxy.At the centre of NGC 7496, a barred spiral galaxy, is an active galactic nucleus (AGN). An AGN is a supermassive black hole that is emitting jets and winds. The AGN glows brightly at the centre of this Webb image. Additionally, Webb’s extreme sensitivity also picks up various background galaxies, far distant from NGC 7496, which appear green or red in some instances.NGC 7496 lies over 24 million light-years away from Earth in the constellation Grus.MIRI was contributed by ESA and NASA, with the instrument designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) and NASA’s Jet Propulsion Laboratory, in partnership with the University of Arizona.Credit:NASA, ESA, CSA, and J. Lee (NOIRLab), A. Pagan (STScI)
Webb Reveals Intricate Networks of Gas and Dust in Nearby Galaxies. Scientists are getting their first look with the NASA/ESA/CSA James Webb Space Telescope’s powerful resolution at how the formation of young stars influences the evolution of nearby galaxies. NGC 1365, observed here by Webb’s Mid-Infrared Instrument (MIRI) is one of a total of 19 galaxies targeted for study by the Physics at High Angular resolution in Nearby Galaxies (PHANGS) collaboration.As revealed by the MIRI observations of NGC 1365, clumps of dust and gas in the interstellar medium have absorbed the light from forming stars and emitted it back out in the infrared, lighting up an intricate network of cavernous bubbles and filamentary shells influenced by young stars releasing energy into the galaxy’s spiral arms.Webb’s exquisite resolution also picks up several extremely bright star clusters not far from the core and newly observed recently formed clusters along the outer edges of the spiral arms.Additionally, the Webb images provide insights into how the orbits of stars and gas vary depending on where they form, and how this results in the population of older clusters outside the inner star-formation ring.NGC 1365 is a double-barred spiral galaxy that lies about 56 million light-years away from Earth. It’s one of the largest galaxies currently known to astronomers, spanning twice the length of the Milky Way.In this image of NGC 1356, blue, green, and red were assigned to Webb’s MIRI data at 7.7, 10 and 11.3, and 21 microns (the F770W, F1000W and F1130W, and F2100W filters, respectively).MIRI was contributed by ESA and NASA, with the instrument designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) and NASA’s Jet Propulsion Laboratory, in partnership with the University of Arizona.Credit:NASA, ESA, CSA, and J. Lee (NOIRLab), A. Pagan (STScI)
Webb Reveals Intricate Networks of Gas and Dust in Nearby Galaxies. This image of the nearby galaxy NGC 1365, captured by Webb’s Mid-Infrared Instrument (MIRI) shows compass arrows, scale bar, and color 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). At the lower right is a scale bar labeled 8,000 light-years, 30 arcseconds. The length of the scale bar is approximately one-fifth the total width of the image. Below the image is a color key showing which MIRI filters were used to create the image and which visible-light color is assigned to each filter. In this image of NGC 1365, blue, green, and red were assigned to Webb’s MIRI data at 7.7, 10 and 11.3, and 21 microns (the F770W, F1000W and F1130W, and F2100W filters, respectively).Scientists are getting their first look with the NASA/ESA/CSA James Webb Space Telescope’s powerful resolution at how the formation of young stars influences the evolution of nearby galaxies. NGC 1365, observed here by Webb’s Mid-Infrared Instrument (MIRI) is one of a total of 19 galaxies targeted for study by the Physics at High Angular resolution in Nearby Galaxies (PHANGS) collaboration.As revealed by the MIRI observations of NGC 1365, clumps of dust and gas in the interstellar medium have absorbed the light from forming stars and emitted it back out in the infrared, lighting up an intricate network of cavernous bubbles and filamentary shells influenced by young stars releasing energy into the galaxy’s spiral arms.Webb’s exquisite resolution also picks up several extremely bright star clusters not far from the core and newly observed recently formed clusters along the outer edges of the spiral arms.Additionally, the Webb images provide insights into how the orbits of stars and gas vary depending on where they form, and how this results in the population of older clusters outside the inner ring of star formation.NGC 1365 is a double-barred spiral galaxy that lies about 56 million light-years away from Earth. It’s one of the largest galaxies currently known to astronomers, spanning twice the length of the Milky Way.MIRI was contributed by ESA and NASA, with the instrument designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) and NASA’s Jet Propulsion Laboratory, in partnership with the University of Arizona.Credit:NASA, ESA, CSA, and J. Lee (NOIRLab), A. Pagan (STScI)
The images from Webb’s Mid-Infrared Instrument (MIRI) reveal the presence of a network of highly structured features within these galaxies — glowing cavities of dust and huge cavernous bubbles of gas that line the spiral arms. In some regions of the nearby galaxies observed, this web of features appears built from both individual and overlapping shells and bubbles where young stars are releasing energy.
The high-resolution imaging needed to study these structures has long evaded astronomers — that is, until Webb came into the picture. Webb’s powerful infrared capabilities can pierce through the dust to connect the missing pieces of the puzzle. For example, specific wavelengths observable by MIRI (7.7 and 11.3 microns) are sensitive to emission from polycyclic aromatic hydrocarbons, which play a crucial role in the formation of stars and planets. These molecules were detected by Webb in the first observations by the PHANGS programme.
Studying these interactions at the finest scales can help provide insights into the larger picture of how galaxies have evolved over time.
The PHANGS team will work to create and release datasets that align Webb’s data to each of the complementary datasets obtained previously from the other observatories, to help accelerate discoveries by the broader astronomical community.
The research by the PHANGS team is being conducted as part of the General Observer program 2107. The team’s initial findings, comprising 21 individual studies, were recently published in a special focus issue of The Astrophysical Journal Letters.
Astronomers reveal first image of the black hole at the heart of our galaxy
Today, at simultaneous press conferences around the world, including at the European Southern Observatory (ESO) headquarters in Germany, astronomers have unveiled the first image of the supermassive black hole at the centre of our own Milky Way galaxy. This result provides overwhelming evidence that the object is indeed a black hole and yields valuable clues about the workings of such giants, which are thought to reside at the centre of most galaxies. The image was produced by a global research team called the Event Horizon Telescope (EHT) Collaboration, using observations from a worldwide network of radio telescopes.
The black hole at the heart of our galaxy. This artist’s impression depicts a rapidly spinning supermassive black hole surrounded by an accretion disc. This thin disc of rotating material consists of the leftovers of a Sun-like star which was ripped apart by the tidal forces of the black hole. The black hole is labelled, showing the anatomy of this fascinating object. Credit:ESOThe black hole at the heart of our galaxy. This chart shows the location of the field of view within which Sagittarius A* resides — the black hole is marked with a red circle within the constellation of Sagittarius (The Archer). This map shows most of the stars visible to the unaided eye under good conditions. Credit:ESO, IAU and Sky & Telescope
The image is a long-anticipated look at the massive object that sits at the very centre of our galaxy. Scientists had previously seen stars orbiting around something invisible, compact, and very massive at the centre of the Milky Way. This strongly suggested that this object — known as Sagittarius A* (Sgr A*, pronounced “sadge-ay-star”) — is a black hole, and today’s image provides the first direct visual evidence of it.
The black hole at the heart of our galaxy. This is the first image of Sgr A*, the supermassive black hole at the centre of our galaxy. It’s the first direct visual evidence of the presence of this black hole. It was captured by the Event Horizon Telescope (EHT), an array which linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope. The telescope is named after the event horizon, the boundary of the black hole beyond which no light can escape. Although we cannot see the event horizon itself, because it cannot emit light, glowing gas orbiting around the black hole reveals a telltale signature: a dark central region (called a shadow) surrounded by a bright ring-like structure. The new view captures light bent by the powerful gravity of the black hole, which is four million times more massive than our Sun. The image of the Sgr A* black hole is an average of the different images the EHT Collaboration has extracted from its 2017 observations. In addition to other facilities, the EHT network of radio observatories that made this image possible includes the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Pathfinder EXperiment (APEX) in the Atacama Desert in Chile, co-owned and co-operated by ESO is a partner on behalf of its member states in Europe. Credit: EHT Collaboration
Although we cannot see the black hole itself, because it is completely dark, glowing gas around it reveals a telltale signature: a dark central region (called a shadow) surrounded by a bright ring-like structure. The new view captures light bent by the powerful gravity of the black hole, which is four million times more massive than our Sun.
“We were stunned by how well the size of the ring agreed with predictions from Einstein’s Theory of General Relativity,” said EHT Project Scientist Geoffrey Bower from the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei. “These unprecedented observations have greatly improved our understanding of what happens at the very centre of our galaxy, and offer new insights on how these giant black holes interact with their surroundings.” The EHT team’s results are being published today in a special issue of The Astrophysical Journal Letters.
Because the black hole is about 27 000 light-years away from Earth, it appears to us to have about the same size in the sky as a doughnut on the Moon. To image it, the team created the powerful EHT, which linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope [1]. The EHT observed Sgr A* on multiple nights in 2017, collecting data for many hours in a row, similar to using a long exposure time on a camera.
The black hole at the heart of our galaxy. The Event Horizon Telescope (EHT) Collaboration has created a single image (top frame) of the supermassive black hole at the centre of our galaxy, called Sagittarius A*, or Sgr A* for short, by combining images extracted from the EHT observations. The main image was produced by averaging together thousands of images created using different computational methods — all of which accurately fit the EHT data. This averaged image retains features more commonly seen in the varied images, and suppresses features that appear infrequently. The images can also be clustered into four groups based on similar features. An averaged, representative image for each of the four clusters is shown in the bottom row. Three of the clusters show a ring structure but, with differently distributed brightness around the ring. The fourth cluster contains images that also fit the data but do not appear ring-like. The bar graphs show the relative number of images belonging to each cluster. Thousands of images fell into each of the first three clusters, while the fourth and smallest cluster contains only hundreds of images. The heights of the bars indicate the relative “weights,” or contributions, of each cluster to the averaged image at top. In addition to other facilities, the EHT network of radio observatories that made this image possible includes the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Pathfinder EXperiment (APEX) in the Atacama Desert in Chile, co-owned and co-operated by ESO is a partner on behalf of its member states in Europe. Credit: EHT Collaboration
In addition to other facilities, the EHT network of radio observatories includes the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Pathfinder EXperiment (APEX) in the Atacama Desert in Chile, co-owned and co-operated by ESO on behalf of its member states in Europe. Europe also contributes to the EHT observations with other radio observatories — the IRAM 30-meter telescope in Spain and, since 2018, the NOrthern Extended Millimeter Array (NOEMA) in France — as well as a supercomputer to combine EHT data hosted by the Max Planck Institute for Radio Astronomy in Germany. Moreover, Europe contributed with funding to the EHT consortium project through grants by the European Research Council and by the Max Planck Society in Germany.
This image shows the Atacama Large Millimeter/submillimeter Array (ALMA) looking up at the Milky Way as well as the location of Sagittarius A*, the supermassive black hole at our galactic centre. Highlighted in the box is the image of Sagittarius A* taken by the Event Horizon Telescope (EHT) Collaboration. Located in the Atacama Desert in Chile, ALMA is the most sensitive of all the observatories in the EHT array, and ESO is a co-owner of ALMA on behalf of its European Member States. Credit: ESO/José Francisco Salgado (josefrancisco.org), EHT Collaboration
“It is very exciting for ESO to have been playing such an important role in unravelling the mysteries of black holes, and of Sgr A* in particular, over so many years,” commented ESO Director General Xavier Barcons. “ESO not only contributed to the EHT observations through the ALMA and APEX facilities but also enabled, with its other observatories in Chile, some of the previous breakthrough observations of the Galactic centre.” [2]
The EHT achievement follows the collaboration’s 2019 release of the first image of a black hole, called M87*, at the centre of the more distant Messier 87 galaxy.
These panels show the first two images ever taken of black holes. On the left is M87*, the supermassive black hole at the centre of the galaxy Messier 87 (M87), 55 million light-years away. On the right is Sagittarius A* (Sgr A*), the black hole at the centre of our Milky Way. The two images show the black holes as they would appear in the sky, with their bright rings appearing to be roughly the same size, despite M87* being around a thousand times larger than Sgr A*. The images were captured by the Event Horizon Telescope (EHT), a global network of radio telescopes including the Atacama Large Millimeter/submillimeter Array (ALMA) and Atacama Pathfinder EXperiment (APEX), in which ESO is co-owner. Credit: EHT Collaboration
The two black holes look remarkably similar, even though our galaxy’s black hole is more than a thousand times smaller and less massive than M87* [3].
“We have two completely different types of galaxies and two very different black hole masses, but close to the edge of these black holes they look amazingly similar,” says Sera Markoff, Co-Chair of the EHT Science Council and a professor of theoretical astrophysics at the University of Amsterdam, the Netherlands.
“This tells us that General Relativity governs these objects up close, and any differences we see further away must be due to differences in the material that surrounds the black holes.”
Size comparison of the two black holes imaged by the Event Horizon Telescope (EHT) Collaboration: M87*, at the heart of the galaxy Messier 87, and Sagittarius A* (Sgr A*), at the centre of the Milky Way. The image shows the scale of Sgr A* in comparison with both M87* and other elements of the Solar System such as the orbits of Pluto and Mercury. Also displayed is the Sun’s diameter and the current location of the Voyager 1 space probe, the furthest spacecraft from Earth. M87*, which lies 55 million light-years away, is one of the largest black holes known. While Sgr A*, 27 000 light-years away, has a mass roughly four million times the Sun’s mass, M87* is more than 1000 times more massive. Because of their relative distances from Earth, both black holes appear the same size in the sky. Credit: EHT collaboration (acknowledgment: Lia Medeiros, xkcd)
This achievement was considerably more difficult than for M87*, even though Sgr A* is much closer to us. EHT scientist Chi-kwan (‘CK’) Chan, from Steward Observatory and Department of Astronomy and the Data Science Institute of the University of Arizona, USA, explains:
“The gas in the vicinity of the black holes moves at the same speed — nearly as fast as light — around both Sgr A* and M87*. But where gas takes days to weeks to orbit the larger M87*, in the much smaller Sgr A* it completes an orbit in mere minutes. This means the brightness and pattern of the gas around Sgr A* were changing rapidly as the EHT Collaboration was observing it — a bit like trying to take a clear picture of a puppy quickly chasing its tail.”
The researchers had to develop sophisticated new tools that accounted for the gas movement around Sgr A*. While M87* was an easier, steadier target, with nearly all images looking the same, that was not the case for Sgr A*. The image of the Sgr A* black hole is an average of the different images the team extracted, finally revealing the giant lurking at the centre of our galaxy for the first time.
The effort was made possible through the ingenuity of more than 300 researchers from 80 institutes around the world that together make up the EHT Collaboration. In addition to developing complex tools to overcome the challenges of imaging Sgr A*, the team worked rigorously for five years, using supercomputers to combine and analyse their data, all while compiling an unprecedented library of simulated black holes to compare with the observations.
Scientists are particularly excited to finally have images of two black holes of very different sizes, which offers the opportunity to understand how they compare and contrast. They have also begun to use the new data to test theories and models of how gas behaves around supermassive black holes. This process is not yet fully understood but is thought to play a key role in shaping the formation and evolution of galaxies.
“Now we can study the differences between these two supermassive black holes to gain valuable new clues about how this important process works,” said EHT scientist Keiichi Asada from the Institute of Astronomy and Astrophysics, Academia Sinica, Taipei. “We have images for two black holes — one at the large end and one at the small end of supermassive black holes in the Universe — so we can go a lot further in testing how gravity behaves in these extreme environments than ever before.”
Progress on the EHT continues: a major observation campaign in March 2022 included more telescopes than ever before. The ongoing expansion of the EHT network and significant technological upgrades will allow scientists to share even more impressive images as well as movies of black holes in the near future.
This visible light wide-field view shows the rich star clouds in the constellation of Sagittarius (the Archer) in the direction of the centre of our Milky Way galaxy. The entire image is filled with vast numbers of stars — but far more remain hidden behind clouds of dust and are only revealed in infrared images. This view was created from photographs in red and blue light and form part of the Digitized Sky Survey 2. The field of view is approximately 3.5 degrees x 3.6 degrees. Credit:ESO and Digitized Sky Survey 2. Acknowledgment: Davide De Martin and S. Guisard (www.eso.org/~sguisard)
The black hole at the heart of our galaxy
Notes
[1] The individual telescopes involved in the EHT in April 2017, when the observations were conducted, were: the Atacama Large Millimeter/submillimeter Array (ALMA), the Atacama Pathfinder EXperiment (APEX), the IRAM 30-meter Telescope, the James Clerk Maxwell Telescope (JCMT), the Large Millimeter Telescope Alfonso Serrano (LMT), the Submillimeter Array (SMA), the UArizona Submillimeter Telescope (SMT), the South Pole Telescope (SPT). Since then, the EHT has added the Greenland Telescope (GLT), the NOrthern Extended Millimeter Array (NOEMA) and the UArizona 12-meter Telescope on Kitt Peak to its network.
ALMA is a partnership of the European Southern Observatory (ESO; Europe, representing its member states), the U.S. National Science Foundation (NSF), and the National Institutes of Natural Sciences (NINS) of Japan, together with the National Research Council (Canada), the Ministry of Science and Technology (MOST; Taiwan), Academia Sinica Institute of Astronomy and Astrophysics (ASIAA; Taiwan), and Korea Astronomy and Space Science Institute (KASI; Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, the Associated Universities, Inc./National Radio Astronomy Observatory (AUI/NRAO) and the National Astronomical Observatory of Japan (NAOJ). APEX, a collaboration between the Max Planck Institute for Radio Astronomy (Germany), the Onsala Space Observatory (Sweden) and ESO, is operated by ESO. The 30-meter Telescope is operated by IRAM (the IRAM Partner Organizations are MPG [Germany], CNRS [France] and IGN [Spain]). The JCMT is operated by the East Asian Observatory on behalf of The National Astronomical Observatory of Japan; ASIAA; KASI; the National Astronomical Research Institute of Thailand; the Center for Astronomical Mega-Science and organisations in the United Kingdom and Canada. The LMT is operated by INAOE and UMass, the SMA is operated by Center for Astrophysics | Harvard & Smithsonian and ASIAA and the UArizona SMT is operated by the University of Arizona. The SPT is operated by the University of Chicago with specialised EHT instrumentation provided by the University of Arizona.
The Greenland Telescope (GLT) is operated by ASIAA and the Smithsonian Astrophysical Observatory (SAO). The GLT is part of the ALMA-Taiwan project, and is supported in part by the Academia Sinica (AS) and MOST. NOEMA is operated by IRAM and the UArizona 12-meter telescope at Kitt Peak is operated by the University of Arizona.
A montage of the radio observatories that form the Event Horizon Telescope (EHT) network, used to image the Milky Way’s central black hole, Sagittarius A*. These include the Atacama Large Millimeter/submillimeter Array (ALMA), the Atacama Pathfinder EXperiment (APEX), IRAM 30-meter telescope, James Clark Maxwell Telescope (JCMT), Large Millimeter Telescope (LMT), Submillimeter Array (SMA), Submillimetere Telescope (SMT) and South Pole Telescope (SPT). The slightly transparent telescopes in the background, represent the three telescopes added to the EHT Collaboration after 2018: the Greenland Telescope, the NOrthern Extended Millimeter Array (NOEMA) in France, and the UArizona ARO 12-meter Telescope at Kitt Peak. These telescopes were added to the array after the 2017 observations of Sagittarius A*. Credit: ESO/M. Kornmesser. Images of individual telescopes: ALMA: ESO APEX: ESO LMT: INAOE Archives GLT: N. Patel JCMT: EAO-W. Montgomerie SMT: D. Harvey 30m: N. Billot SPT: Wikipedia SMA: S. R. Schimpf NOEMA: IRAM Kitt Peak: Wikipedia Milky Way: N. Risinger (skysurvey.org)A montage of the radio observatories that form the Event Horizon Telescope (EHT) network used to image the Milky Way’s central black hole, Sagittarius A*. These include the Atacama Large Millimeter/submillimeter Array (ALMA), the Atacama Pathfinder EXperiment (APEX), IRAM 30-meter telescope, James Clark Maxwell Telescope (JCMT), Large Millimeter Telescope (LMT), Submillimeter Array (SMA), Submillimeter Telescope (SMT) and South Pole Telescope (SPT). The slightly transparent telescopes in the background represent the three telescopes added to the EHT network after 2018: the Greenland Telescope, the NOrthern Extended Millimeter Array (NOEMA) in France, and the UArizona ARO 12-meter Telescope at Kitt Peak. These telescopes were added to the array after the 2017 observations of Sagittarius A*. Credit: ESO/M. Kornmesser. Images of individual telescopes: ALMA: ESO APEX: ESO LMT: INAOE Archives GLT: N. Patel JCMT: EAO-W. Montgomerie SMT: D. Harvey 30m: N. Billot SPT: Wikipedia SMA: S. R. Schimpf NOEMA: IRAM Kitt Peak: Wikipedia Milky Way: N. Risinger (skysurvey.org)
[2] A strong basis for the interpretation of this new image was provided by previous research carried out on Sgr A*. Astronomers have known the bright, dense radio source at the centre of the Milky Way in the direction of the constellation Sagittarius since the 1970s. By measuring the orbits of several stars very close to our galactic centre over a period of 30 years, teams led by Reinhard Genzel (Director at the Max –Planck Institute for Extraterrestrial Physics in Garching near Munich, Germany) and Andrea M. Ghez (Professor in the Department of Physics and Astronomy at the University of California, Los Angeles, USA) were able to conclude that the most likely explanation for an object of this mass and density is a supermassive black hole. ESO’s facilities (including the Very Large Telescope and the Very Large Telescope Interferometer) and the Keck Observatory were used to carry out this research, which shared the 2020 Nobel Prize in Physics.
[3] Black holes are the only objects we know of where mass scales with size. A black hole a thousand times smaller than another is also a thousand times less massive.
The black hole at the heart of our galaxy: more information
This research was presented in six papers published today in The Astrophysical Journal Letters.
A global map showing the radio observatories that form the Event Horizon Telescope (EHT) network used to image the Milky Way’s central black hole, Sagittarius A*. The telescopes highlighted in yellow were part of the EHT network during the observations of Sagittarius A* in 2017. These include the Atacama Large Millimeter/submillimeter Array (ALMA), the Atacama Pathfinder EXperiment (APEX), IRAM 30-meter telescope, James Clark Maxwell Telescope (JCMT), Large Millimeter Telescope (LMT), Submillimeter Array (SMA), Submillimetere Telescope (SMT) and South Pole Telescope (SPT). Highlighted in blue are the three telescopes added to the EHT Collaboration after 2018: the Greenland Telescope, the NOrthern Extended Millimeter Array (NOEMA) in France, and the UArizona ARO 12-meter Telescope at Kitt Peak. Credit:ESO/M. Kornmesser
The EHT collaboration involves more than 300 researchers from Africa, Asia, Europe, North and South America. The international collaboration aims to capture the most detailed black hole images ever obtained by creating a virtual Earth-sized telescope. Supported by considerable international efforts, the EHT links existing telescopes using novel techniques — creating a fundamentally new instrument with the highest angular resolving power that has yet been achieved.
This image shows the locations of some of the telescopes making up the EHT, as well as a representation of the long baselines between the telescopes. Credit:ESO/L. Calçada
The EHT consortium consists of 13 stakeholder institutes; the Academia Sinica Institute of Astronomy and Astrophysics, the University of Arizona, the Center for Astrophysics | Harvard & Smithsonian, the University of Chicago, the East Asian Observatory, Goethe-Universitaet Frankfurt, Institut de Radioastronomie Millimétrique, Large Millimeter Telescope, Max Planck Institute for Radio Astronomy, MIT Haystack Observatory, National Astronomical Observatory of Japan, Perimeter Institute for Theoretical Physics, and Radboud University.
This view shows several of the ALMA antennas and the central regions of the Milky Way above. In this wide field view, the zodiacal light is seen upper right and at lower left Mars is seen. Saturn is a bit higher in the sky towards the centre of the image. The image was taken during the ESO Ultra HD (UHD) Expedition. Credit:ESO/B. Tafreshi (twanight.org)
The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of ESO, the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI). ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.
The slumbering Atacama Pathfinder Experiment (APEX) telescope sits beneath reddened skies amongst the snow covered Chajnantor landscape. Snow not only blankets the ground, but also the many peaks that encircle the Chilean plateau which also hosts the Atacama Large Millimeter/submillimeter Array (ALMA). Credit:Carlos A. Durán/ESO
APEX, Atacama Pathfinder EXperiment, is a 12-metre diameter telescope, operating at millimetre and submillimetre wavelengths — between infrared light and radio waves. ESO operates APEX at one of the highest observatory sites on Earth, at an elevation of 5100 metres, high on the Chajnantor plateau in Chile’s Atacama region. The telescope is a collaboration between the Max Planck Institute for Radio Astronomy (MPIfR), the Onsala Space Observatory (OSO), and ESO.
This image shows the dish of the Atacama Pathfinder Experiment (APEX) telescope seen perfectly from the side, including the starry sky. Credit:C. Duran/ESOESO Photo Ambassador Stéphane Guisard captured this astounding panorama from the site of ALMA, the Atacama Large Millimeter/submillimeter Array, in the Chilean Andes. The 5000-metre-high and extremely dry Chajnantor plateau offers the perfect place for this state-of-the-art telescope, which studies the Universe in millimetre- and submillimetre-wavelength light. Numerous giant antennas dominate the centre of the image. When ALMA is complete, it will have a total of 54 of these 12-metre-diameter dishes. Above the array, the arc of the Milky Way serves as a resplendent backdrop. When the panorama was taken, the Moon was lying close to the centre of the Milky Way in the sky, its light bathing the antennas in an eerie night-time glow. The Large and Small Magellanic Clouds, the biggest of the Milky Way’s dwarf satellite galaxies, appear as two luminous smudges in the sky on the left. A particularly bright meteor streak gleams near the Small Magellanic Cloud. On the right, some of ALMA’s smaller 7-metre antennas — twelve of which will be used to form the Atacama Compact Array — can be seen. Still further on the right shine the lights of the Array Operations Site Technical Building. And finally, looming behind this building is the dark, mountainous peak of Cerro Chajnantor. ALMA, an international astronomy facility, is a partnership of Europe, North America and East Asia in cooperation with the Republic of Chile. ALMA construction and operations are led on behalf of Europe by ESO, on behalf of North America by the National Radio Astronomy Observatory (NRAO), and on behalf of East Asia by the National Astronomical Observatory of Japan (NAOJ). The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA. Links ESO Photo Ambassadors More about ALMA at ESO The Joint ALMA Observatory. Links ESO Photo Ambassadors More about ALMA at ESO The Joint ALMA Observatory Credit:ESO/S. Guisard (www.eso.org/~sguisard)
The European Southern Observatory (ESO) enables scientists worldwide to discover the secrets of the Universe for the benefit of all. We design, build and operate world-class observatories on the ground — which astronomers use to tackle exciting questions and spread the fascination of astronomy — and promote international collaboration in astronomy. Established as an intergovernmental organisation in 1962, today ESO is supported by 16 Member States (Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, Sweden, Switzerland and the United Kingdom), along with the host state of Chile and with Australia as a Strategic Partner. ESO’s headquarters and its visitor centre and planetarium, the ESO Supernova, are located close to Munich in Germany, while the Chilean Atacama Desert, a marvellous place with unique conditions to observe the sky, hosts our telescopes. ESO operates three observing sites: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope and its Very Large Telescope Interferometer, as well as two survey telescopes, VISTA working in the infrared and the visible-light VLT Survey Telescope. Also at Paranal ESO will host and operate the Cherenkov Telescope Array South, the world’s largest and most sensitive gamma-ray observatory. Together with international partners, ESO operates APEX and ALMA on Chajnantor, two facilities that observe the skies in the millimetre and submillimetre range. At Cerro Armazones, near Paranal, we are building “the world’s biggest eye on the sky” — ESO’s Extremely Large Telescope. From our offices in Santiago, Chile we support our operations in the country and engage with Chilean partners and society.
The black hole at the heart of our galaxy. This is the first image of Sgr A*, the supermassive black hole at the centre of our galaxy, with an added black background to fit wider screens. It’s the first direct visual evidence of the presence of this black hole. It was captured by the Event Horizon Telescope (EHT), an array which linked together eight existing radio observatories across the planet to form a single “Earth-sized” virtual telescope. The telescope is named after the event horizon, the boundary of the black hole beyond which no light can escape. Although we cannot see the event horizon itself, because it cannot emit light, glowing gas orbiting around the black hole reveals a telltale signature: a dark central region (called a shadow) surrounded by a bright ring-like structure. The new view captures light bent by the powerful gravity of the black hole, which is four million times more massive than our Sun. The image of the Sgr A* black hole is an average of the different images the EHT Collaboration has extracted from its 2017 observations. In addition to other facilities, the EHT network of radio observatories that made this image possible includes the Atacama Large Millimeter/submillimeter Array (ALMA) and the Atacama Pathfinder EXperiment (APEX) in the Atacama Desert in Chile, co-owned and co-operated by ESO is a partner on behalf of its member states in Europe. Credit:EHT Collaboration
