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Webb watches Wolf-Rayet 140: carbon-rich dust shells form, expand in star system

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A three-part graphic showing observations of Wolf-Rayet 140, two massive stars with 17 dust shells around them. An inset appears at right, showing a portion of the two observations matched up to show that the arced dust has moved.

Webb watches Wolf-Rayet 140: carbon-rich dust shells form, expand in star system

Astronomers using the NASA/ESA/CSA James Webb Space Telescope have identified two stars responsible for generating carbon-rich dust a mere 5000 light-years away in our own Milky Way galaxy. As the massive stars in Wolf-Rayet 140 swing past one another on their elongated orbits, their winds collide and produce the carbon-rich dust. For a few months every eight years, the stars form a new shell of dust that expands outward — and may eventually go on to become part of stars that form elsewhere in our galaxy.

Astronomers have long tried to track down how elements like carbon, which is essential for life, become widely distributed across the Universe. Now, the James Webb Space Telescope has examined one ongoing source of carbon-rich dust in our own Milky Way galaxy in greater detail: Wolf-Rayet 140 [1], a system of two massive stars that follow a tight, elongated orbit.

As they swing past one another (within the central white dot in the Webb images), the stellar winds from each star slam together, the material compresses, and carbon-rich dust forms. Webb’s latest observations show 17 dust shells shining in mid-infrared light that are expanding at regular intervals into the surrounding space.

“The telescope confirmed that these dust shells are real, and its data also showed that the dust shells are moving outward at consistent velocities, revealing visible changes over incredibly short periods of time,”

said Emma Lieb, the lead author of the new paper and a doctoral student at the University of Denver in Colorado.

Every shell is racing away from the stars at more than 2600 kilometres per second, almost 1% the speed of light. 

“We are used to thinking about events in space taking place slowly, over millions or billions of years,” added Jennifer Hoffman, a co-author and a professor at the University of Denver. “In this system, the observatory is showing that the dust shells are expanding from one year to the next.”

“Seeing the real-time movement of these shells between Webb’s observations that were taken only 13 months apart is truly remarkable,” said Olivia Jones, a co-author at the UK Astronomy Technology Centre, Edinburgh. “These new results are giving us a first glimpse of the potential role of such massive binaries as factories of dust in the Universe.”

Like clockwork, the stars’ winds generate dust for several months every eight years, as the pair make their closest approach during a wide, elongated orbit. Webb also shows where dust formation stops — look for the darker region at top left in both images.

The telescope’s mid-infrared images detected shells that have persisted for more than 130 years (older shells have dissipated enough that they are now too dim to detect). The researchers speculate that the stars will ultimately generate tens of thousands of dust shells over hundreds of thousands of years.

“Mid-infrared observations are absolutely crucial for this analysis, since the dust in this system is fairly cool. Near-infrared and visible-light observations would only show the shells that are closest to the star,” explained Ryan Lau, a co-author and astronomer at NSF NOIRLab in Tucson, Arizona, who led the initial research about this system. “With these incredible new details, the telescope is also allowing us to study exactly when the stars are forming dust — almost to the day.”

The distribution of the dust isn’t uniform. Though these differences aren’t obvious in Webb’s images, the team found that some of the dust has ‘piled up’, forming amorphous, delicate clouds that are as large as our entire Solar System. Many other individual dust particles float freely. Every speck is as small as one-hundredth the width of a human hair. Clumpy or not, all of the dust moves at the same speed and is carbon rich.

The future of this system

What will happen to these stars over millions or billions of years, after they have finished ‘spraying’ their surroundings with dust? The Wolf-Rayet star in this system is 10 times more massive than the Sun and nearing the end of its life. In its final ‘act’, this star will either explode as a supernova — possibly blasting away some or all of the dust shells — or collapse into a black hole, which would leave the dust shells intact.

Though no one can predict with any certainty what will happen, researchers are rooting for the black hole scenario.

“A major question in astronomy is, where does all the dust in the universe come from?” Lau said. “If carbon-rich dust like this survives, it could help us begin to answer that question.”

“We know carbon is necessary for the formation of rocky planets and solar systems like ours,” Hoffman added. “It’s exciting to get a glimpse into how binary star systems not only create carbon-rich dust, but also propel it into our galactic neighborhood.”

These results have been published in the Astrophysical Journal Letters and were presented in a press conference at the 245th meeting of the American Astronomical Society in National Harbor, Maryland.

Notes

[1] A Wolf-Rayet star is born with at least 25 times more mass than our Sun and is nearing the end of its life, when it will likely collapse directly to black hole, or explode as a supernova. Burning hotter than in its youth, a Wolf-Rayet star generates powerful winds that push huge amounts of gas into space. The Wolf-Rayet star in this particular pair may have shed more than half its original mass via this process.

 

Press release from ESA Webb.

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Hubble sees aftermath of galaxy’s scrape with Milky Way, at the Large Magellanic Cloud (LMC)

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A whitish, whirlpool-like galaxy at middle of top edge, and a tadpole-shaped structure sweeps from left to right across lower half. A label pointing to outer, left of galaxy reads “Earth.” Faint, purple haze labelled “Milky Way Halo” surrounds galaxy and stretches to graphic’s edges. The tadpole-shaped object is the Large Magellanic Cloud, or LMC, with its own halo and streaming tail. Semi-circular, progressively darker layers of purple labelled “LMC Halo” surround the LMC, which appears roughly circular, with a central, light yellow bar. Cloud-like features sprinkled with white specks surround this bar. Trailing the LMC is a large, tail-like feature labelled “Stream.” Three light blue lines point from the label “Earth” through the LMC’s halo, and to three corresponding quasars, which are off screen.

Hubble sees aftermath of galaxy’s scrape with Milky Way, at the Large Magellanic Cloud (LMC)

Encounter blew away most of smaller galaxy’s gaseous halo

Labelled “artist’s concept” at bottom right, the graphic shows a closeup of a dwarf galaxy, which appears roughly circular with a light yellow bar in the centre. Faint, blue, wispy, cloud-like features surround this yellow bar, and they are sprinkled with tiny white specks. A wide, wispy, purple arc appears to the left of the galaxy. Trailing the galaxy is a large, faint, wide, tail-like feature.
This artist’s concept shows a closeup of the Large Magellanic Cloud (LMC), a dwarf galaxy that is one of the Milky Way galaxy’s nearest neighbours. Scientists think that the LMC has just completed its closest approach to the much more massive Milky Way. This encounter has blown away most of the spherical halo of gas that surrounds the LMC. The bright purple bow shocks represent the leading edge of the LMC’s halo, which is being compressed as the Milky Way’s halo pushes back against the incoming LMC. The pressure is stripping much of the LMC’s halo and blowing it backward into a streaming tail of gas. The dwarf galaxy is cocooned within its remaining halo. An actual science image of the LMC is combined with an artist’s rendering of the galaxy’s halo.
Credit: NASA, ESA, R. Crawford (STScI)

In an epic story of survival witnessed by the NASA/ESA Hubble Space Telescope, one of our nearest galactic neighbours has crashed through the Milky Way galaxy’s gaseous halo and lived to tell the tale. But in the process, this dwarf galaxy, called the Large Magellanic Cloud (LMC), has been stripped of most of its own surrounding halo of gas. Researchers were surprised to find such an extremely small gaseous halo remaining — one around 10 times smaller than halos of other galaxies of similar mass. Still, the LMC has held onto enough of its gas to keep forming new stars. A smaller galaxy wouldn’t have survived such an encounter. This is the first time astronomers have been able to measure the size of the LMC’s halo — something they could do only with Hubble.

The Large Magellanic Cloud, also called the LMC, is one of the Milky Way galaxy’s nearest neighbours. This dwarf galaxy looms large in the southern nighttime sky at 20 times the apparent diameter of the full Moon.

Many researchers theorise that the LMC is not in orbit around our galaxy, but is just passing by. Those scientists think that the LMC has just completed its closest approach to the much more massive Milky Way. This passage has blown away most of the spherical halo of gas that surrounds the LMC.

Now, for the first time, astronomers have been able to measure the size of the LMC’s halo — something they could do only with Hubble. In a new study published in the Astrophysical Journal Letters, researchers were surprised to find that it is so extremely small — about 50 000 light-years across. That’s around 10 times smaller than the halos of other galaxies that are the same mass as the LMC. Its compactness tells the story of its encounter with the Milky Way.

“The LMC is a survivor,” said Andrew Fox of AURA/STScI for the European Space Agency in Baltimore, who was principal investigator on the observations. “Even though it’s lost a lot of its gas, it’s got enough left to keep forming new stars. So new star-forming regions can still be created. A smaller galaxy wouldn’t have lasted — there would be no gas left, just a collection of aging red stars.”

Though quite a bit the worse for wear, the LMC still retains a compact, stubby halo of gas — something that it wouldn’t have been able to hold onto gravitationally had it been less massive. The LMC is 10 percent the mass of the Milky Way.

“Because of the Milky Way’s own giant halo, the LMC’s gas is getting truncated, or quenched,” explained STScI’s Sapna Mishra, the lead author of the paper chronicling this discovery. “But even with this catastrophic interaction with the Milky Way, the LMC is able to retain 10 percent of its halo because of its high mass.”

A whitish, whirlpool-like galaxy at middle of top edge, and a tadpole-shaped structure sweeps from left to right across lower half. A label pointing to outer, left of galaxy reads “Earth.” Faint, purple haze labelled “Milky Way Halo” surrounds galaxy and stretches to graphic’s edges. The tadpole-shaped object is the Large Magellanic Cloud, or LMC, with its own halo and streaming tail. Semi-circular, progressively darker layers of purple labelled “LMC Halo” surround the LMC, which appears roughly circular, with a central, light yellow bar. Cloud-like features sprinkled with white specks surround this bar. Trailing the LMC is a large, tail-like feature labelled “Stream.” Three light blue lines point from the label “Earth” through the LMC’s halo, and to three corresponding quasars, which are off screen.
This artist’s concept shows the Large Magellanic Cloud, or LMC, in the foreground as it passes through the gaseous halo of the much more massive Milky Way galaxy. The encounter has blown away most of the spherical halo of gas that surrounds the LMC, as illustrated by the trailing gas stream reminiscent of a comet’s tail. Still, a compact halo remains, and scientists do not expect this residual halo to be lost. The team surveyed the halo by using the background light of 28 quasars, an exceptionally bright type of active galactic nucleus that shines across the Universe like a lighthouse beacon. Their light allows scientists to ‘see’ the intervening halo gas indirectly through the absorption of the background light. The lines represent the Hubble Space Telescope’s view from its orbit around Earth to the distant quasars through the LMC’s gas.
Credit: NASA, ESA, R. Crawford (STScI)

A gigantic hair dryer

Most of the LMC’s halo was blown away by a phenomenon called ram-pressure stripping. The dense environment of the Milky Way pushes back against the incoming LMC and creates a wake of gas trailing the dwarf galaxy — like the tail of a comet.

“I like to think of the Milky Way as this giant hairdryer, and it’s blowing gas off the LMC as it comes into us,” said Fox. “The Milky Way is pushing back so forcefully that the ram pressure has stripped off most of the original mass of the LMC’s halo. There’s only a little bit left, and it’s this small, compact leftover that we’re seeing now.”

As the ram pressure pushes away much of the LMC’s halo, the gas slows down and eventually will rain into the Milky Way. But because the LMC has just passed its closest approach to the Milky Way and is moving outward into deep space again, scientists do not expect the whole halo will be lost.

Only with Hubble

To conduct this study, the research team analysed ultraviolet observations from the Mikulski Archive for Space Telescopes at STScI. Most ultraviolet light is blocked by Earth’s atmosphere, so it cannot be observed with ground-based telescopes. Hubble is currently the only space telescope that is tuned to detect these wavelengths of light, so this study was only possible with Hubble.

The team surveyed the halo by using the background light of 28 bright quasars. The brightest type of active galactic nucleus, quasars are believed to be powered by supermassive black holes. Shining like lighthouse beacons, they allow scientists to ‘see’ the intervening halo gas indirectly through the absorption of the background light. Quasars reside throughout the Universe at extreme distances from our galaxy.

The scientists used data from Hubble’s Cosmic Origins Spectrograph (COS) to detect the presence of the halo gas by the way it absorbs certain colours of light from background quasars. A spectrograph breaks light into its component wavelengths to reveal clues to the object’s state, temperature, speed, quantity, distance, and composition. With COS, they measured the velocity of the gas around the LMC, which allowed them to determine the size of the halo.

Because of its mass and proximity to the Milky Way, the LMC is a unique astrophysics laboratory. Seeing the LMC’s interplay with our galaxy helps scientists understand what happened in the early Universe, when galaxies were closer together. It also shows just how messy and complicated the process of galaxy interaction is.

“This is a fantastic example of the cutting-edge science still being enabled by Hubble’s unique capabilities,” said Professor Carole Mundell, Director of Science at the European Space Agency. “This result gives us precious new insights into the complex history of the Milky Way and its nearby satellite galaxies.”

Looking to the future

The team will next study the front side of the LMC’s halo, an area that has not yet been explored.

“In this new programme, we are going to probe five sightlines in the region where the LMC’s halo and the Milky Way’s halo are colliding,” said co-author Scott Lucchini of the Center for Astrophysics | Harvard & Smithsonian. “This is the location where the halos are compressed, like two balloons pushing against each other.”

A 3-panel graphic labelled “artist’s concept” at bottom, right corner. Each of the three panels shows the same whitish, whirlpool-like spiral galaxy at middle of top edge. A faint, purple haze surrounds galaxy and stretches to panel’s edges. At the middle of the right side of the first panel, a white dot surrounded by fuzzy, lighter purple halo approaches. In middle panel, a pronounced, light purple bow shock develops to left part of the halo. The right part of halo is being stripped and blown back into a streaming tail of gas. The bottom panel shows the tail becoming longer and more defined as the now tadpole-like object curves below the spiral galaxy and sweeps toward the upper left.
This artist’s concept illustrates the Large Magellanic Cloud’s (LMC’s) encounter with the Milky Way galaxy’s gaseous halo. In the top panel, at the middle of the right side, the LMC begins crashing through our galaxy’s much more massive halo. The bright purple bow shock represents the leading edge of the LMC’s halo, which is being compressed as the Milky Way’s halo pushes back against the incoming LMC. In the middle panel, part of the halo is being stripped and blown back into a streaming tail of gas that eventually will rain into the Milky Way. The bottom panel shows the progression of this interaction, as the LMC’s comet-like tail becomes more defined. A compact LMC halo remains. Because the LMC is just past its closest approach to the Milky Way and is moving outward into deep space again, scientists do not expect the residual halo will be lost.
Credit: NASA, ESA, R. Crawford (STScI)

More information

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.
Image credit: NASA, ESA, R. Crawford (STScI)

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Press release from ESA Hubble

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Webb Draws Back Curtain On Universe’s Early Galaxies

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Webb Draws Back Curtain On Universe’s Early Galaxies

Webb Draws Back Curtain On Universe’s Early Galaxies

Telescope’s Infrared Vision Explores The Final Frontier

The powerful NASA/ESA/CSA James Webb Space Telescope has found an unexpectedly rich ‘undiscovered country’ of early galaxies that has been largely hidden until now.

A few days after officially starting science operations, the NASA/ESA/CSA James Webb Space Telescope propelled astronomers into a realm of early galaxies, previously hidden beyond the grasp of all other telescopes. Webb is now unveiling a very rich Universe where the first forming galaxies look remarkably different from the mature galaxies seen around us today. Researchers have found two exceptionally bright galaxies that existed approximately 300 and 400 million years after the Big Bang. Their extreme brightness is puzzling to astronomers. The young galaxies are transforming gas into stars as fast as they can and they appear compacted into spherical or disc shapes that are much smaller than our Milky Way galaxy. The onset of stellar birth may have been just 100 million years after the Big Bang, which happened 13.8 billion years ago.

“Everything we see is new. Webb is showing us that there’s a very rich Universe beyond what we imagined,” said Tommaso Treu of the University of California at Los Angeles, a co-investigator on one of the Webb programmes. “Once again the Universe has surprised us. These early galaxies are very unusual in many ways.”

The results are from Webb’s GLASS-JWST Early Release Science Program (Grism Lens-Amplified Survey from Space), and Cosmic Evolution Early Release Science Survey (CEERS). Two research papers, led by Marco Castellano of the National Institute for Astrophysics in Rome, Italy, and Rohan Naidu of the Center for Astrophysics | Harvard & Smithsonian and the Massachusetts Institute of Technology in Cambridge, Massachusetts have been published in the Astrophysical Journal Letters.

Webb Draws Back Curtain On Universe’s Early Galaxies
Two images showing thousands of galaxies of different colours, shapes, and sizes. In between the two images are two pull-outs showing details from the large images. Credit: NASA, ESA, CSA, T. Treu (UCLA)

In just four days of analysis, researchers found two exceptionally bright galaxies in the GLASS-JWST images. These galaxies existed approximately 450 and 350 million years after the Big Bang (with redshifts of approximately 10.5 and 12.5, respectively), which future spectroscopic measurements with Webb will help confirm.

“With Webb, we were amazed to find the most distant starlight that anyone had ever seen, just days after Webb released its first data,”

said Rohan Naidu of the more distant GLASS galaxy, referred to as GLASS-z12, which is believed to date back to 350 million years after big bang. The previous record holder is galaxy GN-z11, which existed 400 million years after the big bang (redshift 11.1), and identified in 2016 by Hubble and Keck Observatory in deep-sky programmes.

“Based on all the predictions, we thought we had to search a much bigger volume of space to find such galaxies,” said Castellano.

“These observations just make your head explode. This is a whole new chapter in astronomy. It’s like an archaeological dig, when suddenly you find a lost city or something you didn’t know about. It’s just staggering,” added Paola Santini, fourth author of the Castellano et al. GLASS-JWST paper.

“While the distances of these early sources still need to be confirmed with spectroscopy, their extreme brightnesses are a real puzzle, challenging our understanding of galaxy formation,” noted Pascal Oesch of the University of Geneva in Switzerland.

Graphic titled “James Webb Space Telescope: Pandora’s Cluster, Abell 2744,” with compass arrows, scale bar, and colour key for reference. Credit: NASA, ESA, CSA, T. Treu (UCLA)

The Webb observations nudge astronomers toward a consensus that an unusual number of galaxies in the early Universe were much brighter than expected. This will make it easier for Webb to find even more early galaxies in subsequent deep sky surveys, say researchers.

“We’ve nailed something that is incredibly fascinating. These galaxies would have had to have started coming together maybe just 100 million years after the Big Bang. Nobody expected that the dark ages would have ended so early,” said Garth Illingworth of the University of California at Santa Cruz. “The primal Universe would have been just one hundredth of its current age. It’s a sliver of time in the 13.8-billion-year-old evolving cosmos.”

Naidu/Oesch team member Erica Nelson of the University of Colorado noted that “our team was struck by being able to measure the shapes of these first galaxies; their calm, orderly discs question our understanding of how the first galaxies formed in the crowded, chaotic early Universe.” This remarkable discovery of compact discs at such early times was only possible because Webb’s images are so much sharper, in infrared light, than Hubble’s.

“These galaxies are very different from the Milky Way or other big galaxies we see around us today,” said Treu.

Illingworth emphasised that the two bright galaxies found by these teams have a lot of light. He said one option is that they could have been very massive, with lots of low-mass stars, like later galaxies. Alternatively, they could be much less massive, consisting of far fewer extraordinarily bright stars, known as Population III stars. Long theorised, they would be the first stars ever born, blazing at blistering temperatures and made up of only primordial hydrogen and helium; only later would stars cook up heavier elements in their nuclear fusion furnaces. No such extremely hot, primordial stars are seen in the local Universe.

“Indeed, the most distant source is very compact, and its colours seem to indicate that its stellar population is particularly devoid of heavy elements and could even contain some Population III stars. Only Webb spectra will tell,” said Adriano Fontana, second author of the Castellano et al. paper and a member of the GLASS-JWST team.

Present Webb distance estimates to these two galaxies are based on measuring their infrared colours. Eventually, follow-up spectroscopy measurements showing how light has been stretched in the expanding Universe will provide independent verification of these cosmic yardstick measurements.

Webb Draws Back Curtain On Universe’s Early Galaxies
Graphic titled “Abell 2744 GLASS JWST/NIRCam” with two large images showing thousands of galaxies of different colours, shapes, and sizes, and two smaller pull-outs showing details in the large images. Credit: NASA, ESA, CSA, T. Treu (UCLA)

More information

Webb is the largest, most powerful telescope ever launched into space. Under an international collaboration agreement, ESA provided the telescope’s launch service, using the Ariane 5 launch vehicle. Working with partners, ESA was responsible for the development and qualification of Ariane 5 adaptations for the Webb mission and for the procurement of the launch service by Arianespace. ESA also provided the workhorse spectrograph NIRSpec and 50% of the mid-infrared instrument MIRI, which was designed and built by a consortium of nationally funded European Institutes (The MIRI European Consortium) in partnership with JPL and the University of Arizona.

Webb is an international partnership between NASA, ESA and the Canadian Space Agency (CSA).

Press release from ESA Webb

 

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Hubble data confirms galaxies lacking dark matter

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NGC1052-DF2 Hubble galaxies dark matter

Hubble data confirms galaxies lacking dark matter

NGC1052-DF2 Hubble galaxies dark matter
Hubble data confirms galaxies lacking dark matter: NGC1052-DF2. Credits: NASA, ESA, Z. Shen and P. van Dokkum (Yale University), and S. Danieli (Institute for Advanced Study)

The most accurate distance measurement yet of ultra-diffuse galaxy (UDG) NGC1052-DF2 (DF2) confirms beyond any shadow of a doubt that it is lacking in dark matter. The newly measured distance of 22.1 +/-1.2 megaparsecs was obtained by an international team of researchers led by Zili Shen and Pieter van Dokkum of Yale University and Shany Danieli, a NASA Hubble Fellow at the Institute for Advanced Study.

“Determining an accurate distance to DF2 has been key in supporting our earlier results,” stated Danieli. “The new measurement reported in this study has crucial implications for estimating the physical properties of the galaxy, thus confirming its lack of dark matter.”

The results, published in Astrophysical Journal Letters on June 9, 2021, are based on 40 orbits of NASA’s Hubble Space Telescope, with imaging by the Advanced Camera for Surveys and a “tip of the red giant branch” (TRGB) analysis, the gold standard for such refined measurements. In 2019, the team published results measuring the distance to neighboring UDG NGC1052-DF4 (DF4) based on 12 Hubble orbits and TRGB analysis, which provided compelling evidence of missing dark matter. This preferred method expands on the team’s 2018 studies that relied on “surface brightness fluctuations” to gauge distance. Both galaxies were discovered with the Dragonfly Telephoto Array at the New Mexico Skies observatory.

NGC1052-DF2 Hubble galaxies dark matter
Hubble data confirms galaxies lacking dark matter: NGC1052-DF2. Credits: NASA, ESA, Z. Shen and P. van Dokkum (Yale University), and S. Danieli (Institute for Advanced Study)

“We went out on a limb with our initial Hubble observations of this galaxy in 2018,” van Dokkum said. “I think people were right to question it because it’s such an unusual result. It would be nice if there were a simple explanation, like a wrong distance. But I think it’s more fun and more interesting if it actually is a weird galaxy.”

In addition to confirming earlier distance findings, the Hubble results indicated that the galaxies were located slightly farther away than previously thought, strengthening the case that they contain little to no dark matter. If DF2 were closer to Earth, as some astronomers claim, it would be intrinsically fainter and less massive, and the galaxy would need dark matter to account for the observed effects of the total mass.

Dark matter is widely considered to be an essential ingredient of galaxies, but this study lends further evidence that its presence may not be inevitable. While dark matter has yet to be directly observed, its gravitational influence is like a glue that holds galaxies together and governs the motion of visible matter. In the case of DF2 and DF4, researchers were able to account for the motion of stars based on stellar mass alone, suggesting a lack or absence of dark matter. Ironically, the detection of galaxies deficient in dark matter will likely help to reveal its puzzling nature and provide new insights into galactic evolution.

While DF2 and DF4 are both comparable in size to the Milky Way galaxy, their total masses are only about one percent of the Milky Way’s mass. These ultra-diffuse galaxies were also found to have a large population of especially luminous globular clusters.

This research has generated a great deal of scholarly interest, as well as energetic debate among proponents of alternative theories to dark matter, such as Modified Newtonian dynamics (MOND). However, with the team’s most recent findings–including the relative distances of the two UDGs to NGC1052–such alternative theories seem less likely. Additionally, there is now little uncertainty in the team’s distance measurements given the use of the TRGB method. Based on fundamental physics, this method depends on the observation of red giant stars that emit a flash after burning through their helium supply that always happens at the same brightness.

“There’s a saying that extraordinary claims require extraordinary evidence, and the new distance measurement strongly supports our previous finding that DF2 is missing dark matter,” stated Shen. “Now it’s time to move beyond the distance debate and focus on how such galaxies came to exist.”

Moving forward, researchers will continue to hunt for more of these oddball galaxies, while considering a number of questions such as: How are UDGs formed? What do they tell us about standard cosmological models? How common are these galaxies, and what other unique properties do they have? It will take uncovering many more dark matter-less galaxies to resolve these mysteries and the ultimate question of what dark matter really is.

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The published ApJL article is available here: https://iopscience.iop.org/article/10.3847/2041-8213/ac0335

A pre-publication is available at: https://arxiv.org/abs/2104.03319

About the Institute

The Institute for Advanced Study is one of the world’s foremost centers for theoretical research and intellectual inquiry. Located in Princeton, N.J., the IAS is dedicated to independent study across the sciences and humanities. Founded in 1930, the Institute is devoted to advancing the frontiers of knowledge without concern for immediate application. From founding IAS Professor Albert Einstein to the foremost thinkers of today, the IAS enables bold, curiosity-driven innovation to enrich society in unexpected ways.

Each year, the Institute welcomes more than 200 of the world’s most promising post-doctoral researchers and scholars who are selected and mentored by a permanent Faculty, each of whom are preeminent leaders in their fields. Among present and past Faculty and Members there have been 35 Nobel Laureates, 42 of the 60 Fields Medalists, and 21 of the 24 Abel Prize Laureates, as well as many MacArthur Fellows and Wolf Prize winners.

 

Press release from the Institute for Advanced Study

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ALMA spots twinkling heart of Milky Way

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ALMA Milky Way

Astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) found quasi-periodic flickers in millimeter-waves from the center of the Milky Way, Sagittarius (Sgr) A*. The team interpreted these blinks to be due to the rotation of radio spots circling the supermassive black hole with an orbit radius smaller than that of Mercury. This is an interesting clue to investigate space-time with extreme gravity.

“It has been known that Sgr A* sometimes flares up in millimeter wavelength,” tells Yuhei Iwata, the lead author of the paper published in the Astrophysical Journal Letters and a graduate student at Keio University, Japan. “This time, using ALMA, we obtained high-quality data of radio-wave intensity variation of Sgr A* for 10 days, 70 minutes per day. Then we found two trends: quasi-periodic variations with a typical time scale of 30 minutes and hour-long slow variations.”

The different color dots show the flux at different frequencies (blue: 234.0 GHz, green: 219.5 GHz, red: 217.5 GHz). Variations with about a 30-minute period are seen in the diagram. Credits: Y. Iwata et al./Keio University

Astronomers presume that a supermassive black hole with a mass of 4 million suns is located at the center of Sgr A*. Flares of Sgr A* have been observed not only in millimeter wavelength, but also in infrared light and X-ray. However, the variations detected with ALMA are much smaller than the ones previously detected, and it is possible that these levels of small variations always occur in Sgr A*.

ALMA Milky Way
Hot spots circling around the black hole could produce the quasi-periodic millimeter emission detected with ALMA. Credits: Keio University

The black hole itself does not produce any kind of emission. The source of the emission is the scorching gaseous disk around the black hole. The gas around the black hole does not go straight to the gravitational well, but it rotates around the black hole to form an accretion disk.

The team focused on short timescale variations and found that the variation period of 30 minutes is comparable to the orbital period of the innermost edge of the accretion disk with the radius of 0.2 astronomical units (1 astronomical unit corresponds to the distance between the Earth and the Sun: 150 million kilometers). For comparison, Mercury, the solar system’s innermost planet, circles around the Sun at a distance of 0.4 astronomical units. Considering the colossal mass at the center of the black hole, its gravity effect is also extreme in the accretion disk.

“This emission could be related with some exotic phenomena occurring at the very vicinity of the supermassive black hole,” says Tomoharu Oka, a professor at Keio University.

Their scenario is as follows. Hot spots are sporadically formed in the disk and circle around the black hole, emitting strong millimeter waves. According to Einstein’s special relativity theory, the emission is largely amplified when the source is moving toward the observer with a speed comparable to that of light. The rotation speed of the inner edge of the accretion disk is quite large, so this extraordinary effect arises. The astronomers believe that this is the origin of the short-term variation of the millimeter emission from Sgr A*.

The team supposes that the variation might affect the effort to make an image of the supermassive black hole with the Event Horizon Telescope. “In general, the faster the movement is, the more difficult it is to take a photo of the object,” says Oka. “Instead, the variation of the emission itself provides compelling insight for the gas motion. We may witness the very moment of gas absorption by the black hole with a long-term monitoring campaign with ALMA.” The researchers aim to draw out independent information to understand the mystifying environment around the supermassive black hole.

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The research team members are: Yuhei Iwata (Keio University), Tomoharu Oka (Keio University), Masato Tsuboi (Japan Space Exploration Agency/The University of Tokyo), Makoto Miyoshi (National Astronomical Observatory of Japan/SOKENDAI), and Shunya Takekawa (National Astronomical Observatory of Japan)

Press release on ALMA spotting twinkling heart of Milky Way from the National Institutes of Natural Sciences

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