Wednesday, November 20, 2024

ALMA Reveals Planets Can Form ALMA Reveals Planets Can Form Under Harsh RadiationUnder Harsh Radiation

Images captured by ALMA's most extended antenna configuration reveal surprisingly rich disk structures in the sigma Ori cluster. Credit: ALMA (ESO/JAO/NAOJ/NRAO), J. Huang et. al. Hi-Res File

Artist concept of planet formation occuring in harsh stellar environments.
Credit: NSF/AUI/NSF NRAO/S.Dagnello.
Hi-Res File



International team of astronomers reveal high-resolution look at protoplanetary disks in extreme environment

New observations from the Atacama Large Millimeter/submillimeter Array (ALMA) suggest that planet formation can occur even in harsh stellar environments previously thought to be inhospitable.

An international team of astronomers used ALMA to capture high-resolution images of eight protoplanetary disks in the Sigma Orionis cluster, which is irradiated by intense ultraviolet light from a massive nearby star. To their surprise, they found evidence of gaps and rings in most of the disks—structures commonly associated with the formation of giant planets, like Jupiter.

“We expected the high levels of radiation in this cluster to inhibit planet formation in the outer regions of these disks,” said lead author Jane Huang. “But instead, we’re seeing signs that planets may be forming at distances of tens of astronomical units from their stars, similar to what we’ve observed in less harsh environments.”

Previous studies had focused on disks in regions with low ultraviolet radiation. This new research provides the ALMA’s highest resolution look at disks in a more extreme environment. “These observations suggest that the processes driving planet formation are quite robust and can operate even under challenging circumstances,” Huang noted. “This gives us more confidence that planets may be forming in even more places throughout the galaxy, even in regions we previously thought were too harsh.”

The findings have implications for understanding the formation of our own Solar System, which likely evolved in a similarly high-radiation environment. They also motivate future studies of disks in even more extreme stellar neighborhoods.

The research team used ALMA’s most extended antenna configuration to obtain unprecedented detail in their disk images, achieving a resolution of about 8 astronomical units. This allowed them to resolve multiple distinct gaps and rings in several of the disks. While the exact nature of these disk structures is still debated, they are thought to be either conducive to planet formation or a consequence of interactions between forming planets and the disk material.

This study demonstrates the power of ALMA to probe planet formation in diverse environments across the galaxy. As astronomers build a more complete picture of how planets form under different conditions, they come closer to understanding the origins of Earth and the prevalence of planets around other stars.

This research was published in the Astrophysical Journal.




About ALMA

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 National Science and Technology Council (NSTC) in Taiwan 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.

About NRAO

The National Radio Astronomy Observatory (NRAO) is a facility of the U.S. National Science Foundation, operated under cooperative agreement by Associated Universities, Inc.

Link: Scientific Paper


Tuesday, November 19, 2024

Spiral from the side

A spiral galaxy seen directly from the side, such that its disc looks like a narrow diagonal band across the image. A band of dark dust covers the disc in the centre most of the way out to the ends, and the disc glows around that. In the centre a whitish circle of light bulges out above and below the disc. The tips of the disc are a bit bent. The background is black and mostly empty. Credit: ESA/Hubble & NASA, R. Windhorst, W. Keel

What kind of astronomical object is this? It doesn’t look quite like the kinds of galaxies, nebulae, star clusters or galaxy clusters which Hubble normally brings us images of. In fact, this is a spiral galaxy, named UGC 10043 — we just happen to be seeing it directly from the side! Located roughly 150 million light-years from Earth in the constellation Serpens, UGC 10043 is one of the somewhat rare spiral galaxies that are seen edge-on.

From this point of view, we see the galaxy’s disc as a sharp line through space, overlain with a prominent dust lane. This dust is spread across the spiral arms of UGC 10043, but it looks very thick and cloudy when viewed from the side. You can even see the lights of some active star-forming regions in the arms, shining out from behind the dust. Strikingly, we can also see that the centre of the galaxy sports a glowing, almost egg-shaped ‘bulge’, rising far above and below the disc. All spiral galaxies have a bulge like this one as part of their structure, containing stars that orbit the galactic centre on paths above and below the whirling disc; it’s a feature that isn’t normally obvious in pictures of galaxies. The unusually large size of this bulge compared to the galaxy’s disc is possibly thanks to UGC 10043 siphoning material from a nearby dwarf galaxy. This may also be why the disc is warped, bending up at one end and down at the other.

Like most of the full-colour Hubble images released by ESA/Hubble, this image is a composite, made up of several individual snapshots taken by Hubble at different times and capturing different wavelengths of light. You can see the exact images used in the sidebar on this page. A notable aspect of this image is that the two sets of Hubble data used were collected 23 years apart, in 2000 and 2023! Hubble’s longevity doesn’t just afford us the ability to produce new and better images of old targets; it also provides a long-term archive of data which only becomes more and more useful to astronomers.



Monday, November 18, 2024

Astronomers discover two galaxies aligned in a way where their gravity acts as a compound lens

Summary of evidence showing the unique source and double lens nature of J1721+8842.
Credit: arXiv (2024). DOI: 10.48550/arxiv.2411.04177


An international team of astronomers has discovered an instance of two galaxies aligned in a way where their gravity acts as a compound lens. The group has written a paper describing the findings and posted it on the arXiv preprint server.

Prior research has led to many findings of galaxies, or clusters of them, bending light in ways that were predicted by Einstein's theory of general relativity. Astronomers have noted that some of them work as imperfect lenses, distorting the light behind them in interesting ways.

Some researchers have also noted that elliptical galaxies can serve as a lens, serving to brighten the light behind them. In this new effort, the research team has found, for the first time, two galaxies that align in a way that allows their gravity to work as a compound lens.

A compound lens, as its name suggests, is made up of two lenses. Those made artificially are cemented together and work to correct each other's dispersion. In the astronomical case, a compound lens can be made by the dual effects of two galaxies lined up next to one another just right.

The researchers note that when the system, J1721+8842, was first discovered, it was believed that there was just one elliptical galaxy bending the light from a quasar behind it. In analyzing data over a two-year period, the researchers of this new effort found variations in the quasar imagery. They also found small bits of light that, at first glance, appeared to be duplicates from a single source.

A closer look revealed that they matched the light from the main quartet of lights—a finding that showed that all six bits of light were from the same source. Prior research had suggested such an image could be the result of a natural compound lens.

When adding data from the James Webb Space Telescope, the team found that a reddish ring that was mixed with the other lights and was thought to be an Einstein ring was, in reality, a second lensing galaxy. The researchers next built a computer model and used it to confirm that the observation they had made was indeed that of a compound lens.

The research team expects the finding will allow other researchers to more precisely calculate the Hubble constant, perhaps leading to a resolution of conflict over its actual value.

by Bob Yirka , Phys.org




More information: F. Dux et al, J1721+8842: The first Einstein zig-zag lens, arXiv (2024). DOI: 10.48550/arxiv.2411.04177

Journal information: arXiv

© 2024 Science X Network


Sunday, November 17, 2024

A formula for life? New model calculates chances of intelligent beings in our Universe and beyond

How the same region of the Universe would look in terms of the amount of stars for different values of the dark energy density. Clockwise, from top left, no dark energy, same dark energy density as in our Universe, 30 and 10 times the dark energy density in our Universe. The images are generated from a suite of cosmological simulations.Credit:Oscar Veenema
Licence type: Attribution (CC BY 4.0)

The chances of intelligent life emerging in our Universe – and in any hypothetical ones beyond it – can be estimated by a new theoretical model which has echoes of the famous Drake Equation.

This was the formula that American astronomer Dr Frank Drake came up with in the 1960s to calculate the number of detectable extraterrestrial civilisations in our Milky Way galaxy.

More than 60 years on, astrophysicists led by Durham University have produced a different model which instead focuses on the conditions created by the acceleration of the Universe's expansion and the amount of stars formed.

It is thought this expansion is being driven by a mysterious force called dark energy that makes up more than two thirds of the Universe.

What is the calculation?

Since stars are a precondition for the emergence of life as we know it, the model could therefore be used to estimate the probability of generating intelligent life in our Universe, and in a multiverse scenario of hypothetical different universes.

The new research does not attempt to calculate the absolute number of observers (i.e. intelligent life) in the universe but instead considers the relative probability of a randomly chosen observer inhabiting a universe with particular properties.

It concludes that a typical observer would expect to experience a substantially larger density of dark energy than is seen in our own Universe – suggesting the ingredients it possesses make it a rare and unusual case in the multiverse.

>This Hubble Space Telescope image captures a triple-star system, which can host potentially-habitable planets. Our nearest stellar neighbour, the Alpha Centauri system, includes three stars. Credit: NASA, ESA, G. Duchene (Universite de Grenoble I); Image Processing: Gladys Kober (NASA/Catholic University of America)
Licence type: Attribution (CC BY 4.0)

The approach presented in the paper involves calculating the fraction of ordinary matter converted into stars over the entire history of the Universe, for different dark energy densities.

The model predicts this fraction would be approximately 27 per cent in a universe that is most efficient at forming stars, compared to 23 per cent in our own Universe.

This means we don't live in the hypothetical universe with the highest odds of forming intelligent life forms. Or in other words, the value of dark energy density we observe in our Universe is not the one that would maximise the chances of life, according to the model.

Dark energy's impact on our existence

Lead researcher Dr Daniele Sorini, of Durham University's Institute for Computational Cosmology, said: "Understanding dark energy and the impact on our Universe is one of the biggest challenges in cosmology and fundamental physics.

"The parameters that govern our Universe, including the density of dark energy, could explain our own existence.

"Surprisingly, though, we found that even a significantly higher dark energy density would still be compatible with life, suggesting we may not live in the most likely of universes."

The new model could allow scientists to understand the effects of differing densities of dark energy on the formation of structures in the Universe and the conditions for life to develop in the cosmos.

The Drake Equation, a mathematical formula for the probability of finding life or advanced civilisations in the Universe, as revised by two University of Rochester researchers in 2016. Credit: University of Rochester
Licence type: Attribution (CC BY 4.0)

Dark energy makes the Universe expand faster, balancing gravity's pull and creating a universe where both expansion and structure formation are possible.

However, for life to develop, there would need to be regions where matter can clump together to form stars and planets, and it would need to remain stable for billions of years to allow life to evolve.

Crucially, the research suggests that the astrophysics of star formation and the evolution of the large-scale structure of the Universe combine in a subtle way to determine the optimal value of the dark energy density needed for the generation of intelligent life.

Professor Lucas Lombriser, Université de Genève and co-author of the study, added: "It will be exciting to employ the model to explore the emergence of life across different universes and see whether some fundamental questions we ask ourselves about our own Universe must be reinterpreted."

Drake Equation explained

Dr Drake's equation was more of a guide for scientists on how to go about searching for life, rather than an estimating tool or serious attempt to determine an accurate result.

Its parameters included the rate of yearly star formation in the Milky Way, the fraction of stars with planets orbiting them and the number of worlds that could potentially support life.

By comparison, the new model connects the rate of yearly star formation in the Universe with its fundamental ingredients, such as the aforementioned dark energy density.

The study, which was funded by the European Research Council and also involved scientists at the University of Edinburgh and the Université de Genève, has been published today in Monthly Notices of the Royal Astronomical Society.




Media contacts

Sam Tonkin
Royal Astronomical Society
Mob: +44 (0)7802 877 700

press@ras.ac.uk

Dr Robert Massey
Royal Astronomical Society
Mob: +44 (0)7802 877 699

press@ras.ac.uk

Scientific contacts

Dr Daniele Sorini
Durham University

daniele.sorini@durham.ac.uk



Further information

The paper ‘
The impact of the cosmological constant on past and future star formation’, by Daniele Sorini, John A. Peacock and Lucas Lombriser, has been published in Monthly Notices of the Royal Astronomical Society. DOI: 10.1093/mnras/stae2236.

The Drake Equation's parameters in full are:

R* = the rate of yearly star formation in the Galaxy

fp= the fraction of stars with planets orbiting them

fg= the fraction of stars that could support habitable planets

ne = the number of planets that can potentially support life (per star with planets)

fl = the fraction of planets that actually develop life at some point

fc= the fraction of civilisations that emit detectable signs of their presence



Notes for editors

About the Royal Astronomical Society

The Royal Astronomical Society (RAS), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science.

The RAS organises scientific meetings, publishes international research and review journals, recognises outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 4,000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

The RAS accepts papers for its journals based on the principle of peer review, in which fellow experts on the editorial boards accept the paper as worth considering. The Society issues press releases based on a similar principle, but the organisations and scientists concerned have overall responsibility for their content.

Keep up with the RAS on
X, Facebook, LinkedIn and YouTube.

About Durham University

Durham University is a globally outstanding centre of teaching and research based in historic Durham City in the UK. We are a collegiate university committed to inspiring our people to do outstanding things at Durham and in the world.

We conduct research that improves lives globally and we are ranked as a world top 100 university with an international reputation in research and education (QS World University Rankings 2024).

We are a member of the Russell Group of leading research-intensive UK universities and we are consistently ranked as a top 10 university in national league tables (Times and Sunday Times Good University Guide, Guardian University Guide and The Complete University Guide).

For more information about Durham University visit:
www.durham.ac.uk/about/

Submitted by Sam Tonki


Saturday, November 16, 2024

Finding, Tracking and Characterizing Asteroids

Top-down view of the Solar System showing the position on August 9, 2024 UTC of all asteroids and comets detected by NEOWISE during the Reactivation Mission. The blue circles and points indicate the orbits and locations of Mercury, Venus and Mars. The Earth and its orbit are shown in cyan. Filled gray circles are Main Belt asteroids, filled green circles are Near Earth asteroids and the filled yellow squares are comets. The white points indicate the objects NEOWISE detected during the last week of surveying. The tick marks on the x and y axes are in increments of 1 AU. This animation shows how solar system object detections accumulated over the course of the survey. The white points show the new detections from each successive run of the WISE Moving Object Pipeline System, and illustrate how the NEOWISE scan longituded progress around the sky.

The Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) and IPAC at the California Institute of Technology announce the NEOWISE Final Data Release.

The Final Data Release includes data acquired during the eleventh year of the NEOWISE Reactivation mission (Mainzer et al. 2014, ApJ, 792, 30), 13 December 2023 to 1 August 2024. These data are combined with data from the first ten years of NEOWISE mission into a single archive that contains ~26.9 million sets of 3.4 and 4.6 micron images and a database of ~199 billion source detections extracted from those images.

NEOWISE scanned the sky over twenty-one complete times during its 10.6 years of survey operations, with approximately six months between survey passes. Twelve or more independent exposures are made on each point of the sky during each survey epoch making the NEOWISE archive a time-domain resource for extracting multiple, independent thermal flux and position measurements of solar system small bodies and background galactic and extragalactic sources.

A guide to the NEOWISE data release, data access instructions, and supporting documentation are available at http://wise2.ipac.caltech.edu/docs/release/neowise. Access to the NEOWISE data products is available via the on-line and API services of the NASA/IPAC Infrared Science Archive (IRSA) at https://irsa.ipac.caltech.edu.

NEOWISE is a joint project of the Jet Propulsion Laboratory/California Institute of Technology and the University of California, Los Angeles, funded by the National Aeronautics and Space Administration Planetary Science Division.

This top-down view of the Solar System shows the positions of all asteroids and comets detected by NEOWISE during the Reactivation Mission, which concluded operations on August 8, 2024. The blue circles and points indicate the orbits and locations of Mercury, Venus and Mars. The Earth and its orbit are shown in cyan. Filled gray circles are Main Belt asteroids, filled green circles are Near Earth asteroids and the filled yellow squares are comets. The white points indicate the objects NEOWISE detected during the last week of surveying. The tick marks on the x and y axes are in increments of 1 AU. This animation shows how solar system object detections accumulated over the course of the survey. The white points show the new detections from each successive run of the WISE Moving Object Pipeline System, and illustrate how the NEOWISE scan longituded progress around the sky. Credit: Tommy Grav (Univ. of Arizona)

Source: NEOWISE/News


Friday, November 15, 2024

NASA's Hubble Sees Aftermath of Galaxy's Scrape with Milky Way

Credits/Artwork: NASA, ESA, Ralf Crawford (STScI)

LMC Passing through Milky Way Halo (3-Panel Artist's Concept)
Credits/Artwork: NASA, ESA, Ralf Crawford (STScI)

Closeup of the LMC and Its Halo (Artist's Concept)
Credits/Artwork: NASA, ESA, Ralf Crawford (STScI)



A story of survival is unfolding at the outer reaches of our galaxy, and NASA's Hubble Space Telescope is witnessing the saga.

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

Many researchers theorize that the LMC is not in orbit around our galaxy, but is just passing by. These 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 been able to measure the size of the LMC's halo – something they could do only with Hubble. In a new study to be 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 halos of other galaxies that are the LMC's mass. 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 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, making it heftier than most dwarf galaxies.

"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 on 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 Gigantic Hair Dryer

Most of the LMC's halo was blown away due to 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 gotten past 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 analyzed ultraviolet observations from the Mikulski Archive for Space Telescopes at STScI. Most ultraviolet light is blocked by the Earth's atmosphere, so it cannot be observed with ground-based telescopes. Hubble is the only current space telescope 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's gas by the way it absorbs certain colors 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.

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 program, 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."

The Hubble Space Telescope has been operating for over three decades and continues to make ground-breaking discoveries that shape our fundamental understanding of the universe. Hubble is a project of international cooperation between NASA and ESA (European Space Agency). NASA's Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope and mission operations. Lockheed Martin Space, based in Denver, Colorado, also supports mission operations at Goddard. The Space Telescope Science Institute in Baltimore, Maryland, which is operated by the Association of Universities for Research in Astronomy, conducts Hubble science operations for NASA.




About This Release

Credits:

Media Contact:

Ann Jenkins
Space Telescope Science Institute, Baltimore, Maryland

Ray Villard
Space Telescope Science Institute, Baltimore, Maryland

Permissions: Content Use Policy

Contact Us:
  Direct inquiries to the
News Team.

Related Links and Documents



Thursday, November 14, 2024

A Bubbly Origin for Odd Radio Circles

A radio image of the first odd radio crdit: circle to be discovered, ORC-1, with a visible-light image of stars and galaxies forming the background. Credit:
Jayanne English (U. Manitoba), EMU (ASKAP/CSIRO), MeerKAT, DES (CTIO)

Discovered in 2019, odd radio circles (ORCs) are among the newest and most mysterious astrophysical phenomena. New research examines how bubbles blown by black hole jets could create these striking features.

The active galactic nucleus of the galaxy Hercules A powers the pair of immense jets emanating from the galactic center. Credit:
X-ray: NASA/CXC/SAO, Optical: NASA/STScI, Radio: NSF/NRAO/VLA

Stumped by Space ORCs

ORCs are faint extragalactic circles of radio emission that appear to be invisible at other wavelengths. As the number of known ORCs slowly climbs, researchers have begun to test possible formation mechanisms. Among the many possibilities are the jets of active galactic nuclei: luminous galactic centers powered by accreting supermassive black holes.

In this hypothesis, active galactic nucleus jets filled with fast-moving charged particles carve out bubbles in the surrounding gas of the intracluster medium. When the cosmic rays smash into the intracluster gas, they produce electrons and positrons, which spiral around tangled magnetic field lines and emit radio waves. If the jets are viewed precisely on-axis, the resulting radio bubbles would be circular. Previous simulations of active galactic nucleus jets colliding with surrounding gas have created bubbles, but these bubbles haven’t reached the size of ORCs, which are hundreds of thousands or millions of light-years across.

Now, Yen-Hsing Lin (National Tsing Hua University) and Hsiang-Yi Karen Yang (National Tsing Hua University and National Center for Theoretical Sciences, Taiwan) have shown how active galactic nuclei can blow ORC-sized bubbles.

Comparison of simulated radio images (left column) and observations (right column) of ORCs. 
 Credit: Lin & Yang 2024

Galaxies Blowing Bubbles

Using three-dimensional magnetohydrodynamics simulations, Lin and Yang shot bipolar jets into intracluster gas, tracking the jet evolution and bubble formation across 200 million years of simulation time. The team focused on two of their simulation runs, which created bright-edged circles of radio emission that are roughly the size of known ORCs.

These simulated ORCs arise from jet-inflated bubbles viewed straight down the axis, as predicted, but further simulations showed that the bubbles produce ORCs when viewed up to 30 degrees off-axis. (At larger angles, they still produce intriguing radio structures but lose their distinct circular shape.) This result relaxes the requirement that the jets be viewed exactly on-axis.

A critical factor in determining whether a galaxy’s jets produce an ORC is the ability of the tenuous jets to completely excavate the higher-density intracluster gas that it interacts with. For this reason, low-mass galaxy clusters, which contain less intracluster gas, may be more likely to host ORCs.

Simulated X-ray observations by Chandra (top), AXIS (middle), and Athena (bottom). The planned AXIS and Athena missions could achieve higher signal to noise than Chandra can in far less time. Credit: Lin & Yang 2024

Another Way of Looking

Lin and Yang explored other characteristics that could support the jet-blown bubble hypothesis. They found that the simulated radio rings are clumpy, varying in brightness around the ring, which could potentially be seen in high-resolution observations.

As for observations outside radio wavelengths, the team found that only certain ORCs would produce enough X-rays to be picked up by the Chandra X-ray Observatory, and even those would require 11.5 days of observing time. Based on these results, it’s unsurprising that ORCs have so far appeared invisible at X-ray wavelengths — but that might change. Two X-ray telescopes slated to launch in the 2030s, NASA’s Advanced X-ray Imaging Satellite (AXIS) and the European Space Agency’s Advanced Telescope for High-ENergy Astrophysics (Athena), could reduce the necessary observing time to just 4 hours.

Going forward, Lin and Yang aim to continue their simulations, investigating the absolute brightness, polarization, and other properties of the radio emission, allowing for better comparisons with observations and a greater understanding of ORC origins.

By Kerry Hensley

Citation

“Active Galactic Nucleus Jet-Inflated Bubbles as Possible Origin of Odd Radio Circles,” Yen-Hsing Lin and H.-Y. Karen Yang 2024 ApJ 974 269. doi:10.3847/1538-4357/ad70af

Wednesday, November 13, 2024

Tangled galaxies

In the centre is a large, oval-shaped galaxy, with a shining, ringed core. Left of its centre is a second, smaller galaxy with two spiral arms. The pair of galaxies are close enough that they appear to be merging: a tail of material with a few glowing spots connects from one of the smaller galaxy’s spiral arms to the larger galaxy. Both are surrounded in a faint halo. Several stars can be seen around the pair. Credit: ESA/Hubble & NASA, R. J. Foley (UC Santa Cruz)

Previously the Hubble Picture of the Week series has featured a jewel in the queen’s hair — a spiral galaxy in the constellation Coma Berenices, named for the hair of the historical Egyptian queen. However, that galaxy is only one of many known in this constellation. This week’s new image from the NASA/ESA Hubble Space Telescope depicts the cosmic tangle that is MCG+05-31-045, a pair of interacting galaxies located 390 million light-years away and a part of the so-called Coma galaxy cluster.

The Coma cluster is a particularly rich cluster and contains over a thousand known galaxies. Several can be easily seen with amateur telescopes. Most of them are elliptical galaxies, and that’s typical of a dense galaxy cluster like the Coma cluster: many elliptical galaxies are formed in close encounters between galaxies that stir them up, or even collisions that rip them apart. While the stars in the interacting galaxies can stay together, the gas in the galaxies is a different story — it’s twisted and compressed by gravitational forces, and rapidly used up to form new stars. When the hot, massive, blue stars die, there is little gas left to replace them with new generations of young stars. For interacting spiral galaxies, the regular orbits that produce their striking spiral arms are also disrupted. Whether through mergers or simple near misses, the result is a galaxy almost devoid of gas, with ageing stars orbiting in uncoordinated circles: an elliptical galaxy.

It’s very likely that a similar fate will befall MCG+05-31-045. As the smaller spiral galaxy is torn up and integrated into the larger galaxy, many new stars will form, and the hot, blue ones will quickly burn out, leaving cooler, redder stars behind in an elliptical galaxy much like the others in the Coma cluster. But this process won’t be complete for many millions of years — until then, Queen Berenice II will have to suffer the knots in her hair!



Tuesday, November 12, 2024

Down to the Core: Dark Matter Deviations in Ultra-Faint Dwarf Galaxies

Barely visible, the Sculptor Dwarf Galaxy orbits the Milky Way as one of many small satellite galaxies
Credit:
NASA, ESA/Hubble.org, DSS2

Though the majority of the mass in the universe lies in dark matter, many mysteries remain about its nature. A new study suggests that the smallest and faintest galaxies hold the key to unlocking how dark matter interacts within the universe.

From simulations, the expected shape (cusp) of a galaxy’s dark matter density profile is shown with the red curve, while the observed shape (core) is shown with the blue curve. As we approach the galactic center, a cuspy profile peaks at high density, and the cored profile levels off at a lower density. Credit: Lexi Gault

Core-Cusp Conundrum

Surrounding the Milky Way are tiny faint galaxies — known as satellite galaxies — millions of times smaller than the massive galaxy they orbit. Despite their small sizes, these satellites are of huge importance in understanding the behavior of dark matter. In the leading cosmological model, called lambda cold dark matter (ΛCDM), dark matter is cold, collisionless, and interacts with normal matter only by way of gravity.

Galaxy formation and evolution simulations using the ΛCDM model predict galaxies to form within dark matter halos that have density distributions that peak in the center, or reach a cusp. While this seems to be true on large scales like galaxy clusters, individual galaxies often appear to have smoother dark matter distributions. When enough normal matter enters the picture, feedback from newborn stars, tidal interactions, and other processes can flatten out the dark matter distribution, transforming the central cusp into a central core.

However, according to ΛCDM, there should exist very low-mass galaxies — like the faintest satellite galaxies that orbit the Milky Way — that do not have enough mass to change an originally cuspy dark matter distribution into a cored one. If observations reveal that even these small galaxies have cored dark matter distributions, that may mean that dark matter may not behave as expected in the ΛCDM paradigm.

Histograms showing how each considered dark matter profile compares to the observations, where NFW corresponds to a cuspy distribution, Plummer corresponds to a cored distribution, and the ρ230 is in the middle of the two. The the histograms plot the distributions of the innermost slopes for the fits where a slope close to 0 means the profile flattens, and a more negative slope means a steeper rise in the center. The cored (Plummer) fit aligns best with the observed galaxies. Modified from Sánchez Almeida et al 2024

Dark Matter Distributions

In order to investigate dark matter distributions at the smallest scales, Jorge Sánchez Almeida (Institute of Astrophysics of the Canary Islands; University of La Laguna) and collaborators analyze the stellar count distribution of six ultra-faint dwarf satellites of the Milky Way and the Large Magellanic Cloud. These galaxies have cored stellar surface density distributions, suggesting that their underlying dark matter distributions may be cored as well.

Beyond Standard

Given that a cored dark matter distribution seems to fit best for these ultra-faint galaxies, the authors suggest that dark matter may not behave as the standard cold dark matter model anticipates. Instead, dark matter may be warm, self-interacting, or fuzzy. However, could other factors be driving the cored distributions of these galaxies?

The author’s analysis hinges on several assumptions that could blur their results. To address these concerns, they carefully consider properties like stellar feedback contributions, tidal interactions, velocity distributions, and other properties important to their analysis. When changing these assumptions slightly, in ways still physically reasonable for very low-mass galaxies, the ultra-faint dwarfs still appear to reside in cored dark matter distributions.

What does this mean? While the standard ΛCDM model explains large-scale structures of the universe well, it does not adequately characterize what is observed on smaller scales — like the Milky Way’s satellites. Though the exact nature of dark matter is still unknown, cold and collisionless dark matter does not likely produce the ultra-faint galaxies’ cored profiles. Thus, further studying the lowest-mass galaxies in the universe may reveal new characteristics of dark matter beyond the standard model.

By Lexi Gault

Citation

“The Stellar Distribution in Ultrafaint Dwarf Galaxies Suggests Deviations from the Collisionless Cold Dark Matter Paradigm,” Jorge Sánchez Almeida et al 2024 ApJL 973 L15. doi:10.3847/2041-8213/ad66bc



Monday, November 11, 2024

NSF NOIRLab Astronomers Discover the Fastest-Feeding Black Hole in the Early Universe

PR Image noirlab2427a
Artist’s Impression of Fastest-feeding Black Hole in the Early Universe

PR Image noirlab2427b
Artist concept of JWST

PR Image noirlab2427c
Chandra X-Ray Observatory

PR Image noirlab2427d
Artist’s Impression of Black Hole LID-568

PR Image noirlab2427e
Artist’s Impression of Early-Universe Dwarf Galaxy



Videos

Cosmoview Episode 89: NSF NOIRLab Astronomers Discover the Fastest-Feeding Black Hole in the Early Universe
PR Video noirlab2427a
Cosmoview Episode 89: NSF NOIRLab Astronomers Discover the Fastest-Feeding Black Hole in the Early Universe

Cosmoview Episodio 88: Astrónomos de NOIRLab descubren el agujero negro más voraz del Universo primitivo
PR Video noirlab2427b
Cosmoview Episodio 88: Astrónomos de NOIRLab descubren el agujero negro más voraz del Universo primitivo



Observations from JWST and Chandra reveal a low-mass supermassive black hole that appears to be consuming matter at over 40 times the theoretical limit

Using data from NASA's JWST and Chandra X-ray Observatory, a team of U.S. National Science Foundation NOIRLab astronomers have discovered a supermassive black hole at the center of a galaxy just 1.5 billion years after the Big Bang that is consuming matter at a phenomenal rate — over 40 times the theoretical limit. While short lived, this black hole’s ‘feast’ could help astronomers explain how supermassive black holes grew so quickly in the early Universe.

Supermassive black holes exist at the center of most galaxies, and modern telescopes continue to observe them at surprisingly early times in the Universe’s evolution. It’s difficult to understand how these black holes were able to grow so big so rapidly. But with the discovery of a low-mass supermassive black hole feasting on material at an extreme rate, seen just 1.5 billion years after the Big Bang, astronomers now have valuable new insights into the mechanisms of rapidly growing black holes in the early Universe.

LID-568 was discovered by a cross-institutional team of astronomers led by International Gemini Observatory/NSF NOIRLab astronomer Hyewon Suh. They used the James Webb Space Telescope (JWST) to observe a sample of galaxies from the Chandra X-ray Observatory’s COSMOS legacy survey. This population of galaxies is very bright in the X-ray part of the spectrum, but are invisible in the optical and near-infrared. JWST’s unique infrared sensitivity allows it to detect these faint counterpart emissions.

LID-568 stood out within the sample for its intense X-ray emission, but its exact position could not be determined from the X-ray observations alone, raising concerns about properly centering the target in JWST’s field of view. So, rather than using traditional slit spectroscopy, JWST’s instrumentation support scientists suggested that Suh’s team use the integral field spectrograph on JWST’s NIRSpec. This instrument can get a spectrum for each pixel in the instrument’s field of view rather than being limited to a narrow slice.

“Owing to its faint nature, the detection of LID-568 would be impossible without JWST. Using the integral field spectrograph was innovative and necessary for getting our observation,” says Emanuele Farina, International Gemini Observatory/NSF NOIRLab astronomer and co-author of the paper appearing in Nature Astronomy.

JWST’s NIRSpec allowed the team to get a full view of their target and its surrounding region, leading to the unexpected discovery of powerful outflows of gas around the central black hole. The speed and size of these outflows led the team to infer that a substantial fraction of the mass growth of LID-568 may have occurred in a single episode of rapid accretion. “This serendipitous result added a new dimension to our understanding of the system and opened up exciting avenues for investigation,” says Suh.

In a stunning discovery, Suh and her team found that LID-568 appears to be feeding on matter at a rate 40 times its Eddington limit. This limit relates to the maximum luminosity that a black hole can achieve, as well as how fast it can absorb matter, such that its inward gravitational force and outward pressure generated from the heat of the compressed, infalling matter remain in balance. When LID-568’s luminosity was calculated to be so much higher than theoretically possible, the team knew they had something remarkable in their data.

“This black hole is having a feast,” says International Gemini Observatory/NSF NOIRLab astronomer and co-author Julia Scharwächter. “This extreme case shows that a fast-feeding mechanism above the Eddington limit is one of the possible explanations for why we see these very heavy black holes so early in the Universe.”

These results provide new insights into the formation of supermassive black holes from smaller black hole ‘seeds’, which current theories suggest arise either from the death of the Universe’s first stars (light seeds) or the direct collapse of gas clouds (heavy seeds). Until now, these theories lacked observational confirmation. “The discovery of a super-Eddington accreting black hole suggests that a significant portion of mass growth can occur during a single episode of rapid feeding, regardless of whether the black hole originated from a light or heavy seed,” says Suh.

The discovery of LID-568 also shows that it’s possible for a black hole to exceed its Eddington limit, and provides the first opportunity for astronomers to study how this happens. It’s possible that the powerful outflows observed in LID-568 may be acting as a release valve for the excess energy generated by the extreme accretion, preventing the system from becoming too unstable. To further investigate the mechanisms at play, the team is planning follow-up observations with JWST.




More information

This research was presented in a paper entitled “A super-Eddington-accreting black hole ~1.5 Gyr after the Big Bang observed with JWST” to appear in Nature Astronomy. DOI: 10.1038/s41550-024-02402-9

The team is composed of Hyewon Suh (International Gemini Observatory/NSF NOIRLab, USA), Julia Scharwächter (International Gemini Observatory/NSF NOIRLab, USA), Emanuele Paolo Farina (International Gemini Observatory/NSF NOIRLab, USA), Federica Loiacono (INAF – Astrophysics and Space Science Observatory, Italy), Giorgio Lanzuisi (INAF – Astrophysics and Space Science Observatory, Italy), Günther Hasinger (Institute of Nuclear and Particle Physics/DESY/German Center for Astrophysics, Germany), Stefano Marchesi (INAF-Astrophysics and Space Science Observatory, Italy), Mar Mezcua (Institute of Space Sciences/Institute of Spatial Studies of Catalonia, Spain), Roberto Decarli (INAF – Astrophysics and Space Science Observatory, Italy), Brian C. Lemaux (International Gemini Observatory/NSF NOIRLab, USA, Institute of Astrophysics, Italy), Marta Volonteri (Paris Institute of Astrophysics, France), Francesca Civano (NASA Goddard Space Flight Center, USA), Sukyoung K. Yi (Department of Astronomy and Yonsei University Observatory, Republic of Korea), San Han (Department of Astronomy and Yonsei University Observatory, Republic of Korea), Mark Rawlings (International Gemini Observatory/NSF NOIRLab, USA), Denise Hung (International Gemini Observatory/NSF NOIRLab, USA)


NSF NOIRLab (U.S. National Science Foundation National Optical-Infrared Astronomy Research Laboratory), the U.S. center for ground-based optical-infrared astronomy, operates the International Gemini Observatory (a facility of NSF, NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and KASI–Republic of Korea), Kitt Peak National Observatory (KPNO), Cerro Tololo Inter-American Observatory (CTIO), the Community Science and Data Center (CSDC), and Vera C. Rubin Observatory (operated in cooperation with the Department of Energy’s SLAC National Accelerator Laboratory). It is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with NSF and is headquartered in Tucson, Arizona. The astronomical community is honored to have the opportunity to conduct astronomical research on I’oligam Du’ag (Kitt Peak) in Arizona, on Maunakea in Hawai‘i, and on Cerro Tololo and Cerro Pachón in Chile. We recognize and acknowledge the very significant cultural role and reverence that these sites have to the Tohono O’odham Nation, to the Native Hawaiian community, and to the local communities in Chile, respectively.



Links



Contacts:

Hyewon Suh
Associate Scientist
International Gemini Observatory/NSF NOIRLab
Email:
hyewon.suh@noirlab.edu

Julia Scharwächter
Scientist
International Gemini Observatory/NSF NOIRLab
Email:
julia.scharwaechter@noirlab.edu

Josie Fenske
Jr. Public Information Officer
NSF NOIRLab
Email:
josie.fenske@noirlab.edu


Sunday, November 10, 2024

Triple Ring Galaxy

Triple Ring Galaxy
Detail :
Low Res. (96 KB) / Mid. Res. (813 KB) / High Res. (7.6 MB)

The Hubble Classification, also known as the Hubble Sequence, is a widely recognized method for systematically categorizing galaxy morphology. Galaxies are classified into elliptical, lenticular, and spiral (or barred spiral) galaxies. Galaxies with irregular shapes that do not fit into any categories are classified as irregular galaxies. While this classification can be used for most galaxies, some do not fit into any category, though they have regular shapes.

A ring galaxy is one of them that has a ring feature. There are various theories about their origin, but one leading hypothesis asserts that ring galaxies originate from galactic interactions and mergers. The citizen science project GALAXY CRUISE, using vast cosmic images captured by the Subaru Telescope, regards ring galaxies as interacting.

Ring galaxies are rare and difficult to find. This galaxy features three rings, which is exceptionally rare and valuable to scientific research.

Distance from Earth: About 800 million light-years
Instrument: Hyper Suprime-Cam (HSC)

Relevant Links



Saturday, November 09, 2024

Rapidly merging stars and black holes - the birth of supermassive black holes in dense star clusters in the early Universe

Fig 1: The complex formation channel of a supermassive black hole with 2200 solar masses. Six sub-clusters in the collapsing region contribute stars and black holes for the forming massive star cluster. Many stellar collisions (red and blue circles) rapidly form a 2025 solar mass black hole within only a few million years. Thereafter the black hole grows by mergers with other, smaller, black holes and by tidally disrupting stars. Some lower mass black holes are ejected by gravitational recoil kicks.

New observations by the James Webb Space Telescope (JWST) have revealed that supermassive black holes (SMBHs) of more than one million solar masses were already present only 450 million years after the Big Bang. How did these first SMBHs form? A team of researchers at MPA has used modern supercomputer simulations to show that progenitors of SMBHs (seeds) of a few thousand solar masses can form rapidly in dense and structured star clusters forming in the early Universe. They emerge from collisions of massive stars which form supermassive stars and then collapse directly into black holes, which can further grow by merging with other black holes. This new and more realistic model resembles JWST observations and can explain the formation of SMBH seeds which are massive enough to further grow into the earliest SMBHs observed. For this SMBH seed formation process, the researchers predict a unique gravitational wave fingerprint from black hole merger that can be directly tested with the next-generation gravitational wave observatories.

Supermassive black holes (SMBHs) with masses exceeding one million solar masses are found in all nearby massive galaxies including our own Milky Way. New observations by the James Webb Space Telescope (JWST) have revealed that SMBHs were already present only 450 million years after the Big Bang. The origin of these most massive black holes in the Universe is a major unsolved puzzle in modern astrophysics and an active area of research.

The very first stars in the Universe may have left behind black holes with masses up to a few hundred solar masses. However, models with such ‘light’ SMBH seeds struggle to explain the observed high redshift population of accreting SMBHs. The maximum sustainable SMBH gas accretion rate, the so-called Eddington rate, places limits on how fast SMBH seeds may grow after their formation. The light SMBH seeds simply do not have enough time to grow enough only in a few hundred million years. Therefore, more popular theoretical SMBH formation models assume that the SMBH seeds formed ‘heavy’ with masses exceeding a thousand solar masses. These heavy seeds black holes have a head start against the light seeds in their growth into the observed population of early accreting SMBHs. The major proposed heavy seed formation scenarios include runaway stellar collisions in dense star clusters, directly collapsing metal-free gas clouds in atomic cooling halos, and more exotic ‘new’ physics such as primordial black holes.

In dense star clusters, repeated stellar collisions may build up very massive and even supermassive stars. In early Universe which is still little enriched with heavy elements, stellar winds are typically weak and the stellar collision products will retain most of their mass. At the ends of their lives, these collisionally formed supermassive stars collapse and form the seeds for SMBHs.

Past simulations had focused on studying isolated, spherical star clusters. Both the JWST observations and state-of-the-art hydrodynamical galaxy formation simulations instead support the picture that massive star clusters form through a complex hierarchical assembly. This was the key motivation for the researchers at the MPA to re-explore the runaway collisional SMBH seed formation scenario in the more realistic clustered setup. Such a scenario is very different to the direct collapse gas cloud scenario which relies on avoiding cloud cooling and fragmentation into clusters of stars.

The researchers performed new simulations of massive star clusters with several million individual stars forming from the rapid assembly of several hundred proto-clusters. The newly developed direct N-body simulation code BIFROST used for the simulations runs on energy-efficient GPU hardware can follow stellar evolution, stellar mergers and accurately accounts for general relativistic effects during the interaction of black holes. In particular, the code computes the gravitational wave emission when two black holes merge. At the end of the merger anisotropic gravitational wave emission can kick the newly formed black holes up to speeds of several thousand km/s. These gravitational wave recoil kicks which can eject black hole merger remnants from their birth clusters are also modelled with the code.

Fig 2: Primary and secondary masses of black holes merging in early star clusters by the emission of gravitational waves from the simulation (black circles). Observed gravitational waves from black hole mergers are indicated by yellow crosses (Advanced LIGO and Advanced Virgo). The model predicts mergers of ~ 1000 solar mass black holes with several 10 to 100 solar mass black holes which can be detected with the next generation gravitational wave telescopes like the Einstein Telescope (https://en.wikipedia.org/wiki/Einstein_Telescope) or LISA (https://de.wikipedia.org/wiki/Laser_Interferometer_Space_Antenna)

The collision pathways massive stars and the formed SMBH seeds are illustrated in Fig. 1. Typically, only the most massive star in sub-clusters grows rapidly by collisions with other massive stars. Once the stars exceed the mass of several hundred solar masses, stellar evolution models predict that they directly collapse into black holes at the end of their lives. After their formation, the several SMBH seeds in the assembled massive star cluster experience a rich history of interactions and mergers by which the SMBH seeds can further grow. Several black holes are ejected from the cluster through strong Newtonian few-body interactions or relativistic gravitational wave recoil kicks. The hierarchical runaway scenario predicts a population of gravitational wave mergers at high redshifts in which the SMBH seeds merge with stellar mass black holes of several 10 to 100 solar masses (Fig. 2). Current gravitational wave observatories cannot detect black hole mergers above 500 solar masses or high redshifts very well. However, the scenario of the MPA researchers can be tested with the next-generation gravitational wave experiments such as LISA and the Einstein Telescope.
 

Antti Rantala, Thorsten Naab & Natalia Lahen


The authors thank Markus Rampp and Klaus Reuter of the Max Planck Computing and Data Facility (MPCDF) for performance optimization of the BIFROST GPU code. The simulations for the study were run using the MPCDF supercomputer Raven in Garching




Author:

Antti Rantala
Postdoc
tel:2253

anttiran@mpa-garching.mpg.de

Natalia Lahén
Postdoc
tel:2253

nlahen@mpa-garching.mpg.de

Thorsten Naab
Scientific Staff
tel:2295

tnaab@mpa-garching.mpg.de

Original Publication

https://ui.adsabs.harvard.edu/abs/2024MNRAS.531.3770R/abstract

https://ui.adsabs.harvard.edu/abs/2023MNRAS.522.5180R/abstract
BIFROST Code


Friday, November 08, 2024

Physicists discover first “black hole triple”

Depicted in this artist’s rendering is the central black hole, V404 Cygni (black dot), in the process of consuming a nearby star (orange body at left), while a second star (upper white flash) orbits at a much farther distance. Credits: Image: Jorge Lugo

System observed 8,000 light-years away may be the first direct evidence of “gentle” black hole formation.

Many black holes detected to date appear to be part of a pair. These binary systems comprise a black hole and a secondary object — such as a star, a much denser neutron star, or another black hole — that spiral around each other, drawn together by the black hole’s gravity to form a tight orbital pair.

Now a surprising discovery is expanding the picture of black holes, the objects they can host, and the way they form.

In a study appearing today in Nature, physicists at MIT and Caltech report that they have observed a “black hole triple” for the first time. The new system holds a central black hole in the act of consuming a small star that’s spiraling in very close to the black hole, every 6.5 days — a configuration similar to most binary systems. But surprisingly, a second star appears to also be circling the black hole, though at a much greater distance. The physicists estimate this far-off companion is orbiting the black hole every 70,000 years.

That the black hole seems to have a gravitational hold on an object so far away is raising questions about the origins of the black hole itself. Black holes are thought to form from the violent explosion of a dying star — a process known as a supernova, by which a star releases a huge amount of energy and light in a final burst before collapsing into an invisible black hole.

The team’s discovery, however, suggests that if the newly-observed black hole resulted from a typical supernova, the energy it would have released before it collapsed would have kicked away any loosely bound objects in its outskirts. The second, outer star, then, shouldn’t still be hanging around.

Instead, the team suspects the black hole formed through a more gentle process of “direct collapse,” in which a star simply caves in on itself, forming a black hole without a last dramatic flash. Such a gentle origin would hardly disturb any loosely bound, faraway objects.

Because the new triple system includes a very far-off star, this suggests the system’s black hole was born through a gentler, direct collapse. And while astronomers have observed more violent supernovae for centuries, the team says the new triple system could be the first evidence of a black hole that formed from this more gentle process.

“We think most black holes form from violent explosions of stars, but this discovery helps call that into question,” says study author Kevin Burdge, a Pappalardo Fellow in the MIT Department of Physics. “This system is super exciting for black hole evolution, and it also raises questions of whether there are more triples out there.”

The study’s co-authors at MIT are Erin Kara, Claude Canizares, Deepto Chakrabarty, Anna Frebel, Sarah Millholland, Saul Rappaport, Rob Simcoe, and Andrew Vanderburg, along with Kareem El-Badry at Caltech.

Tandem motion

The discovery of the black hole triple came about almost by chance. The physicists found it while looking through Aladin Lite, a repository of astronomical observations, aggregated from telescopes in space and all around the world. Astronomers can use the online tool to search for images of the same part of the sky, taken by different telescopes that are tuned to various wavelengths of energy and light.

The team had been looking within the Milky Way galaxy for signs of new black holes. Out of curiosity, Burdge reviewed an image of V404 Cygni — a black hole about 8,000 light years from Earth that was one of the very first objects ever to be confirmed as a black hole, in 1992. Since then, V404 Cygni has become one of the most well-studied black holes, and has been documented in over 1,300 scientific papers. However, none of those studies reported what Burdge and his colleagues observed.

As he looked at optical images of V404 Cygni, Burdge saw what appeared to be two blobs of light, surprisingly close to each other. The first blob was what others determined to be the black hole and an inner, closely orbiting star. The star is so close that it is shedding some of its material onto the black hole, and giving off the light that Burdge could see. The second blob of light, however, was something that scientists did not investigate closely, until now. That second light, Burdge determined, was most likely coming from a very far-off star.

“The fact that we can see two separate stars over this much distance actually means that the stars have to be really very far apart,” says Burdge, who calculated that the outer star is 3,500 astronomical units (AU) away from the black hole (1 AU is the distance between the Earth and sun). In other words, the outer star is 3,500 times father away from the black hole as the Earth is from the sun. This is also equal to 100 times the distance between Pluto and the sun.

The question that then came to mind was whether the outer star was linked to the black hole and its inner star. To answer this, the researchers looked to Gaia, a satellite that has precisely tracked the motions of all the stars in the galaxy since 2014. The team analyzed the motions of the inner and outer stars over the last 10 years of Gaia data and found that the stars moved exactly in tandem, compared to other neighboring stars. They calculated that the odds of this kind of tandem motion are about one in 10 million.

“It’s almost certainly not a coincidence or accident,” Burdge says. “We’re seeing two stars that are following each other because they’re attached by this weak string of gravity. So this has to be a triple system.”

Pulling strings

How, then, could the system have formed? If the black hole arose from a typical supernova, the violent explosion would have kicked away the outer star long ago.

“Imagine you’re pulling a kite, and instead of a strong string, you’re pulling with a spider web,” Burdge says. “If you tugged too hard, the web would break and you’d lose the kite. Gravity is like this barely bound string that’s really weak, and if you do anything dramatic to the inner binary, you’re going to lose the outer star.”

To really test this idea, however, Burdge carried out simulations to see how such a triple system could have evolved and retained the outer star.

At the start of each simulation, he introduced three stars (the third being the black hole, before it became a black hole). He then ran tens of thousands of simulations, each one with a slightly different scenario for how the third star could have become a black hole, and subsequently affected the motions of the other two stars. For instance, he simulated a supernova, varying the amount and direction of energy that it gave off. He also simulated scenarios of direct collapse, in which the third star simply caved in on itself to form a black hole, without giving off any energy.

“The vast majority of simulations show that the easiest way to make this triple work is through direct collapse,” Burdge says.

In addition to giving clues to the black hole’s origins, the outer star has also revealed the system’s age. The physicists observed that the outer star happens to be in the process of becoming a red giant — a phase that occurs at the end of a star’s life. Based on this stellar transition, the team determined that the outer star is about 4 billion years old. Given that neighboring stars are born around the same time, the team concludes that the black hole triple is also 4 billion years old.

“We’ve never been able to do this before for an old black hole,” Burdge says. “Now we know V404 Cygni is part of a triple, it could have formed from direct collapse, and it formed about 4 billion years ago, thanks to this discovery.”

This work was supported, in part, by the National Science Foundation.

Jennifer Chu | MIT News