Friday, August 12, 2022

Not All Black Holes That Wander Are Lost — and Now, Some May Have Been Found


Dwarf galaxies, like NGC 5949 pictured here in this Hubble Space Telescope image, may be an excellent place to hunt for massive black holes. Credit:ESA/Hubble & NASA 

Title: Wandering Black Hole Candidates in Dwarf Galaxies at VLBI Resolution
Authors: Andrew J. Sargent et al.
First Author’s Institution: United States Naval Observatory and The George Washington University
Status: Published in ApJ

How do you make a black hole billions of times the mass of the Sun? Even for the planet-building Magratheans, this seems like a tall order. Plenty of mechanisms have been proposed to explain the formation of these supermassive black holes found at the centers of most galaxies. Some involve the mergers of “seeds” — massive black holes weighing in at merely hundreds to hundreds of thousands of solar masses. A simple way to test these theories is to search for relic massive black holes, and low-mass dwarf galaxies are excellent targets. Since dwarf galaxies haven’t undergone many mergers, any massive black holes they harbor should have avoided being gobbled up by growing supermassive black holes.

Today’s article studies 13 possible massive black hole candidates in dwarf galaxies, some of which may have wandered to the edges of their hosts. What’s up with that — and are they really massive black holes? Let’s dive in!

Here’s a question: since supermassive black holes are usually found near the center of their galaxies, why might we expect some massive black holes in dwarf galaxies to lie further out? The answer has to do with gravity: since dwarf galaxies are much less massive than the galaxies that host supermassive black holes, their gravitational potential is lower, making it easier for massive black holes to “wander” away from their centers. This means that if you see a radio source that appears far to the side of a dwarf galaxy’s center, it could be an massive black hole — or it could be an accreting supermassive black hole (an active galactic nucleus) in a galaxy far, far away that by chance simply happens to lie behind the dwarf galaxy. These unwanted interlopers can pose a challenge for identifying massive black holes.

Another issue with finding massive black holes is that they’re faint. While massive black holes go through periods of accretion like supermassive black holes, their low masses mean that they don’t accrete as quickly, reducing their luminosities. By the early 2000s, only two accreting black holes had been found in dwarf galaxies. Fortunately, this changed with the advent of sky surveys like the now famous Sloan Digital Sky Survey (SDSS), which has been running since 2000 and has amassed detections of close to a billion unique sources.

The 13 massive black hole candidates, shown in Figure 1, were assembled in an article from 2020 by some of the same astronomers who authored today’s article. In the 2020 article, the team sifted through 43,707 low-mass dwarf galaxies from SDSS, looking for sources that had been detected at radio frequencies by the Very Large Array. After keeping the matches and eliminating the radio sources that were background active galactic nuclei or could be explained by processes related to star formation, the team ended up with 13 massive black hole candidates, many of which aren’t aligned with the centers of their host galaxies.

Figure 1:The 13 dwarf galaxies hosting possible massive black hole candidates, as seen by the Dark Energy Camera Legacy Survey at optical wavelengths. The red crosses show the location of the compact radio sources that may be massive black holes. While some appear close to their host’s center, others are significantly farther away. Credit: Reines et al. 2020

In this more recent article, the authors performed follow-up observations using the Very Long Baseline Array (VLBA). The VLBA uses radio telescopes thousands of kilometers apart to reach high angular resolution and allow astronomers to see fine details. Unfortunately, the VLBA was only able to detect four of the 13 candidates — and those four, because of their luminosity and position, seemed most likely to be active galactic nuclei in galaxies far beyond the dwarfs the team was targeting. The detected candidates are shown in Figure 2


Figure 2: The four sources the team was able to detect with the VLBA. Here, S is flux density, a quantity that describes the intensity of radio emission. As these sources are actually background active galactic nuclei rather than massive black holes in the targeted dwarf galaxies, the physical scales in the lower right are inaccurate. Credit: Sargent et al. 2022

This seems like an enormous problem! Only four detections, all of which appear to be imposters? Fortunately, the situation isn’t as dire as it might seem. While the VLBA is good at resolving sources on small scales in the configuration the team used, it may not resolve large-scale sources — and the radio emission from accreting massive black holes might be in the form of larger structures like radio lobes, rather than central point sources.

Multiwavelength observations confirmed that two of the remaining nine candidates are likely accreting supermassive black holes near the center of their host galaxies, but the other seven remain unknown. Five of those seven candidates are too bright to be from star formation and, based on their positions, could be either more background active galactic nucleus interlopers or, tantalizingly, wandering massive black holes.

Where do we go next? Follow-up observations at other wavelengths could be useful. The group suggests the Hubble Space Telescope in particular as a means of figuring out what those seven sources truly are. Given the difficulties involved in detecting massive black holes, even one more could prove valuable as astronomers try to understand the formation of the largest black holes in the universe.

Original astrobite edited by Suchitra Narayanan.

ByAstrobites





About the author, Graham Doskoch:

I’m a graduate student at West Virginia University, pursuing a PhD in radio astronomy. My research focuses on pulsars and efforts to use them to detect gravitational waves as part of pulsar timing arrays like NANOGrav and the IPTA. I love running, hiking, reading, and just enjoying nature.


Thursday, August 11, 2022

Hubble Sees Red Supergiant Star Betelgeuse Slowly Recovering After Blowing Its Top


This illustration plots changes in the brightness of the red supergiant star Betelgeuse, following the titanic mass ejection of a large piece of its visible surface. The escaping material cooled to form a cloud of dust that temporarily made the star look dimmer, as seen from Earth. This unprecedented stellar convulsion disrupted the monster star’s 400-day-long oscillation period that astronomers had measured for more than 200 years. The interior may now be jiggling like a plate of gelatin dessert.Release Images

Analyzing data from NASA's Hubble Space Telescope and several other observatories, astronomers have concluded that the bright red supergiant star Betelgeuse quite literally blew its top in 2019, losing a substantial part of its visible surface and producing a gigantic Surface Mass Ejection (SME). This is something never before seen in a normal star's behavior.

Our Sun routinely blows off parts of its tenuous outer atmosphere, the corona, in an event known as a Coronal Mass Ejection (CME). But the Betelgeuse SME blasted off 400 billion times as much mass as a typical CME!

The monster star is still slowly recovering from this catastrophic upheaval. "Betelgeuse continues doing some very unusual things right now; the interior is sort of bouncing," said Andrea Dupree of the Center for Astrophysics | Harvard & Smithsonian in Cambridge, Massachusetts.

These new observations yield clues as to how red stars lose mass late in their lives as their nuclear fusion furnaces burn out, before exploding as supernovae. The amount of mass loss significantly affects their fate. However, Betelgeuse's surprisingly petulant behavior is not evidence the star is about to blow up anytime soon. So the mass-loss event is not necessarily the signal of an imminent explosion.

Dupree is now pulling together all the puzzle pieces of the star's petulant behavior before, after, and during the eruption into a coherent story of a never-before-seen titanic convulsion in an aging star.

This includes new spectroscopic and imaging data from the STELLA robotic observatory , the Fred L. Whipple Observatory's Tillinghast Reflector Echelle Spectrograph (TRES) , NASA's Solar Terrestrial Relations Observatory spacecraft (STEREO-A) , NASA's Hubble Space Telescope , and the American Association of Variable Star Observers (AAVSO) . Dupree emphasizes that the Hubble data was pivotal to helping sort out the mystery.

"We've never before seen a huge mass ejection of the surface of a star. We are left with something going on that we don't completely understand. It's a totally new phenomenon that we can observe directly and resolve surface details with Hubble. We're watching stellar evolution in real time."

The titanic outburst in 2019 was possibly caused by a convective plume, more than a million miles across, bubbling up from deep inside the star. It produced shocks and pulsations that blasted off the chunk of the photosphere leaving the star with a large cool surface area under the dust cloud that was produced by the cooling piece of photosphere. Betelgeuse is now struggling to recover from this injury.

Weighing roughly several times as much as our Moon, the fractured piece of photosphere sped off into space and cooled to form a dust cloud that blocked light from the star as seen by Earth observers. The dimming, which began in late 2019 and lasted for a few months, was easily noticeable even by backyard observers watching the star change brightness. One of the brightest stars in the sky, Betelgeuse is easily found in the right shoulder of the constellation Orion.

Even more fantastic, the supergiant's 400-day pulsation rate is now gone, perhaps at least temporarily. For almost 200 years astronomers have measured this rhythm as evident in changes in Betelgeuse's brightness variations and surface motions. Its disruption attests to the ferocity of the blowout.

The star's interior convection cells, which drive the regular pulsation may be sloshing around like an imbalanced washing machine tub, Dupree suggests. TRES and Hubble spectra imply that the outer layers may be back to normal, but the surface is still bouncing like a plate of gelatin dessert as the photosphere rebuilds itself.

Though our Sun has coronal mass ejections that blow off small pieces of the outer atmosphere, astronomers have never witnessed such a large amount of a star's visible surface get blasted into space. Therefore, surface mass ejections and coronal mass ejections may be different events.

Betelgeuse is now so huge now that if it replaced the Sun at the center of our solar system, its outer surface would extend past the orbit of Jupiter. Dupree used Hubble to resolve hot spots on the star's surface in 1996. This was the first direct image of a star other than the Sun.

NASA's Webb Space Telescope may be able to detect the ejected material in infrared light as it continues moving away from the star.

The Hubble Space Telescope 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. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, in Washington, D.C.



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Wednesday, August 10, 2022

Colliding Galaxies Dazzle in Gemini North Image

The merging galaxy pair NGC 4568 and NGC 4567

The merging galaxy pair NGC 4568 and NGC 4567 and supernova SN 2020fqv (callout box)


Videos

Cosmoview Episode 50: The Merging Galaxy Pair NGC 4568 and NGC 4567
Cosmoview Episode 50: The Merging Galaxy Pair NGC 4568 and NGC 4567
 
Zooming in on Merging Spiral Galaxies
Zooming in on Merging Spiral Galaxies
 
CosmoView Episodio 50: Detectan titánica colisión galáctica
CosmoView Episodio 50: Detectan titánica colisión galáctica in English only



 
NSF’s NOIRLab unveils stunning image of merging spiral galaxies

An evocative new image captured by the Gemini North telescope in Hawai‘i reveals a pair of interacting spiral galaxies — NGC 4568 and NGC 4567 — as they begin to clash and merge. These galaxies are entangled by their mutual gravitational field and will eventually combine to form a single elliptical galaxy in around 500 million years. Also visible in the image is the glowing remains of a supernova that was detected in 2020.

Gemini North, one of the twin telescopes of the International Gemini Observatory, operated by NSF’s NOIRLab, has observed the initial stages of a cosmic collision approximately 60 million light-years away in the direction of the constellation Virgo. The two stately spiral galaxies, NGC 4568 (bottom) and NGC 4567 (top), are poised to undergo one of the most spectacular events in the Universe, a galactic merger. At present, the centers of these galaxies are still 20,000 light-years apart (about the distance from Earth to the center of the Milky Way) and each galaxy still retains its original, pinwheel shape. Those placid conditions, however, will change.

As NGC 4568 and NGC 4567 draw together and coalesce, their dueling gravitational forces will trigger bursts of intense stellar formation and wildly distort their once-majestic structures. Over millions of years, the galaxies will repeatedly swing past each other in ever-tightening loops, drawing out long streamers of stars and gas until their individual structures are so thoroughly mixed that a single, essentially spherical, galaxy emerges from the chaos. By that point, much of the gas and dust (the fuel for star formation) in this system will have been used up or blown away.

This merger is also a preview of what will happen when the Milky Way and its closest large galactic neighbor the Andromeda Galaxy collide in about 5 billion years. 

A bright region in the center of one of NGC 4568’s sweeping spiral arms is the fading afterglow of a supernova — known as SN 2020fqv — that was detected in 2020. The new Gemini image was produced from data taken in 2020. 

By combining decades of observations and computer modeling, astronomers now have compelling evidence that merging spiral galaxies like these go on to become elliptical galaxies. It is likely that NGC 4568 and NGC 4567 will eventually resemble their more-mature neighbor Messier 89, an elliptical galaxy that also resides in the Virgo Cluster. With its dearth of star-forming gas, Messier 89 now exhibits minimal star formation and is made up primarily of older, low-mass stars and ancient globular clusters.

Advanced technology on the Gemini North telescope, including the Gemini Multi-Object Spectrograph North (GMOS-N) and the dry air above the summit of Maunakea, allowed astronomers to capture this spectacular image. 

The image was obtained by NOIRLab’s Communication, Education & Engagement team, as part of the NOIRLab Legacy Imaging Program.



More Information

NSF’s NOIRLab (National Optical-Infrared Astronomy Research Laboratory), the US 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 Iolkam 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

Travis Rector
NSF's NOIRLab & University of Alaska
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Charles Blue
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NSF's NOIRLab
Tel: +1 202 236 6324
Email:
charles.blue@noirlab.edu

Tuesday, August 09, 2022

ALMA Makes First-Ever Detection of Gas in a Circumplanetary Disk


Scientists studying the young star AS 209 have detected gas in a circumplanetary disk for the first time, which suggests the star system may be harboring a very young Jupiter-mass planet. Science images from the research show (right) blob-like emissions of light coming from otherwise empty gaps in the highly-structured, seven-ring disk (left). Credit: ALMA (ESO/NAOJ/NRAO), J. Bae (U. Florida)

1. First Detection of Gas in Circumplanetary Disk Builds on Prior Research and Reveals New Secrets

Scientists using the Atacama Large Millimeter/submillimeter Array (ALMA)— in which the National Radio Astronomy Observatory (NRAO) is a partner— to study planet formation have made the first-ever detection of gas in a circumplanetary disk. What’s more, the detection also suggests the presence of a very young exoplanet. The results of the research are published in The Astrophysical Journal Letters.

Circumplanetary disks are an amassing of gas, dust, and debris around young planets. These disks give rise to moons and other small, rocky objects, and control the growth of young, giant planets. Studying these disks in their earliest stages may help shed light on the formation of our own Solar System, including that of Jupiter’s Galilean moons, which scientists believe formed in a circumplanetary disk of Jupiter around 4.5 billion years ago.

While studying AS 209— a young star located roughly 395 light-years from Earth in the constellation Ophiuchus— scientists observed a blob of emitted light in the middle of an otherwise empty gap in the gas surrounding the star. That led to the detection of the circumplanetary disk surrounding a potential Jupiter-mass planet. Scientists are watching the system closely, both because of the planet’s distance from its star and the star’s age. The exoplanet is located more than 200 astronomical units, or 18.59 billion miles, away from the host star, challenging currently accepted theories of planet formation. And if the host star’s estimated age of just 1.6 million years holds true, this exoplanet could be one of the youngest ever detected. Further study is needed, and scientists hope that upcoming observations with the James Webb Space Telescope will confirm the planet’s presence.

“The best way to study planet formation is to observe planets while they’re forming. We are living in a very exciting time when this happens thanks to powerful telescopes, such as ALMA and JWST,” said Jaehan Bae, a professor of astronomy at the University of Florida and the lead author of the paper.

Resources

“Molecules with ALMA at Planet-forming Scales (MAPS). A Circumplanetary Disk Candidate in Molecular Line Emission in the AS 209 Disk,” Bae et al (2022), The Astrophysical Journal Letters, doi: 10.3847/2041-8213/ac7fa3

Noticias en español
 

AS 209 is a young star in the Ophiuchus constellation that scientists have now determined is host to what may be one of the youngest exoplanets ever. Credit: ALMA (ESO/NAOJ/NRAO), A. Sierra (U. Chile)


2. What is AS 209?

AS 209 is a young star located roughly 395 light-years from Earth in the constellation Ophiuchus. The star system has been of interest to scientists working in the ALMA MAPS— Molecules with ALMA at Planet-forming Scales— collaboration for more than five years due to the presence of seven nested rings, which scientists believed to be associated with ongoing planet formation. The new results provide further evidence of planet formation around the young star.



Artist impression of the circumplanetary disk discovered in 2021 around a young planet in the PDS 70 star system. Credit: ALMA (ESO/NAOJ/NRAO), S. Dagnello (NRAO/AUI/NSF)

3. The Discovery at AS 209 is Only the Third Confirmed Detection Ever of a Circumplanetary Disk

Scientists have long suspected the presence of circumplanetary disks around exoplanets, but until recently were unable to prove it. In 2019, ALMA scientists made the first-ever detection of a circumplanetary, moon-forming disk while observing the young exoplanet PDS 70c, and confirmed the find in 2021. The new observations of gas in a circumplanetary disk at AS 209 may shed further light on the development of planetary atmospheres and the processes by which moons are formed.



About NRAO

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

About ALMA

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.

Media Contact:

Amy C. Oliver
Public Information and News Manager, NRAO
Public Information Officer, ALMA-North America
Tel: +1 434-296-0314

aoliver@nrao.edu



Monday, August 08, 2022

Celestial Cloudscape in the Orion Nebula

Orion Nebula
Credit: ESA/Hubble & NASA, J. Bally
Acknowledgement: M. H. Özsaraç

This celestial cloudscape from the NASA/ESA Hubble Space Telescope captures the colourful region surrounding the Herbig-Haro object HH 505. Herbig-Haro objects are luminous regions surrounding newborn stars, and are formed when stellar winds or jets of gas spewing from these newborn stars form shockwaves colliding with nearby gas and dust at high speeds. In the case of HH 505, these outflows originate from the star IX Ori, which lies on the outskirts of the Orion Nebula around 1000 light-years from Earth. The outflows themselves are visible as gracefully curving structures at the top and bottom of this image, and are distorted into sinuous curves by their interaction with the large-scale flow of gas and dust from the core of the Orion Nebula.

This observation was captured with Hubble’s Advanced Camera for Surveys (ACS) by astronomers studying the properties of outflows and protoplanetary discs. The Orion Nebula is awash in intense ultraviolet radiation from bright young stars. The shockwaves formed by the outflows are brightly visible to Hubble, but the slower-moving currents of stellar material are also highlighted by this radiation. That allows astronomers to directly observe jets and outflows and learn more about their structures.

The Orion Nebula is a dynamic region of dust and gas where thousands of stars are forming, and is the closest region of massive star formation to Earth. As a result, it is one of the most scrutinised areas of the night sky and has often been a target for Hubble. This observation was also part of a spellbinding Hubble mosaic of the Orion Nebula, which combined 520 ACS images in five different colours to create the sharpest view ever taken of the region.

Friday, August 05, 2022

Webb’s Instruments Reveal New Details About Star Formation

Cartwheel Galaxy (NIRCam and MIRI Composite Image)
Credits: ImageE: NASA, ESA, CSA, STScI, Webb ERO Production Team

Release Images

The Cartwheel Galaxy, a rare ring galaxy once shrouded in dust and mystery, has been unveiled by the imaging capabilities of NASA’s James Webb Space Telescope. 

The galaxy, which formed as a result of a collision between a large spiral galaxy and another smaller galaxy, not only retained a lot of its spiral character, but has also experienced massive changes throughout its structure. 

Webb’s high-precision instruments resolved individual stars and star-forming regions within the Cartwheel, and revealed the behavior of the black hole within its galactic center. These new details provide a renewed understanding of a galaxy in the midst of a slow transformation.

NASA’s James Webb Space Telescope has peered into the chaos of the Cartwheel Galaxy, revealing new details about star formation and the galaxy’s central black hole. Webb’s powerful infrared gaze produced this detailed image of the Cartwheel and two smaller companion galaxies against a backdrop of many other galaxies. This image provides a new view of how the Cartwheel Galaxy has changed over billions of years.

The Cartwheel Galaxy, located about 500 million light-years away in the Sculptor constellation, is a rare sight. Its appearance, much like that of the wheel of a wagon, is the result of an intense event – a high-speed collision between a large spiral galaxy and a smaller galaxy not visible in this image. Collisions of galactic proportions cause a cascade of different, smaller events between the galaxies involved; the Cartwheel is no exception. 

The collision most notably affected the galaxy’s shape and structure. The Cartwheel Galaxy sports two rings — a bright inner ring and a surrounding, colorful ring. These two rings expand outwards from the center of the collision, like ripples in a pond after a stone is tossed into it. Because of these distinctive features, astronomers call this a “ring galaxy,” a structure less common than spiral galaxies like our Milky Way. 

The bright core contains a tremendous amount of hot dust with the brightest areas being the home to gigantic young star clusters. On the other hand, the outer ring, which has expanded for about 440 million years, is dominated by star formation and supernovas. As this ring expands, it plows into surrounding gas and triggers star formation.

Other telescopes, including the Hubble Space Telescope, have previously examined the Cartwheel. But the dramatic galaxy has been shrouded in mystery – perhaps literally, given the amount of dust that obscures the view. Webb, with its ability to detect infrared light, now uncovers new insights into the nature of the Cartwheel.

The Near-Infrared Camera (NIRCam), Webb’s primary imager, looks in the near-infrared range from 0.6 to 5 microns, seeing crucial wavelengths of light that can reveal even more stars than observed in visible light. This is because young stars, many of which are forming in the outer ring, are less obscured by the presence of dust when observed in infrared light. In this image, NIRCam data are colored blue, orange, and yellow. The galaxy displays many individual blue dots, which are individual stars or pockets of star formation. NIRCam also reveals the difference between the smooth distribution or shape of the older star populations and dense dust in the core compared to the clumpy shapes associated with the younger star populations outside of it.

Learning finer details about the dust that inhabits the galaxy, however, requires Webb’s Mid-Infrared Instrument (MIRI). MIRI data are colored red in this composite image. It reveals regions within the Cartwheel Galaxy rich in hydrocarbons and other chemical compounds, as well as silicate dust, like much of the dust on Earth. These regions form a series of spiraling spokes that essentially form the galaxy’s skeleton. These spokes are evident in previous Hubble observations released in 2018, but they become much more prominent in this Webb image.

Webb’s observations underscore that the Cartwheel is in a very transitory stage. The galaxy, which was presumably a normal spiral galaxy like the Milky Way before its collision, will continue to transform. While Webb gives us a snapshot of the current state of the Cartwheel, it also provides insight into what happened to this galaxy in the past and how it will evolve in the future.

The James Webb Space Telescope is the world's premier space science observatory. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

Thursday, August 04, 2022

Gemini Telescopes Help Uncover Origins of Castaway Gamma-Ray Bursts


Neutron Star Merger in the Early Universe. This artist's impression illustrates the merger of two neutron stars, which produces the remarkably brief (1 to 2 second) yet intensely powerful event known as a short gamma-ray burst. The corresponding explosion, known as a kilonova, also forges the heaviest elements in the Universe, such as gold and platinum. Recent observations have found that some of these bursts, rather than occurring in the vastness of intergalactic space as was initially suggested, actually happen in previously undiscovered galaxies in the very distant Universe, up to 10 billion light-years away. NOIRLabs’ two Gemini telescopes were instrumental in helping make this discovery. Credit: NOIRLab/NSF/AURA/J. da Silva/Spaceengine.  download Large JPEG


Hidden Galaxy Home to GRB. This image captured by the Gemini North telescope reveals the previously unrecognized galactic home of the gamma-ray burst identified as GRB 151229A. Astronomers calculate that this burst, which lies in the direction of the constellation Capricornus, occurred approximately 9 billion years ago. Credit: International Gemini Observatory/NOIRLab/NSF/AURA. Acknowledgment: Image processing: T.A. Rector (University of Alaska Anchorage/NSF’s NOIRLab), M. Zamani (NSF’s NOIRLab) & D. de Martin (NSF’s NOIRLab).  download Large JPEG


Cosmoview Episode 49: Gemini Telescopes Help Uncover Origins of Castaway Gamma-Ray Bursts. Credit: Images and Videos: International Gemini Observatory/NOIRLab/NSF/AURA/J. da Silva/Fermilab Image Processing: M. Zamani (NSF’s NOIRLab) & D. de Martin (NSF’s NOIRLab) Music: Stellardrone - In Time



NSF’s NOIRLab-operated Gemini telescopes aid in revealing that seemingly lonely bursts came from previously undiscovered galaxies in the early Universe.

A number of mysterious gamma-ray bursts appear as lonely flashes of intense energy far from any obvious galactic home, raising questions about their true origins and distances. Using data from some of the most powerful telescopes on Earth and in space, including the twin Gemini telescopes, astronomers may have finally found their true origins — a population of distant galaxies, some nearly 10 billion light-years away.

An international team of astronomers has found that certain short gamma-ray bursts (GRBs) did not originate as castaways in the vastness of intergalactic space as they initially appeared. A deeper multi-observatory study instead found that these seemingly isolated GRBs actually occurred in remarkably distant — and therefore faint — galaxies up to 10 billion light-years away. 

This discovery suggests that short GRBs, which form during the collisions of neutron stars, may have been more common in the past than expected. Since neutron-star mergers forge heavy elements, including gold and platinum, the Universe may have been seeded with precious metals earlier than expected as well. 

This cosmic sleuthing required the combined power of some of the most powerful telescopes on Earth and in space, including the Gemini North telescope in Hawai‘i and the Gemini South telescope in Chile. The two Gemini telescopes comprise the International Gemini Observatory, operated by NSF’s NOIRLab. Other observatories involved in this research include the NASA/ESA Hubble Space Telescope, the Lowell Discovery Telescope in Arizona, the Gran Telescopio Canarias in La Palma in the Canary Islands, ESO’s Very Large Telescope in Cerro Paranal in Chile, and the Keck Observatory in Hawai‘i.

“Many short GRBs are found in bright galaxies relatively close to us, but some of them appear to have no corresponding galactic home,” said Brendan O’Connor, first author of the paper presenting the results and an astronomer at both the University of Maryland and the George Washington University. “By pinpointing where the short GRBs originate, we were able to comb through troves of data from observatories like the twin Gemini telescopes to find the faint glow of galaxies that were simply too distant to be recognized before.”

The researchers began their quest by reviewing data on 120 GRBs captured by two instruments aboard NASA’s Neil Gehrels Swift Observatory: Swift’s Burst Alert Telescope, which signaled a burst had been detected; and Swift’s X-ray Telescope, which identified the general location of the GRB’s X-ray afterglow. Additional afterglow studies made with the Lowell Observatory more accurately pinpointed the location of the GRBs.

The afterglow studies found that 43 of the short GRBs were not associated with any known galaxy and appeared in the comparatively empty space between galaxies. “These hostless GRBs presented an intriguing mystery and astronomers had proposed two explanations for their seemingly isolated existence,” said O’Connor. 

One hypothesis was that the progenitor neutron stars formed as a binary pair inside a distant galaxy, drifted together into intergalactic space, and eventually merged billions of years later. The other hypothesis was that the neutron stars merged many billions of light-years away in their home galaxies, which now appear extremely faint due to their vast distance from Earth. 

“We felt this second scenario was the most plausible to explain a large fraction of hostless events,” said O’Connor. “We then used the most powerful telescopes on Earth to collect deep images of the GRB locations and uncovered otherwise invisible galaxies 8 to 10 billion light-years away from Earth.”

To make these detections, the astronomers utilize a variety of optical and infrared instruments mounted on the twin 8.1-meter Gemini telescopes. The Gemini Observatory offers the capability for observations from both hemispheres, which is incredibly important for GRB follow-up due to their ability to survey the entire sky. Gemini data were used to localize 17 out of 31 GRBs analyzed in their sample. 

This result could help astronomers better understand the chemical evolution of the Universe. Merging neutron stars trigger a cascading series of nuclear reactions that are necessary to produce heavy metals, like gold, platinum, and thorium. Pushing back the cosmic timescale on neutron-star mergers means that the young Universe was far richer in heavy elements than previously known. 

“This pushes the timescale back on when the Universe received the ‘Midas touch’ and became seeded with the heaviest elements on the periodic table," said O’Connor.

“This survey for GRB host galaxies has delivered a compelling answer to the long-standing mystery of the nature of neutron star environments,” said Martin Still, Gemini Program Officer at the National Science Foundation. “Among the largest open-access telescopes in the world, the Gemini Observatories provide powerful and flexible laboratories for a broad range of experiments and international collaboration.”


Links




Contacts:

Brendan O'Connor
University of Maryland and George Washington University
Tel: +1 301 286 1237
Email:
oconnorb@umd.edu

Charles Blue
Public Information Officer
NSF’s NOIRLab
Tel: +1 202 236 6324
Email:
charles.blue@noirlab.edu

Wednesday, August 03, 2022

Out With a Bang: Explosive Neutron Star Merger Captured for the First Time in Millimeter Light


In the first-ever time-lapse movie of a short-duration gamma-ray burst in millimeter-wavelength light, we see GRB 21106A as captured with the Atacama Large Millimeter/submillimeter Array (ALMA). The millimeter light seen here pinpoints the location of the event to a distant host galaxy in images captured using the Hubble Space Telescope. The evolution of the millimeter light’s brightness provides information on the energy and geometry of the jets produced in the explosion. Credit: ALMA (ESO/NAOJ/NRAO), T. Laskar (Utah), S. Dagnello (NRAO/AUI/NSF)


In a first for radio astronomy, scientists have detected millimeter-wavelength light from a short-duration gamma-ray burst. This artist's conception shows the merger between a neutron star and another star (seen as a disk, lower left) which caused an explosion resulting in the short-duration gamma-ray burst, GRB 211106A (white jet, middle), and left behind what scientists now know to be one of the most luminous afterglows on record (semi-spherical shock wave mid-right). While dust in the host galaxy obscured most of the visible light (shown as colors), millimeter light from the event (depicted in green) was able to escape and reach the Atacama Large Millimeter/submillimeter Array (ALMA), giving scientists an unprecedented view of this cosmic explosion. From the study, the team confirmed that GRB 211106A is one of the most energetic short-duration GRBs ever observed. Credit: ALMA (ESO/NAOJ/NRAO), M. Weiss (NRAO/AUI/NSF)



Scientists using the Atacama Large Millimeter/submillimeter Array (ALMA) have for the first time recorded millimeter-wavelength light from a fiery explosion caused by the merger of a neutron star with another star. The team also confirmed this flash of light to be one of the most energetic short-duration gamma-ray bursts ever observed, leaving behind one of the most luminous afterglows on record. The results of the research will be published in an upcoming edition of The Astrophysical Journal Letters

Gamma-ray bursts (GRBs) are the brightest and most energetic explosions in the Universe, capable of emitting more energy in a matter of seconds than our Sun will emit during its entire lifetime. GRB 211106A belongs to a GRB sub-class known as short-duration gamma-ray bursts. These explosions— which scientists believe are responsible for the creation of the heaviest elements in the Universe, such as platinum and gold— result from the catastrophic merger of binary star systems containing a neutron star. “These mergers occur because of gravitational wave radiation that removes energy from the orbit of the binary stars, causing the stars to spiral in toward each other,” said Tanmoy Laskar, who will soon commence work as an Assistant Professor of Physics and Astronomy at the University of Utah. “The resulting explosion is accompanied by jets moving at close to the speed of light. When one of these jets is pointed at Earth, we observe a short pulse of gamma-ray radiation or a short-duration GRB.”

A short-duration GRB usually lasts only a few tenths of a second. Scientists then look for an afterglow, an emission of light caused by the interaction of the jets with surrounding gas. Even still, they’re difficult to detect; only half-a-dozen short-duration GRBs have been detected at radio wavelengths, and until now none had been detected in millimeter wavelengths. Laskar, who led the research while an Excellence Fellow at Radboud University in The Netherlands, said that the difficulty is the immense distance to GRBs, and the technological capabilities of telescopes. “Short-duration GRB afterglows are very luminous and energetic. But these explosions take place in distant galaxies which means the light from them can be quite faint for our telescopes on Earth. Before ALMA, millimeter telescopes were not sensitive enough to detect these afterglows.”

Having occurred when the Universe was just 40-percent of its current age, GRB 211106A is no exception. The light from this short-duration gamma-ray burst was so faint that while early X-ray observations with NASA’s Neil Gehrels Swift Observatory saw the explosion, the host galaxy was undetectable at that wavelength, and scientists weren’t able to determine exactly where the explosion was coming from. “Afterglow light is essential for figuring out which galaxy a burst comes from and for learning more about the burst itself. Initially, when only the X-ray counterpart had been discovered, astronomers thought that this burst might be coming from a nearby galaxy,” said Laskar, adding that a significant amount of dust in the area also obscured the object from detection in optical observations with the Hubble Space Telescope.

Each wavelength added a new dimension to scientists’ understanding of the GRB, and millimeter, in particular, was critical to uncovering the truth about the burst. “The Hubble observations revealed an unchanging field of galaxies. ALMA’s unparalleled sensitivity allowed us to pinpoint the location of the GRB in that field with more precision, and it turned out to be in another faint galaxy, which is further away. That, in turn, means that this short-duration gamma-ray burst is even more powerful than we first thought, making it one of the most luminous and energetic on record,” said Laskar.

Wen-fai Fong, an Assistant Professor of Physics and Astronomy at Northwestern University added, “This short gamma-ray burst was the first time we tried to observe such an event with ALMA. Afterglows for short bursts are very difficult to come by, so it was spectacular to catch this event shining so bright. After many years of observing these bursts, this surprising discovery opens up a new area of study, as it motivates us to observe many more of these with ALMA, and other telescope arrays, in the future.” 

Joe Pesce, National Science Foundation Program Officer for NRAO/ALMA said, “These observations are fantastic on many levels. They provide more information to help us understand the enigmatic gamma-ray bursts (and neutron-star astrophysics in general), and they demonstrate how important and complementary multi-wavelength observations with space- and ground-based telescopes are in understanding astrophysical phenomena.”

And there’s plenty of work still to be done across multiple wavelengths, both with new GRBs and with GRB 211106A, which could uncover additional surprises about these bursts. “The study of short-duration GRBs requires the rapid coordination of telescopes around the world and in space, operating at all wavelengths,” said Edo Berger, Professor of Astronomy at Harvard University. “In the case of GRB 211106A, we used some of the most powerful telescopes available— ALMA, the National Science Foundation’s Karl G. Jansky Very Large Array (VLA), NASA’s Chandra X-ray Observatory, and the Hubble Space Telescope. With the now-operational James Webb Space Telescope (JWST), and future 20-40 meter optical and radio telescopes such as the next generation VLA (ngVLA) we will be able to produce a complete picture of these cataclysmic events and study them at unprecedented distances.”

Laskar added, “With JWST, we can now take a spectrum of the host galaxy and easily know the distance, and in the future, we could also use JWST to capture infrared afterglows and study their chemical composition. With ngVLA, we will be able to study the geometric structure of the afterglows and the star-forming fuel found in their host environments in unprecedented detail. I am excited about these upcoming discoveries in our field.”




Additional Information


“The First Short GRB Millimeter Afterglow: The Wide-Angled Jet of the Extremely Energetic SGRB 211106A,” Laskar et al (2022),The Astrophysical Journal Letters, pre-printarxiv

The Atacama Large Millimeter/submillimeter Array (ALMA), an international astronomy facility, is a partnership of the European Organisation for Astronomical Research in the Southern Hemisphere (ESO), the U.S. National Science Foundation (NSF) and the National Institutes of Natural Sciences (NINS) of Japan in cooperation with the Republic of Chile. ALMA is funded by ESO on behalf of its Member States, by NSF in cooperation with the National Research Council of Canada (NRC) and the Ministry of Science and Technology (MOST) and by NINS in cooperation with the Academia Sinica (AS) in Taiwan and the Korea Astronomy and Space Science Institute (KASI).

ALMA construction and operations are led by ESO on behalf of its Member States; by the National Radio Astronomy Observatory (NRAO), managed by Associated Universities, Inc. (AUI), on behalf of North America; and by the National Astronomical Observatory of Japan (NAOJ) on behalf of East Asia. The Joint ALMA Observatory (JAO) provides the unified leadership and management of the construction, commissioning and operation of ALMA.



 
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Tuesday, August 02, 2022

Scientists Reveal Distribution of Dark Matter around Galaxies 12 billion Years Ago - Further Back than Ever Before


Figure 1: Conceptual image of this research. Distribution of invisible "dark matter" was investigated by combining the cosmic microwave background (CMB) and the HSC-SSP images. Credit: Reiko Matsushita (Nagoya University)

How do we see something that happened so long ago? Because of the finite speed of light, we see distant galaxies not as they are today, but rather as they were billions of years in the past. But even more challenging, how do we see something like dark matter, that by its nature does not emit light? Consider a very distant source galaxy, even further away than the galaxy whose dark matter one wants to investigate. The gravitational pull of the foreground galaxy, including its dark matter, distorts the surrounding space and time, as predicted by Einstein’s theory of General Relativity. As the light from the source galaxy travels through this distortion, it bends, changing the apparent shape of the galaxy in the sky. The greater the amount of dark matter, the greater the distortion. Thus, scientists can measure the amount of dark matter around the foreground galaxy (the "lens" galaxy) from the distortion.

However, at this point, scientists encounter a problem. The galaxies in the deepest reaches of the Universe are incredibly faint. As a result, the further away from Earth you look, the less effective this technique becomes. The lensing distortion is subtle and difficult to detect in most cases, so one needs many background galaxies to detect the signal. Most previous studies remained stuck at the same limits. Unable to detect enough distant source galaxies to measure the distortion, they could only analyze dark matter from no further back than 8-10 billion years ago. These limitations left open the question about the distribution of dark matter between this time and 13.7 billion years ago, around the beginnings of our Universe.

To overcome these challenges and observe dark matter in the furthest reaches of the Universe, a research team led by Nagoya University’s Hironao Miyatake, in collaboration with the University of Tokyo, National Astronomical Observatory of Japan, and Princeton University, used a different source of background light, the microwaves released from the Big Bang itself.

How did they do this? First, using data from the observations of the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP), the team identified 1.5 million lens galaxies using visible light, selected to be seen 12 billion years ago. Next, to overcome the lack of galaxy light even further away, they employed microwaves from the cosmic microwave background (CMB), the radiation residue from the Big Bang. Using microwaves observed by the European Space Agency’s Planck satellite, the team measured how the dark matter around the lens galaxies distorted the microwaves.

"Look at dark matter around distant galaxies?" asks Professor Masami Ouchi of the National Astronomical Observatory of Japan and the University of Tokyo, who made many of the observations. "It was a crazy idea. No one realized we could do this. But after I gave a talk about a large distant galaxy sample, Hironao came to me and said it may be possible to look at dark matter around these galaxies with the CMB."

"Most researchers use source galaxies to measure dark matter distribution from the present to eight billion years ago", adds Assistant Professor Yuichi Harikane of the Institute for Cosmic Ray Research, University of Tokyo. "However, we could look further back into the past because we used the more distant CMB to measure dark matter. For the first time, we were measuring dark matter from almost the earliest moments of the Universe."

After a preliminary analysis, the researchers soon realized they had a large enough sample to detect the distribution of dark matter. Combining the large distant galaxy sample and the lensing distortions in the CMB, they detected dark matter even further back in time, from 12 billion years ago. This is only 1.7 billion years after the beginning of the Universe, and thus these galaxies are seen soon after they first formed.

"I was happy that we opened a new window into that era," Miyatake says. "12 billion years ago, things were very different. You see more galaxies that are in the process of formation than at the present; the first galaxy clusters are starting to form as well." Galaxy clusters consist of 100-1000 galaxies bound by gravity with large amounts of dark matter.

"This result gives a very consistent picture of galaxies and their evolution, as well as the dark matter in and around galaxies, and how this picture evolves with time," says Neta Bahcall, Eugene Higgins Professor of Astronomy, professor of astrophysical sciences, and director of undergraduate studies at Princeton University.

One of the most exciting of the researchers’ findings was related to the clumpiness of the dark matter. According to the standard theory of cosmology, the Lambda-CDM (Cold Dark Matter) model, subtle fluctuations in the CMB form pools of densely packed matter by attracting surrounding matter through gravity. This creates inhomogeneous clumps that form stars and galaxies in these dense regions. The group’s findings suggest that their clumpiness measurement was lower than predicted by the Lambda-CDM model. Miyatake is excited about the possibilities. "Our finding is still uncertain", he says. "But if it is true, it would suggest that the entire model is flawed as you go further back in time. This is exciting, because it could suggest – if the result holds after the uncertainties are reduced – an improvement of the model that may give insight into the nature of dark matter itself."

This study used data available from existing telescopes, including Planck and the Subaru Telescope. The group has only reviewed a third of the HSC-SSP data. The next step will be to analyze the entire data set, which should allow for a more precise measurement of the dark matter distribution. In the future, the team expects to use an advanced data set like the Vera C. Rubin Observatory's Legacy Survey of Space and Time (LSST) to explore more of the earliest parts of space. "LSST will allow us to observe half the sky," Harikane says. "I don’t see any reason we couldn’t see the dark matter distribution 13 billion years ago next."

These results appeared as Miyatake et al. "First Identification of a CMB Lensing Signal Produced by 1.5 Million Galaxies at z∼4: Constraints on Matter Density Fluctuations at High Redshift" in Physical Review Letters on August 1, 2022.



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Monday, August 01, 2022

Super-Earth Skimming Habitable Zone of Red Dwarf


Schematic diagram of the newly discovered Ross 508 planetary system. The green region represents the habitable zone where liquid water can exist on the planetary surface. The planetary orbit is shown as a blue line. Ross 508 b skims the inner edge of the habitable zone (solid line), possibly crossing into the habitable zone for part of the orbit (dashed line). (Credit: Astrobiology Center) Original size (100KB) 

A super-Earth planet has been found near the habitable zone of a red dwarf star only 37 light-years from the Earth. This is the first discovery by a new instrument on the Subaru Telescope and offers a chance to investigate the possibility of life on planets around nearby stars. With such a successful first result, we can expect that the Subaru Telescope will discover more, potentially even better, candidates for habitable planets around red dwarfs.

Red dwarfs, stars smaller than the Sun, account for three-quarters of the stars in the Milky Way Galaxy, and are abundant in the neighborhood around the Sun. As such, they are important targets in the search for nearby extra-solar planets and extraterrestrial life. But red dwarfs are cool and don’t emit much visible light compared to other types of stars, making it difficult to study them.

In the infrared wavelengths red dwarfs are brighter. So the Astrobiology Center in Japan developed an infrared observational instrument mounted on the Subaru Telescope to search for signs of planets around red dwarf stars. The instrument is called IRD for Infrared Doppler, the observational method used in this search.

The first fruits of this search are signs of a super-Earth four times the mass of the Earth circling the star Ross 508, located 37 light-years away in the constellation Serpens. This planet, Ross 508 b, has a year of only 11 Earth-days, and lies at the inner edge of the habitable zone around its host star. Interestingly, there are indications that the orbit is elliptical, which would mean that for part of the orbit the planet would be in the habitable zone, the region where conditions would be right for liquid water to exist on the surface of the planet. Whether or not there is actually water or life are questions of further study.

To have the very first planet discovered by this new method be so tantalizingly close to the habitable zone seems too good to be true and bodes well for future discoveries. Bun’ei Sato, a Professor at the Tokyo Institute of Technology and the principal investigator in this search comments, “It has been 14 years since the start of IRD’s development. We have continued our development and research with the hope of finding a planet exactly like Ross 508 b.”

These results appeared as Harakawa et al. “A Super-Earth Orbiting Near the Inner Edge of the Habitable Zone around the M4.5-dwarf Ross 508” in Publication of the Astronomical Society of Japan on June 30, 2022.



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Friday, July 29, 2022

New Results from a Survey of Active Galactic Nuclei


This mosaic contains 2,200 ultraviolet images taken by the Neil Gehrels Swift Observatory of the Large Magellanic Cloud, requiring 5.4 days of exposure time. Credit:
NASA/Swift/S. Immler (Goddard) and M. Siegel (Penn State)

An illustration of the Neil Gehrels Swift Observatory in front of a gamma-ray burst.
Credit:
Spectrum and NASA E/PO, Sonoma State University, Aurore Simonnet


Locations of the objects surveyed in the second BASS data release. The symbol shape and color indicates the instrument and telescope used to collect that object’s spectrum. Credit: Koss et al. 2022


Redshift distribution of AGN in the BASS second data release.
Credit:Oh et al. 2022




Across the universe, luminous galactic centers are fueled by supermassive black holes that accrete gas, dust, and stars from their surroundings. These powerful active galactic nuclei (AGN) radiate across the electromagnetic spectrum and emit jets of energetic particles, potentially shaping the evolution of the galaxies they inhabit. Collecting spectra of AGN is key to understanding the structure of the material that surrounds them and the role they may play in galaxy evolution — and a new public data release from a spectroscopic survey of AGN discovered by the Neil Gehrels Swift Observatory has expanded our ability to probe these objects.

Since 2005, the Neil Gehrels Swift Observatory has monitored the sky from gamma-ray to optical wavelengths, primarily in pursuit of the sources of gamma-ray bursts: extragalactic explosions potentially caused by massive stars going supernova or compact objects merging. However, Swift sees far more than just gamma-ray bursts — its Burst Alert Telescope (BAT), which scans 80% of the sky each day at X-ray and gamma-ray energies (14–195 kiloelectronvolts), has discovered hundreds of AGN in the local universe.

But detecting AGN is just the first step toward understanding the nature and importance of these objects — dedicated spectroscopic follow-up is a critical next step. Enter the BAT AGN Spectroscopic Survey (BASS): a project that aims to survey the most powerful AGN that have been detected in high-energy X-rays by Swift Observatory. In a new special issue of the Astrophysical Journal Supplement Series, the BASS team presents the latest step toward their goal of producing an immense catalog of AGN spectra.

This data release contains 1,449 optical spectra — 1,181 of which have never been released before — and 233 near-infrared spectra, all from 858 AGN in the local universe. The just published special issue presents catalogs of spectra, derived quantities, and first science results, including the following important findings:
  • The objects discovered by the Burst Alert Telescope span a wide range of properties. Namely, the black hole masses, luminosities, accretion rates, and degree to which the targets are obscured by gas and dust all vary by at least five orders of magnitude, making this survey a useful probe of a wide variety of AGN. Additionally, few of the sources observed in this survey are contained in other surveys, making the BASS project a source of unique information.
  • For the first time, the black hole mass function and the Eddington ratio distribution function — how the black hole mass and AGN luminosity vary with other factors — have been determined directly for heavily obscured objects. The resulting distribution functions show that obscured AGN are intrinsically less luminous compared to their theoretical maximum luminosities than their unobscured counterparts. This suggests that radiation plays a large role in determining the structure of the material close to an AGN.
  • The masses of the supermassive black holes at the heart of obscured AGN tend to be underestimated when the mass is determined from measurements of hydrogen emission lines. Researchers can reduce this effect in the future studies by applying multiplicative factors when estimating masses this way.
  • New diagnostics based on mid-infrared luminosities can distinguish between obscured and unobscured AGN, yielding new candidate sources that are heavily obscured. However, separating out star-forming galaxies remains a challenge.
The publicly available sample of spectra developed by the BASS team provides a valuable tool for researchers wishing to study AGN in the local universe. Looking forward, the team plans to supplement their current catalog with observations of fainter sources made by the Burst Alert Telescope, expanding our understanding of these cosmic engines.

Citation

Special ApJS Issue on the BAT AGN Spectroscopic Survey Second Data Release

“BAT AGN Spectroscopic Survey XXI: The Data Release 2 Overview,” Michael J. Koss et al 2022 ApJS 261
1. doi:10.3847/1538-4365/ac6c8f