From AAS NOVA : “Connecting the Pieces of a Black Hole Temper Tantrum”

From AAS NOVA

7 July 2021
Susanna Kohler

Artist’s illustration of a black hole X-ray binary, in which a black hole accretes matter from a companion star. Credit: Gabriel Pérez, Solar Maximum Mission (SMM) | High Altitude Observatory (Center for Astrophysics in La Palma | Instituto de Astrofísica de Canarias • IAC (ES)]

Accreting, stellar-mass black holes are anything but predictable. A new study explores what’s happening as these feeding monsters erupt in violent outbursts and then settle down again.

This illustration shows some of the possible transient behavior of the gas flowing onto and away from a black hole in an X-ray binary. [NASA/JPL-Caltech (US)]

An Unsteady Existence

Black hole X-ray binaries (BHXBs) consist of a stellar-mass black hole that siphons material from an ordinary companion star. As this material flows between the objects, it forms an accretion disk around the black hole. BHXBs shine in X-rays from the hot material of this disk, and from a mysterious corona — ultra-hot gas that exists in some unknown form above the disk.

BHXBs may accrete quietly and steadily much of the time, but on occasion, they undergo sudden outbursts, substantially brightening in X-rays. Unlike supermassive black holes, which evolve on extremely long timescales, stellar-mass black holes can change over just days or weeks — short enough for us to watch!

In a new study led by Jingyi Wang (MIT Kavli Institute for Astrophysics and Space Research (US)), a team of scientists presents observations by NICER — an X-ray telescope installed on the International Space Station — of a BHXB throwing such a temper tantrum.

MIT Kavli Institute for Astrophysics and Space Research.

NICER on the ISS

Reflections of a Transition

During an outburst, a BHXB undergoes state transitions, displaying changes in the X-ray luminosities and energies as either the corona or the disk takes over to dominate the emission. In addition to the X-ray changes, persistent radio emission from a slow and steady jet can be suddenly replaced by a short-lived radio flare that then subsides.

Despite many observations, we lack the details of what’s happening on small scales, close around the black hole. What form does the corona take? Does its size or extent change over time? What drives the state transitions? And how are the different components of this system — disk, corona, and jet — related, if at all?

The top plot (a) shows the inferred corona height (black line) over the span of the outburst. The radio emission, including the flare, can be seen in red. The bottom two diagrams show the authors’ picture of the geometry of the black hole, disk, and corona at two points during the state changes: during the rise from quiescence (b), and at the end of the outburst when the jet base is ejected (c). [Adapted from Wang et al. 2021.]

Wang and collaborators used NICER data of the BHXB system MAXI J1820+070 during a 2018 outburst to track the lag caused by light travel time between X-rays that arrived directly from the corona and light from the corona that was reflected by the disk before reaching us. By modeling the changes in this reverberation lag as the system underwent state transitions, the team could infer the geometry on the small scales we can’t observe, helping us to understand the tantrum.

A Connected Picture

Wang and collaborators show that the best explanation of NICER’s observations is that the height of the X-ray corona changes during the BHXB’s state transitions. They argue that the corona first contracts, and then rapidly expands during the outburst, preceding a radio flare by ~5 days.

Under the authors’ interpretation, these signs point to a neat picture of BHXB outbursts: a quietly accreting black hole has a disk and a steady jet, and the corona makes up the base of that jet. When the BHXB goes into outburst, it ejects that jet base as a bright knot in its final moments of outburst, before fading back to quiescence.

While this model isn’t yet definitive, this latest evidence points to a clear connection between the disk, jet, and corona of a BHXB. We’re sure to gain more insight ahead!

Citation

“Disk, Corona, Jet Connection in the Intermediate State of MAXI J1820+070 Revealed by NICER Spectral-timing Analysis,” Jingyi Wang et al 2021 ApJL 910 L3.
https://iopscience.iop.org/article/10.3847/2041-8213/abec79

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

From AAS NOVA : “Observing ‘The Accident’- an Enigmatic Brown Dwarf”

From AAS NOVA

2 July 2021
Susanna Kohler

Artist’s illustration of a Y-type brown dwarf. [NASA/JPL-Caltech (US)]

It’s human nature to try to categorize the things we observe in the universe. But what happens when something doesn’t fit into the neat categories we’ve established? A new study explores one such object: an especially perplexing brown dwarf.

Brown dwarfs are intermediate in size between the largest planets and the smallest stars. [NASA/JPL-Caltech/UCB]

A Hidden Population

Brown dwarfs — substellar objects that aren’t massive enough to fuse hydrogen in their cores — are an intriguing population. Not quite stars and not quite planets, these objects occupy an uneasy in-between space that’s worth studying further.

But the coldest brown dwarfs — which fall into spectral category Y and have effective temperatures below ~450 K — are a challenging population to study! These chilly objects don’t emit much light, and what little they do radiate is concentrated in the infrared near 5 µm. These objects are therefore difficult to observe from the ground, so we rely on space-based missions to discover the faint light from these objects.

An Accidental Find

Thus far, we’ve managed to detect around 50 of these cold Y dwarfs. To better categorize them, we plot them on color–color and color–magnitude plots to compare their brightnesses at different wavelengths. A recent discovery, however, isn’t behaving as expected.

WISE 1534–1043 nicknamed “The Accident” when it was found serendipitously in a field imaged by the Wide-field Infrared Survey Explorer, is a lone brown dwarf speeding across the sky.

National Aeronautics and Space Administration(US) Wise/NEOWISE Telescope.

An article led by J. Davy Kirkpatrick (California Institute of Technology (US)) now presents new, follow-up observations of this puzzling object collected with the Hubble Space Telescope and with the Keck Observatory in Hawaii.

National Aeronautics Space Agency(USA) European Space Agency [Agence spatiale européenne][Europäische Weltraumorganisation](EU)/ Hubble Wide Field Camera 3

National Aeronautics and Space Administration(US)/European Space Agency [Agence spatiale européenne] [Europäische Weltraumorganisation] (EU) Hubble Space Telescope

Keck/MOSFIRE on Keck 1, Mauna Kea, Hawaii, USA.

W.M. Keck Observatory two ten meter telescopes operated by California Institute of Technology(US) and the University of California(US), Maunakea Hawaii USA, altitude 4,207 m (13,802 ft). Credit: Caltech.

Color–color (top) and color–magnitude (bottom) plots exploring WISE 1534–1043’s photometric properties (red data points, plotted using two different models) show that its behavior is unique among known, nearby, cold brown dwarfs. [Adapted from Kirkpatrick et al. 2021]

Defying Categorization

These new observations pinpoint WISE 1534–1043’s location — just ~50 light-years away — and confirm its bizarre observational properties. Looking at the color–color and color–magnitude plots to the right, it’s clear that WISE 1534–1043 lies in a quadrant entirely on its own.

Measurements of The Accident’s absolute brightness at different wavelengths are all in line with the coldest known Y dwarfs. But its relative colors (as shown by the W1 – W2, ch1 – ch2, and J – ch2 measurements in the plots) and magnitudes fall entirely outside of the range of known brown dwarfs.

Identity Options

What could be the explanation for these enigmatic properties? Kirkpatrick and collaborators use their observations to consider four possible identities for The Accident:

An extremely low-metallicity, old, cold brown dwarf
An extremely low-mass, low-gravity, young brown dwarf
An ejected exoplanet
An ultracold stellar remnant (like a white dwarf or an exotic ablated stellar core)

Of these options, the authors determine that the first is the most likely. If WISE 1534–1043 is old and remarkably low-metallicity, then the outer layers of its atmosphere would have decreased opacity, allowing us to see deeper into it and potentially explaining the unusual photometric properties. This could mean that The Accident represents the first known Y-type subdwarf — a brand new category of star.

“Verification, refutation, or further befuddlement” should be possible in the future with observations from the upcoming James Webb Space Telescope, suggest the authors. In the meantime, the refusal of objects like The Accident to fit neatly into boxes continues to keep us on our toes!

Citation

“The Enigmatic Brown Dwarf WISEA J153429.75-104303.3 (a.k.a. “The Accident”),” J. Davy Kirkpatrick et al 2021 ApJL 915 L6.
https://iopscience.iop.org/article/10.3847/2041-8213/ac0437

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

From AAS NOVA : “Searching for Spots with Interferometry”

From AAS NOVA

23 June 2021
Tarini Konchady

Credit: http://www.chara.gsu.edu/instrumentation/chara-array

One of the telescopes in the CHARA array as seen at sunrise. The pipe directs light to the central Beam Synthesis Facility, which combines the light from all six telescopes. Credit: Steve Golden/CHARA.

One of the six telescopes that are part of the CHARA array at Mount Wilson Observatory, Los Angeles County, California.

Starspots are regions on the surface of a star that are cooler than their surroundings. Temperature affects brightness, so starspots can significantly alter the overall appearance of a star even when individual starspots can’t be distinguished. But if we characterize starspots in detail, we should be able to account for their effects.

Old and New Ways of Finding Starspots

Starspots are thought to be caused by stellar magnetic activity, so as much as they can obscure true stellar properties, they can also help us learn about the interiors of stars. We’ve also noticed that our Sun’s starspots behave very differently than starspots on other stars, adding another motivation to examine these phenomena on other stars.

Until recently, starspots have been studied through indirect methods like light curve modeling and Doppler imaging, which measures changes in stellar spectra caused by magnetic fields. These techniques have broadened our understanding of starspots, but they are also hamstrung by requiring certain assumptions about the stars being observed.

Direct imaging of starspots has been made possible through a relatively new technique called long-baseline optical/near-infrared interferometry (LBI). A recent study led by James Parks (Georgia State University (US)) uses this technique to observe starspots on λ Andromedae, a giant star in a binary with a less massive companion.

Stellar surface images based on observations taken in 2010. The top row is the starspot model images, the middle row is the observations, and the bottom row is the simulated images. The white dot is the resolution of the CHARA array, which was used to take the observations. The starspot models were constructed independently of the simulated images and vice-versa[Parks et al. 2021].

Telescopes in Tandem

Interferometry is an imaging technique that combines the input of multiple telescopes as though they were a single and much larger telescope. LBI refers to interferometry conducted with telescopes that are spread out across a fairly large distance. For instance, the Event Horizon Telescope image of Messier 87’s central black hole-Messier 87*- was taken by eight radio telescopes spread out across an entire hemisphere!

To image the starspots on λ Andromedae, Parks and collaborators used observations taken by the Center for High Angular Resolution Astronomy (CHARA) array, which consists of six 1-meter optical telescopes arranged in a Y-shape. The highest resolution allowed by these observations was 0.4 milliarcseconds (for context, the Moon spans roughly 0.5 degrees, or nearly 2 million milliarcseconds). Data was also taken on the 0.4-meter telescope at Fairborn Observatory to obtain light curves of λ Andromedae that were roughly concurrent to the LBI observations.

Two Different Ways to Model Starspots

Parks and collaborators used the CHARA observations to model λ Andromedae’s starspots in two different ways. The first method was to model the star’s surface while allowing for starspots, where the resulting models were informed by the CHARA observations. The second way was image reconstruction, which uses the observing conditions during which images were taken to determine the underlying astrophysical components. The advantage of using image reconstruction over surface modeling is that image reconstruction requires fewer assumptions about the object in question. However, false artifacts can be generated during the reconstruction process.

Both methods found between one and four starspots on λ Andromedae at any given time. The starspots also pointed to a rotation period that matched the period determined from the concurrent light curves. Overall, the study was a successful demonstration of using LBI to image starspots on λ Andromedae and, excitingly, more detailed studies are to follow!

Citation

“Interferometric Imaging of λ Andromedae: Evidence of Starspots and Rotation,” J. R. Parks et al 2021 ApJ 913 54.

https://iopscience.iop.org/article/10.3847/1538-4357/abb670

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

From AAS NOVA : “Probing Dust Close to Supermassive Black Holes”

From AAS NOVA

16 June 2021
Susanna Kohler

Artist’s illustration of the surroundings of a supermassive black hole at the heart of an active galaxy. Credit: M. Kornmesser/ European Southern Observatory [Observatoire européen austral][Europäische Südsternwarte] (EU) (CL)]

What’s going on deep in the centers of active galaxies, close around the supermassive black holes feeding off of their surroundings? A new study uses infrared observations to explore this inner region in one active galaxy.

Artist’s impression of the active galactic nucleus (DESY, Science Communication Lab)

A Unified Picture?

We know that active galactic nuclei (AGN) consist of a supermassive black hole accreting surrounding material and shining brightly across the electromagnetic spectrum. But the structure of the gas and dust close around the black hole, and the causes of the different emission we see, have remained a topic of debate.

Decades ago, scientists proposed that Type 1 and Type 2 AGN — two different categories of active galaxies with different observational properties — might be the same objects viewed from different angles. This unification scheme relies on the presence of a dusty torus — a puffed-up, donut-like dust structure close to the black hole. In this model, the torus obscures the inner, emission-line-producing gas from some viewing angles, changing the appearance of the AGN based on its orientation.

But recent infrared observations have challenged this view. With powerful mid-infrared telescopes, we’ve taken a closer look at the inner few hundred light-years of nearby active galaxies — and instead of revealing an obscuring torus of dust, these observations have shown polar dust structures.

European Southern Observatory(EU) , Very Large Telescope at Cerro Paranal in the Atacama Desert •ANTU (UT1; The Sun ) •KUEYEN (UT2; The Moon ) •MELIPAL (UT3; The Southern Cross ), and •YEPUN (UT4; Venus – as evening star). Elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo.

A Search for Distant Dust

How can we explain these observations? Theorists have a solution: in the disk–wind model, the dust close to the black hole is arranged in a hot, equatorial disk rather than a torus. Radiation pressure then blows some of this dust off into a cooler wind from the poles, producing the polar structures we’ve seen in mid-infrared observations. Obscuration comes from the disk and the launch region of the wind.

The equatorial disk in this model should lie on scales too small to have been previously observed in mid-infrared — but there’s a new tool on the scene! GRAVITY, an interferometric instrument on the Very Large Telescope Interferometer in Chile, operates in the near-infrared.

ESO VLTI GRAVITY

European Southern Observatory(EU) VLTI Interferometer image, Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level, •ANTU (UT1; The Sun ),
•KUEYEN (UT2; The Moon ),
•MELIPAL (UT3; The Southern Cross ), and
•YEPUN (UT4; Venus – as evening star).

This makes it the perfect instrument to search for the very hot dust that would lie in a disk at the heart of an AGN.

In a new study led by James Leftley (University of Southampton (UK); University of Côte d’Azur [Université Côte d’Azur](FR); ESO, Chile), a team of scientists has now used GRAVITY to obtain near-infrared observations of the center of ESO 323-G77, a local active galactic nucleus.

Getting to the Heart of the Matter

Through careful analysis and modeling, Leftley and collaborators interpret their observations on scales of less than a light-year (for an object that’s hundreds of millions of light-years away!). The result? The near-infrared observations are consistent with an extended, equatorially aligned hot dust disk. The scale of this disk neatly matches the size predicted in disk–wind models.

Though the data are still too sparse and noisy to rule out the torus model in favor of the disk–wind model, these observations represent an important step in understanding how dust may be distributed in the heart of active galaxies.

Citation

“Resolving the Hot Dust Disk of ESO323-G77,” James H. Leftley et al 2021 ApJ 912 96 6
https://iopscience.iop.org/article/10.3847/1538-4357/abee80

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

From AAS NOVA : “New Insights from LIGO/Virgo’s Merging Black Holes”

From AAS NOVA

Still from a simulation showing how black holes might interact in the chaotic cores of globular clusters. [Carl Rodriguez/Northwestern University (US) Visualization]

Since the first merger of two black holes detected in 2015, the LIGO/Virgo gravitational-wave detectors have observed a total of 47 confident collisions of black holes and neutron stars through the end of September 2019. What’s the big picture behind these events? The second gravitational-wave catalog is officially out — and the population statistics are in!

A New Catalog

In recent years, the Advanced LIGO detectors in Hanford, WA and Livingston, LA and the Advanced Virgo detector in Europe have kept a watchful vigil for ripples in spacetime that let us know that a pair of compact objects — black holes or neutron stars — has spiraled in and merged.

Caltech/MIT Advanced aLigo at Hanford, WA(US), Livingston, LA(US) and VIRGO Gravitational Wave interferometer, near Pisa(IT).

Masses in the Stellar Graveyard GWTC-2 plot v1.0 BY LIGO-Virgo. Credit: Frank Elavsky and Aaron Geller at Northwestern University(US)

During LIGO’s first two observational runs (O1 in 2015–16 and O2 in 2016–17) the two LIGO detectors discovered 11 merger events. After a series of upgrades to the detectors, the system came back online in April 2019 for its third run (O3). In just the first 26 weeks of the run (O3a), LIGO/Virgo jointly found another 36 mergers!

In a new publication recently accepted to Physical Review X, the collaboration has released its second catalog of gravitational-wave events (GWTC–2), which includes data from O1, O2, and O3a. And in a companion publication in The Astrophysical Journal Letters, the team has now analyzed the broader set of all 47 mergers in the catalog, using population models to gain deeper insight into the binary properties and how these systems form and evolve.

Learning About Collisions

So what have we learned from the GWTC–2 population?

Black-hole mass is more complicated than we originally thought.
The merging black holes in O1 and O2 all had primary masses below 45 solar masses, consistent with the theory that black holes of ~50–120 solar masses shouldn’t be able to form. But O3a included several primaries above 45 solar masses, so we can’t model the primary mass distribution as a single power law with a sharp cutoff at 45 solar masses anymore. This may suggest that we’re looking at different populations of black holes that formed in different ways.
Some black holes have spins that are misaligned with the angular momentum of the binary.
Nine of the recent detections exhibit misaligned spins, which is another clue about their formation. Black hole binaries that form and evolve in isolated pairs are expected to have aligned spins, whereas black hole binaries that form dynamically — due, for instance, to interactions in clusters of stars or in the disk of an active galactic nucleus — should have isotropically distributed spins. The authors show that the spinning GWTC–2 population is consistent with 25–93% of black holes forming dynamically. That’s a large range, but what’s important is that this also indicates there’s more than one formation channel at work!
The black hole merger rate probably increases with redshift.
Updated estimates suggest that binary black holes merge at a rate of 15–38 Gpc–3 yr-1 and binary neutron stars at a rate of 80–810 Gpc-3 yr-1. The merger rate appears to be higher at higher redshift, but this increase doesn’t quite parallel the known increase in star formation rate with redshift. An intriguing mystery!

The modeled median merger rate density (solid curve) as a function of redshift suggests that the merger rate increases with redshift. Still, the increase is not as steep as the increase in the star formation rate (dashed line). [Abbott et al. 2021]

A Smashing Good Time Ahead

These takeaways clearly represent a dramatic increase in our understanding of how and where black hole binaries form and evolve — but we still have so much left to learn! Luckily, there’s plenty more data ahead: the collaboration is now analyzing the remaining 5 months of data from O3, and the detectors are currently undergoing upgrades in preparation for O4, which is slated to begin in mid-2022.

Citation

“Population Properties of Compact Objects from the Second LIGO–Virgo Gravitational-Wave Transient Catalog,” R. Abbott et al 2021 ApJL 913 L7.

https://iopscience.iop.org/article/10.3847/2041-8213/abe949

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

From AAS NOVA : “Finding Just the Right Type of Detonation”

From AAS NOVA

26 May 2021
Tarini Konchady

Image of a type Ia supernova in the galaxy NGC 4526. The supernova is the bright white object just below the galaxy’s dark disk. [National Aeronautics Space Agency (US)/European Space Agency [Agence spatiale européenne][Europäische Weltraumorganisation](EU)]

Type Ia supernovae are a cornerstone of extragalactic distance measurements, so it’s important that we understand them very well. Right now, we’re fairly certain that Type Ia supernovae are the result of white dwarfs exploding. But how they explode is still an open question.

To Explode a White Dwarf

A creation mechanism for Type Ia supernovae where a white dwarf accretes mass from a companion (upper panel) till it explodes as a supernova (lower panel). [M. Weiss/NASA/Chandra X-ray Center (US)]

White dwarfs are remnants of relatively low-mass stars like our Sun. They are essentially exposed stellar cores, typically dominated by carbon and oxygen with an outer layer of helium. White dwarfs don’t produce energy of their own. Instead, they just cool off, slowly radiating away residual energy from when they were part of a star.

So how do you make something like a white dwarf explode? Just add mass! If a white dwarf accretes enough matter from a nearby companion, it can approach the Chandrasekhar limit of 1.4 solar masses and explode. This process seems fairly straightforward, but it turns out there are several potential ways to explode a white dwarf.

One scenario involves “double detonation”, where the helium shell of a white dwarf detonates and causes the carbon core to detonate in turn. Another scenario considers white dwarfs in a binary, with one white dwarf accreting material and exploding to knock the other one away.

Interestingly, observations suggest that a combination of these two scenarios — double detonation in white dwarf binaries — may be the likely progenitor of many Type Ia supernovae. One important constraint in this model is that the exploding white dwarf’s mass remains just below the Chandrasekhar limit.

With this in mind, a group of researchers led by Ken Shen (University of California-Berkeley (US)) considered sub-Chandrasekhar-mass explosion scenarios with a tricky but realistic assumption: that local thermodynamic equilibrium (LTE) does not hold.

Model and observed supernova light curves in different bands. The solid lines and the colored circles represent the model, while the unfilled shapes are observed supernovae. The model colors correspond to different white dwarf masses. The white dwarf’s carbon/oxygen ratio was assumed to be 50:50. [Shen et al. 2021]

Explosions Not in Equilibrium

When a system is in LTE, the energies and ionization levels of particles in the system are in some fixed relation with each other while temperature remains consistent across the system. There are astrophysical scenarios where LTE is a safe assumption, like in stars, but LTE certainly doesn’t hold in an event like a supernova.

To model explosions with non-LTE assumptions, Shen and collabors used two different modeling codes. A major difference between the two codes was computation time, and running the same explosion scenarios through both codes allowed Shen and collaborators to determine if the more time-efficient code could stand up to the other. The model outputs included spectra of the ensuing supernovae as well as their light curves across different filters.

Model Matches

A diagram showing the Phillips relation, with peak B-band brightness plotted against the decrease in B-band magnitude 15 days after the peak. Crosses correspond to observations of Type Ia supernovae. The colored shapes correspond to the models, with color representing white dwarf mass, shape representing the carbon/oxygen ratio, and shape outline representing the modeling code used. [Shen et al. 2021]

Shen and collaborators found that the model light curves were excellent matches to observed supernovae out to 15 days after the brightest point in the B-band light curve (“B-band maximum”). This means that the codes also successfully model an observed relation called the Phillips relation — the brighter a supernova’s peak B-band magnitude, the more slowly it will evolve past that peak. This can be seen by plotting peak B-band brightness against B-band brightness 15 days after the peak.

The model spectra are also good matches to observations, sometimes even out to 30 days after the peak. They are especially accurate near the peak, save for spectral features from “intermediate mass elements”, which generally include elements heavier than carbon up to calcium.

All in all, these initial non-LTE models of sub-Chandrasekhar detonations are an excellent match to a broad range of observed Type Ia supernovae near peak brightness! Future models will have to account for more conditions, but non-LTE seems to be the way to go.
Citation

“Non-local Thermodynamic Equilibrium Radiative Transfer Simulations of Sub-Chandrasekhar-mass White Dwarf Detonations,” Ken J. Shen et al 2021 ApJL 909 L18.

https://iopscience.iop.org/article/10.3847/2041-8213/abe69b

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

From AAS NOVA : “What Fast Radio Bursts Tell Us About Galaxy Halos”

From AAS NOVA

21 May 2021
Susanna Kohler

This artist’s impression represents the path of the fast radio burst FRB 181112 traveling from a distant host galaxy to reach the Earth. Along its way, the burst passes through the halo of an intervening galaxy. Credit: M. Kornmesser/ESO [Observatoire européen austral][Europäische Südsternwarte] (EU) (CL).

In recent years, we’ve recorded hundreds of brief, powerful flashes of radio light originating from outside of our galaxy. In new work, scientists are now leveraging these enigmatic fast radio bursts to learn about the hot gas around galaxies.

An Epic Voyage

Artist’s conception of a fast radio burst originating in a distant galaxy. Credit: Danielle Futselaar.

Fast radio bursts (FRBs) are intense bursts of radio emission that last only milliseconds. At their source, the light of these powerful eruptions contain as much energy in a single millisecond as the Sun emits across 3 days. But FRBs primarily arise from distant sources that can lie billions of light-years away — so that light has a long journey ahead of it.

To reach us, this emission first passes through the source’s local environment, then through the interstellar medium (ISM) of its host galaxy, and then through that galaxy’s halo.

Caterpillar Project A Milky-Way-size dark-matter halo and its subhalos circled, an enormous suite of simulations . Griffen et al. 2016.

Once free of the galaxy, the light must traverse the intergalactic medium (IGM) — potentially passing through intervening galactic halos — before it eventually enters the circumgalactic environment around the Milky Way. There, it travels through the halo and ISM of the Milky Way and finally arrives at our detectors here on Earth.

This epic voyage is fraught with obstructions: the burst emission encounters clumps of hot, ionized, and turbulent gas that slows its passage and leaves distinct imprints on the signal we eventually see. In a new study led by Stella Ocker (Cornell University (US)), scientists have used these signatures to probe the ionized gas that lies between us and distant FRBs.

Schematic illustrating how transient radio signals travel to us. Pulsars (marked by sun symbols) lie in the galaxy, interior to the halo; their signals are affected only by the Milky Way’s interstellar matter. Fast radio bursts (marked by lightning symbol) lie in other galaxies; their signals travel through multiple different regions. [Platts et al. 2020]

Constraints from Bursts and Pulses

Ocker and collaborators combine multiple different diagnostics:

dispersion of bursts, which occurs when different frequencies of light travel at different speeds through intervening gas
pulse and angular broadening, or smearing in time and space due to scatter as light travels along multiple different paths through the gas
scintillation, or twinkling of a compact source caused by turbulence in the intervening medium

To disentangle the relative contributions of the ionized gas in the different regions of the FRB’s journey, the authors took advantage of data from multiple FRBs along various lines of sight passing through different sections of our galaxy. They combined this information with further constraints from pulsars — pulsing, magnetized neutron stars — that lie within our galaxy, to better understand the density fluctuations along these varying lines of sight.

Downplaying Halo Contributions

A representation of the scattering contributions estimated by the authors for different regions of ionized gas. The scattering that occurs due to intervening galactic halos (Messier 33 and FG–181112) is consistent with the upper limits found for the Milky Way’s halo, and substantially smaller than the scattering caused within the inner disk of our galaxy (Milky Way Inner Galaxy). [Ocker et al. 2021]

From their work, Ocker and collaborators were able to place an upper limit on the amount of scattering contributed by the Milky Way’s halo to the FRBs that they explored. The authors then compared these results to data from FRB signals that passed through additional, intervening galaxy halos on their way to us. They found that the scattering contributions from other halos are consistent with the upper limits set on the Milky Way’s halo.

Ocker and collaborators’ study suggests that galaxy halos have only a very small impact on the scattering of light in FRBs. While additional FRB and pulsar data will be helpful in constraining more lines of sight, this work provides a valuable step in disentangling different reservoirs of ionized gas to ultimately probe the density fluctuations across our universe.

Citation

“Constraining Galaxy Halos from the Dispersion and Scattering of Fast Radio Bursts and Pulsars,” Stella Koch Ocker et al 2021 ApJ 911 102.

https://iopscience.iop.org/article/10.3847/1538-4357/abeb6e

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

From NSF’s NOIRLab (National Optical-Infrared Astronomy Research Laboratory) (US) via AAS NOVA : “Accretion in Action in an Angled Disk”

NOIRLab

From NSF’s NOIRLab (National Optical-Infrared Astronomy Research Laboratory) (US)

via

AAS NOVA

12 May 2021
Susanna Kohler

Artist’s impression of a young star surrounded by an accreting circumstellar disk. [NASA/JPL-Caltech]

How does material move through an accretion disk to the young star at its center? Surprising detections from a fortuitously angled disk have now provided new insights.

Driving Inflow

When stars are born from the collapse of a dense molecular cloud, they spend their early stages surrounded by circumstellar disks: disks of gas and dust that we understand to be accreting onto the young stars at their centers.

Herschel infrared view of the Taurus Molecular Cloud complex, the home of GV Tau. Credit: R. Hurt [European Space Agency [Agence spatiale européenne][Europäische Weltraumorganisation](EU)/Herschel/National Aeronautics and Space Administration (US)/Jet Propulsion Laboratory-California Institute of Technology(US)]

European Space Agency Herschel spacecraft active from 2009 to 2013.

How do we know that the disk matter is flowing onto the stars? Evidence for accretion comes from the high-energy light emitted when inflowing material strikes the surface of young stars, producing accretion shocks. But, though these observations provide evidence that accretion is occurring, they don’t tell us much about the mechanisms that drive these flows within the disk.

For material to move inwards within a disk, it must first lose angular momentum — but where does that momentum go? What processes remove or redistribute it? In a new study led by Joan Najita (National Science Foundation (US)’s NOIRLab [National Optical-Infrared Astronomy Research Laboratory] (US)), a team of scientists presents high-resolution observations of an unusual disk — one that happens to be angled in such a way as to help us answer these questions.

Lucky Alignment

Schematics representing the likely observing geometry of GV Tau N; the observer is on the right. Top: The line of sight to the disk continuum (orange) passes through the warm molecular atmosphere at larger radii (pink), producing absorption. Bottom: View of the molecular gas velocities. The combination of rotation (blue arrows) and inflow (green arrows) produces net redshifted (red arrows) absorption velocities. [Adapted from Najita et al. 2021]

Najita and collaborators used the TEXES spectrograph on the Gemini North 8-m telescope to conduct mid-infrared observations of GV Tau N, a young star surrounded by a nearly edge-on circumstellar disk. The authors’ observations revealed rare molecular absorption lines, a result of the nearly edge-on inclination of the disk.

National Science Foundation(US) NOIRLab’s Gemini North Frederick C Gillett MaunaKea Hawai’i (US) Altitude 4,213 m (13,822 ft)

The unique viewing angle for GV Tau N means that our sightline passes through the disk atmosphere in the inner few au of the disk — the region where planet formation is thought to occur. The molecules in this gas absorb some of the continuum light emitted by the interior disk, leaving signatures in the spectrum that provide valuable insight into the composition and motions of the gas at the surface of the inner disk.

Caught in the Act

Najita and collaborators found evidence for a variety of molecular species in the disk: acetylene (C2H2), hydrogen cyanide (HCN), water (H20), and even ammonia (NH3), which has never before been detected in an inner accretion disk. But the especially interesting result is that these molecules’ absorption lines are redshifted, lying at longer wavelengths than expected if the gas were moving in a stable circular orbit.

Spectrum showing various ammonia absorption lines from GV Tau N. [Adapted from Najita et al. 2021]

This redshift is an indication that the gas observed is flowing rapidly (about 1 au per year) inward along the disk surface — direct evidence for accretion in action. The authors show that their observations match expected mass accretion rates for active T Tauri stars: roughly a few to a few tens of Earth masses per year. The observations fit neatly with a disk accretion model in which angular momentum is redistributed within the disk, causing surface gas to flow in and accrete while the midplane of the disk spreads outward.

GV Tau N is a lucky break — its orientation allowed us to make these unique measurements. But it’s surely not alone! With more observations of systems like GV Tau N, we’ll be able to further deepen our understanding of disk accretion.
Citation

“High-resolution Mid-infrared Spectroscopy of GV Tau N: Surface Accretion and Detection of NH3 in a Young Protoplanetary Disk,” Joan R. Najita et al 2021 ApJ 908 171.
https://iopscience.iop.org/article/10.3847/1538-4357/abcfc6

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

What is NOIRLab?

NSF’s NOIRLab (National Optical-Infrared Astronomy Research Laboratory) (US), the US center for ground-based optical-infrared astronomy, operates the international Gemini Observatory (US) (a facility of National Science Foundation (US), NRC–Canada, ANID–Chile, MCTIC–Brazil, MINCyT–Argentina, and Korea Astronomy and Space Science Institute [한국천문연구원] (KR)), NOAO Kitt Peak National Observatory(US) (KPNO), Cerro Tololo Inter-American Observatory(CL) (CTIO), the Community Science and Data Center (CSDC), and Vera C. Rubin Observatory (in cooperation with DOE’s SLAC National Accelerator Laboratory (US)). It is managed by the Association of Universities for Research in Astronomy (AURA) (US) 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 Hawaiʻi, 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.

National Science Foundation(US)’s NSF NOIRLab Gemini North Frederick C Gillett MaunaKea Hawai’i (US) Altitude 4,213 m (13,822 ft).

NOIRLab(US) NOAO(US) Gemini South telescope (US) Cerro Tololo Inter-American Observatory(CL) campus near La Serena, Chile, at an altitude of 7200 feet on the summit of Cerro Pachon.

National Science Foundation(US) NOIRLab (US) NOAO (US) Kitt Peak National Observatory (US) on Kitt Peak of the Quinlan Mountains in the Arizona-Sonoran Desert on the Tohono O’odham Nation, 88 kilometers (55 mi) west-southwest of Tucson, Arizona, Altitude 2,096 m (6,877 ft). annotated.

NOIRLab(US)NOAO Cerro Tololo Inter-American Observatory(CL) approximately 80 km to the East of La Serena, Chile, at an altitude of 2200 meters.

The NOAO-Community Science and Data Center(US)

The NSF NOIRLab Vera C. Rubin Observatory. It is managed by the Association of Universities for Research in Astronomy(US) 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 Hawaiʻi, 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.

NSF (US) NOIRLab (US) NOAO (US) Vera C. Rubin Observatory [LSST] Telescope currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing NSF (US) NOIRLab (US) NOAO (US) Gemini South Telescope and NSF (US) NOIRLab (US) NOAO (US) Southern Astrophysical Research Telescope.

From AAS NOVA : “A Relic Black Hole in a Dwarf Galaxy”

From AAS NOVA

19 May 2021
Susanna Kohler

Henize 2-10 is an example of a dwarf galaxy that hosts an active galactic nucleus. A new technique may help us to discover similarly low-mass galaxies hosting the relics of supermassive black hole seeds. [X-ray (NASA/CXC/Virginia/A.Reines et al); Radio (NRAO/AUI/NSF); Optical (NASA/STScI)]

National Aeronautics and Space Administration(US) Chandra X-ray telescope(US).

National Radio Astronomy Observatory(US)Karl G Jansky Very Large Array located in central New Mexico on the Plains of San Agustin, between the towns of Magdalena and Datil, ~50 miles (80 km) west of Socorro. The VLA comprises twenty-eight 25-meter radio telescopes.

National Aeronautics and Space Administration(US)/European Space Agency [Agence spatiale européenne] [Europäische Weltraumorganisation] (EU) Hubble Space Telescope

Using a new technique, scientists have identified a supermassive black hole lurking in a low-mass, low-metallicity galaxy. Could this discovery be just the tip of the iceberg?

Hunting for Seeds

How did the first supermassive black holes — black holes of millions or billions of solar masses — form?

SXS – Simulating eXtreme Spacetimes

ESO/M. Kornmesser now iconic impression of a galaxy forming stars, as powerful jets that are flung from its central black hole collide with the surrounding matter of a galaxy forming stars within powerful outflows of material blasted out from supermassive black holes at its core. Results from ESO’s Very Large Telescope are the first confirmed observations of stars forming in this kind of extreme environment. The discovery has many consequences for understanding galaxy properties and evolution.

Today, we know that giant black holes lie at the heart of most galaxies. Many of them have grown substantially since they first formed, via galaxy mergers and accretion of mass around them. But did they start out as large stars? Or collapse directly from molecular clouds? Or build up rapidly from the merger of smaller black holes?

To identify the seeds of supermassive black holes and address these questions, we need to explore the least-disturbed supermassive black holes that we can find today. Small, low-metallicity galaxies — those that have had a peaceful cosmic history, devoid of the mergers that drive significant black-hole growth — are thus the perfect targets to search for the relics of supermassive black hole seeds.

The catch? These are precisely the environments in which it’s difficult to spot black holes!

A New Approach

The easiest black holes to detect are those that are actively feeding, known as active galactic nuclei (AGNs). But the typical method for identifying an AGN — which relies on specific signatures in the source’s optical spectrum — is biased against low-metallicity and relatively merger-free galaxies, missing the precise population we want to find! Only a handful of AGNs have been identified in dwarf galaxies, and most of these lie in high-metallicity environments. So how do we find our seed relics?

According to a team of scientists led by Jenna Cann (George Mason University (US)), it’s time for a different approach. Instead of relying on optical signatures, Cann and collaborators focus on finding coronal lines — near-infrared emission lines produced by ions that are excited by high-energy radiation. The presence of these lines can reveal a hidden AGN, even when a galaxy shows no sign of an AGN in optical emission.

Discovery of a Relic

In a recent study, Cann and collaborators demonstrate that their unique method works: they detected a coronal line in J1601+3113: a nearby, low-metallicity galaxy that’s only a tenth of the mass of the Large Magellanic Cloud! The authors’ detection is consistent with the presence of a supermassive black hole of roughly 100,000 solar masses, opening a window onto precisely the relic black hole seeds we’re hoping to find.

Cann and collaborators’ discovery marks the first time that an AGN has been identified in a low-mass, low-metallicity galaxy with no optical signs of AGN activity, underscoring how the coronal-line technique can help us find AGNs that might otherwise go undetected.

And with the James Webb Space Telescope scheduled to launch this year, we’ll (hopefully!) soon be collecting infrared spectra with unprecedented sensitivity. With any luck, we’re about to have access to a remarkable new population of lightweight AGNs hiding in small, low-metallicity galaxies — and with it, valuable insight into how these objects were born.

Citation

“Relics of Supermassive Black Hole Seeds: The Discovery of an Accreting Black Hole in an Optically Normal, Low Metallicity Dwarf Galaxy,” Jenna M. Cann et al 2021 ApJL 912 L2.

https://iopscience.iop.org/article/10.3847/2041-8213/abf56d

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.

From AAS NOVA : “Seeing Star Formation at Cosmic Noon”

From AAS NOVA

14 May 2021
Tarini Konchady

The spiral galaxy NGC 1559 is an example of a local star-forming galaxy. [National Aeronautics Space Agency (US)/European Space Agency [Agence spatiale européenne][Europäische Weltraumorganisation](EU)/ Hubble Space Telescope (US)]

National Aeronautics and Space Administration(US)/European Space Agency [Agence spatiale européenne] [Europäische Weltraumorganisation] (EU) Hubble Space Telescope

Star formation in galaxies appears to be highly regulated by the flow of gas into and out of galaxies. We still haven’t pinned down the specifics of these flows, but we can learn a lot about them by studying galaxies during “cosmic noon”, when star formation rates across the universe were at their highest.

The Ins and Outs at Cosmic Noon

Star formation rates versus redshift (lower axis) and lookback time (upper axis). The star formation rates were determined from infrared and ultraviolet observations. The peak around redshifts 2 and 3, or “cosmic noon”, is evident. [Madau & Dickinson, 2014]

“Cosmic noon” corresponds to redshifts of z = 2–3, when the universe was roughly between 2 to 3 billion years old (coincidentally). Over this relatively short period, galaxies formed about half of their current stellar mass. This makes cosmic noon an ideal time to examine mechanisms of star formation.

Stars form from gas, and gas is constantly flowing in and out of galaxies. Specifically, gas flows between the intergalactic and the interstellar mediums, passing through the circumgalactic medium (CGM) as it does. So, the CGM is a record-keeper of what sort of gas has flowed in and out of a given galaxy.

Since stars convert lighter elements into heavier elements, we’d expect that the gas flowing into a galaxy is dominated by light elements while the gas flowing out contains more heavy elements. However, we haven’t observed this effect at low redshifts, likely due to several intervening factors like dust and gas mixing. But could it be more apparent at higher redshifts, like at cosmic noon?

A recent study led by Nikole Nielsen (Swinburne University of Technology (AU)/ARC Centre of Excellence for All Sky Astrophysics in 3 Dimensions (AU)) presents the first results from the “CGM at Cosmic Noon with Keck Cosmic Web Imager” program, which aims to study gas flows from galaxies during cosmic noon.

W.M. Keck Observatory two ten meter telescopes operated by California Institute of Technology(US) and the University of California(US) Maunakea Hawaii USA, altitude 4,207 m (13,802 ft). Credit: Caltech,.

Keck Cosmic Web Imager on Keck 2.

Using data taken by the Keck Cosmic Web Imager (KCWI), the Hubble Space Telescope, and the Very Large Telescope, Nielsen and collaborators studied the properties of one particular galaxy at z ~ 2 in great detail.

European Southern Observatory(EU) , Very Large Telescope at Cerro Paranal in the Atacama Desert •ANTU (UT1; The Sun ) •KUEYEN (UT2; The Moon ) •MELIPAL (UT3; The Southern Cross ), and •YEPUN (UT4; Venus – as evening star). Elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo.

Absorbing as Much Information as Possible

The Hubble Space Telescope’s view of the focus galaxy in this study (G) along with the quasar that lights up its absorber (QSO, or “quasi stellar object”). [Adapted from Nielsen et al. 2020]

The CGM at Cosmic Noon with KCWI program specifically aims to obtain “absorber–galaxy pairs” suitable for studying gas flows. “Absorbers” are bodies of material that are backlit by quasars, extremely bright, active galaxies. As light from a quasar passes through an absorber, the quasar light is altered by the absorber in ways unique to the contents of the absorber. Nielsen and collaborators were especially interested in absorbers that showed signatures of magnesium and carbon, since those elements are easily detectable during cosmic noon and can be used to trace metal-enriched, ionized gas. The relevant absorbers in this study were observed by the Very Large Telescope.

We don’t take it for granted that an absorber is associated with a galaxy, which is where the KCWI and Hubble data come in. The KCWI data can be used to find the characteristic hydrogen emission from a galaxy, while the Hubble images allow for galaxy shape to be determined. The focus galaxy of this study appears edge-on to us, with the quasar shining down its narrower axis.

The left plot is the KCWI view of the quasar (QSO) and focus galaxy (G); the upper right plot is the Hubble image of the focus galaxy. The middle and lower right plots show the hydrogen emission from the galaxy and the absorption signature in the quasar spectrum respectively.[Nielsen et al. 2020]

Likely on Its Way Out

Based on features of our own galaxy and the focus galaxy’s likely orientation, Nielsen and collaborators assumed that the gas flows associated with magnesium are outflows. If this is the case, then the authors estimate that gas is flowing out of the galaxy at a rate of perhaps 50 solar masses per year. The CGM of the focus galaxy does appear to be more enriched with heavy elements than average, but not so enriched that it’s completely dominated by outflows.

Nielsen and collaborators noted that there are many viable interpretations of these data, so no absolute conclusions can be made based on this one galaxy. More detailed models that account for the effects of different elements and galaxy orientations will be useful in the future. However, this study is an excellent demonstration of what can be done by combining data from different instruments. So, on to the next galaxy!

Citation

“The CGM at Cosmic Noon with KCWI: Outflows from a Star-forming Galaxy at z = 2.071,” Nikole M. Nielsen et al 2020 ApJ 904 164.
https://iopscience.iop.org/article/10.3847/1538-4357/abc561

See the full article here .

five-ways-keep-your-child-safe-school-shootings

Please help promote STEM in your local schools.

Stem Education Coalition

AAS Mission and Vision Statement

The mission of the American Astronomical Society is to enhance and share humanity’s scientific understanding of the Universe.

The Society, through its publications, disseminates and archives the results of astronomical research. The Society also communicates and explains our understanding of the universe to the public.
The Society facilitates and strengthens the interactions among members through professional meetings and other means. The Society supports member divisions representing specialized research and astronomical interests.
The Society represents the goals of its community of members to the nation and the world. The Society also works with other scientific and educational societies to promote the advancement of science.
The Society, through its members, trains, mentors and supports the next generation of astronomers. The Society supports and promotes increased participation of historically underrepresented groups in astronomy.
The Society assists its members to develop their skills in the fields of education and public outreach at all levels. The Society promotes broad interest in astronomy, which enhances science literacy and leads many to careers in science and engineering.

Adopted June 7, 2009

The society was founded in 1899 through the efforts of George Ellery Hale. The constitution of the group was written by Hale, George Comstock, Edward Morley, Simon Newcomb and Edward Charles Pickering. These men, plus four others, were the first Executive Council of the society; Newcomb was the first president. The initial membership was 114. The AAS name of the society was not finally decided until 1915, previously it was the “Astronomical and Astrophysical Society of America”. One proposed name that preceded this interim name was “American Astrophysical Society”.

The AAS today has over 7,000 members and six divisions – the Division for Planetary Sciences (1968); the Division on Dynamical Astronomy (1969); the High Energy Astrophysics Division (1969); the Solar Physics Division (1969); the Historical Astronomy Division (1980); and the Laboratory Astrophysics Division (2012). The membership includes physicists, mathematicians, geologists, engineers and others whose research interests lie within the broad spectrum of subjects now comprising contemporary astronomy.

In 2019 three AAS members were selected into the tenth anniversary class of TED Fellows.

The AAS established the AAS Fellows program in 2019 to “confer recognition upon AAS members for achievement and extraordinary service to the field of astronomy and the American Astronomical Society.” The inaugural class was designated by the AAS Board of Trustees and includes an initial group of 232 Legacy Fellows.