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  • richardmitnick 9:06 pm on April 30, 2021 Permalink | Reply
    Tags: "Signs of Extreme Survivor Stars", AAS NOVA, Active galactic nuclei are exactly what they sound like — central regions of galaxies that emit enormous amounts of energy., , , , Typically AGN's consist of a supermassive black hole surrounded by a hot disk of material being accreted onto the black hole.   

    From AAS NOVA : “Signs of Extreme Survivor Stars” 

    AASNOVA

    From AAS NOVA

    30 April 2021
    Tarini Konchady

    1
    Artist’s illustration of an active galactic nucleus shrouded by gas and dust. [NASA/JPL-Caltech (US)]

    Active galactic nuclei are exactly what they sound like — central regions of galaxies that emit enormous amounts of energy. Typically they consist of a supermassive black hole surrounded by a hot disk of material being accreted onto the black hole. Hardly the most hospitable environment, but stars can still live in these surroundings!

    2
    This now iconic composite image reveals Centaurus A, a galaxy with an active nucleus spewing fast-moving jets into its surroundings. [European Southern Observatory (EU)/Wide Field Imager(Optical); MPIfR/ESO/APEX/A.Weiss et al. (Submillimetre); National Aeronautics Space Agency (US)/Chandra X-ray Center (US)/Harvard Smithsonian Center for Astrophysics (US)/R.Kraft et al. (X-ray)]

    Actively Hostile Environments

    It would be hard to overstate how energetic active galactic nuclei (AGN) are.

    Some can outshine the rest of their host galaxy at almost all detectable wavelengths! Spectra of material near the central black hole have shown that AGN environments contain a higher abundance of heavier elements than the environment of our Sun. So it’s possible that those heavier elements were produced in the accretion disk and then swept closer in towards the black hole.

    But what produces heavier elements? Stars! Stars can be found near the central supermassive black holes of galaxies, like the Milky Way’s Sagittarius A*, but AGN have far more extreme environments than our placid central black hole.

    So what sort of stars live in AGN environments? A recent study led by Matteo Cantiello (Flatiron Institute/ Princeton University (US) dives into this question.

    3
    The mass and brightness of an AGN star over time. This star was modeled under specific AGN conditions. LEdd stands for Eddington luminosity, which is the maximum brightness a star can have when it has balanced its outward radiative pressure with its inward gravitational contraction. Mass loss starts roughly around when the star’s luminosity reaches the Eddington luminosity. [Cantiello et al. 2021]

    What Massive Stars Make

    Cantiello and collaborators were especially interested in how the evolution of stars in AGN environments differs from stellar evolution in calmer environments. To get where they are, AGN stars have to either form in accretion disks or get captured and pulled into the disks. Both models are viable and supported by looking at stellar populations around central black holes that were previously active, like Sagittarius A*.

    Once in the disk, stars can rapidly accrete material and become hundreds of times more massive than the Sun. Massive stars experience more internal mixing than less massive stars, so the contents of a massive star are evenly distributed within the star’s interior. This is very different from stars like our Sun, where the outer layers of the star contain lighter elements like hydrogen and helium while inner layers are dominated by heavier elements.

    However, massive stars are also unstable and can lose mass quickly as they teeter between expansion and collapse. Their sheer bulk also means that they will end their lives through core collapse — forming heavier and heavier elements through fusion until they run out of material to fuse and collapse onto themselves. The bottom line is that AGN stars are good at producing heavy elements and sending those elements out into the accretion disk.

    4
    A schematic showing stellar evolution in the accretion disk of an AGN. Low mass stars can be formed in or accreted by the disk, where they gain mass and eventually evolve to leave behind compact remnants near the center of the disk. [Cantiello et al. 2021]

    Signs of Stellar Life and Death

    So Cantiello and collaborators identified two signatures of AGN stars: high abundances of heavy elements and compact stellar remnants left behind from core collapse. There are studies showing evidence for the first signature, and interestingly, this abundance of heavy elements doesn’t seem to depend on redshift.

    The second signature is a bit trickier to tease out. Before gravitational-wave observatories, our best bet would be to search for the explosions associated with core collapse in the accretion disk of an AGN. Now, we can also look for the gravitational-wave signatures of the mergers of dense objects, with an expectation of how often these mergers would occur.

    Sagittarius A* is a good proving ground for the findings of this study, since our galaxy’s nucleus may approximate the aftermath of an AGN. With predictions in hand, it’s now time to observe!

    Citation

    “Stellar Evolution in AGN Disks,” Matteo Cantiello et al 2021 ApJ 910 94.
    https://iopscience.iop.org/article/10.3847/1538-4357/abdf4f

    See the full article here .


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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    1

    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.

     
  • richardmitnick 3:15 pm on April 12, 2021 Permalink | Reply
    Tags: AAS NOVA, , , , , Flares from the Milky Way’s Supermassive Black Hole,   

    From AAS NOVA via From Sky & Telescope : “Flares from the Milky Way’s Supermassive Black Hole” 

    AASNOVA

    From AAS NOVA

    via

    Sky & Telescope

    April 12, 2021

    The supermassive black hole at the center of the Milky Way released an unusual number of strong flares in 2019. Now, astronomers are trying to figure out why.

    1
    Artist’s impression of the disruption of a gas cloud as it passes close to Sgr A*, the supermassive black hole at the center of our galaxy.
    European Southern Observatory(EU) / MPG Institute for extraterrestrial Physics [MPG Institut für extraterrestrische Physik] ( DE)/ Marc Schartmann

    In 2019, the supermassive black hole at the center of our galaxy woke up and emitted a series of burps. A new study now examines what meal may have led to this indigestion.

    Waking Up for a Snack

    3
    Artist’s impression of the dramatic outflows from an active galaxy’s nucleus. The Milky Way’s supermassive black hole, in contrast, is very quiet.

    Lynette Cook

    Sgr A*, the 4.6-million-solar-mass black hole that lies at the center of the Milky Way, is normally a fairly quiet beast. The black hole slowly feeds on accreting material in the galactic center — but this food source is sparse, and Sgr A*’s accretion doesn’t produce anything like the fireworks we associate with supermassive black holes in active galaxies.

    In May 2019, however, Sgr A* suddenly became substantially more active than usual, producing an unprecedented bright, near-infrared flare that lasted roughly 2.5 hours. This flare was more than 100 times brighter than the typical emission from Sgr A*’s casual accretion, and more than twice as bright as the brightest flare we’ve ever measured from our neighborhood monster.

    The May 2019 flare marked the start of prolonged increased activity — an unusual number of strong flares that continued at least throughout 2019 (currently analyzed data extends only to the end of that year). What caused Sgr A* to wake up? And do we expect more flaring ahead? A new study by Lena Murchikova (Institute for Advanced Study (US)) explores the options.

    Star S0-2 Andrea Ghez Keck/UCLA Galactic Center Group (US) at SGR A*, the supermassive black hole at the center of the Milky Way.

    Sgr A*’s flares likely came from an abrupt increase in the amount of material available to accrete onto this black hole. Murchikova identifies two likely sources of this excess material.

    Shedding S stars
    The dense nucleus of our galaxy hosts a population of stars on tight orbits around Sgr A*. These stars shed mass via stellar winds, and when the stars swing close around Sgr A* at the pericenter of their orbit, this shed mass could accrete onto Sgr A*.
    Disintegrating G objects
    Also known to orbit close to Sgr A* are so-called G objects. These extended sources may be gas clouds, stars, or a combination of the two — we’re not sure yet! Tenuous G objects lose mass as a result of friction as they orbit, exhibiting higher rates of mass loss as they get closer to Sgr A* and are stretched out into shapes with large surfaces areas passing through dense background material. The mass they lose through this disintegration at pericenter could then accrete onto Sgr A*.

    3
    The objects G2 (colored red) and G1 (colored blue) and the star S2 are visible in these high-resolution images of the galactic center, taken in 2006 (left) and in 2008 (right). The position of Sgr A* is marked with an X.
    SOFIA / Lynette Cook [above]

    Through a series of calculations, Murchikova estimates how much material is shed by these two types of objects and how long it would take that material to accrete onto Sgr A*. Based on the available observations, the author finds that the most likely explanation for our black hole’s unexpected rumblings in 2019 is currently accreting material from the combined past pericenter passages of the objects G1 and G2.

    If this interpretation is correct, we would expect to see flaring continue for a limited time, but Sgr A* should then return to its quiescent state. If the flaring was instead a part of normal variability in the flow of accreting material onto Sgr A*, we would expect the activity to continue for years to come. Continued observations of this rumbling giant will tell!

    Citation

    “S0-2 Star, G1- and G2-objects, and Flaring Activity of the Milky Way’s Galactic Center Black Hole in 2019,” Lena Murchikova 2021 ApJL 910 L1. https://iopscience.iop.org/article/10.3847/2041-8213/abeb70

    See the full article here .

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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    Sky & Telescope, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

    Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

    Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

    “Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”

    From AAS NOVA

    1

    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.

     
  • richardmitnick 6:08 pm on April 10, 2021 Permalink | Reply
    Tags: "Multimessenger Cosmology of the Future", AAS NOVA, , , ,   

    From AAS NOVA : “Multimessenger Cosmology of the Future” 

    AASNOVA

    From AAS NOVA
    1
    Artist’s impression of the collision of two neutron stars, which produces both a gravitational wave signal and an electromagnetic signal in the form of a short gamma-ray burst and a kilonova. [European Southern Observatory (EU)/L. Calçada/M. Kornmesser]

    Collisions of neutron stars and black holes provide insights beyond stellar evolution: these mergers may also be the key to unlock precise measurements of the cosmological parameters that describe our universe. A recent study explores what we can hope to learn with multimessenger cosmology in the next few decades.

    Pinning Down Parameters

    21
    Measurements of the Hubble constant via different methods show a discrepancy in measured value that has only grown over time. [Freedman et al. 2019]

    Obtaining precise measurements for cosmological parameters is critical as we attempt to understand the origins, the evolution, and even the composition of our universe. Estimates of figures like the Hubble parameter (H0), the matter density parameter (Ωm), and the dark energy equation of state parameter (w) abound.

    Unfortunately, different measurement techniques produce a wide spread in values for these parameters. Scientists have long waited for a new, independent approach that will provide a resolution to the tension between past measurements. Now, in the age of gravitational astronomy, we have one: the standard siren technique.

    3
    Diagram illustrating the stages of a neutron-star collision. In the model, 1) two neutron stars inspiral, 2) they merge and produce a gamma-ray burst lasting a tenth of a second, 3) a small fraction of their mass is flung out and radiates on timescales of weeks as a kilonova, 4) a massive neutron star or black hole with a disk remains after the event. [National Aeronautics Space Agency(US), European Space Agency [Agence spatiale européenne][Europäische Weltraumorganisation](EU), and A. Feild (NASA Space Telescope Science Institute(US))]

    Insights from Sirens

    We have previously discussed the use of dark sirens — black hole–black hole mergers — as a tool to measure cosmological parameters. Standard sirens — the mergers of neutron stars with either black holes or other neutron stars — are a similarly useful tool, but they rely on multimessenger observations rather than only gravitational waves.

    The idea is straightforward: by simultaneously observing the gravitational-wave and electromagnetic signals from these explosive mergers, we can obtain both an absolute distance scale and a redshift measurement for the source. This combination allows us to obtain an independent measurement of cosmological parameters — and the more of these joint detections we make, the more precise our measurements will be.

    But implementing this approach efficiently requires some planning. What’s the best observing strategy to ensure we can pin these parameters down with the gravitational-wave and electromagnetic observatories planned for the next few decades? A new study led by Hsin-Yu Chen (Harvard University (US) and Massachusetts Institute of Technology(US)) explores this question.

    The Promise of Future Detectors

    Chen and collaborators evaluate the impact of a number of expected future observatories. These include:

    Three eras of gravitational-wave detectors with increasing sensitivity (A+, Voyager, and Cosmic Explorer)

    Wide-field survey telescopes like the Vera Rubin Observatory that can detect kilonovae, the optical and infrared counterparts of mergers involving neutron stars.

    NOIRLab(US) Vera C. Rubin Observatory 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 NOIRLab Gemini South Telescope (US) and NSF NOIRLab NOAO Southern Astrophysical Research Telescope , altitude 2,715 m (8,907 ft).

    High-energy observatories like Swift and its successors to detect short gamma-ray bursts, a highly directional but bright counterpart to mergers.

    4
    Uncertainty in the measurement of H0 for a variety of different observing strategies. Orange bars indicate the fraction of total observing time available to VRO for each kilonova scenario. [Adapted from Chen et al. 2021]

    Based on the capabilities and limitations of these observatories, Chen and collaborators estimate how many mergers we’ll be able to detect via joint gravitational-wave and electromagnetic observations each year with different observing campaigns and demonstrate what constraints these detections will place on cosmological parameters.

    Using these calculations, the authors outline an observing strategy for the next three decades. They demonstrate that with clever use of resources, we could soon reach sub-percent-level precision on H0 and tight constraints on the amount and form of dark energy in the universe. This work shows the great potential ahead using standard sirens for precision cosmology.
    Citation

    “A Program for Multimessenger Standard Siren Cosmology in the Era of LIGO A+, Rubin Observatory, and Beyond,” Hsin-Yu Chen et al 2021 ApJL 908 L4 6.

    https://iopscience.iop.org/article/10.3847/2041-8213/abdab0

    See the full article here .


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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    1

    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.

     
  • richardmitnick 4:04 pm on April 2, 2021 Permalink | Reply
    Tags: "Seeking the Origins of Galactic Stellar Streams", AAS NOVA, , , ,   

    From AAS NOVA : “Seeking the Origins of Galactic Stellar Streams” 

    AASNOVA

    From AAS NOVA

    31 March 2021
    Susanna Kohler

    1
    Like NGC 5907, the edge-on galaxy shown here, our own Milky Way hosts faint streams of stars that loop around it. But where did those streams originate? Credit:R. Jay GaBany]

    The Milky Way is enwreathed in long streams of stars that hold clues to everything from our galaxy’s history to the nature of dark matter. New research has now identified the likely origins of some of these subtle ribbons.

    Streams Across the Sky

    2
    The orbital energy vs. angular momentum of the stars in 23 of the Milky Way’s stellar streams (colored and labeled data), as compared to field stars (black data). Credit:Bonaca et al. 2021.

    Stellar streams are associations of stars that are grouped into elongated filaments arcing around a host galaxy. These filaments are thought to be produced when a stream progenitor — like a globular cluster or a satellite dwarf galaxy — is disrupted by its host galaxy’s tidal forces. Stars are drawn out from the progenitor into a tidal stream that then orbits the host galaxy; the progenitor itself may remain connected to the stream, orbit separately, or disrupt entirely.

    We’ve observed stellar streams in other galaxies (like NGC 5907, shown above), but we needn’t look that far away — our own Milky Way is host to more than 60 catalogued streams. Of these thin trails, only a handful have been connected to a known progenitor, like a surviving globular cluster. The rest have unknown origins, leaving a number of open questions that only now, with current observations, have answers within reach.

    In a recent study led by Ana Bonaca (Center for Astrophysics | Harvard & Smithsonian), a team of scientists has leveraged the incredible precision of the Gaia space observatory to hunt for the origins of 23 cold stellar streams in the Milky Way halo.

    3
    Locations in orbital phase space of the 23 stellar streams, labeled by whether they have a dwarf galaxy progenitor (pentagon) or globular cluster progenitor (star). Only one stream, Svöl, falls into the region associated with possible in situ formation (rather than having been brought in via a dwarf galaxy). Credit: Bonaca et al. 2021.

    A Disrupted Home

    Bonaca and collaborators make use of improved proper motions provided in Gaia’s Early Data Release 3 for stars in these 23 streams. By analyzing the energies and 3D angular momenta of these streams, and by examining how the streams are distributed in physical space, the authors are able to identify the probable progenitors for most of the streams.

    According to the authors’ results, only 1 of the streams plausibly originated from a globular cluster that was born in the Milky Way. The vast majority instead originated from dwarf galaxies that the Milky Way has accreted. Some of the streams were produced from the dwarf galaxies themselves; others were likely formed from disrupted globular clusters that orbited those dwarf galaxies.

    Several of the 23 streams have similar properties, suggesting that many originated from the same progenitors. The authors identify original host dwarf galaxy candidates for 20 of the streams, and they point to 6 specific globular clusters as the origin of 8 of the streams.

    Illuminating Dark Matter

    4
    Sky map showing the 6 globular clusters (crosses) that the authors associate with 8 stellar streams (circles). Credit: Bonaca et al. 2021.

    What can we do with this information? Understanding the origin of these stellar streams allows us to better trace their paths, how long they’ve been orbiting, and what other gravitational interactions they may have had over time. These details are valuable not just for understanding galaxy evolution, but also for mapping out the big-picture distribution of dark matter in our galaxy and studying the small-scale structure of dark matter in the streams’ host galaxies.

    Further expansion of Bonaca and collaborators’ work to the other stellar streams orbiting the Milky Way will rely on continued high-quality proper motion measurements of these faint and distant sources. Look for more results as future Gaia data is released!

    Citation

    “Orbital Clustering Identifies the Origins of Galactic Stellar Streams,” Ana Bonaca et al 2021 ApJL 909 L26.

    https://iopscience.iop.org/article/10.3847/2041-8213/abeaa9

    See the full article here .


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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    1

    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.

     
  • richardmitnick 10:25 pm on March 19, 2021 Permalink | Reply
    Tags: "Searching the Surroundings of a Fast Radio Burst", AAS NOVA, , , , , , FRB 20180916B   

    From AAS NOVA: “Searching the Surroundings of a Fast Radio Burst” 

    AASNOVA

    From AAS NOVA

    19 March 2021
    Tarini Konchady

    1
    Artist’s conception of the localization of a fast radio burst to its host galaxy. Credit: Danielle Futselaar.

    Fast radio bursts are mysterious astronomical phenomena — for now. To understand how they form, we need to take a closer look at where they live. A new study does just that, with the help of some very sensitive astronomical instruments.

    The Fascination of Fast Radio Bursts

    Fast radio bursts (FRBs) are exactly what they say they are: short, bright radio signals that last milliseconds at most. Their energy levels make them especially intriguing, since there aren’t many processes that can produce such large amounts of energy so quickly. Another constraint is that FRBs have been detected in all kinds of galaxies, meaning that whatever produces FRBs can’t be overly unique.

    Radio telescopes today have the capability to precisely isolate FRBs in their host galaxies, meaning that we can probe the environments that produce FRB sources. The closest known FRB we’ve confidently isolated is called FRB 20180916B (though see this post for a new discovery that may be closer!), which is nearly 500 million light-years away. High-resolution observations have shown that FRB 20180916B is located in a distinct star-forming region, but what can we see if we look even closer?

    In a recent study, a group of researchers led by Shriharsh P. Tendulkar (Tata Institute of Fundamental Research(IN)) studied the surroundings of FRB 20180916B in the highest detail yet, getting down to a scale of hundreds of light-years.

    Searching Through Gas and Stars

    For their study, Tendulkar and collaborators used the Wide Field Camera 3 (WFC3) on the Hubble Space Telescope and the MEGARA spectrograph on the Gran Telescopio Canarias. Taken together, the observations span mainly optical wavelengths, which are sensitive to gas and stars.

    Gran Telescopio Canarias at the Roque de los Muchachos Observatory [Instituto de Astrofísica de Canarias ](ES) on the island of La Palma sited on a volcanic peak 2,267 metres (7,438 ft) above sea level.

    3
    The velocity of gas in the host galaxy of FRB 20180916B, with the location of the FRB shown by a red cross. The contours come from Hubble images of the galaxy and depend on the flux detected in the image. [Adapted from Tendulkar et al. 2021]

    The gas serves two important functions: it can be used to determine how much star formation is happening in a region, and it can also be used to measure motion. Tendulkar and collaborators used the latter property to determine that FRB 20180916B’s home region is likely rotating with the large galaxy in its vicinity. This rules out the possibility that the FRB source is actually hosted in a smaller, less distinct satellite galaxy.

    4
    The star-forming region closest to FRB 20180916B as seen by Hubble, with its V-shape highlighted. The FRB’s location is shown by the green ellipse with a green arrow pointing towards it. [Adapted from Tendulkar et al. 2021]

    Running Away from Home

    Tendulkar and collaborators also found that the star formation happening around FRB 20180916B is at an interesting stage: it’s not extremely active, but it hasn’t gone placid either, suggesting that the region is still rather young.

    FRB 20180916B is also a significant distance from the nearest group of stars. So, if the FRB source was born in that group, it had to have traveled between 800,000 to 7 million years to get to where it is now. This puts constraints on what the source of FRB 20180916B is, since not many astronomical objects can remain as energetic as FRB sources as they age.

    So what’s behind FRB 20180916B? After considering possible scenarios, Tendulkar and collaborators zero in on X-ray or gamma-ray binaries, which consist of a neutron star and a massive companion star. However, to be certain that these sorts of objects are FRB sources, we’d need large samples of well-studied binaries — which is certainly doable with the radio telescopes we have now!

    Citation

    “The 60 pc Environment of FRB 20180916B,” Shriharsh P. Tendulkar et al 2021 ApJL 908 L12.
    https://iopscience.iop.org/article/10.3847/2041-8213/abdb38

    See the full article here .


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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    1

    The American Astronomical Society(US) is an American society of professional astronomers and other interested individuals, headquartered in Washington, DC. The primary objective of the AAS is to promote the advancement of astronomy and closely related branches of science, while the secondary purpose includes enhancing astronomy education and providing a political voice for its members through lobbying and grassroots activities. Its current mission is to enhance and share humanity’s scientific understanding of the universe.

    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.

     
  • richardmitnick 2:23 pm on March 13, 2021 Permalink | Reply
    Tags: "Gravitational Waves Shed Light on How Heavy a Neutron Star Can Be", AAS NOVA, , , , , From AAS NOVA   

    From AAS NOVA: “Gravitational Waves Shed Light on How Heavy a Neutron Star Can Be” 

    AASNOVA

    From AAS NOVA

    10 March 2021
    Susanna Kohler

    1
    This still comes from a simulation of two neutron stars merging. Observations of collisions like these may help us determine the maximum mass a neutron star can attain. [National Aeronautics and Space Administration(US)/</a>MPG Institute for Gravitational Physics [Max-Planck-Institut für Gravitationsphysik] (Albert Einstein Institute)(DE)/ZIB/M. Koppitz and L. Rezzolla]

    What’s the largest mass that a neutron star — the dense, collapsed core of a massive star — can grow to before further collapsing into a black hole? Recent gravitational-wave events are providing new insight.

    Finding the Maximum

    2
    Artist’s impression of a strongly magnetized neutron star. [NASA/Penn State University(US)/Casey Reed.]

    Neutron stars consist almost entirely of neutrons packed together at the density of atomic nuclei. This extreme mass in such a small space results in an extraordinary inward gravitational pull that increases as more neutrons are packed in. When the crushing gravitational force exceeds the combined quantum and nuclear forces pushing outward, the star collapses to form a black hole.

    What is the maximum mass limit above which a neutron star collapses? Theory suggests that, for a non-rotating neutron star, it’s somewhere around 2 or 3 times the mass of the Sun — but the precise value relies on the unknown state of matter inside the neutron star. To get around this missing information, we need observational constraints to help us pin down how heavy a neutron star can be.

    Collisional Clues

    In recent years, gravitational waves have provided valuable new insight. Two particular mergers of compact objects have tempted us with clues:

    GW170817
    In this event, two neutron stars in the range of 1.1–1.6 solar masses merged to form a larger object, which we think collapsed into a black hole shortly after merger. The gravitational-wave and electromagnetic observations of this process point to a maximum neutron star mass that’s less than 2.3 solar masses.
    GW190814
    In this event, a black hole of more than 20 solar masses merged with an object of just 2.5–2.7 solar masses — but we don’t know whether that smaller object was a black hole or a neutron star. If it was a non-rotating neutron star, then this would imply that the upper limit for neutron star mass is above 2.5 solar masses.

    Can we reconcile these two potentially conflicting pieces of information? A study led by Antonios Nathanail (Institute for Theoretical Physics(DE) presents new analysis that further explores what these mergers tell us about neutron star limits.

    A Lower Upper Limit

    Nathanail and collaborators analyzed these two mergers by employing a genetic algorithm — an algorithm that explores a large parameter space and looks for optimized solutions by mimicking the process of natural selection. Using this algorithm, the authors identified which maximum mass solutions are consistent with gravitational-wave and electromagnetic observations of GW170817 and GW190814 and numerical simulations of mergers.

    3
    Probability distribution function for the maximum mass of a non-rotating neutron star, as estimated by the authors’ genetic algorithm (blue curve) and in a previous study of GW170817 (purple curve). [Nathanail et al. 2021]

    From their systematic investigation, the authors show that a large maximum neutron star mass — like the 2.5 solar masses required if GW190814’s secondary was a non-rotating neutron star — doesn’t mesh with our observations of GW170817 or with expectations from numerical simulations of gravitational wave production.

    Instead, the authors find that a maximum neutron star mass of about 2.2 solar masses neatly reproduces the observations of GW170817 and is consistent with numerical simulations. This upper limit implies that GW190814’s secondary was too large to have been a non-rotating neutron star. Instead, GW190814 was likely the merger of two unequal-mass black holes.

    Citation

    “GW170817 and GW190814: Tension on the Maximum Mass,” Antonios Nathanail et al 2021 ApJL 908 L28.
    https://iopscience.iop.org/article/10.3847/2041-8213/abdfc6

    See the full article here .


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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    1

    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

     
  • richardmitnick 4:40 pm on February 21, 2021 Permalink | Reply
    Tags: "A Long Wavelength Look at Distant Quasar Hosts", AAS NOVA, , , ,   

    From AAS NOVA: “A Long Wavelength Look at Distant Quasar Hosts” 

    AASNOVA

    From AAS NOVA

    19 February 2021
    Tarini Konchady

    1
    An artist’s impression of a quasar. [NASA, ESA and J. Olmsted (STScI)]

    NASA/ESA Hubble Telescope.

    Some quasar host galaxies live in the early universe. This makes them especially interesting, since they had to have accumulated a lot of mass very quickly. Luckily for us, radio telescopes like ALMA can peer back in time and tell us more about these galaxies and their environments.

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres.

    Finding Far-Off Quasars

    Quasars are absurdly energetic objects. They are a version of the supermassive black holes at the centers of galaxies, and what makes them unique is the large amounts of energy they emit while actively accreting material. A significant portion of this energy is emitted as short-wavelength ultraviolet (UV) light, which is the key to studying quasars that live in the early universe.

    The farther away an object is, the more its light becomes redshifted as it travels to us — that is, the wavelength at which light from the object was first emitted is shorter than the wavelength we observe when that light reaches us. So in the case of far-off quasars, their UV emission will be redshifted into radio wavelengths, where we can still observe it!

    2
    FIR (left) and [C II] (right) emission maps (distances shown in arcseconds) for two galaxies from this study. The redder regions indicate higher emission levels; bluer regions point to the absence of emission. [Adapted from Venemans et al. 2020]

    In a recent study, a group of researchers led by Bram P. Venemans (Max-Planck Institute for Astronomy, Germany) used radio observations of distant quasar host galaxies to learn more about them, as well as conditions in the early universe.

    Evidence from Emissions

    All 27 galaxies in this study live at a redshift of roughly z = 6, or when the universe was just under a billion years old. Venemans and collaborators were especially interested in two types of emission from these galaxies: singly ionized carbon ([C II]) emission, which tracks the gas of the interstellar medium; and the general continuum brightness in the far-infrared (FIR), which is associated with dust. The spatial extent of the [C II] emission in particular is also sensitive to the motions of a galaxy and its surroundings.

    The galaxies were observed by Atacama Large Millimeter/submillimeter Array (ALMA) in September 2019. The observations had a resolution of roughly a kiloparsec (or 19 trillion miles), which is pretty high definition for the early universe! This allowed Venemans and collaborators to examine the central regions of their galaxies. They were also able to probe the surrounding space for any companion galaxies.

    Seeing Into the Center

    3
    Star formation rates versus distance from galaxy center. Each track represents a quasar host galaxy, with the color of the track corresponding to the FIR brightness of the galaxy. [Venemans et al. 2020]

    It turned out that for the galaxies in this study, the central dust regions mapped closely onto the positions of central supermassive black holes. This may not sound like a profound observation, but it is observational evidence to support that these central black holes live at the hearts of dark matter halos, which are cosmological building blocks.

    The [C II] emission revealed that about half of the quasar-hosting galaxies in this sample had companions. The FIR emission also allowed Venemans and collaborators to determine that in the central regions of their galaxies, star formation peaks at the center and then declines moving outward. The outer regions of these distant galaxies currently remain elusive, but as Venemans and collaborators noted, ALMA is quite capable of probing these galaxies further!

    Citation:

    “Kiloparsec-scale ALMA Imaging of [C II] and Dust Continuum Emission of 27 Quasar Host Galaxies at z ~ 6,” Bram P. Venemans et al 2020 ApJ 904 130.

    https://iopscience.iop.org/article/10.3847/1538-4357/abc563

    See the full article here .


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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    1

    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

     
  • richardmitnick 4:22 pm on February 21, 2021 Permalink | Reply
    Tags: "A Map of a Stellar Explosion", AAS NOVA, , , ,   

    From AAS NOVA: “A Map of a Stellar Explosion” 

    AASNOVA

    From AAS NOVA

    17 February 2021
    Susanna Kohler

    1
    This composite, false-color image reveals an explosive outflow of molecular gas within the Orion Nebula. A new study explores another such explosion and examines how it relates to the birth of massive stars. [ALMA/ESO/NAOJ/NRAO/J. Bally/H. Drass et al.]

    ESO/NRAO/NAOJ ALMA Array in Chile in the Atacama at Chajnantor plateau, at 5,000 metres.

    There’s still much we don’t know about the birth of massive stars — stars with more than 8 times the mass of the Sun. A recent study reveals details of a thousand-year-old explosion that might provide clues about the formation of these giants.

    An Unexpected Explosion

    2
    The clouds of molecular gas in regions like the Orion nebula provide nurseries in which massive stars form and evolve. Credit: ESO/G. Beccari.

    Several decades ago, astronomers discovered something odd. In a region inside the Orion nebula where massive star formation is underway, scientists detected signs of an explosive outflow: dense molecular gas streaming outward from a central point at rapid speeds. Surprisingly, there was nothing at the center of this explosion.

    This one-off discovery was intriguing. One could imagine a number of sudden, energy-liberating events that could occur in a massive star-forming environment — like the formation of a close massive stellar binary, or the merger of two young, massive protostars. And the discovery of several candidate runaway stars at the fringes of the explosion provided another hint to a dynamical origin.

    Could this explosion help us understand the process of how massive stars form in their birth environments? Or was it just a fluke event? As years passed without astronomers finding evidence of another, similar outflow, these questions remained unanswered.

    3
    This ALMA SiO map of the star-forming region G5.89 shows outflowing molecular gas surrounding an expanding, shell-like HII region (white contours). Two stars moving away from the origin are marked in magenta and cyan. Credit: Adapted from Zapata et al. 2020.

    Two of a Kind

    Forty years later, we now have proof of another such explosive outflow in a massive star-forming environment. In a recent publication led by Luis Zapata (UNAM Radio Astronomy and Astrophysics Institute(MX)), a team of scientists has used the Atacama Large Millimeter/submillimeter Array (ALMA) to confirm the presence of streamers of molecular gas flowing isotropically outward from a central point in the massive stellar birthplace G5.89, which lies roughly 10,000 light-years away from us.

    Zapata and collaborators measured 34 molecular filaments in this explosive outflow, finding that the streamers are accelerating as they expand outward. This is consistent with behavior of the Orion explosion and shows that the density of the ejecta is substantially larger than the surrounding medium.

    As with the Orion explosive outflow, the point of origin of the filaments contains no source. Previous studies, however, have identified several young, massive stars in the periphery of the G5.89 explosion that are speeding away from the point of origin at roughly the right speed to have been at the center 1,000 years previously at the time of explosion.

    Learning about Stellar Birth

    What does all this tell us about the origins of massive stars? Explosive outflows like this — caused by dynamical interactions during the birth of massive stars — may be more common than we previously thought!

    The authors estimate a rate for such outflows based on our limited observations, finding that there should be one every ~100 years. The fact that this is very close to the rate of supernovae further solidifies the connection of explosive molecular outflows to massive star formation.

    Dedicated, high-sensitivity searches for more such outflows in nearby massive star-forming regions will certainly go a long way toward confirming this theory. In the meantime, the authors argue, we should consider revising high-mass star formation models to include dynamical interactions, as these stellar explosions may prove to be regular occurrences!

    Citation

    “Confirming the Explosive Outflow in G5.89 with ALMA,” Luis A. Zapata et al 2020 ApJL 902 L47.
    https://iopscience.iop.org/article/10.3847/2041-8213/abbd3f

    See the full article here .


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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    1

    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

     
  • richardmitnick 10:32 pm on February 5, 2021 Permalink | Reply
    Tags: "The Signature of a Pre-Merger System", AAS NOVA, , , , , , ,   

    From AAS NOVA: “The Signature of a Pre-Merger System” 

    AASNOVA

    From AAS NOVA

    5 February 2021
    Tarini Konchady

    1
    Numerical simulation of two black holes that inspiral and merge, emitting gravitational waves. [N. Fischer, H. Pfeiffer, A. Buonanno (Max Planck Institute for Gravitational Physics [Max-Planck-Institut für Gravitationsphysik] (Albert Einstein Institute) (DE)), Simulating eXtreme Spacetimes (SXS) Collaboration]

    Since beginning operation, gravitational-wave observatories have observed several mergers involving neutron stars and black holes. Both black holes and neutron stars are the result of supernovae, so is it possible for us to identify a pair of these objects pre-merger?

    Some Go Supernova First

    2
    An artist’s impression of a black hole–neutron star binary. [Carl Knox, OzGrav – Home ARC CENTRE OF EXCELLENCE FOR GRAVITATIONAL WAVE DISCOVERY At Swinburne University Of Technology]

    The first black hole–black hole (BH–BH) merger was detected by the Laser Interferometer Gravitational-wave Observatory (LIGO) in 2015. Since then, LIGO and the Virgo interferometer have observed several BH–BH and neutron star–neutron star (NS–NS) mergers.

    Interestingly, the two observatories have also found candidates for BH–NS mergers. So how are the progenitors of these mergers formed?

    One possibility is that black holes and neutron stars encounter each other in densely populated areas of space and just happen to pair off. Another possibility is that these pairs of dense objects start off as massive stars in a binary and evolve until they reach their pre-merger form.

    Both scenarios involve supernovae, as the stars evolve to become neutron stars or black holes. But there’s an interesting consideration for the latter scenario, if one star becomes a black hole before the other finishes evolving: How would the black hole interact with the supernova caused by its companion?

    In a recent study, a group of researchers led by He Gao (Beijing Normal University [北京師範大學; pinyin: Běijīng Shīfàn Dàxué] (CN)) tackle that question.

    3
    The light curves from two instances of a black hole interacting with material ejected from its companion’s supernova. In the upper panel, the energy from the interaction is larger than the energy associated solely with the supernova. In the lower panel, the energy from the interaction is comparable to the energy associated with the supernova. LBP is the brightness from black hole outflows, Ldisk is from the black hole’s accretion disk, and LNi comes from the radioactive decay of nickel associated with the supernova. Lmag is the total brightness from the system. [Gao et al. 2020]

    Just Add Ejected Mass

    Gao and collaborators first estimated how much mass and energy would be released by a massive star going supernova. They also put constraints on the velocity of the ejected mass, since it would play an important role in determining any interaction with the black hole.

    If any material fell into the black hole’s sphere of influence, it would result in energy being released in multiple ways, like through jets and outflows. Gao and collaborators determined that these releases of energy could happen on timescales similar to the supernova. So what do you get when you look at the total energy released by the merger progenitor?

    Energetically Interfering with Supernovae

    If we plot the brightness of a supernova from start to finish, we get a light curve that peaks very quickly and then slowly tapers off. This curve can change based on the type of supernova involved, but broadly speaking, most supernovae have this characteristic shape in brightness–time space.

    In the merger progenitor, energy released by ejected material interacting with the black hole would disrupt this characteristic supernova light curve. The extent of this disruption would depend on a variety of factors, but Gao and collaborators noted that at least a small fraction of these disrupted supernovae could be detected.

    If we observed a number of these disrupted supernovae, we could compare the rate at which they occur to the rate of relevant mergers being detected by gravitational-wave observatories. The result could point us towards one of the two scenarios that produce merger progenitors. So, as with most things astronomy, more observations please!

    Citation:

    “Special Supernova Signature from BH–NS/BH Progenitor Systems,” He Gao et al 2020 ApJL 902 L37.
    https://iopscience.iop.org/article/10.3847/2041-8213/abbef7

    See the full article here .


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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    1

    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

     
  • richardmitnick 4:33 pm on January 23, 2021 Permalink | Reply
    Tags: "Holding the System of HR 8799 Together", AAS NOVA, All four planets orbiting the star HR 8799 were identified via "direct imaging.", , , , , Planetary systems with these characteristics often have difficulty holding themselves together under all of the gravitational influences involved. But could the HR 8799 system somehow stay intact?, Resonance and Periodic Orbits   

    From AAS NOVA: “Holding the System of HR 8799 Together” 

    AASNOVA

    From AAS NOVA

    22 January 2021
    Tarini Konchady

    1
    The HR 8799 system as seen by the Keck II telescope. The planets are highlighted with arrows showing the direction in which they’re moving along their orbits. HR 8799 itself is the speckled region at the center of the image. Credit: NRC-HIA, C. Marois, and Keck Observatory.

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

    All four planets orbiting the star HR 8799 were identified via direct imaging — a feat made possible only because of the planets’ large sizes and their wide orbits.

    Example of direct imaging-This false-color composite image traces the motion of the planet Fomalhaut b, a world captured by direct imaging. Credit: NASA, ESA, and P. Kalas, University of California, Berkeley and SETI Institute.

    Planetary systems with these characteristics often have difficulty holding themselves together under all of the gravitational influences involved. But could the HR 8799 system somehow stay intact?

    Subtracting Light to Find Planets

    The direct imaging technique involves taking an image of a star and removing all the light associated with the star to see what remains (hopefully planets!). When astronomers used this technique on infrared observations of the star HR 8799, they discovered four planets in orbit around it.

    4
    An animation showing observations of the HR 8799 system taken over seven years. The observations were taken at the W.M. Keck observatory. Credit: J. Wang/C. Marois.

    3

    Images show that the innermost planet lies roughly 16 astronomical units from the star — a bit nearer than Uranus is to the Sun — and all of the planets have orbital periods ranging from 50 to 500 years. But, given that astronomers haven’t been able to observe this system for very long, uncertainty remains about the long-term behavior of the planetary orbits in the HR 8799 system. In fact, some previous studies have suggested that the system might come apart in the distant future.

    5
    The inner debris disk from an N-body simulation of the HR 8799 system. Initial positions of the planets are marked by the red circles. The gray orbits are from a different simulation of the system that was allowed to run for ten million years. The colors of points correspond to their eccentricity as indicated in the color bar. Credit: Goździewski & Migaszewski, 2020.

    But in a recent study, Krzysztof Goździewski and Cezary Migaszewski (Nicolaus Copernicus University, Poland) consider a scenario in which the HR 8799 is able to remain intact — we just need to involve mean-motion resonance (MMR) and periodic orbits.

    Resonance and Periodic Orbits

    When orbiting bodies are in MMR, the ratio of their orbital periods is a small integer ratio (a 5:2 resonance, for example, means that one object orbits five times in the time it takes the other to orbit twice). There are examples of MMR in the solar system: Neptune and Pluto are in a 3:2 resonance, and Jupiter’s moons Io, Europa, and Ganymede are in a 4:2:1 resonance.

    Goździewski and Migaszewski have previously demonstrated that the four planets orbiting HR 8799 could be in a stable 8:4:2:1 MMR. In this study, they revisited the MMR of the HR 8799 planets in the context of periodic orbits, where particular elements associated with the planetary orbits vary periodically with time.

    Mass Determination from Models

    Goździewski and Migaszewski used observations from a particular point in time to create an initial model of the HR 8799 system. They then let the system evolve under the constraints of MMR and periodic orbits. The resulting model not only aligned with measurements of the system made since the initial observation, but it could also be used to determine the masses of the HR 8799 planets. All we’d need is a few more future observations!

    HR 8799 could have planets that are closer in than the known four. However, they might not drastically interfere with MMR in the system. In either case, HR 8799 is a good testing ground for theories of planetary formation — we just need to keep an eye on it!

    Citation:

    “An Exact, Generalized Laplace Resonance in the HR 8799 Planetary System,” Krzysztof Goździewski and Cezary Migaszewski 2020 ApJL 902 L40.

    https://iopscience.iop.org/article/10.3847/2041-8213/abb881

    See the full article here .


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

    Please help promote STEM in your local schools.

    Stem Education Coalition

    1

    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

     
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