Tagged: AAS NOVA Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 3:53 pm on June 24, 2022 Permalink | Reply
    Tags: "A New Angle on Forming Misaligned Stellar Systems", a team of astronomers led by Marguerite Epstein-Martin (California Institute of Technology and Columbia University) posit that the troublemaker was instead internal: forces within the disk itself., AAS NOVA, An ongoing orbital alignment mystery seen in some stellar systems isn’t caused by disruptions from the outside but rather comes from within the stellar systems themselves., , , , , One proposed explanation is that an external companion star could exert a torque on a star-forming region and misalign everything., Recent observations show ~85% of the disks that can be resolved contain gaps with misalignments between the inner and outer disks., Recent space missions started uncovering thousands of new planets and began to tilt this theory on its head., The outer disk has the largest angular momentum and will apply a torque on the inner disk which will itself exert a torque on the star., The team theorized that the outer disk can play the role of a stellar companion and influence the dynamics of the inner disk–star orientation., When a stellar system forms everything is thought to be aligned.   

    From AAS NOVA: “A New Angle on Forming Misaligned Stellar Systems” 

    AASNOVA

    From AAS NOVA

    1
    Star surrounded by a planet-forming disk. [NASA/JPL-Caltech]

    In mystery thriller books, the authors always lead you to suspect that the culprit is someone outside the group: the gardener or the locksmith, perhaps. Sometimes, however, the answer is right in front of you, and the perpetrator is in the inner circle. A group of astronomers has recently reached the same conclusion: that an ongoing orbital alignment mystery seen in some stellar systems isn’t caused by disruptions from the outside but rather comes from within the stellar systems themselves.

    1
    A schematic of the geometry of a misaligned system, showing the angular momentum direction of the star, the inner disk, and the outer disk. [Epstein-Martin et al. 2022]

    A Mystery Arises

    When a stellar system forms everything is thought to be aligned: the star forms, it ignites nuclear fusion, and all of the leftover gas and dust orbit in a single plane and in the same direction that the star spins. This theoretical picture initially seemed to fit the planetary systems we had found…. that is, until recent space missions started uncovering thousands of new planets and began to tilt this theory on its head. All of a sudden, astronomers were discovering stars whose spin axes were misaligned with the orbits of their planets. But how does this situation arise? Shouldn’t the angular momentum of the system extend to the stellar spin axes, and everything should be aligned? According to recent exoplanet discoveries, apparently not!

    These questions remain a hot topic in the field of planet formation. One proposed explanation is that an external companion star could exert a torque on a star-forming region and misalign everything. In counterpoint, a team of astronomers led by Marguerite Epstein-Martin (California Institute of Technology and Columbia University) posit that the troublemaker was instead internal: forces within the disk itself.

    3
    The angular momentum ranges for the three components in the authors’ modeled system of a star and its surrounding disk. The yellow line shows a solar-mass star, the red region shows the inner disk, and the purple region shows the range of values for an outer disk. This figure clearly shows the hierarchy of angular momentum in the system. [Epstein-Martin et al. 2022]

    An Unexpected Suspect

    Protoplanetary disks are typically modeled as rigid objects. However, recent observations show ~85% of the disks that can be resolved contain gaps with misalignments between the inner and outer disks, which result from the formation of massive planets or the presence of a stellar binary companion. The team theorized that in these cases of an inner and outer disk misalignment, the outer disk can play the role of a stellar companion and influence the dynamics of the inner disk–star orientation. From there, the team used equations to model these systems and found that there’s a hierarchy to the angular momentum within the system: the outer disk has the largest angular momentum and will apply a torque on the inner disk which will itself exert a torque on the star. This is analogous to the dynamics between a star, an unbroken disk, and an outside companion that caused the misalignment in previous theories.

    Identification of the Culprit

    By using a series of complex equations that represent the dynamics in these misaligned systems, the team determined that, given the timescale of the contraction of the star and the lifetime of the disk, there would be just enough time for the disruptions to take place that cause the star’s misalignment with its eventual planets’ orbits. Though this does fit observations, the team notes that they employed several simplifications and assumptions. Overall, this study provides a new avenue for the formation of disks misaligned from the spins of their host star. So next time, don’t get distracted by the outside characters, because the culprit could come from within!

    Citation

    Generating Stellar Obliquity in Systems with Broken Protoplanetary Disks, Marguerite Epstein-Martin et al 2022 ApJ 931 42.

    https://iopscience.iop.org/article/10.3847/1538-4357/ac5b79/pdf

    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 1:03 pm on June 22, 2022 Permalink | Reply
    Tags: "Insights from Binary Stars in the Milky Way", AAS NOVA, , , , , Maybe They’re Born with It; Maybe It’s the Tidal Influence of the Milky Way., Nature vs. Nurture, Stars Awash in the Galactic Tide   

    From AAS NOVA: “Insights from Binary Stars in the Milky Way” 

    AASNOVA

    From AAS NOVA

    22 June 2022
    Kerry Hensley

    1
    This collage shows dozens of binary star systems seen by the Gaia spacecraft. [ESA/Gaia/DPAC]

    Many stars travel through space with a binary companion, and large-scale surveys allow us to study enormous numbers of these stellar pairs. What do these surveys tell us about the characteristics of binary stars in the Milky Way?

    2
    Tidal forces are perhaps best known for generating tidal tails and streams in interacting galaxies, but a galaxy’s tidal pull can have subtle effects on binary star systems as well. [NASA, H. Ford (JHU), G. Illingworth (UCSC/LO), M. Clampin (STScI), G. Hartig (STScI), the ACS Science Team and ESA]

    Stars Awash in the Galactic Tide

    The orbital parameters of a binary star system — namely, the distance between the stars and how eccentric (non-circular) their orbits are — can encode information about the formation and evolution of the binary system as well as the evolution of the stars themselves. The orbits of binary stars are susceptible to outside influence, too; gravitational nudges from passing stars, nearby gas clouds, and the overall tidal pull of the galaxy can change a binary system’s orbits over time.

    When we examine the orbits of binary systems in the Milky Way with observations from the sky-mapping Gaia spacecraft, we find unexpected trends in the orbital parameters of binary systems near the Sun. Namely, among binary systems separated by large distances (>1,000 au), there are more systems with highly eccentric orbits than expected. What’s the origin of this trend?

    Nature vs. Nurture

    3
    The final distribution of eccentricities (black lines) and best-fitting power laws (green lines) acquired from various initial distributions (red lines). These results show that a superthermal eccentricity distribution, as is seen in binary systems near the Sun, can only arise from a distribution that is initially superthermal. [Adapted from Hamilton 2022]

    As Chris Hamilton (Institute for Advanced Study) explains in a recent research article, understanding the current orbits of binary stars in the Milky Way requires separating the effects of nature (the eccentricities that the binary systems are born with) and nurture (the outside gravitational effects of passing stars and the background galactic pull).

    Hamilton approached this problem by modeling the effects of the Milky Way’s overall gravitational pull on populations of synthetic binary stars in the outer regions of the galaxy. In order to test the effects of nature as well as nurture, Hamilton modeled populations with different initial eccentricity distributions: uniform (all eccentricities are equally common), thermal (the binaries have reached statistical equilibrium through gravitational interactions; represented by the gray lines in the figure to the right), subthermal (fewer eccentric binaries than the thermal case), and superthermal (more eccentric binaries than the thermal case, as we see near the Sun).

    Maybe They’re Born with It, Maybe It’s the Tidal Influence of the Milky Way

    The model results show that the tidal pull of the Milky Way tends not to change the eccentricity distribution of a population of binary stars. Put another way, this means that the high number of wide, eccentric binary systems in the solar neighborhood can’t have been caused by the Milky Way’s gravitational influence — another factor, such as the combined effects of individual gravitational nudges from passing stars and gas clouds, must have caused this trend, or binary systems in the solar neighborhood must be born with a similar distribution of eccentricities.

    As is so often the case, there’s plenty more work to be done to understand this issue fully. In particular, modeling the effects of gravitational tugs from passing stars and applying new techniques to study the time evolution of binary systems will be critical to reaching a conclusion.

    Citation

    “On the Phase-mixed Eccentricity and Inclination Distributions of Wide Binaries in the Galaxy,” Chris Hamilton 2022 ApJL 929 L29.

    https://iopscience.iop.org/article/10.3847/2041-8213/ac6600

    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 1:51 pm on May 25, 2022 Permalink | Reply
    Tags: "The Life and Times of Immortal Stars", AAS NOVA, , , ,   

    From AAS NOVA: “The Life and Times of Immortal Stars” 

    AASNOVA

    From AAS NOVA

    25 May 2022
    Kerry Hensley

    1
    This image, which combines X-ray and infrared data from NASA telescopes with optical observations from an amateur astronomer, shows Centaurus A, the fifth brightest galaxy in the night sky. It’s one of many galaxies that host an active galactic nucleus. [Credit: X-ray: NASA/CXC/SAO; Optical: Rolf Olsen; Infrared: NASA/JPL-Caltech]

    Stars have been singing the same song since the beginning of the universe: you’re born, you fuse hydrogen into helium, you drift off the main sequence, and finally, you’re recycled into the cosmos. Under the right conditions, though, stars could become immortal. How is this possible, and what does it mean for these stars’ surroundings?

    Live Fast, Die Never

    2
    Artist’s illustration of the surroundings of a supermassive black hole at the heart of an active galaxy. [ESO/M. Kornmesser]

    Many galaxies host an active galactic nucleus — a luminous disk of gas and dust circling a central supermassive black hole. Extreme though this environment may be, stars can live within these disks, and astronomers suggest that some of these stars might be immortal.

    As these stars churn hydrogen into helium in their cores, they constantly replenish their hydrogen stores from the surrounding disk. As a result, they never run out of fuel, never leave the main sequence, and never die. Now, a team led by Adam Jermyn (Flatiron Institute) has explored how these extreme stars might affect the evolution of the disk that surrounds them.

    3
    The disk around an active galactic nucleus (AGN) captures most stars within rcap. The stars within rmax grow and become immortal, while those outside the disk or beyond rmax accrete little gas. [Jermyn et al. 2022]

    Drinking from the Stellar Fountain of Youth

    Jermyn and collaborators considered disks with short (0.1 million years) and long (10 million year) lifetimes, estimating that these disks would capture 1,000 and 20,000 stars, respectively, from the inner regions of their galaxies. The short-lived disk only contains enough mass to raise 300 of these stars to immortality, while the long-lived disk can support all 20,000 stars.

    In both disks, the immortal stars grow to 300 solar masses and have massive convective cores. The constant churning brings fresh hydrogen to their cores and transports helium outward to their surfaces. From there, fierce stellar winds carry the helium-rich gas out into the disk, boosting the abundance of helium near the black hole. The consequences of this chemical enhancement aren’t yet clear — it might rob immortal stars of their superpowers, since sucking up helium-rich material will make them burn through their hydrogen faster than it can be replenished — but measuring helium abundances in active galactic nuclei may provide a way to test the degree of chemical enrichment.

    Immortal No More

    5
    This illustration shows that the gas in stellar winds feeds the disk in the innermost regions where the escape velocity is high and escapes from the disk in the outer regions, where the escape velocity is low. [Jermyn et al. 2022]

    Do immortal stars help or hinder the disk’s survival? Both outcomes are possible. These stars’ winds likely replenish the inner regions of the disk, but they may also drive material to escape the outer regions of the disk. In addition, active galactic nuclei don’t remain active forever — as the disk begins to dissipate, the stars shed much of their mass, giving the disk a last boost before the stars cross back to the mortal realm and evolve into black holes.

    The authors note that their estimates are still uncertain, but it’s clear that immortal stars can play an important role in the evolution of the innermost regions of a galaxy. Future work might explore the consequences of helium-enriched gas spiraling around a supermassive black hole or assess the impacts of stars that form within the disk itself. Clearly, immortal stars provide plenty of work for modelers and observers alike — immortality might be beyond our reach, but at least we can live vicariously through these stars!

    Citation

    “Effects of an Immortal Stellar Population in AGN Disks,” Adam S. Jermyn et al 2022 ApJ 929 133.

    https://iopscience.iop.org/article/10.3847/1538-4357/ac5d40/pdf

    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 1:32 pm on May 23, 2022 Permalink | Reply
    Tags: "Surveying Young Stars in the North America and Pelican Nebulae", AAS NOVA, , , ,   

    From AAS NOVA: “Surveying Young Stars in the North America and Pelican Nebulae” 

    AASNOVA

    From AAS NOVA

    23 May 2022
    Kerry Hensley

    1
    Dust clouds ripple across the Pelican Nebula, creating a dramatic environment for star formation. [Wikipedia user Urmymuse; CC BY-SA 4.0]

    Since 2018, the Zwicky Transient Facility has kept tabs on fleeting events and variable objects in the universe, scanning the entire northern sky every two days.

    What can this expansive survey tell us about the variability of young stellar objects?

    2
    Full sample of young stellar objects overlaid on an image of the North America Nebula (light-colored area on the left) and the Pelican Nebula (light-colored area on the right). The final sample of variable stars is indicated by the darker blue circles. [Hillenbrand et al. 2022]

    Stellar Surveys

    Stars of all ages show a broad variety of variability, from slow pulsations to quick bursts of accretion. Young stellar objects seem especially prone to interesting variations, perhaps thanks to the influence of their natal nebulae. In a new publication, Lynne Hillenbrand (California Institute of Technology) led a team of astronomers, which included four high school students, on a hunt for variability in young stellar objects.

    The team surveyed stars in the North America and Pelican Nebulae, which lie 2,590 light-years away in the direction of the brightest star in the constellation Cygnus. Though they bear different names, the nebulae are actually connected, separated visually by a dark band of dust. The North America and Pelican Nebulae complex contains thousands of candidate young stellar objects, dozens of which have been monitored for signs of variability. Astronomers have previously used Zwicky Transient Facility data to study individual young stellar objects, but never a large sample — until now.

    3
    Examples of light curves with low, medium, and high (from left to right) values of the flux asymmetry parameter (M, top row) and quasiperiodicity parameter (Q, bottom row).
    [Hillenbrand et al. 2022]

    Digging In to the Data

    Hillenbrand and collaborators analyzed more than two years of Zwicky Transient Facility observations of 392 young stars, searching for signs of variability and classifying each star’s quasiperiodicity and flux asymmetry. As the names suggest, quasiperiodicity refers to how periodic or random an object’s variation is, while flux asymmetry quantifies how symmetrical an object’s light curve is. Both metrics are valuable ways to describe a variable star’s behavior, distinguishing those that vary smoothly and reliably from those that suddenly and haphazardly burst or flare.

    The team found that 323 of the stars in their sample vary in brightness, and 15% do so with a regular period and symmetric light curves. Another 39% of the stars have symmetric light curves but vary either quasiperiodically or randomly. Roughly 14% of the stars are “bursters” and 29% are “dippers,” with abrupt increases and decreases in brightness, respectively.

    The team also examined the colors of the objects, since color changes can give us clues as to why an object’s brightness is varying. The color analysis suggested that dippers might be due to changes in the dusty, light-absorbing material surrounding the young stars, while bursters may signal accretion episodes.

    Broad Applicability

    5
    Categorizations of all stars in the sample according to their flux asymmetry and quasiperiodicity. [Hillenbrand et al. 2022]

    This work not only provides information about hundreds of young stars, but also reflects on the metrics we use to study them. The quasiperiodicity index was designed for data from space telescopes, and some studies suggest that it can’t be used with less precise and lower cadence ground-based data. However, Hillenbrand and collaborators make a compelling case that applying thoughtful boundary conditions makes the quasiperiodicity index viable for ground-based applications as well.

    This study marks the first time that Zwicky Transient Facility data have been used to investigate a large sample of young stellar objects, but surely not the last — be on the lookout for more exciting results from this survey!

    Citation

    A Zwicky Transient Facility Look at Optical Variability of Young Stellar Objects in the North America and Pelican Nebulae Complex, Lynne A. Hillenbrand et al 2022 AJ 163 263.

    https://iopscience.iop.org/article/10.3847/1538-3881/ac62d8

    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 3:05 pm on May 21, 2022 Permalink | Reply
    Tags: "A Massive Reanalysis of Microlensing Events", AAS NOVA, , , , ,   

    From AAS NOVA: “A Massive Reanalysis of Microlensing Events” 

    AASNOVA

    From AAS NOVA

    20 May 2022
    Kerry Hensley

    1
    Observing area for the fourth phase of the Optical Gravitational Lensing Experiment (outlined in white). The survey has observed more than 10,000 gravitational microlensing events. [S. Brunier/ESO; J. Skowron/OGLE]

    Researchers have reanalyzed nearly 10,000 light curves from the Optical Gravitational Lensing Experiment [OGLE]. The resulting catalog, which is publicly available, provides new opportunities to study black holes, exoplanets, and much more.

    Making Sense of Microlensing

    2
    An illustration of a gravitational microlensing event. In this case, the lensing object is a star with an exoplanet in orbit around it. Click
    here to see an animation of this event. [NASA]

    When one astronomical object passes in front of another, the background object’s light is lensed, or focused, by the foreground object’s gravity, and we see a temporary jump in the background object’s brightness. This process of gravitational microlensing can clue us in to the presence of objects that emit little or no light, like black holes, exoplanets, and dark matter candidate objects, as they pass in front of stars or other luminous sources. Gravitational microlensing events are one of the most promising ways to find isolated stellar-mass black holes, which have long been difficult to track down.

    The Optical Gravitational Lensing Experiment (OGLE) has observed more than 10,000 microlensing events since the survey began in 1992. But recording the event is just the first step to understanding what caused it. Researchers model microlensing light curves to estimate the properties of the objects involved, but many factors can complicate these calculations; our vantage point — Earth — is in constant motion, stars vary in brightness for a multitude of reasons, and instruments aren’t perfect. How can we account for all those factors and extract useful information from a microlensing light curve?

    3
    An example of a gravitational microlensing event drawn from the sample analyzed in this work. In this event, OGLE BLG 156.7.141434, the brightness of the background source is variable. [Golovich et al. 2022]

    New and Improved

    That’s where today’s article comes in. In a new publication, a team led by Nathan Golovich (Lawrence Livermore National Laboratory) reanalyzed nearly 10,000 microlensing events in the third and fourth OGLE catalogs. The team’s new model accounts for Earth’s motion — which affects our perception of how quickly the background and foreground objects move relative to one another — as well as variability in the brightness of the background object and systematic instrumental effects.

    This type of model has been applied to a single microlensing event, but it has never been used on a full survey because of the immense computing power it requires — Golovich and coathors used about a million hours of computer processing time to analyze their sample! The team showed that their model was able to separate the desired signal from competing factors like Earth’s motion and the variability of the object being lensed, greatly reducing sources of bias.

    A Curated Catalog

    4

    What does this updated catalog mean for the search for isolated black holes? Golovich and collaborators used the open-source Population Synthesis for Compact object Lensing Events tool (PopSyCLE) to simulate microlensing events and identify locations in parameter space that isolated black holes are likely to inhabit. Based on the results of these simulations, the authors estimate that 50% or more of the 390 OGLE events in that region of parameter space are most likely due to foreground black holes.

    The catalog — the largest of its kind, to date — is free to anyone who wishes to use it; if you’re interested in black holes, exoplanets, or any other kind of dark object, there’s no better time to be on the hunt!

    Citation

    “A Reanalysis of Public Galactic Bulge Gravitational Microlensing Events from OGLE-III and -IV,” Nathan Golovich et al 2022 ApJS 260 2.

    https://iopscience.iop.org/article/10.3847/1538-4365/ac5969

    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 5:15 pm on May 11, 2022 Permalink | Reply
    Tags: "Diving Deep into Bright Galaxies with SCUBA-2 COSMOS", AAS NOVA, , Millimeter/sub-millimeter Astronomy   

    From AAS NOVA: “Diving Deep into Bright Galaxies with SCUBA-2 COSMOS” 

    AASNOVA

    From AAS NOVA

    11 May 2022
    Kerry Hensley

    1
    The authors of today’s article examined the properties of galaxies in the 18 fields shown here. [Chen et al. 2022.]

    Early in the history of the universe, huge, dusty galaxies churned out new stars. A new survey performed with a highly sensitive array of radio telescopes is poised to teach us more about this active period in our universe’s history.

    Early Galactic Goings-On

    Galaxies that shine at submillimeter wavelengths — often referred to simply as submillimeter galaxies — offer a window into the evolution of massive galaxies in the distant past. These galaxies generate copious amounts of optical and ultraviolet radiation from their furious star formation, but they’re so dusty that most of the emission that reaches us is longer in wavelength, in the submillimeter range. Submillimeter galaxies are a challenge for observers and modelers alike, as the two groups struggle to agree on how numerous these galaxies are and how their brightness varies over the course of the universe’s history. Can a new, high-resolution survey of the brightest of these galaxies shine a light on the matter?

    Submillimeter Survey

    In a recent publication, a team led by Chian-Chou Chen (陳建州) from The Academia Sinica Institute of Astronomy & Astrophysics [中央研究院天文及天文物理研究所](TW), presented the first results from a new survey of bright submillimeter galaxies from when the universe was 1.2–3.3 billion years old. The sample was drawn from the Cosmological Evolution Survey, which was carried out with the Submillimetre Common-User Bolometer Array 2 instrument, giving the survey the moniker SCUBA-2 COSMOS.

    Using the Atacama Large Millimeter/submillimeter Array (ALMA), the team explored several characteristics of 18 of the brightest galaxies surveyed in SCUBA-2 COSMOS:

    2
    Redshift distribution as a function of flux density at 870 microns for this survey (black circles) and previous works (blue squares and peach diamonds). [Chen et al. 2022]

    Redshift distribution: The median redshift for this sample is z = 3.3, which is higher than that of less luminous galaxies, suggesting that brighter submillimeter galaxies are found at higher redshifts (i.e., earlier in the universe).

    Galaxy pairs: Five of the 18 galaxies investigated in this study are actually two galaxies. Of these, two appear to be physically associated. This implies that 40% of the paired galaxies in the sample are interacting.

    Magnification: By modeling the gravitational field surrounding the galaxies, the team finds that only one is likely to be strongly lensed by a foreground galaxy.
    Mass and number density: The authors estimated the average mass (350 billion solar masses, or about a third of the mass of the Milky Way) and number density (roughly 1 x 10-6 cMpc-3) of the galaxies to compare them to galaxy populations later in the universe.

    Interaction Implications

    3
    Images at a wavelength of 870 microns for the five galaxy pairs in the sample (top row). Spectra of the primary (middle row) and secondary (bottom row) galaxies in each pair. [Chen et al. 2022]

    What do these findings imply about galaxies during this time period? The high proportion of submillimeter galaxies that are paired up suggests that interactions between galaxies play a large role in star formation at this stage in the universe’s development. And the true proportion of interacting galaxies may be higher — future surveys tailored to detecting faint emission lines from companion galaxies might reveal more interactions.

    Given the masses and numbers of the galaxies studied in this work, it’s possible that bright submillimeter galaxies are an important missing link in the lineage of ancient galaxies: they may be the forebears of quiescent (i.e., not star-forming) galaxies that appear later in the universe — a population whose galactic ancestors have been difficult to determine.

    Citation

    An ALMA Spectroscopic Survey of the Brightest Submillimeter Galaxies in the SCUBA-2-COSMOS Field (AS2COSPEC): Survey Description and First Results, Chian-Chou Chen et al 2022 ApJ 929 159.
    https://iopscience.iop.org/article/10.3847/1538-4357/ac61df

    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 8:53 pm on May 4, 2022 Permalink | Reply
    Tags: "Could Binary Stars Help Trace the Milky Way’s Dark Matter?", AAS NOVA, , , ,   

    From AAS NOVA: “Could Binary Stars Help Trace the Milky Way’s Dark Matter?” 

    AASNOVA

    From AAS NOVA

    4 May 2022
    Kerry Hensley

    1
    A view of the Milky Way containing 1.7 billion stars observed by the Gaia spacecraft. [ESA/Gaia/ESA Data Processing and Analysis Consortium (EU), CC BY-SA 3.0 IGO]

    How can we measure something we can’t see? When it comes to dark matter, astronomers are always finding new ways to track it down.

    On a Hunt for Dark Matter

    The motion of each star in our galaxy reflects the combined gravitational influence of all the stars, gas, dust, and dark matter in the Milky Way. In theory, we should be able to separate out the effect of the dark matter, giving us a sense of how it’s distributed throughout the galaxy. In practice, though, this is a tricky thing to measure!

    Previous work has attempted to suss out the Milky Way’s gravitational field — and, by extension, its dark matter distribution — by measuring tiny shifts in the timing of the signals from extremely dense, rapidly spinning stellar remnants called pulsars. However, pulsars are relatively rare, leading astronomers to search for ways to discern the Milky Way’s dark matter distribution by keeping a close eye on some of the most common stars in the galaxy.

    Measuring Midpoints

    Sukanya Chakrabarti (Institute for Advanced Study and The Rochester Institute of Technology) and collaborators explored the possibility of using binary stars as a probe of the Milky Way’s gravitational field. This technique hinges on making careful measurements of eclipsing binaries — those in which the stars repeatedly pass in front of each other as seen from our perspective. The team proposed that it’s possible to tease out the tiny nudge of the Milky Way’s overall gravitational field by measuring changes in the timing of the eclipse midpoint, when one star is perfectly centered on the other.

    However, the effect of the Milky Way’s pull is small — shifting the eclipse midpoint by just 0.1 second over the course of a decade — and other factors might also impact the eclipse timing: exoplanets tug on their parent stars, relativistic effects slowly alter elongated orbits, and stars in tight binary systems draw closer together over time. To determine if there are systems in which these other effects are small compared to the effect of the Milky Way’s pull, Chakrabarti and collaborators analyzed a sample of ~800 eclipsing binary systems. They estimated that more than 400 of these systems have orbits that are circular enough and periods that are long enough — lessening relativistic and tidal effects — for the Milky Way signal to be discernible, and they found that exoplanets don’t influence the timing of the eclipse midpoint much at all. The eclipse timing of ~200 of these systems can be measured to within 0.5 second, with some within 0.1 second.

    Capable Spacecraft

    While this work by Chakrabarti and coauthors demonstrates the feasibility of this technique, putting it into practice will require patience. The authors demonstrated that the Hubble Space Telescope is able to determine eclipse timings to within 0.1 second for some systems, and JWST and the Nancy Grace Roman Space Telescope will make even more exacting measurements. Luckily, the shift due to the Milky Way’s overall gravitational pull grows over time; the longer we look, the better our measurements and our understanding of the Milky Way’s dark matter distribution will be.

    Citation

    “Eclipse Timing the Milky Way’s Gravitational Potential,” Sukanya Chakrabarti et al 2022 ApJL 928 L17.
    https://iopscience.iop.org/article/10.3847/2041-8213/ac5c43/pdf

    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 1:41 pm on April 27, 2022 Permalink | Reply
    Tags: "Crustal Clues to Earth’s Formation", AAS NOVA, Calm accretion model: there is no disturbance from a giant planet., , The Grand Tack model: a simulated Jupiter barrels into the inner solar system before retreating to its current location.   

    From AAS NOVA: “Crustal Clues to Earth’s Formation” 

    AASNOVA

    From AAS NOVA

    27 April 2022
    Kerry Hensley

    1
    An illustration of rocky material bombarding the young Earth. [NASA Goddard]

    Earth’s crust contains chemical elements that we’d expect to find in its core, not near its surface. What can detailed simulations of planet formation tell us about the likely origins of these elements?

    2
    A plot of the abundances of individual chemical elements in Earth’s crust. The siderophile elements, outlined in yellow, are rare in Earth’s crust, though not as rare as expected. [Gordon B. Haxel, Sara Boore, and Susan Mayfield from USGS]

    A Crash Course in Earth History

    Early in the solar system’s history, rocky planetesimals collided to form larger bodies and eventually planets. As early Earth accreted material through collisions, siderophile (“iron-loving”) elements like gold and platinum dissolved into the young planet’s iron-rich core. However, present-day Earth has an unexpectedly large amount of these elements in its crust, indicating that they were added to the planet late in its formation.

    The number, size, origin, and composition of the objects that delivered this final sprinkling of siderophile elements is still uncertain, though. Now, astronomers have used simulations to make sense of the elements found in Earth’s crust and reconstruct our home planet’s formation history.

    3
    Location, masses, and origins of planetesimals in the Grand Tack simulation (left) and the calm accretion simulation (right). The top row shows the beginning of the simulation and the bottom row shows the end. In the calm accretion scenario, the planetesimals tend to contain material sourced from their location (indicated by the symbol color). In the Grand Tack model, the planetesimals tend to become “bluer” because of material moved inward by Jupiter. Click to enlarge. [Adapted from Carter & Stewart 2022]

    Plentiful Planetesimals

    Philip Carter (University of Bristol, UK, and University of California-Davis) and Sarah Stewart (University of California-Davis) set out to understand if Earth’s unusual crustal composition could be due to collisions with planetesimals late in the planet’s formation history. To do so, the team used numerical models to track the composition of tens of thousands of simulated planetesimals as they migrated and collided over a period of 21 million years. The authors explored two scenarios for the dynamics of the inner solar system: the Grand Tack model, in which a simulated Jupiter barrels into the inner solar system before retreating to its current location, and the calm accretion model, in which there is no disturbance from a giant planet.

    In the calm accretion model, planetesimals tended to collect material from very close to their birthplace. Since the composition of the planet-forming disk changes as a function of distance from the Sun, this means that planetesimals forming at different distances from the Sun had different compositions.

    In the Grand Tack model, on the other hand, Jupiter’s migration mixes the material in the inner solar system, leading to the formation of planetesimals containing a blend of material from throughout the inner solar system. In this scenario, planetesimals at a range of distances from the Sun had similar compositions.

    Ample Earth-Like Material

    4
    The Grand Tack model concentrates mass in a region located 0.8–1.3 au from the Sun. The Jupiter-induced mixing in this region results in a substantial fraction of planetesimals with similar composition to the planetary embryos that are present within 0.2 au. [Adapted from Carter & Stewart 2022.]

    If Jupiter’s migration shook up the inner solar system, it may have created plenty of planetesimals similar in composition to Earth. If those planetesimals collided with Earth late in its formation, they could distribute the siderophile elements in their cores over Earth’s surface.

    This scenario could also explain why the Moon has the same chemical signature as Earth; if the Mars-sized protoplanet hypothesized to have collided with Earth to form the Moon contained elements in similar ratios to Earth, that would naturally explain the Moon’s composition.

    Plenty of questions remain, but the new simulations make a compelling case that collisions between early Earth and material similar in composition could explain many aspects of present-day Earth. For more details and future prospects, be sure to read the full article cited below!

    Citation

    Did Earth Eat Its Leftovers? Impact Ejecta as a Component of the Late Veneer, Philip J. Carter and Sarah T. Stewart 2022 Planet. The Planetary Science Journal 3 83.

    https://iopscience.iop.org/article/10.3847/PSJ/ac6095

    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 10:27 am on April 27, 2022 Permalink | Reply
    Tags: "A Spiral Galaxy That Doesn’t Play by the Rules", AAS NOVA, ,   

    From AAS NOVA: “A Spiral Galaxy That Doesn’t Play by the Rules” 

    AASNOVA

    From AAS NOVA

    5 April 2022 [Just now in social media.]

    1
    The brightest galaxy at the center of a galaxy cluster is almost always elliptical. How might a spiral galaxy end up in that position instead? Credit: B. Holwerda (The University of Louisville)/ The National Aeronautics and Space Administration/The European Space Agency [La Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganisation](EU).

    Title: Detection of a Superluminous Spiral Galaxy in the Heart of a Massive Galaxy Cluster
    Authors: Ákos Bogdán et al.
    First Author’s Institution: Center for Astrophysics | Harvard & Smithsonian
    Status: Accepted to ApJ

    Galaxy clusters contain hundreds of galaxies in a huge variety of shapes and sizes, ranging from irregular dwarf galaxies to giant ellipticals. The most luminous member of a cluster is known as the brightest cluster galaxy. Each brightest cluster galaxy is different, but there are some properties that they tend to have in common — most brightest cluster galaxies are found at the very centre of their host cluster and are large, elliptical galaxies, containing little gas and forming very few new stars.

    The reason why most brightest cluster galaxies look so similar is well understood, as it is thought that these large galaxies form via a series of galaxy mergers. These are violent cosmic events that slowly increase the size of the galaxy, whilst also destroying any delicate disk or spiral arms that the galaxy may have (click here to see a simulation of two merging spiral galaxies). Additionally, mergers can lead to gas being expelled from a galaxy, resulting in the gas-poor, quenched brightest cluster galaxies that we see today.

    However, today’s article presents an exciting twist to this story by presenting data from three galaxy clusters that do not appear to follow this trend, including one brightest cluster galaxy that doesn’t fit with our current theories at all.

    Suspicious Spirals

    The authors begin by introducing seven superluminous spiral galaxies, a recently discovered class of huge galaxies with spiral or lenticular shapes. The great size of these galaxies is what motivates the main question of today’s article: could these superluminous spiral galaxies actually be brightest cluster galaxies, despite not looking like them?

    To answer this, we can look at the amount of X-ray radiation surrounding these galaxies. X-rays are emitted by the intracluster medium, a vast cloud of incredibly hot gas that fills a cluster, occupying the space between galaxies: if a cluster was a tasty chocolate chip muffin, the intracluster medium would be the cake, filled with chocolate chip galaxies. Using the X-ray telescope XMM-Newton, the authors found no X-ray emission surrounding two of their galaxies.

    However, as Figure 1 shows, the remaining five have large amounts of X-rays being produced nearby. This indicates the presence of the intracluster medium, meaning that these galaxies are nearby to a galaxy cluster.

    2
    Figure 1: X-ray observations of the region surrounding each of the seven superluminous disk galaxies. Regions of stronger X-ray emission are represented by lighter colour, and the centre of each X-ray region (i.e., the cluster centre) is marked by a green cross. The position of each superluminous disk galaxy is shown by the green circle. Note that the two galaxies in the bottom right (J11380 and J09354) have no associated clusters, and that the top-left galaxy (J16273) is located at the centre of its cluster. [Adapted from Bogdán et al. 2022.]

    It’s unusual to find spiral galaxies inside of clusters, but not unheard of. However, what makes this work so exciting is that in three of these clusters, there is not a single other galaxy that is brighter than the superluminous spiral — in other words, they are the brightest cluster galaxy. Finally, one of these galaxies (J16273 in Figure 1) is not only the brightest galaxy in the cluster, but is found directly in the cluster centre, in exactly the position that we would usually expect to find a brightest cluster galaxy!

    Galaxy Mergers, but Not as You Know Them

    The fact that J16273 is the brightest galaxy in a cluster and lives right in the cluster centre makes it look like a fairly typical brightest cluster galaxy. However, brightest cluster galaxies are elliptical because of the large numbers of galaxy mergers that they experience. How can we explain why this one is so different from all of those that we’ve seen before?

    Surprisingly, one explanation is mergers themselves. The authors suggest that J16273 was previously a regular, elliptical brightest cluster galaxy that recently merged with a smaller gas-rich galaxy. Under the right conditions, this merger could spin up the elliptical galaxy, with the remnants of the gas-rich galaxy forming a brand new spinning disk.

    In order to really understand these giant spiral galaxies, future work will need to look at many more than just seven of them. The authors acknowledge this and suggest that eROSITA, an ongoing X-ray survey of the sky, will be able to look at many more of these galaxies and determine whether they live in clusters, groups, or alone.

    eROSITA is due to release its first data at the end of 2022 and should help us to solve the mystery of how these huge spirals ended up in places we never expected to find them.

    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 9:08 pm on April 25, 2022 Permalink | Reply
    Tags: "Solving a Fifty-Year Star-Formation Mystery", AAS NOVA, , , ,   

    From AAS NOVA: “Solving a Fifty-Year Star-Formation Mystery” 

    AASNOVA

    From AAS NOVA

    25 April 2022
    Kerry Hensley

    1
    Young stars illuminate dark, dusty clouds in this European Southern Observatory photo of Lupus 3, a star-forming region about 600 light-years distant. Can new models finally resolve a long-lasting discrepancy between the observed and predicted Milky Way star formation rates? Credit: R. Colombari/ The European Southern Observatory [La Observatorio Europeo Austral][Observatoire européen austral][Europäische Südsternwarte](EU)(CL).

    For nearly 50 years, models have predicted that the Milky Way should be forming new stars far faster than it currently is. Can a reassessment of our models solve this long-standing mystery?

    Stymied Star-Formation or Mistaken Models?

    1
    The Milky Way hosts thousands of clouds of molecular gas — the sites of star formation. This map shows the locations and surface densities of molecular hydrogen clouds with a map of the Milky Way’s spiral arms on top. [Miville-Deschênes et al. 2017]

    All across the galaxy, cold clouds of molecular gas are churning and collapsing, forming dense cores where stars are born. Each year in the Milky Way, 1.65–1.90 solar masses of gas are converted into stars, but theoretical work claims that this number should be 150–180 times larger.

    Theorists have suggested that magnetic fields, turbulence, and massive stars injecting energy into their natal clouds suppress the Milky Way’s star-formation rate, but these solutions require unrealistically strong magnetic fields and constant, widespread turbulence. And this star-formation conundrum extends beyond the Milky Way — studies have found that models predict a speedier star-forming rate for our galactic neighbors as well. What might be amiss with our models?

    A Milky Way Mystery

    A team led by Neal Evans (University of Texas-Austin) approached this long-standing problem by considering the two main quantities that determine a galaxy’s star-formation rate: the masses of molecular gas clouds and how efficiently they form stars.

    3
    Plot of the efficiency with which molecular clouds collapse into star-forming cores per unit freefall time as a function of the virial parameter, αvir, which describes whether the cloud is gravitationally bound. (A high αvir value indicates that the cloud is not gravitationally bound and thus forms stars less efficiently.) The blue squares represent the new simulations from this work. The shaded green area indicates a constraint from observations. [Evans et al. 2022]

    The mass of a molecular cloud determines, in part, whether or not the cloud is gravitationally bound and how long it will take to collapse. Since we can’t put molecular clouds on a scale, and they’re mainly composed of hard-to-detect molecular hydrogen, we measure emission from other molecules that are present in the clouds to determine the clouds’ total masses. The authors used maps of carbon monoxide emission in the Milky Way to estimate the masses of the star-forming clouds, using a conversion factor that depends on the abundance of metals (elements heavier than helium) and varies with distance from the galactic center.

    The authors also considered how to improve our estimates of the star-formation efficiency — the fraction of gas in a star-forming cloud that eventually forms stars. Simple models of star formation assume that all gravitationally bound clouds will be entirely converted into stars, while those that are not bound won’t form any stars at all. However, the authors posit that star-formation efficiency likely varies from cloud to cloud rather than being all or nothing. To capture this subtlety, they developed a framework in which turbulence, high-energy radiation from newly formed stars, and energy injected by supernovae moderate the star-formation efficiency.

    Closing In on a Solution

    4
    Star-formation rate surface density as a function of distance from the galactic center. Observational estimates are shown in magenta. The numbers in parentheses give the total star-forming rate of each model in solar masses per year. [Evans et al. 2022]

    Citation

    Slow Star Formation in the Milky Way: Theory Meets Observations, Neal J. Evans II et al 2022 ApJL 929 L18.

    https://iopscience.iop.org/article/10.3847/2041-8213/ac6427

    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.

     
c
Compose new post
j
Next post/Next comment
k
Previous post/Previous comment
r
Reply
e
Edit
o
Show/Hide comments
t
Go to top
l
Go to login
h
Show/Hide help
shift + esc
Cancel
%d bloggers like this: