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  • richardmitnick 12:39 pm on October 5, 2022 Permalink | Reply
    Tags: , , , , Astrobites, , "A Stellar ‘Light Switch’ Orbiting a Black Hole", The event was called AT2018fyk and further analysis found that the emission was coming from the nucleus of a galaxy named LCRS B224721.6−450748., 600 days after the initial discovery there was a sharp decrease in the brightness of the X-ray and UV emission., 600 days after the dimming began the ‘light switch’ was flipped and the X-ray and UV emission from AT2018fyk have returned to close to pre-dimming levels.   

    From Astrobites : “A Stellar ‘Light Switch’ Orbiting a Black Hole” 

    Astrobites bloc

    From Astrobites

    10.5.22
    Evan Lewis

    Title: The rebrightening of AT2018fyk as a repeating partial tidal disruption event

    Authors: T. Wevers, E.R. Coughlin, D.R. Pasham, M. Guolo, Y. Sun, S. Wen, P.G. Jonker, A. Zabludoff, A. Malyali, R. Arcodia, Z. Liu, A. Merloni, A. Rau, I. Grotova, P. Short, Z. Cao

    First Author’s Institution: The European Southern Observatory [La Observatorio Europeo Austral] [Observatoire européen austral][Europaiche Sûdsternwarte] (EU)(CL)
    Status: Submitted to ApJ Letters [open access]

    Out in the center of a distant galaxy, a star is being torn apart as it circles the drain around an enormous black hole! Today’s paper reports on the re-emergence of X-ray and UV emission from a star orbiting a supermassive black hole (SMBH). After being discovered, this emission suddenly flicked off and stayed undetectable for ~600 days, before it quickly returned like a light switch being turned back on after a blackout– making this a very dynamic system to study.

    In 2018, optical emission from the star was discovered by the All-Sky Automated Survey for Supernovae (ASASSN), a supernova search using 24 telescopes around the world which can see objects 50,000 times dimmer than we can see with our naked eyes!

    The event was called AT2018fyk and further analysis found that the emission was coming from the nucleus of a galaxy named LCRS B224721.6−450748. These super catchy and memorable names are thanks to astronomers using astrometric coordinates and dates of discovery to name new objects, since there are too many in the sky to give each a unique name! But 600 days after the initial discovery there was a sharp decrease in the brightness of the X-ray and UV emission, with the X-ray emission plummeting to less than 1/6,000th of its original brightness. For 600 days, this dimming persisted, suggesting that the star had been torn apart by the gravitational pull of the black hole, and all of the stellar material had fallen onto the surface of the black hole, leaving nothing behind. This is known as a tidal disruption event (TDE), since the tidal forces (yes, the same ones that cause the ocean tides on Earth!) rip the star apart.

    However, today’s authors report that 600 days after the dimming began the ‘light switch’ was flipped and the X-ray and UV emission from AT2018fyk have returned to close to pre-dimming levels. In most tidal disruptions, the star is totally torn apart and the emission slowly fades, never to return– so their hypothesis is that this event was only a partial TDE, where the core of the star remained intact while only the outer layers were stripped away.

    1
    Figure 1: Cartoons illustrating the evolution of the star/SMBH system over time. The binary system is torn apart in panels a) and b), the stellar material begins to fall onto the black hole in panel c), the star moves away from the black hole in panel e), and the tidal disruption begins once again in panel f). Figure 3 from today’s paper.

    Figure 1 shows a schematic which illustrates the key phases of AT2018fyk’s history. The origins of this system are unique- given the previously estimated SMBH mass, a star should theoretically take at least a few thousand years to make one full orbit around the central black hole– way longer than the timescales of a few years that we’re seeing! But, if the star was originally part of a binary system, the black hole can disrupt the binary, pulling one star into an orbit around the black hole while the other star is shot at extremely high speeds away from the galaxy. Panels a) and b) of Figure 1 show this process, with the yellow dot representing the star’s ex-binary companion (now called a hypervelocity star) which is flung off into space.

    Panel c), at t=0, matches up with the initial discovery of the system, with material falling onto the surface of the supermassive black hole and getting heated up, which creates X-rays. This process is called accretion, or stellar fallback. Panel e), at t=600 days after discovery, shows that at this point the core of the star has moved farther away from the SMBH, and the stellar material remains gravitationally attracted to the stellar core, so it has stopped falling onto the SMBH– this is the point at which the X-ray and UV emission got much dimmer. At t=1200 days (the focus of this paper), what remains of the star has moved back into the region where the outer material of the star will be pulled onto the SMBH, and the emission ‘turns on’ once again.

    2
    Figure 2- the light curve of the stellar/SMBH system over time, since its discovery. Both the UV (green diamond; from Swift) and X-ray (black, from Swift/XMM-Newton/Chandra/eROSITA) light curves are shown. The x-axis is measured in days, with t=0 equal to the discovery of the system. Top left panel of Figure 1 from today’s paper.

    Figure 2 shows the light curve, or the luminosity of the emission over time, in the UV (green) and X-ray (black) wavelength ranges over the course of the observational history of AT2018fyk. Letters A-D represent the first 600 days of bright emission: at first, the UV emission is brighter (higher up on the y-axis) than the X-ray emission, but they switch around letter C. Why do we observe this behavior? At early times, the gas surrounding SMBH will be optically thick, but when the star moves away and the rate of fallback declines, the gas is able to expand and cool, becoming more optically thin (puffier) so it’s easier to see through to the hot inner region of the system, leading to brighter X-ray emission. At letter E, the dimming period begins as the star moves away from the SMBH, and the emission brightness drops sharply into its “quiescent” state. Finally, at letter F, the bright emission returns at similar luminosity levels to before, implying that the same star has orbited back around to a point where material is falling onto the SMBH.

    The authors predict that there will be another sharp brightness decline in August 2023 and, if the star survives this second encounter, a third episode of re-brightening should begin around March 2025. This gives astronomers an exciting prediction to look forward to confirming or denying, as we continue to learn about exotic systems like this!

    See the full article here .


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

    Please help promote STEM in your local schools.


    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 12:56 pm on October 3, 2022 Permalink | Reply
    Tags: "Could Stripped Stars be False Positives in the Search for the Missing Black Holes?", Astrobites, , , , , , Theories suggest we should see ~10^7 stellar-mass black holes in the Milky Way.   

    From Astrobites : “Could Stripped Stars be False Positives in the Search for the Missing Black Holes?” 

    Astrobites bloc

    From Astrobites

    10.3.22
    Aldo Panfichi

    Title: Detecting Stripped Stars While Searching for Quiescent Black Holes

    Authors: Julia Bodensteiner et al.

    First Author’s Institution: The European Southern Observatory [La Observatorio Europeo Austral] [Observatoire européen austral][Europaiche Sûdsternwarte] (EU)(CL)

    Status: Published on ESO’s The Messenger [open access]

    Unraveling the mysteries behind the fates of the most massive stars is key to understanding the present state of the universe. This is because massive stars are origins of elements heavier than helium, as a result of thermonuclear interactions in their cores; as well as being sources of electromagnetic radiation, strong stellar winds, and supernovae, which help seed these elements throughout the cosmos. Since the most massive stars end their lives as black holes, understanding the distribution and characteristics of these objects is key to understanding the lifecycle of said stars.

    The problem with searching for black holes, however, is that by their very nature, they are nearly impossible to detect on their own. We infer their existence through two main techniques. The first is when a black hole accretes material from a stellar binary companion – this gas and dust can form an accretion disk around the black hole, heating up and emitting x-ray radiation. The second is from the detection of gravitational waves that occur when a black hole merges with another compact object.

    In our galaxy, we have detected around 100 or so black holes from X-ray binaries. However, since we expect most massive stars to end their lives as black holes, theories suggest we should see ~10^7 stellar-mass black holes in the Milky Way. As such, it is suspected that the vast majority of black holes are what we call quiescent – that is, they do not accrete enough to show up on x-ray observations, and thus can only be detected via gravitational effects on other nearby bodies.

    Searching Spectroscopically

    To date there have been only a handful of reported candidate quiescent black holes. These have all been in binary systems, whose initial signature was detected through spectroscopy and radial velocity measurements. In short, if looking at the light spectrum of a star shows its spectral lines varying sinusoidally, as if orbiting a companion, but there are no appropriate lines that vary in opposite cadence, it could represent an unseen companion that does not emit light – such as a black hole.

    The authors of today’s paper, however, caution that a black hole need not be the only explanation for this. There could instead be a companion star that is emitting light, but is not detected due to low-quality data or being relatively faint compared to the much brighter companion. Alternatively, it could be rotating so fast that its spectral lines are broad and shallow, and thus are much less distinguishable, among other theories.

    In particular, the authors look in detail at two systems – LB-1 and HR 6819 – whose initial spectra prompted them to be reported as quiescent black holes orbited by a B-type star (luminous, blue, and usually more massive than the sun). However, subsequent analyses have proposed that they are instead binary star systems that consist of a B-type star whose atmosphere has been stripped, and another luminous star.

    The spectra of LB-1 and HR 6819 both share similar features that are shown in Figure 1. In particular, in this wavelength region there are two bright, stationary, broad emission lines, and two dark, narrow, shallow absorption lines, which vary sinusoidally in time. The absorption lines are those of the B-type star, and vary on a scale of tens of days. The emission lines are instead characteristic of a classical Be star – a specific kind of B-type star that contains an emitting circumstellar gaseous disk.

    1
    Figure 1: Spectra of HR 6189, cut around the Fe II spectral line region at 5316 Angstroms, over the full orbital period of 40 days. The top panel shows the two bright, stationary emission lines of a classical Be star, and two darker, sinusoidally-varying absorption lines from a typical B-type star. The bottom panel shows three normalized spectra taken at three different phases in the orbit. Figure 2 in the paper.

    The initial hypothesis was that since the Be emission lines appear stationary, the B-star and Be star did not orbit one another closely. Either the B-star must orbit with an invisible companion, and the Be emission corresponded to either an unrelated third star which appeared in the spectra due to chance superposition, or this was a triple star system and the Be-star orbited much further away. These ideas were backed up by calculations which showed that if the B-type star had its typical mass of ~5 solar masses, the Be star would need to have an unphysical mass to have such an effect on the radial velocity of the B-type star’s spectral lines.

    The Stripped Star Solution

    However, subsequent studies have since suggested that such a triple system would most likely be unstable. Furthermore, the Be star’s emission lines do in fact seem to show a very small, subtle variation in opposite cadence to the B-star’s absorption lines; thus the two stars could in fact be orbiting one another, removing the need for a third, invisible companion. If this is the case, then, how do we justify the non-physicality of the Be star’s estimated mass? The projected orbital velocity of the B-type stars, based on the movement of their spectral lines, is much larger than it should be in comparison to that of the Be stars, in both the LB-1 and HR 6819 systems.

    We can resolve this by reinterpreting the physical nature of the B-type star. If we assume its mass to be on the order of ~0.5 solar masses, rather than the typical ~5-6, the radial velocities would make sense. Under this interpretation, the B-type star is not a standard main-sequence B-type star, but is instead in a “post-mass-transfer” phase – a star that has been fully ‘stripped’ by its binary companion, losing the majority of its mass, while its companion accreted all that matter and angular momentum, spinning up into a rapidly rotating Be star. As the outer hydrogen layers were stripped away from the B-type star, its now exposed Helium core would puff outwards and re-contract into a new equilibrium phase. In the early contraction phase, its luminosity and surface temperature can appear to overlap with those of a typical main-sequence B-type star, and thus it could be easily confused for one. If this is the case, then said B-type star would continue contracting over millions of years, eventually becoming a sub-dwarf OB star. The start of the contraction phase, however, is the brightest and most easily spectroscopically detectable phase of this evolution, and so it makes sense that these systems are detected in this phase.

    2
    Figure 2: Two hypotheses for the observed spectra of HR 6819. The first scenario corresponds to a stripped B-type star and a Be star orbiting each other. The second scenario shows a normal B-type star orbiting a black hole, with a Be star forming a part of this triple system, orbiting from much further away. Figure 3 in the paper.

    The authors posit that high-resolution interferometry might be the definitive way to determine whether these systems contain quiescent black holes or stripped B-type stars. The binary scenario has the two companions orbiting at 1-2 milliarcsecond separations, with an orbital period on the order of tens of days. On the other hand, the triple scenario should have the Be star orbiting much further apart, and appearing stationary on month-long timescales. Initial observations of HR 6819 from the GRAVITY instrument at the VLT Interferometer seem to favor the binary hypothesis, and further observations in April-September of 2022 will allow for the derivation of stellar parameters such as an accurate mass of the stripped B-type star. Similarly, GRAVITY observations of LB-1 are planned for this year, and will hopefully shed light on the nature of that system as well.

    With the possible elimination of these two candidates, however, the search for the missing quiescent black holes continues, and the authors hope that the lessons learned from these two systems pushes for an interdisciplinary approach to finding and characterizing these objects, in particular with ongoing and upcoming large scale surveys on the horizon.

    See the full article here .


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

    Please help promote STEM in your local schools.


    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 11:37 am on October 2, 2022 Permalink | Reply
    Tags: "Asteroids in the Archives", Astrobites, , , , ,   

    From Astrobites : “Asteroids in the Archives” 

    Astrobites bloc

    From Astrobites

    10.1.22
    Ben Cassese

    Title: Hubble Asteroid Hunter. I. Identifying asteroid trails in Hubble Space Telescope images

    Authors: Sandor Kurk + 13 others

    First Author’s Institution: European Space Research and Technology Centre (ESA), Keplerlaan 1, 2201 AZ Noordwijk, The Netherlands

    Status: Published in A&A [open access]

    ______________________________________________________________
    Strong Motivations for Small Targets

    Though none of them were around to see it, astronomers are pretty confident that the early days of the solar system’s life were chaotic and violent. Scores of newly formed asteroids, planetesimals, and a few bona fide giant planets were all buzzing around the sun in a tightly packed disk: Collisions were inevitable, though their aftermaths varied. Sometimes two clumsy objects would merge together, and sometimes one or both would shatter into smaller pieces.

    To get a handle on just how lawless this epoch of our history was, astronomers would love to perform a forensic analysis on the asteroids that survived to the comparatively quiescent present; if they could measure the current ratio of smaller asteroids to larger ones, they could constrain how common destructive collisions were in the past. This in turn would inform models of where objects were and how fast they moved in the early days around the sun.

    Unfortunately, the most valuable asteroids for such a study –the very smallest remains– are also the hardest to find. We can only see asteroids when they reflect some sunlight back towards the earth, and small rocks just don’t reflect much light, making them very faint.

    Enter the Hubble Space Telescope. Hubble is a very capable, very busy space-based telescope that is able to see these dim asteroid remnants.

    However, although Hubble is able to image solar system objects, it spends most of its time gazing much further afield, staring longingly at distant galaxies, quasars, and other targets at cosmic distances.

    But, sometimes would-be asteroid hunters get lucky, and even when Hubble is trying to measure something else, a local space rock serendipitously wanders into the field of view. Since both the asteroid and the earth are moving around the sun, the photobombing asteroid appears as a curved streak in the image, a hairline fracture in the otherwise dark background of the universe.

    1
    Figure 1: An example of an asteroid trail in a Hubble image and the AutoML model’s successful recovery of it. The large galaxy is HCG007. Source: Figure 4a in the paper.

    Today’s authors aimed to wring as much information as possible out of these happy coincidences, and ambitiously sought to search the entire archive of relevant Hubble images for fortuitous streaks caused by covert, small asteroids .

    Citizen Science + Deep Learning

    Every picture Hubble takes eventually becomes public, freely downloadable to anyone who wants to see some corner of the universe. The archive of these images is immense, containing more than 37,000 images taken with the instruments and filters the authors deemed most likely to catch their targets. The scale of the database necessitates automation, and to meet this need the authors turned to deep learning, specifically Google’s Cloud AutoML Vision model. When fed an image, this algorithm reports back what’s in the picture (in this case, an asteroid, while in others, a dog for example). While they don’t detail the specifics of the architecture in this article, they share that the model consists of several interwoven machine learning components: they use a convolutional neural network to actually find the asteroid arcs in the images, but that network was itself designed by a reinforcement learning algorithm, an artificial intelligence paradigm that trains a computer to find an optimal solution via trial and error and feedback from its own actions.

    Such a machine learning model needs to be trained, and training requires a catalog of known examples for the model to study. Since such a catalog didn’t yet exist, the authors had to build their own, and to do so they enlisted the help of citizen scientists. They set up a project on Zooniverse called Hubble Asteroid Hunter, and over about a year more than 11,000 volunteers logged on to comb through the data and search for asteroid arcs by eye. Each volunteer was shown several Hubble pictures, asked “Is there an asteroid in this image?” for each one, then prompted to dismiss images with no streaks and flag pictures that contained the telltale curves. These volunteers collectively submitted more than 2 million yes/no answers to the query, and in total this tremendous effort uncovered asteroid streaks in about 1% of all images.

    Model Performance

    Combining the trails found by volunteers and those found by the model, the authors assembled a pile of 2,487 possible asteroid arcs. They then went through each of these candidates manually, and after removing duplicates and accounting for false positives caused by cosmic rays, gravitational lenses, or earth-bound satellites, they culled the list down to 1,701 confident asteroid detections.

    2
    Figure 2: The distribution of apparent magnitude, or perceived brightness, of the asteroids found in Hubble images. In blue are objects that the authors could trace back to previously-recorded asteroids, while in orange are the authors’ new candidate discoveries. Note that their new asteroids are systematically fainter than previous discoveries due to the challenges of detecting fainter bodies from Earth’s surface. Source: Figure 9a in the paper.

    After checking if any of these streaks could be attributed to any of the more than 1.2 million known asteroids, the authors concluded that 670 of the streaks corresponded to previously discovered sources and that the remaining 1,031 were caused by never-before-seen asteroids. They also found that these freshly discovered asteroids were systematically fainter than the known bodies, which they expected: the brighter an asteroid is, the higher the chance that it was already detected by a ground-based survey. This general faintness also hinted that many of their new discoveries are exactly the type of small asteroid which we’ve struggled to count in other surveys.

    The authors also start to explore other properties of their sample of new asteroids, including their spatial distribution and brightness variability. Though they do not account for the biases of Hubble’s preferential pointing and leave much of this further analysis for future work, their presentation of this new sample and demonstration of the power of merging citizen science and machine learning is an exciting step forward in the small-asteroid accounting business. The more confidently we can count the small asteroids, the closer we can come to understanding our solar system’s early history: now, if more drift into our view, we’ll be ready for 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

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 4:25 pm on September 15, 2022 Permalink | Reply
    Tags: "UR: The Atomic Dark Matter Model:: A Possible Solution to the Shortcomings of CDM", Astrobites, , , , ,   

    From Astrobites : “UR: The Atomic Dark Matter Model:: A Possible Solution to the Shortcomings of CDM” 

    Astrobites bloc

    From Astrobites

    9.15.22
    John Blakely | The Pennsylvania State University

    A significant amount of modern cosmological research has been in the pursuit of understanding dark matter. Dark matter (DM) has long been assumed as the solution to the “missing mass” problem, originating from astrophysicist Fritz Zwicky’s 1933 observations of the Coma Cluster.
    __________________________________
    Dark Matter Background
    Fritz Zwicky discovered Dark Matter in the 1930s when observing the movement of the Coma Cluster., Vera Rubin a Woman in STEM, denied the Nobel, some 30 years later, did most of the work on Dark Matter.

    Fritz Zwicky.
    Coma cluster via NASA/ESA Hubble, the original example of Dark Matter discovered during observations by Fritz Zwicky and confirmed 30 years later by Vera Rubin.

    In modern times, it was astronomer Fritz Zwicky, in the 1930s, who made the first observations of what we now call dark matter. His 1933 observations of the Coma Cluster of galaxies seemed to indicated it has a mass 500 times more than that previously calculated by Edwin Hubble. Furthermore, this extra mass seemed to be completely invisible. Although Zwicky’s observations were initially met with much skepticism, they were later confirmed by other groups of astronomers.

    Thirty years later, astronomer Vera Rubin provided a huge piece of evidence for the existence of dark matter. She discovered that the centers of galaxies rotate at the same speed as their extremities, whereas, of course, they should rotate faster. Think of a vinyl LP on a record deck: its center rotates faster than its edge. That’s what logic dictates we should see in galaxies too. But we do not. The only way to explain this is if the whole galaxy is only the center of some much larger structure, as if it is only the label on the LP so to speak, causing the galaxy to have a consistent rotation speed from center to edge.

    Vera Rubin, following Zwicky, postulated that the missing structure in galaxies is dark matter. Her ideas were met with much resistance from the astronomical community, but her observations have been confirmed and are seen today as pivotal proof of the existence of dark matter.
    Astronomer Vera Rubin at the Lowell Observatory in 1965, worked on Dark Matter (The Carnegie Institution for Science).

    Vera Rubin, with Department of Terrestrial Magnetism (DTM) image tube spectrograph attached to the Kitt Peak 84-inch telescope, 1970.

    Vera Rubin measuring spectra, worked on Dark Matter(Emilio Segre Visual Archives AIP SPL).
    Dark Matter Research

    Super Cryogenic Dark Matter Search from DOE’s SLAC National Accelerator Laboratory at Stanford University at SNOLAB (Vale Inco Mine, Sudbury, Canada).

    LBNL LZ Dark Matter Experiment xenon detector at Sanford Underground Research Facility Credit: Matt Kapust.


    DAMA at Gran Sasso uses sodium iodide housed in copper to hunt for dark matter LNGS-INFN.

    Yale HAYSTAC axion dark matter experiment at Yale’s Wright Lab.

    DEAP Dark Matter detector, The DEAP-3600, suspended in the SNOLAB (CA) deep in Sudbury’s Creighton Mine.

    The LBNL LZ Dark Matter Experiment Dark Matter project at SURF, Lead, SD.

    DAMA-LIBRA Dark Matter experiment at the Italian National Institute for Nuclear Physics’ (INFN’s) Gran Sasso National Laboratories (LNGS) located in the Abruzzo region of central Italy.

    DARWIN Dark Matter experiment. A design study for a next-generation, multi-ton dark matter detector in Europe at The University of Zurich [Universität Zürich](CH).

    PandaX II Dark Matter experiment at Jin-ping Underground Laboratory (CJPL) in Sichuan, China.

    Inside the Axion Dark Matter eXperiment U Washington (US) Credit : Mark Stone U. of Washington. Axion Dark Matter Experiment.


    __________________________________

    This so-called “dark matter” would not emit any light, or interact with light, but would contain most of the mass of the galaxy cluster. Zwicky discovered that the galaxies in the Coma Cluster [above] were moving too fast to be held together by the gravity of the visible matter in the cluster. Since then, many observations have been made, at a wide range of scales, which all point to the existence of dark matter. Despite this, the physics of the dark matter is still largely not known. A model of dark matter that is able to connect observed data with our understanding of physics is sought after. Though there have been many attempts, none have been able to successfully do this completely.

    The Cold Dark Matter Model: Our Best Guess So Far

    The most popular model held is the Cold Dark Matter paradigm (CDM). CDM provides a satisfyingly simple answer to the “missing mass” in our observations, stating that there is a cold, dark matter component of the universe. Cold means that it is not energetic and is nonrelativistic, and dark means that it only interacts with itself, and baryonic matter, via gravity. However, the scenario, which CDM creates, provides predictions which are in tension with our observations, specifically on smaller scales. A solution to this can either be in the form of a new understanding of the interactions between CDM and the Standard Model, or a new dark matter model which maintains the successes of CDM, but succeeds where CDM fails. A model which could fulfill this is the Atomic Dark Matter Model.

    The Atomic Dark Matter Model: A Possible Solution to the Shortcomings of CDM

    The atomic dark matter model (ADM) consists of a type of matter quite similar to Standard Model atomic and molecular hydrogen. ADM consists of a dark “electron” and “proton” of masses mL and mH, respectively, which interact via a massless dark “photon” at a strength governed by a dark fine structure constant, ɑD. With the model still in its youth, much of the current research in ADM is purposed to whittling down the possible values of mH, mL, and ɑD by restricting them according to our observations and previous theories. In this article we introduce the beginning of how these parameters could be restricted by gravitational wave data.

    In ADM, the dark matter particles are able to form atomic and molecular bound states, analogous to baryonic or ‘regular’ hydrogen, and radiate away some of their initial energy in the form of a dark photon, as well as break these bound states and radiate away energy. This is particularly interesting because the dark halos in ADM, unlike in CDM, can dissipate energy and cool, allowing for some to collapse and form dark compact structures, solving some of CDM’s problems. It’s useful to know which dark halos are able to collapse and form compact structures, like black holes, because it allows us to use gravitational wave data to validate the model and restrict the possible parameter values.

    Which Dark Halos Can Collapse?

    To determine whether a dark halo can collapse, we have to see whether the halo will radiate away the energy it needs to support itself fast enough. To determine this we need to compare the time it takes to collapse under its own gravity to the time it takes to dissipate all of its energy. The free-fall time only depends on the mass density of the halo, but the cooling time depends on the evolution of the number of free and bound dark particles as well as how quickly it can remove its energy. To get the number of free and bound dark particles, we will use what’s known as the ionization fraction, which is just the ratio of how quickly bound states are broken to how quickly they are formed. Once we have this we can compute the volumetric cooling rate, we can get the time it takes to radiate away all of the halos energy. If the halo cools faster than a free-fall time it will collapse, if not then it will remain in hydrostatic equilibrium. This comparison was calculated by Matthew R. Buckley in 2017, and in Figure 1 the solid colored regions show the dark halo masses that can collapse as a function of dark electron mass, mL.

    2
    Figure 1: The solid regions are the results of Matthew R. Buckley in 2017, showing the masses of dark halos that can collapse in collisional ionization equilibrium as a function of dark electron mass (mL), whereas the hatched regions show the halo masses that violate equilibrium as a function of mL. The red and blue regions correspond to a ɑD value of 10^-1 and 10^-2 respectively.

    However, determining whether or not a halo will collapse relies on the dark halo remaining in equilibrium between the rate it forms dark bound states and the rate at which they are broken, but for certain assumptions about the ADM particles this doesn’t hold. If the dark halo violates equilibrium, it doesn’t mean that it won’t collapse, just that it can’t be determined with an ionization fraction dependent on equilibrium.

    To determine the dark halo masses which violate equilibrium over the ADM parameter space as a function of the mass of the dark electron, we have to compare the time it takes for the dark halo to fully ionize versus the time it takes to cool completely. This results in a region of uncertainty in the results of Matthew R. Buckley in 2017, shown in Figure 1 as the hatched regions. Dark halos that fall in these regions will require to be reanalyzed using an ionization fraction that does not rely on equilibrium.

    With this region of indeterminacy defined, finding a simple expression for an ionization fraction which can account for out-of-equilibrium cooling will be much easier. Ultimately, this simpler expression will make tracking the evolution of ADM dark matter much less rigorous and would provide a useful insight into the dynamics of structure formation in the atomic dark sector.

    Special thanks to the STAR undergraduate research program at Penn State for facilitating this project, as well as to James Gurian for advising and teaching the cosmology, physics, and general skills needed for this research.

    See the full article here .


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

    Please help promote STEM in your local schools.


    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 12:15 pm on September 13, 2022 Permalink | Reply
    Tags: "The Continued Hunt for the Neutron Star at the Heart of SN 1987A", Astrobites, , , ,   

    From Astrobites : “The Continued Hunt for the Neutron Star at the Heart of SN 1987A” 

    Astrobites bloc

    From Astrobites

    9.12.22
    Sonja Panjkov

    Title: Additional evidence for a pulsar wind nebula in the heart of SN 1987A from multi-epoch X-ray data and MHD modeling

    Authors: Emanuele Greco, Marco Miceli, Salvatore Orlando, Barbara Olmi, Fabrizio Bocchino, Shigehiro Nagataki, Lei Sun, Jacco Vink, Vincenzo Sapienza, Masaomi Ono, Akira Dohi, Giovanni Peres

    First Author’s Institution: Anton Pannekoek Institute for Astronomy, University of Amsterdam, The Netherlands

    Status: Published in The Astrophysical Journal [open access]

    When the famed Supernova 1987A (SN 1987A) exploded on 23 February 1987 in the Tarantula Nebula of the Large Magellanic Cloud, it provided a valuable opportunity to probe the final stages of stellar evolution.

    SN 1987A’s potential to reveal the hidden nature of core-collapse supernovae was almost immediately apparent. For the first time, the neutrino burst expected from the core-collapse of massive stars was detected at three neutrino observatories around the world and provided solid evidence of a neutron star at the heart of SN 1987A.

    However, the postulated neutron star has long remained elusive as it can be camouflaged by the cold, dense supernova material in the way. Or at least that was the case until evidence of SN 1987A’s central neutron star was published, led by researchers at the University of Amsterdam, who searched for emission from its associated pulsar wind nebula.

    Pulsar wind nebulae are the powerful winds from rapidly rotating neutron stars, which accelerate charged particles to relativistic velocities and emit high-energy X-rays. Thus, the identification of a pulsar wind nebula within SN 1987A would solve the mystery of its missing neutron star.

    Is a Pulsar Wind Nebula Hidden in the X-ray Spectrum of SN 1987A?

    Building on the results from an earlier paper covered in this astrobite, the authors of today’s paper searched for traces of SN 1987A’s pulsar wind nebula. To do this, they conducted a simultaneous analysis of X-ray observations captured by Chandra, XMM-Newton and NuSTAR, spanning eight years of SN 1987A’s evolution.

    In the earlier paper, the authors analyzed two years of X-ray data and found evidence of high-energy X-ray emission from SN 1987A, however they were unable to determine the precise nature of the source. With the addition of more recent data, the authors of today’s paper were not only able to detect high-energy X-ray emission, but they were also able to identify its likely origin.

    The authors first determined whether certain features of the X-ray spectrum may be attributed to a pulsar wind nebula by testing two different models.

    The first model they consider is the 3-kT model, which does not account for a central pulsar wind nebula. The second model they test is called the 3-kT plus power-law model. It adds a heavily absorbed power-law component to the 3-kT model to describe the emission from a pulsar wind nebula that is blocked by the intervening cold, dense supernova material. If the 3-kT plus power-law model provides a better fit to the data, it’s likely there is a pulsar wind nebula at the heart of SN 1987A!

    The results using the 2014 data are shown in Figure 2, with the spectra in the top panes and residuals below. Residuals tell you how well your model replicates your observations, with a residual of 0 indicating a perfect fit.

    2
    Figure 2: Spectra of SN 1987A using the 2014 data are shown in the top panes, with the residuals plotted beneath. The colours represent the data from each telescope: Chandra (black and red), XMM-Newton (blue, yellow, cyan, orange and light green) and NuSTAR­ (green) spectra of SN 1987A. The left panel shows the fit for the 3-kT model, which does not account for a pulsar wind nebula, while the right shows the fit for the 3-kT plus power-law model, as would be expected from a central pulsar wind nebula. At energies greater than roughly 8 keV, the residuals are smaller for the 3-kT plus power-law model, indicating it is a better fit to the data. Figure 1 in the paper.

    On the left, the data are fitted with the 3-kT ­model that does not account for a pulsar wind nebula, while on the right they fit the 3-kT ­plus power-law model. Evidently, both models do a good job of replicating the observations up until roughly 8 keV, however it is at the high energy end of the spectrum that things become interesting.

    For the 3-kT model, the residuals are significantly greater than 0 above 8 keV, while they disappear for the model that accounts for a pulsar wind nebula. Thus, the 3-kT plus power-law model provides the better fit, and it is likely that a hidden pulsar wind nebula is indeed altering the X-ray spectrum of SN 1987A above 8 keV!

    Could it be a Pulsar Wind Nebula Imposter?

    What makes this work even more exciting is that the authors rule out the other possible explanation for this high-energy emission, namely diffusive shock acceleration, which accelerates particles to high energies at supernova shock fronts. Diffusive shock acceleration would also be described by a power-law model, however it would be distinct from the pulsar wind nebula scenario due to the different physical sites where these processes occur.

    More specifically, the high-energy emission from diffusive shock acceleration would be unabsorbed, since it occurs at the periphery of SN 1987A where there is no supernova material blocking our line of sight. In comparison, the emission from a pulsar wind nebula would be highly absorbed due to its origins deep within the supernova remnant.

    To distinguish between these scenarios, the authors again test two models: one with a highly absorbed power-law, representing the emission from a central pulsar wind nebula, and another with an unabsorbed power-law, representing the high-energy emission that would result from diffusive shock acceleration.

    They find that the best fit to the observational data occurs when heavy absorption is included, suggesting that the source of the high-energy emission is located at the heart of SN 1987A. Exactly where we would expect to see the elusive neutron star!

    Even though the neutron star in SN 1987A remains hidden, there’s good evidence for its existence in the X-ray spectrum if you look close enough. Excitingly, as SN 1987A ages and expands, a direct detection of its neutron star may become possible by the 2030s. All that’s left to do is wait.

    See the full article here .


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

    Please help promote STEM in your local schools.


    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 1:57 pm on September 10, 2022 Permalink | Reply
    Tags: "LAEs": Lyman-alpha emitters, "Quench your inner star formation", Astrobites, , , , , Left with questions about the underlying physics the authors remind us that the environments of LAEs are subject to complex processes., The role of environment on galaxy formation and evolution is a complex problem that remains unclear.   

    From Astrobites : “Quench your inner star formation” 

    Astrobites bloc

    From Astrobites

    9.10.22
    Olivia Cooper

    Paper Title: Can luminous Lyman alpha emitters at z ~ 5.7 and z ~ 6.6 suppress star formation?

    Authors: Daryl Joe D. Santos, Tomotsugu Goto, Tetsuya Hashimoto, Seong Jin Kim, Ting-Yi Lu, Yi-Hang Valerie Wong, Simon C.-C. Ho, Tiger Y.-Y. Hsiao

    First Author’s Institution: Institute of Astronomy, National Tsing Hua University, Taiwan & Max Planck Institute for Extraterrestrial Physics, Germany

    Status: Accepted in MNRAS [closed access]

    How does the lone, rural galaxy evolve compared to one in a crowded city full of lights? The role of environment on galaxy formation and evolution is a complex problem that remains unclear. How densely surrounded galaxies are – by other galaxies and by radiation – has implications for how big structures and clusters of galaxies form, as well as how star formation gets triggered and later turned off or quenched.

    Star-forming galaxies, which are commonly detected through an emission line from the Lyman-alpha (n=2 to n=1) transition of hydrogen, are a source of high energy radiation and are potentially a site of galaxy clustering. The impact of environment on the evolution of these Lyman-alpha emitters (LAEs) is still hazy enough that many studies have somewhat conflicting conclusions as to what’s going on. Do they tend to cluster? Does their presence enhance or suppress the formation of stars? In today’s paper, the authors venture to answer these questions by taking a statistical sample of LAEs at early times, about a billion years after the Big Bang.

    More specifically, their investigation centers around the impact of ionizing radiation in the ultraviolet wavelength range on the evolution of and star formation within galaxies in the early Universe. While the physical processes to suppress or quench ongoing star formation is also not fully understood, the presence of strong ultraviolet radiation is one potential method of quenching, as it prevents gas from collapsing into stars.

    If you emit it then you shoulda put a ring on it

    A defining characteristic of LAEs is their ionizing emission in the ultraviolet wavelength range. This radiation can come from ongoing star formation and/or an active central supermassive black hole. From their prominent Lyman-alpha emission lines, LAEs can be selected either via precise spectroscopic observations or through narrow band imaging, which uses a filter to take an image while only collecting light around a specific wavelength range (in other words, a narrow band of the electromagnetic spectrum). If a galaxy has excess brightness in the narrow band image and we have some guess already that the source of the detection is a Lyman-alpha emission line, we can calculate an approximate redshift.

    This paper relies on this technique for a large area narrow band survey with Hyper Suprime-Cam on the Subaru Telescope, which resulted in a large sample of candidate LAEs at z ~ 5.7 and z ~ 6.6.

    These specific redshifts are derived from to the redshifted the Lyman-alpha line corresponding to the wavelength of the narrow band filters used. Once the sample was built, with ~1000 LAEs in each redshift bin, the authors analyzed the number of faint LAEs around bright LAEs (therefore, those with more ionizing radiation) within rings of increasing radius around the central LAE. They then placed these rings at certain distances from the central bright LAE to probe their environments on different scales, from the individual galaxy level to large voids in the cosmic web.

    Why we should care about the environment

    For the z ~ 5.7 sample, the authors found that the density of faint LAEs around the central bright LAEs decreased as the intrinsic brightness of the central galaxy increased (see Figure 1). Their interpretation: central LAEs’ ionizing photons suppress star formation of galaxies around them. With their star formation quenched, the galaxies around them tend to not emit Lyman-alpha, so fewer galaxies in the environment are observed as LAEs. While stronger radiation within smaller rings explains a higher efficiency of suppression of faint LAEs closer in, the authors caution that based on their quick analytical calculations, this physical explanation is not enough to explain the amount of suppression seen here.

    1
    Figure 1. The density of faint LAEs within rings versus the intrinsic brightness of the central bright LAE. The different colors show the varying ring sizes. The left panel shows the z~5.7 sample, with a decrease in density over brightness, and the right shows the z~6.6 sample, with a more constant trend. (Figure 3 in the paper)

    At early times (the higher redshift z ~ 6.6 sample), the picture is slightly different, and the density of faint LAEs tends to be more constant across brightnesses of central LAEs. The authors note that the faint LAEs here could be outside the bubble of ionized gas surrounding the central LAE. Since Lyman-alpha photons are opaque to the neutral hydrogen gas still dominant at early times, galaxies outside the bubble may not be detectable as LAEs. Yet, this scenario is still not enough to explain their findings.

    Left with questions about the underlying physics the authors remind us that the environments of LAEs are subject to complex processes, including feedback from star formation and black hole activity, the timescales of the activity, the motions of the galaxies, metals and dust content, and the opacity of neutral gas to Lyman-alpha photons. Overall, their results support a scenario where fewer LAEs exist around brighter central LAEs, with the suppression of star formation not solely caused by Lyman-alpha photons. Future work is crucial to disentangling all of the complex effects involved in environmental suppression of star formation, but the big picture is that the environment is at work for galaxy formation in the early Universe.

    See the full article here .


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

    Please help promote STEM in your local schools.


    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 12:58 pm on September 6, 2022 Permalink | Reply
    Tags: "Sparkling Stars:: Discovering Evolved Globular Clusters at High Redshift with Webb", Astrobites, , , ,   

    From Astrobites : “Sparkling Stars:: Discovering Evolved Globular Clusters at High Redshift with Webb” 

    Astrobites bloc

    From Astrobites

    9.6.22
    Katya Gozman

    Title: The Sparkler: Evolved High-Redshift Globular Clusters Captured by Webb
    Authors: Lamiya A. Mowla, Kartheik G. Iyer, Guillaume Desprez, Nelson Caldwell, et al.

    First Author’s Institution: Dunlap Institute for Astronomy and Astrophysics, 50 St. George Street, Toronto, Ontario M5S 3H4, Canada

    Status: Submitted to ApJL [open access]

    It’s only been a month, but the James Webb Space Telescope (JWST) has already captured the hearts of millions with its stunning first images of galaxy clusters, massive nebulae, and views of Jupiter like you’ve never seen before. And with the help of these images, scientists are already making record-breaking discoveries, such as the oldest galaxy ever found, detecting water and CO2 in the atmosphere of an alien exoplanet, and spiral galaxies that are red and dead. These images are a seemingly endless treasure trove of information, and the authors of today’s paper have unearthed some shiny stars in JWST’s first and deepest image.

    That image is of the large galaxy cluster SMACS J0723 (shown below).

    1
    Figure 1: a) a Webb image of SMACS J0723, the galaxy cluster lensing the Sparkler. Credit: NASA, ESA, CSA, and STScI. b) The leftmost image is the Sparkler’s three lensed images inside SMACS J0723, the other three show the three images in detail. Their positions are numerically labeled in the leftmost subplot. Figure 1 in the paper.

    This giant cluster exhibits a phenomena called strong gravitational lensing: it is so massive that it acts like a magnifying glass, bending the light of much more distant objects so strongly that astronomers can see and detect light from sources that are too far away to see otherwise.

    There are hundreds of lensed objects in the JWST image, but a particularly glittery one caught the authors’ eye: a lensed galaxy surrounded by lots of bright points of light that they aptly named “the Sparkler”, shown below in Figure 1.

    If you look at Figure 1, you might think that you’re looking at 3 different objects, none of which look like the typical galaxies you might be used to seeing. Due the wacky geometry of how light bends around massive objects, a lensed galaxy frequently appears like it’s been stretched out from its original disk-like form, and usually we see multiple images of the same galaxy in different positions around the lensing cluster. In this case, we see three images of the Sparkler, the second image being magnified by a factor of anywhere from 10-100x! The authors were interested in figuring out the nature of the point sources surrounding the galaxy – are these highly concentrated conglomerations of stars we call globular clusters, or very dense clumps of stars that are actively forming?

    Shine Bright like a Sparkle

    In order to answer this question, the authors used imaging and spectra taken from JWST in tandem. Their first step was to select candidate “sparkles” around the galaxy in regions that are uncontaminated by other sources. They then performed aperture photometry on these sources in different filters – drawing a circle around each source and using an algorithm that measures how much light it emits in different wavelengths. This is a measure of a sparkle’s magnitude in various filters. Since the Sparkler is in a very dense region, the authors also injected fake point sources with known fluxes into the images to see how well the algorithm could recover their true fluxes while being in a crowded field.

    After finding how much light each source emits, they used that information to make a spectral energy distribution (SED) for each individual sparkle. An SED shows us a plot of how much energy a certain object emits in different wavelengths and can tell us about properties such as age, metallicity, mass, and star formation history of an object.

    Each sparkle is labeled in Figure 2 below. The authors IDed them using Image 2, and labeled some of the sparkles’ potential counterparts in Images 1 and 3. Since they figured out each sparkles’ magnitude in different filters, they then measured the difference between different magnitudes – a quantity astronomers call color. They then plotted the colors of each sparkle, along with the color of the Sparkler galaxy itself, in a color-color diagram (Fig 3). Plotting a bunch of sources on such a diagram usually leads to a pattern – sources that are quiescent (no on-going star-formation) will fall along the “red cloud”: an area at the top with redder colors (hence why we sometimes call quiescent galaxies “red and dead”), while sources that are actively star-forming will be at the bottom in the “blue cloud”. Sparkler itself, along with 7 of its sparkles, fall in the blue star-forming region, while 5 of the sparkles fall in the red quiescent region.

    2
    Figure 2: The 12 sparkles the authors chose to analyze identified in Image 2 (center). Their possible counterparts are labeled for Images 1 and 3 (left and right, respectively). Part of Figure 3a in the paper, modified by Katya Gozman.

    Using a program called GALFIT to model the structure and brightness of these 5 red sources, the authors found that they are compact and unresolved by Webb. From the SED model, they also found that these sources were actively star forming very early on in their formation history at extremely high redshifts of z = 7-9. They also looked at spectra of the Sparkler and measured the strength of the [OIII] emission line – an indicator of recent star formation – in its three images. This emission appears in all three images of the Sparkler, but is absent in the locations of the red sparkles they marked earlier.

    3
    Figure 3: A color-color diagram. The gray points are galaxies at comparable redshift to the Sparkler in the COSMOS2020 catalog. The blue point is the Sparkler galaxy itself, the orange points are 7 sparkles that are star-forming, and the pink points are the 5 sparkles that are evolved globular cluster candidates. Figure 3c in the paper.

    Baby You’re a Firework

    All these pieces of evidence – the sparkles’ red colors, unresolved structures appearing in multiple images, and no [OIII] emission – all point to these five sources being old, quiescent globular clusters associated with their host galaxy. This means that these clusters are evolved systems and, from their star-formation histories, most likely formed only 0.5 Gyr after the Big Bang! This would make these sparkles the first ever found globular clusters to have shut off their star formation so early in their evolutionary history.

    The authors do warn that there are some caveats to these results. The conclusion that these sparkles are evolved globular clusters depends on the exact magnification of the Sparkler which the authors have yet to determine, so it is possible that a different magnification could yield a different measurement of the sparkles’ mass and put them outside the possible mass range for globular clusters. They also note that results from SED modeling should be taken with a grain of salt as astronomers are very early in the process of understanding how best to calibrate JWST data.

    Despite these limitations, the possibility that we’re seeing such systems extremely early in our universe’s history is exciting. If the ages the authors found for the clusters are correct, this indicates that some of these clusters formed at the time as cosmic reionization, the era when the first galaxies were forming and radiating enough energy to turn neutral gas into ionized gas.

    The specific mechanism by which reionization happened is still a mystery, and this work may provide a link between globular clusters and galaxy formation. Astronomers are also still trying to piece together how globular clusters themselves form, so these sparkles can hopefully ignite a new stage in globular cluster research and establish our hunt for systems at the earliest stages of their lives.

    See the full article here .


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

    Please help promote STEM in your local schools.


    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 2:21 pm on September 2, 2022 Permalink | Reply
    Tags: "Webb takes a peek at the first ever galaxies", A large galaxy cluster called SMACS 0723, Astrobites, , , ,   

    From Astrobites and The NASA/ESA/CSA James Webb Space Telescope: “Webb takes a peek at the first ever galaxies” 

    Astrobites bloc

    From Astrobites

    and

    NASA Webb Header

    National Aeronautics Space Agency/European Space Agency [La Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganisation](EU)/ Canadian Space Agency [Agence Spatiale Canadienne](CA) James Webb Infrared Space Telescope annotated, finally launched December 25, 2021, ten years late.

    The NASA/ESA/CSA James Webb Space Telescope

    9.3.22
    Roan Haggar

    Title: Panic! At the Disks: First Rest-frame Optical Observations of Galaxy Structure at z>3 with JWST in the SMACS 0723 Field

    Authors: Leonardo Ferreira, Nathan Adams, Christopher J. Conselice, Elizaveta Sazonova, Duncan Austin, Joseph Caruana, Fabricio Ferrari, Aprajita Verma, James Trussler, Tom Broadhurst, Jose Diego, Brenda L. Frye, Massimo Pascale, Stephen M. Wilkins, Rogier A. Windhorst, Adi Zitrin

    First Author’s Institution: University of Nottingham, Nottingham, UK

    Status: Accepted to The Astrophysical Journal Letters, available on arXiv

    Ever since the first data release of the James Webb Space Telescope (JWST) in July, it has become clear that this telescope is going to completely transform our view of the distant Universe. Galaxies that looked like featureless blobs when viewed through the Hubble Space Telescope can now be resolved in incredible detail (see Figure 1), despite the fact that Hubble has been one of the world’s leading telescopes for the past 30 years.

    1
    Figure 1: Four galaxies from the SMACS 0723 field (the focus of today’s paper), as seen by the Hubble Space Telescope (left) and the James Webb Space Telescope (right). Each one displays features that were undetected with Hubble, but can easily be seen with Webb. Credit: NASA/ESA/STScI.

    Being able to measure the shapes of galaxies (known as their morphology) is vital if we want to understand how galaxies, including our own, were formed. Galaxies typically come in two shapes: thin, delicate disk-shaped galaxies, and spheroid-shaped elliptical galaxies, but it is still not really clear how and when these different galactic structures emerged. Today’s paper uses early JWST observations of a large galaxy cluster called SMACS 0723, to measure the shapes of very distant galaxies. With this exciting new data, the authors hope to expand our knowledge of galaxy evolution all the way to the very dawn of our Universe.

    2
    SMACS 0723 via Webb

    Zooming in on the first galaxies

    This photo of SMACS 0723 is one of the first images to be released from JWST. The cluster is located about four billion light years away at a redshift of 0.4, but today’s paper actually looks at even more distant galaxies, in the background of this image — many of these have been magnified by the gravitational lensing of the cluster.

    Specifically, it looks at 280 background galaxies at redshifts between 1.5 and 8, meaning we are seeing them just 1-4 billion years after the beginning of the Universe.

    The authors firstly measure galaxy shapes using quantitative properties of galaxies, such as their concentration and asymmetry. Their really exciting findings, however, come from classifying these galaxies by eye, splitting them into three categories: disks, spheroids, and “peculiars”.

    Galaxies in this third class have an irregular shape, which can be caused by processes such as starbursts or tidal interactions. Alternatively, collisions between galaxies (known as “galaxy mergers“) that are currently in-progress can lead to these “peculiar” galaxies. These violent events are thought to play a major role in galaxy evolution: in the early Universe mergers allow large amounts of mass to clump together, which can later form a galactic disk. Later on, they can destroy these fragile disk structures, turning disk galaxies into featureless ellipticals.

    It turns out that at high redshifts (between 3 and 6), about half of galaxies have a disk shape (Figure 2). This is much higher than we previously thought — the data from the Hubble telescope shows that it found a disk fraction of less than 10% at similar redshifts! Interestingly, according to JWST, the disk fraction also stays roughly constant across the whole range of redshifts.

    3
    Figure 2: Fraction of spheroid, disk, and peculiar galaxies at different redshifts, measured with JWST in today’s paper, and with Hubble (HST) in previous work. The trends found by Hubble had predicted the number of disks would decrease at redshifts greater than three, and that most galaxies would be peculiar. JWST shows that this is not the case. Figure 4 in today’s paper.

    A less turbulent Universe?

    Our current idea that mergers assemble galaxies in the early Universe means that we would expect to find lots of peculiar galaxies and few disks at high redshift, as these disks are still in the process of forming. However, the near-constant disk fraction found in this study indicates that disk galaxies (like the Milky Way) have existed in a fairly stable state for more than 10 billion years, seemingly contradicting our old ideas.

    So what’s going on? There are several ways to interpret these results. It could be that almost all mergers occur extremely early in the Universe, quickly forming disk galaxies, and that these disks survive until the present day because recent mergers are far less common than our current theories suggest. Alternatively, it could be that only some classes of galaxies are built up by mergers, or even that mergers are simply far less likely to destroy disk structures than we previously thought.

    Whatever the case, it indicates that we may need to refine current theoretical ideas about how galaxies assemble and evolve through mergers, which is one of the key predictions of our widely-accepted model of the Universe (the Lambda cold dark matter, or ΛCDM, model).

    Some articles based on this work have gone a step further, stating that this research disproves ΛCDM, or even the Big Bang. However, despite the homage to noughties emo-pop in the title of this paper, there’s really no reason to panic. Tuning and re-tuning theories to fit new data is a normal part of the scientific process. In fact, this paper is exciting: it tells us that we still do not truly know where galactic structure came from, but that new science carried out using this new telescope will finally give us a chance to understand the origins and lives of galaxies.

    See the full article here.


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

    Please help promote STEM in your local schools.


    Stem Education Coalition

    The NASA/ESA/CSA James Webb Space Telescope is a large infrared telescope with a 6.5-meter primary mirror. Webb was finally launched December 25, 2021, ten years late. The James Webb Space Telescope will be the premier observatory of the next decade, serving thousands of astronomers worldwide. It will study every phase in the history of our Universe, ranging from the first luminous glows after the Big Bang, to the formation of solar systems capable of supporting life on planets like Earth, to the evolution of our own Solar System.

    The James Webb Space Telescope is the world’s largest, most powerful, and most complex space science telescope ever built. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it.

    Webb telescope will be the premier observatory of the next decade, serving thousands of astronomers worldwide. It will study every phase in the history of our Universe, ranging from the first luminous glows after the Big Bang, to the formation of solar systems capable of supporting life on planets like Earth, to the evolution of our own Solar System.

    Webb telescope was formerly known as the “Next Generation Space Telescope” (NGST); it was renamed in Sept. 2002 after a former NASA administrator, James Webb.

    Webb is an international collaboration between National Aeronautics and Space Administration, the European Space Agency (ESA), and the Canadian Space Agency (CSA). The NASA Goddard Space Flight Center managed the development effort. The main industrial partner is Northrop Grumman; the Space Telescope Science Institute will operate Webb after launch.

    Several innovative technologies have been developed for Webb. These include a folding, segmented primary mirror, adjusted to shape after launch; ultra-lightweight beryllium optics; detectors able to record extremely weak signals, microshutters that enable programmable object selection for the spectrograph; and a cryocooler for cooling the mid-IR detectors to 7K.

    There are four science instruments on Webb: The Near InfraRed Camera (NIRCam), The Near InfraRed Spectrograph (NIRspec), The Mid-InfraRed Instrument (MIRI), and The Fine Guidance Sensor/ Near InfraRed Imager and Slitless Spectrograph (FGS-NIRISS). Webb’s instruments are designed to work primarily in the infrared range of the electromagnetic spectrum, with some capability in the visible range. It will be sensitive to light from 0.6 to 28 micrometers in wavelength.
    National Aeronautics Space Agency Webb NIRCam.

    The European Space Agency [La Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganisation](EU) Webb MIRI schematic.

    Webb Fine Guidance Sensor-Near InfraRed Imager and Slitless Spectrograph FGS/NIRISS.

    Webb has four main science themes: The End of the Dark Ages: First Light and Reionization, The Assembly of Galaxies, The Birth of Stars and Protoplanetary Systems, and Planetary Systems and the Origins of Life.

    Launch was December 25, 2021 on an Ariane 5 rocket. The launch was from Arianespace’s ELA-3 launch complex at European Spaceport located near Kourou, French Guiana. Webb is located at the second Lagrange point, about a million miles from the Earth.

    ESA50 Logo large

    Canadian Space Agency

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 10:37 am on September 1, 2022 Permalink | Reply
    Tags: "Webb’s First Directly Imaged Exoplanet", Astrobites, , , , , The exoplanet HIP 65426 b is a Super-Jupiter sized planet that was already known to us originally discovered with ground-based observations around 2017.   

    From Astrobites And The NASA/ESA/CSA James Webb Space Telescope: “Webb’s First Directly Imaged Exoplanet” 

    Astrobites bloc

    From Astrobites

    And

    The NASA/ESA/CSA James Webb Space Telescope

    9.1.22
    Briley Lewis

    Title: JWST Early Release Science: High Contrast Imaging of the Exoplanet HIP 65426 b from 2−16 µm

    Authors: A. L. Carter, S. Hinkley, J. Kammerer, et al.

    First author’s institution: The University of California-Santa Cruz

    Status: Open access

    This has been the summer of JWST. NASA’s newest major space telescope — a huge step up in size and capabilities from past observatories — finally began its science observations in June after a lengthy commissioning process. So far, we’ve seen stunning vistas of star forming nebulae and an incredible deep field showing lensed galaxies in JWST’s first images. Now, we’re starting to get exciting results from the Early Release Science (ERS) teams, who proposed creative ways to use the telescope in its first few months of observations, such as insight into some of the oldest galaxies we’ve seen.

    Although JWST is somewhat known for its galaxy-hunting capabilities since mid-infrared observations allow us to see the distant redshifted parts of the Universe, it’s also going to be incredible for exoplanet science. One of the first “images” released was a transit spectrum of WASP-96b’s steam-filled atmosphere, and a recent ERS result made the first unambiguous detection of CO2 in its atmosphere, too.

    1
    NASA’s James Webb Space Telescope has captured the distinct signature of water, along with evidence for clouds and haze, in the atmosphere surrounding a hot, puffy gas giant planet orbiting a distant Sun-like star.

    The observation, which reveals the presence of specific gas molecules based on tiny decreases in the brightness of precise colors of light, is the most detailed of its kind to date, demonstrating Webb’s unprecedented ability to analyze atmospheres hundreds of light-years away.

    While the Hubble Space Telescope has analyzed numerous exoplanet atmospheres over the past two decades, capturing the first clear detection of water in 2013, Webb’s immediate and more detailed observation marks a giant leap forward in the quest to characterize potentially habitable planets beyond Earth.

    WASP-96 b is one of more than 5,000 confirmed exoplanets in the Milky Way. Located roughly 1,150 light-years away in the southern-sky constellation Phoenix, it represents a type of gas giant that has no direct analog in our solar system. With a mass less than half that of Jupiter and a diameter 1.2 times greater, WASP-96 b is much puffier than any planet orbiting our Sun. And with a temperature greater than 1000°F, it is significantly hotter. WASP-96 b orbits extremely close to its Sun-like star, just one-ninth of the distance between Mercury and the Sun, completing one circuit every 3½ Earth-days.

    The combination of large size, short orbital period, puffy atmosphere, and lack of contaminating light from objects nearby in the sky makes WASP-96 b an ideal target for atmospheric observations.

    On June 21, Webb’s Near-Infrared Imager and Slitless Spectrograph (NIRISS)[below] measured light from the WASP-96 system for 6.4 hours as the planet moved across the star. The result is a light curve showing the overall dimming of starlight during the transit, and a transmission spectrum revealing the brightness change of individual wavelengths of infrared light between 0.6 and 2.8 microns.

    While the light curve confirms properties of the planet that had already been determined from other observations – the existence, size, and orbit of the planet – the transmission spectrum reveals previously hidden details of the atmosphere: the unambiguous signature of water, indications of haze, and evidence of clouds that were thought not to exist based on prior observations.

    A transmission spectrum is made by comparing starlight filtered through a planet’s atmosphere as it moves across the star to the unfiltered starlight detected when the planet is beside the star. Researchers are able to detect and measure the abundances of key gases in a planet’s atmosphere based on the absorption pattern – the locations and heights of peaks on the graph. In the same way that people have distinctive fingerprints and DNA sequences, atoms and molecules have characteristic patterns of wavelengths that they absorb.

    The spectrum of WASP-96 b captured by NIRISS is not only the most detailed near-infrared transmission spectrum of an exoplanet atmosphere captured to date, but it also covers a remarkably wide range of wavelengths, including visible red light and a portion of the spectrum that has not previously been accessible from other telescopes (wavelengths longer than 1.6 microns). This part of the spectrum is particularly sensitive to water as well as other key molecules like oxygen, methane, and carbon dioxide, which are not immediately obvious in the WASP-96 b spectrum but which should be detectable in other exoplanets planned for observation by Webb.

    Researchers will be able to use the spectrum to measure the amount of water vapor in the atmosphere, constrain the abundance of various elements like carbon and oxygen, and estimate the temperature of the atmosphere with depth. They can then use this information to make inferences about the overall make-up of the planet, as well as how, when, and where it formed. The blue line on the graph is a best-fit model that takes into account the data, the known properties of WASP-96 b and its star (e.g., size, mass, temperature), and assumed characteristics of the atmosphere.

    The exceptional detail and clarity of these measurements is possible because of Webb’s state-of-the-art design. Its 270-square-foot gold-coated mirror collects infrared light efficiently. Its precision spectrographs spread light out into rainbows of thousands of infrared colors. And its sensitive infrared detectors measure extremely subtle differences in brightness. NIRISS is able to detect color differences of only about one thousandth of a micron (the difference between green and yellow is about 50 thousandths of a micron), and differences in the brightness between those colors of a few hundred parts per million.

    In addition, Webb’s extreme stability and its orbital location around Lagrange Point 2 roughly a million miles away from the contaminating effects of Earth’s atmosphere makes for an uninterrupted view and clean data that can be analyzed relatively quickly.

    The extraordinarily detailed spectrum – made by simultaneously analyzing 280 individual spectra captured over the observation – provides just a hint of what Webb has in store for exoplanet research. Over the coming year, researchers will use spectroscopy to analyze the surfaces and atmospheres of several dozen exoplanets, from small rocky planets to gas- and ice-rich giants. Nearly one-quarter of Webb’s Cycle 1 observation time is allocated to studying exoplanets and the materials that form them.

    This NIRISS observation demonstrates that Webb has the power to characterize the atmospheres of exoplanets—including those of potentially habitable planets—in exquisite detail.

    JWST is also going to do wonders for direct imaging — the notoriously tricky way of detecting exoplanets, where we actually resolve light from the exoplanet itself instead of observing the host star. The NIRCam [below] and MIRI [below] instruments have coronagraphs, small optics that block the light from a bright host star so you can see the comparatively faint planets orbiting them. NIRISS [below] also has the ability to do a cutting-edge technique called non-redundant aperture masking and NIRSpec [below] and MIRI have a type of instrument called an Integral Field Unit (IFU), all of which can help directly detect planets. Lucky for us (or more accurately, thanks to the folks who planned this mission), it’s also easier to directly detect exoplanets in the infrared, making JWST extremely well-suited to this task.

    The JWST Direct Imaging ERS team (ERS-1386) is now testing out these direct imaging capabilities, with the goal of determining how well these modes of observing are performing and coming up with advice for observers who want to use these modes in the future. The expectation is that JWST will be able to image planets smaller than Jupiter — which is a big deal! So far, we haven’t been able to spot a planet smaller than ~2 Jupiter masses from the ground.

    In today’s bite, we share a hot-off-the-presses result from the JWST Direct Imaging ERS Team: the first directly imaged exoplanet observed with JWST, HIP 65426 b. This is also the first direct detection (ever!) of an exoplanet at wavelengths longer than 5 microns.

    2
    Newly released image of HIP 65426 b in multiple wavelength bands, as seen by JWST NIRCam and MIRI. Image from A. Carter (UCSC) NASA/ESA/CSA, , the JWST ERS 1386 team, and A. Pagan (STScI).

    HIP 65426 b is a Super-Jupiter sized planet that was already known to us originally discovered with ground-based observations around 2017. It’s part of the Lower Centaurus-Crux association, a grouping of stars that were all born near each other, including the relatively famous PDS 70 b. Moving group associations like this make it possible for us to estimate stellar ages — for example, HIP 65426 is around 14 million years old. This star and its planetary companion were chosen as a relatively easy target to test out JWST’s capabilities, and see what more we could learn about this planet! The team observed it with NIRCam, which covers 2 to 5 microns across five different filters, and MIRI, covering 11-16 microns over two filters — and it was detected in all seven filters, as seen below.

    3
    HIP 65426 b as seen by NIRCam and MIRI in seven different filters, after data processing and PSF subtraction using ADI+RDI KLIP. Figure 8 from the paper.

    The “hamburger-like” shape in some of the wavelengths is an expected effect, just an artifact from the Lyot stop (part of the coronagraph). There aren’t actually multiple real sources there, unfortunately! In addition to the images, the team presented astrometry, photometry, model fits, and more for this observation.

    Since JWST has such a large span of wavelength coverage in the infrared, they were able to constrain this exoplanet’s bolometric luminosity (its energy output across all wavelengths) like never before. No matter what model atmosphere they used, their result was the same thanks to the incredible data they had on hand! Their photometry of the planet was also incredibly precise — 7% precision for NIRCam and 16% for MIRI, compared to the ground-based observations of this star at 13-32% precision. The team also investigated the planet’s spectral energy distribution (SED) using the new photometry, alongside old measurements, shown below.

    3
    SED for HIP 65436 b including existing data from VLT/SPHERE and VLT/NACO, plus the new data from JWST presented in this work. An atmospheric model fit is shown in blue, with the residual error between the best fit model and the data on the bottom. Figure 9 from the paper.

    Using models of the planet’s thermal evolution and atmospheric models, they derived the mass (7.1 Jupiter masses), temperature (1282 K), and radius (1.45 Jupiter radii) of HIP 65426 b. The constraint on radius is ~3x more precise than before the JWST data! They also fit for the planet’s orbit using the package orbitize! and found a semi-major axis of 87 AU and inclination of 100 degrees, which agrees with but doesn’t significantly improve on past measurements.

    To further quantify just how well JWST is doing things, they computed contrast curves for these observations, shown below. Contrast curves show the contrast (how faint of a planet you can detect, compared to its star, at 5 sigma confidence) versus the separation (how far the planet is from the star). So far, JWST appears to be outperforming expectations by about a factor of 10!

    4
    Contrast curves from JWST observations of HIP 65426 b, shown as the black lines. Different line styles represent different data processing (ADI, RDI, ADI+RDI). The vertical dashed red line shows the inner working angle defined by the coronagraphic mask, and the blue lines are previous predictions of JWST’s capabilities using a package called PanCAKE. Excitingly, JWST is outperforming the predictions! Figure 5 from the paper.

    The team also estimated what kinds of planets JWST would be able to detect around this star. From their calculations, NIRCam can easily find a sub-Jupiter mass planet between 150-2000 AU from its star, and might be able to find something as small as 0.4 Jupiter masses. That’s still about 120x bigger than an Earth-like planet, but it’s significantly smaller than what we’ve been able to find with direct imaging before! MIRI is a little less sensitive, able to detect 1-2 Jupiter mass planets from 150-2000 AU.

    5
    Diagrams (often called “tongue plots”) showing the detectable masses and semi-major axes of planets with NIRCam (top) and MIRI (bottom), for the most sensitive filter according to these observations. Figure 6 from the paper.

    Since one of the goals of the ERS program is to make recommendations for best use of the instruments going forward, we’re going to describe a few of these technical pieces of advice here, too. If technical details of coronagraphs are not your jam, feel free to skip this next paragraph!

    One of the tricky parts of direct imaging is always aligning the coronagraph to perfectly cover the star, and they report that coronagraph alignment is still being perfected for NIRCam, whereas the MIRI procedure is further refined, accurate down to 0.1 pixels. The other notorious step of direct imaging is data processing, and this team tried both reference star differential imaging (RDI) and angular differential imaging (ADI) from different “rolls” of the spacecraft. They ended up using a combo of ADI and RDI for this paper, but suggest that future observations can just pick one or the other depending on their needs. RDI worked better in this case, but ADI may be better for wider separations. To do the data processing, they used spaceKLIP, an adaptation of pyKLIP, an image processing algorithm widely used for direct imaging work.

    There is so much more to come with JWST observations, especially in the realm of direct imaging. For example, the authors suggest that for fainter M-type stars, JWST may be able to image even smaller planets than estimated in this investigation. They say in the paper, “It will be possible to detect Uranus and Neptune mass objects beyond 100−200 AU, and Saturn mass objects beyond ∼10 AU [around M dwarfs].” They also mention that JWST’s incredibly precise infrared data might allow measurements of CH4 and CO, providing a fascinating window into the complex chemistry of giant planet atmospheres.

    This result is clearly a harbinger (and a thrilling one at that!) of much more to come — the team even mentions other ERS results coming soon, including a different look into HIP 65426 b, observations of a circumstellar disk, and spectroscopy of another substellar object. Direct imaging, welcome to the era of JWST!

    See the full article here .


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    Please help promote STEM in your local schools.


    Stem Education Coalition

    NASA Webb Header

    National Aeronautics Space Agency/European Space Agency [La Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganisation](EU)/ Canadian Space Agency [Agence Spatiale Canadienne](CA) James Webb Infrared Space Telescope annotated, finally launched December 25, 2021, ten years late.

    The NASA/ESA/CSA James Webb Space Telescope is a large infrared telescope with a 6.5-meter primary mirror. Webb was finally launched December 25, 2021, ten years late. The James Webb Space Telescope will be the premier observatory of the next decade, serving thousands of astronomers worldwide. It will study every phase in the history of our Universe, ranging from the first luminous glows after the Big Bang, to the formation of solar systems capable of supporting life on planets like Earth, to the evolution of our own Solar System.

    The James Webb Space Telescope is the world’s largest, most powerful, and most complex space science telescope ever built. Webb will solve mysteries in our solar system, look beyond to distant worlds around other stars, and probe the mysterious structures and origins of our universe and our place in it.

    Webb telescope will be the premier observatory of the next decade, serving thousands of astronomers worldwide. It will study every phase in the history of our Universe, ranging from the first luminous glows after the Big Bang, to the formation of solar systems capable of supporting life on planets like Earth, to the evolution of our own Solar System.

    Webb telescope was formerly known as the “Next Generation Space Telescope” (NGST); it was renamed in Sept. 2002 after a former NASA administrator, James Webb.

    Webb is an international collaboration between National Aeronautics and Space Administration, the European Space Agency (ESA), and the Canadian Space Agency (CSA). The NASA Goddard Space Flight Center managed the development effort. The main industrial partner is Northrop Grumman; the Space Telescope Science Institute will operate Webb after launch.

    Several innovative technologies have been developed for Webb. These include a folding, segmented primary mirror, adjusted to shape after launch; ultra-lightweight beryllium optics; detectors able to record extremely weak signals, microshutters that enable programmable object selection for the spectrograph; and a cryocooler for cooling the mid-IR detectors to 7K.

    There are four science instruments on Webb: The Near InfraRed Camera (NIRCam), The Near InfraRed Spectrograph (NIRspec), The Mid-InfraRed Instrument (MIRI), and The Fine Guidance Sensor/ Near InfraRed Imager and Slitless Spectrograph (FGS-NIRISS). Webb’s instruments are designed to work primarily in the infrared range of the electromagnetic spectrum, with some capability in the visible range. It will be sensitive to light from 0.6 to 28 micrometers in wavelength.
    National Aeronautics Space Agency Webb NIRCam.

    The European Space Agency [La Agencia Espacial Europea] [Agence spatiale européenne][Europäische Weltraumorganisation](EU) Webb MIRI schematic.

    Webb Fine Guidance Sensor-Near InfraRed Imager and Slitless Spectrograph FGS/NIRISS.

    Webb has four main science themes: The End of the Dark Ages: First Light and Reionization, The Assembly of Galaxies, The Birth of Stars and Protoplanetary Systems, and Planetary Systems and the Origins of Life.

    Launch was December 25, 2021 on an Ariane 5 rocket. The launch was from Arianespace’s ELA-3 launch complex at European Spaceport located near Kourou, French Guiana. Webb is located at the second Lagrange point, about a million miles from the Earth.

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
  • richardmitnick 11:08 am on August 29, 2022 Permalink | Reply
    Tags: "We don’t need Planet 9!", Astrobites, , , ,   

    From Astrobites : “We don’t need Planet 9!” 

    Astrobites bloc

    From Astrobites

    8.29.22
    Sabina Sagynbayeva

    Title: A Lopsided Outer Solar System

    Authors: Alexander Zderic, Maria Tiongco, Angela Collier, Heather Wernke, Aleksey Generozov, Ann-Marie Madigan

    First Author’s Institution: Department of Astrophysical and Planetary Sciences, CU Boulder

    Paper Status: Accepted in ApJ [open access on ApJ]

    We still don’t understand what is going on with the solar-system objects beyond Neptune! No, really, we don’t know much about this region of the solar system. To be fair, these trans-Neptunian objects (TNOs) are weird. Together, they form a disk of icy bodies, called the Kuiper Belt, where some of them, surprisingly, have clustered stable orbits, and others have very unstable orbits due to encounters with Neptune.

    The famous hypothesis that tries to explain the scattering of the TNOs is the hypothesis about Planet 9. The orbits of these TNOs are really hard to explain, because 1) they are too far away and not well-studied 2) we haven’t really had analogies to these kinds of motions. The latter might not be true anymore, because the researchers at CU-Boulder have linked the behavior of these TNOs to the dynamics on a larger scale!

    Physics is the same whether you’re in Africa or in America, you look at the Kuiper Belt or at galaxies. This is the main idea behind today’s paper. The authors decided to use the mechanism that explains stellar bar formation in centers of disk galaxies (the so-called Lynden-Bell mechanism) as an analogy for the dynamics of TNOs. The idea behind this is that galactic bars can be approximated as ellipses that are reminiscent of the lopsided disk that we see in the outer solar system. So, to understand how the outer solar system came to be the way it is right now we need to understand the formation of this lopsided disk. In their previous work [The Astronomical Journal (below)], the authors explained that the main mechanism driving the apsidal clustering (the clustering in perihelia and poles) is the inclination instability, – which exponentially grows the inclinations of orbits while decreasing their eccentricities, raising their perihelia and clustering their arguments of perihelion.

    The authors run a series of N-body simulations of a primordial scattered disk with a different number of objects, and their objects have different semi-major axes from 100 to 1000 AU. They also looked at the simulations with and without the impact from giant planets (such as Jupiter) on the TNOs. Apsidal clustering in their simulations occurs after a Lynden-Bell clustering region appears. What they found is that apsidal clustering occurs because of the inclination instability, and that this inclination instability is key to the formation of the lopsided disk. In Figure 1, they show the results of the simulation with 400 objects without the impact from giant planets. In the top panels, the apsidal precession starts when the curve goes above the gray line. Only the orange curve goes above the gray area, and this tells us that apsidal clustering only forms near the inner edge of the disk in the 100–320 AU. This matches the growth in the middle panel where the inclination instability is the strongest. In the simulations with the giant planets, the results show a weaker clustering. In these simulations, the inclination instability is also slowed down due to the giant planets, and therefore, the apsidal clustering appears at later times.

    1
    Figure 1. Model with 400 objects and not impact from giant planets. Apsidal clustering occurring at the inner edge of the disk. The inclination instability is shown by exponential growth in the middle panel. At t ~ 125 t_sec, the instability is saturated. About 25 t_sec later, the in-plane apsidal clustering appears. About 50 tsec later, slight in-plane apsidal clustering appears in the next bin of semi-major axes. Figure 1 in the paper.

    2
    The visualization of the bowl-shape structure of the scattered disk. Figure 9 in the paper.

    In Figure 2, the x-axis shows the eccentricity and the y-axis shows the semi-major axis. The colors show the region where the apsidal clustering appears for the model without the giant planets (more precisely, the colors show the time derivative of the longitude of the pericenter). The clustering region is the region where the colors switch from warmer to cooler colors. You can see how initially, all bodies in the scattered disk are on one line (left panel). Later (right panel), the inclination instability reduces the disk orbits’ eccentricity at roughly fixed semi-major axis and causes the disk to buckle into a bowl-shape. However, at later times, the authors notice that the clustering will disappear and then appear again. Once apsidal clustering has been established and the lopsided mode has grown, it is no longer reliant on the clustering region produced by the bowl-shape to exist. The bowl-shaped distribution oscillates back and forth across the original plane of the disk, causing the clustering region to repeatedly disappear and reappear, and eventually, the bowl-shape disappears. However, the lopsided mode created by the clustering region persists. The authors hypothesize that the mode eventually becomes massive enough to trap orbits without the help of the background disk.The general features found in this model are repeated in the model where the impact from giant planets is added.

    3
    Figure 2. Model with 400 objects and not impact from giant planets. The eccentricity and semi-major axis of the disk particles are shown with black points. There is a clustering region at t = 104 t_sec and t = 151 t_sec for eccentricities between 0.25 and 0.60, and it is associated with the bowl-shaped orbital configuration (see above) created by the inclination instability. Figure 5 in the paper.

    Trying to see if we actually see this lopsided disk in the observations of debris disks, the authors conclude that the structure in their simulations is reminiscent of some observed debris disks (e.g. of the star HD 61005). They also notice that later, the lopsided mode creates spiral arms. Observational signatures like this in exoplanet disks could be caused by the inclination instability provided there is something to pump-up the orbital eccentricity of the bodies in the disk (e.g. a giant planet).

    The authors of today’s paper modeled the structure of bodies beyond the orbit of Neptune. Even though we would love to have more planets in the solar system, the existence of Planet 9 is still questionable! The authors of today’s paper question whether the clustering of TNOs can be explained using a different model. So, they made models to explain the clustering with inclination instability. Though the models work well and actually show the clustering, there are still some caveats: the clustering appears only for bodies with lower semi-major axes and the number of bodies they used in the simulations might not be large enough! This is how science gets done – we start with simpler models that work and then extend them for more generalized cases. Stay tuned for the authors’ newer models that they’re working on right now!

    Science paper:
    The Astronomical Journal

    See the full article here .


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

    Please help promote STEM in your local schools.


    Stem Education Coalition

    What do we do?

    Astrobites is a daily astrophysical literature journal written by graduate students in astronomy. Our goal is to present one interesting paper per day in a brief format that is accessible to undergraduate students in the physical sciences who are interested in active research.
    Why read Astrobites?

    Reading a technical paper from an unfamiliar subfield is intimidating. It may not be obvious how the techniques used by the researchers really work or what role the new research plays in answering the bigger questions motivating that field, not to mention the obscure jargon! For most people, it takes years for scientific papers to become meaningful.

    Our goal is to solve this problem, one paper at a time. In 5 minutes a day reading Astrobites, you should not only learn about one interesting piece of current work, but also get a peek at the broader picture of research in a new area of astronomy.

     
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