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  • richardmitnick 4:55 pm on January 21, 2020 Permalink | Reply
    Tags: "Global Gaia campaign reveals secrets of stellar pair", , , , , , Gaia16aye, gravitational microlensing   

    From European Space Agency – United space in Europe: “Global Gaia campaign reveals secrets of stellar pair” 

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    From European Space Agency – United space in Europe

    From United Space in Europe

    January 21, 2020
    Łukasz Wyrzykowski (pron. Woo-cash Vi-zhi-kov-ski)
    Gaia Photometric Science Alerts Team
    Astronomical Observatory
    University of Warsaw
    Warsaw, Poland
    Email: lw@astrouw.edu.pl

    Przemek Mróz (pron. Pshe-mek Mrooz)
    California Institute of Technology
    Pasadena, CA, USA
    Email: pmroz@astrouw.edu.pl

    Simon Hodgkin
    Gaia Photometric Science Alerts Team
    Institute of Astronomy
    Cambridge, UK
    Email: sth@ast.cam.ac.uk

    Timo Prusti
    Gaia Project Scientist
    European Space Agency
    Email: tprusti@cosmos.esa.int


    A 500-day global observation campaign spearheaded more than three years ago by ESA’s galaxy-mapping powerhouse Gaia has provided unprecedented insights into the binary system of stars that caused an unusual brightening of an even more distant star.

    The brightening of the star, located in the Cygnus constellation, was first spotted in August 2016 by the Gaia Photometric Science Alerts programme.

    This system, maintained by the Institute of Astronomy at the University of Cambridge, UK, scans daily the huge amount of data coming from Gaia and alerts astronomers to the appearance of new sources or unusual brightness variations in known ones, so that they can quickly point other ground and space-based telescopes to study them in detail. The phenomena may include supernova explosions and other stellar outbursts.

    In this particular instance, follow-up observations performed with more than 50 telescopes worldwide revealed that the source – since then named Gaia16aye – was behaving in a rather strange way.

    “We saw the star getting brighter and brighter and then, within one day, its brightness suddenly dropped,” says Łukasz Wyrzykowski from the Astronomical Observatory at the University of Warsaw, Poland, who is one of the scientists behind the Gaia Photometric Science Alert programme.

    “This was a very unusual behaviour. Hardly any type of supernova or other star does this.”

    Zooming into Gaia16aye

    Łukasz and collaborators soon realised that this brightening was caused by gravitational microlensing – an effect predicted by Einstein’s theory of general relativity, caused by the bending of spacetime in the vicinity of very massive objects, like stars or black holes.

    Gravitational microlensing, S. Liebes, Physical Review B, 133 (1964): 835

    When such a massive object, which may be too faint to be observed from Earth, passes in front of another, more distant source of light, its gravity bends the fabric of spacetime in its vicinity. This distorts the path of light rays coming from the background source – essentially behaving like a giant magnifying glass.
    Gaia16aye is the second micro-lensing event detected by ESA’s star surveyor. However, the astronomers noticed it behaved strangely even for this type of event.

    “If you have a single lens, caused by a single object, there would be just a small, steady rise in brightness and then there would be a smooth decline as the lens passes in front of the distant source and then moves away,” says Łukasz.

    “In this case, not only did the star brightness drop sharply rather than smoothly, but after a couple of weeks it brightened up again, which is very unusual. Over the 500 days of observation, we have seen it brighten up and decline five times.”

    The 500-day global campaign spearheaded by Gaia

    This sudden and sharp drop in brightness suggested that the gravitational lens causing the brightening must consist of a binary system – a pair of stars, or other celestial objects, bound to one another by mutual gravity.

    The combined gravitational fields of the two objects produce a lens with a rather intricate network of high magnification regions. When a background source passes through such regions on the plane of the sky, it lights up, and then dims immediately upon exiting it.

    From the pattern of subsequent brightenings and dimmings, the astronomers were able to deduce that the binary system was rotating at a rather fast pace.

    “The rotation was fast enough and the overall micro-lensing event slow enough that the background star entered the high magnification region, left it and then entered it again,” says Łukasz.

    The long period of observations, which lasted until the end of 2017, and the extensive participation of ground-based telescopes from around the globe enabled the astronomers to gather a large amount of data – almost 25 000 individual data points.

    In addition, the team also made use of dozens of observations of this star collected by Gaia as it kept scanning the sky over the months. These data have undergone preliminary calibration and were made public as part of the Gaia Science Alerts programme.

    From this data set, Łukasz and his colleagues were able to learn a great deal of detail about the binary system of stars.

    “We don’t see this binary system at all, but from only seeing the effects that it created by acting as a lens on a background star, we were able to tell everything about it,” says co-author Przemek Mróz, who was a PhD student at the University of Warsaw when the campaign started, and is currently a postdoctoral scholar at the California Institute of Technology.

    “We could determine the rotational period of the system, the masses of its components, their separation, the shape of their orbits – basically everything – without seeing the light of the binary components.”

    The pair consists of two rather small stars, with 0.57 and 0.36 times the mass of our Sun, respectively. Separated by roughly twice the Earth-Sun distance, the stars orbit around their mutual centre of mass in less than three years.

    “If it wasn’t for Gaia scanning the whole sky and then sending the alerts straight away, we would never have known about this microlensing event,” says co-author Simon Hodgkin from the University of Cambridge, who leads the Gaia Science Alerts programme.

    “Maybe we would have found it later, but then it might have been too late.”

    The detailed understanding of the binary system relied on the extensive observation campaign and on the broad international involvement that the Gaia16aye event attracted.

    “We acknowledge the professional astronomers, amateur astronomers and volunteers from all around the globe who have been observing this event: without the dedication of all those people we wouldn’t have been able to obtain such results,” says Łukasz.

    “Microlensing events like this can shed light on celestial objects that we would otherwise not be able to see,” says Timo Prusti, Gaia Project Scientist at ESA.

    “We are delighted that Gaia’s detection triggered the observation campaign that made this result possible.”

    More information

    “Full Orbital Solution for the Binary System in the Northern Galactic Disk Microlensing Event Gaia16aye” by Ł. Wyrzykowski et al
    Astronomy and Astrophysics.

    See the full article here .

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    The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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  • richardmitnick 3:07 pm on March 1, 2019 Permalink | Reply
    Tags: An unusual microlensing event. The object MOA-2016-BLG-231, , , , , , , , gravitational microlensing, Parallax measurement   

    From Harvard-Smithsonian Center for Astrophysics: “Discovering a Brown Dwarf Binary Star with Microlensing” 

    Harvard Smithsonian Center for Astrophysics

    From Harvard-Smithsonian Center for Astrophysics

    March 1, 2019

    Brown dwarfs are stars less massive than the sun and unable to burn hydrogen.

    Artist’s concept of a Brown dwarf [not quite a] star. NASA/JPL-Caltech

    They comprise (at least in mass) a bridge between planets and stars, and astronomers think that they form and evolve in ways different from either planets or stars. Gravitational microlensing is an excellent method for detecting them because it does not depend on their light, which is dim, but rather their mass.

    Gravitational Lensing NASA/ESA

    Gravitational microlensing, S. Liebes, Physical Review B, 133 (1964): 835

    When the path of light from a star passes by a brown dwarf acting as a lens, it is magnified into a distorted image, like an object seen through the stem of a wineglass, allowing the detection and characterization of the lensing object. Thirty-two brown dwarfs have been detected by microlensing so far. Five are in isolation, but most are in binary systems, companions to faint M-dwarf stars. They provide important constraints on brown dwarf formation scenarios.

    The critical parameter of a brown dwarf is its mass, but it is difficult to measure the mass of a lens using microlensing. Using this method, one measures the magnified and distorted stellar image as it changed in time (it varies as the Earth’s vantage point moves), but the technique offers no handle on the distance, and the larger the distance, the larger is the mass needed to generate the same-sized distortion. Recognizing this problem, scientists had predicted that if it ever became possible to observe a microlensing flash from two well-separated vantage points, a parallax measurement (the apparent angular difference between the positions of the star as seen from the two separated sites) would determine the distance of the dark object. The Spitzer Space Telescope circles the Sun in an Earth-trailing orbit, and is currently 1.66 astronomical units away from Earth (one AU is the average distance of the Earth from the Sun).

    NASA/Spitzer Infrared Telescope

    Spitzer is unique in this capability, and it has in fact been used successfully to measure the parallax distance for hundreds of microlensing events, thereby helping to determine the masses of the lenses.

    CfA astronomers Jennifer Yee and In-Gu Shin were members of a large team of microlensing astronomers who used Spitzer together with ground-based telescopes to study an unusual microlensing event. The object, MOA-2016-BLG-231, is located 9400 light-years away in the disk of our galaxy. The shape of its distorted light curve reveals it probably to be a pair of brown dwarfs of masses approximately twenty-one and nine Jupiter-masses, respectively (the smaller one is right at the lower mass limit for being a brown dwarf rather than a giant planet). This is only the fifth brown dwarf binary system discovered in which both objects are brown dwarfs; improved statistics enable astronomers to address the formation mechanisms needed.

    Science paper:
    “Spitzer Microlensing of MOA-2016-BLG-231L: A Counter-rotating Brown Dwarf Binary in the Galactic Disk,” Sun-Ju Chung et al.”
    The Astrophysical Journal

    See the full article here .

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    The Center for Astrophysics combines the resources and research facilities of the Harvard College Observatory and the Smithsonian Astrophysical Observatory under a single director to pursue studies of those basic physical processes that determine the nature and evolution of the universe. The Smithsonian Astrophysical Observatory (SAO) is a bureau of the Smithsonian Institution, founded in 1890. The Harvard College Observatory (HCO), founded in 1839, is a research institution of the Faculty of Arts and Sciences, Harvard University, and provides facilities and substantial other support for teaching activities of the Department of Astronomy.

  • richardmitnick 10:51 am on December 23, 2018 Permalink | Reply
    Tags: , , , , gravitational microlensing, Planets Outside Our Galaxy, Quasar RX J1131-1231,   

    From Science Alert: “For The First Time Ever, Astronomers Detected Planets Outside Our Galaxy in 2018” 


    From Science Alert

    23 DEC 2018

    RX J1131-1231 split into four images. (NASA/CXC/Univ of Michigan/R.C.Reis et al)

    In an incredible world first, astrophysicists detected multiple planets in another galaxy earlier this year, ranging from masses as small as the Moon to ones as great as Jupiter.

    Given how difficult it is to find exoplanets even within our Milky Way galaxy, this is no mean feat. Researchers at the University of Oklahoma achieved this in February thanks to clever use of gravitational microlensing.

    Gravitational microlensing, S. Liebes, Physical Review B, 133 (1964): 835


    The technique, first predicted by Einstein’s theory of general relativity, has been used to find exoplanets within Milky Way, and it’s the only known way of finding the smallest and most distant planets, thousands of light-years from Earth.

    As a planet orbits a star, the gravitational field of the system can bend the light of a distant star behind it.

    We know what this looks like when it’s just two stars, so when a planet enters the mix, it creates a further disturbance in the light that reaches us – a recognisable signature for the planet.

    So far, 53 exoplanets within the Milky Way have been detected using this method. To find planets farther afield, though, something a little bit more powerful than a single star was required.

    Oklahoma University astronomers Xinyu Dai and Eduardo Guerras studied a quasar 6 billion light-years away called RX J1131-1231, one of the best gravitationally lensed quasars in the sky.

    The gravitational field of a galaxy 3.8 billion light-years away between us and the quasar bends light in such a way that it creates four images of the quasar, which is an active supermassive black hole that’s extremely bright in X-ray, thanks to the intense heat of its accretion disc.

    Using data from NASA’s Chandra X-ray observatory, the researchers found that there were peculiar line energy shifts in the quasar’s light that could only be explained by planets in the galaxy lensing the quasar.

    NASA/Chandra X-ray Telescope

    It turned out to be around 2,000 unbound planets with masses ranging between the Moon and Jupiter, between the galaxy’s stars.

    “We are very excited about this discovery. This is the first time anyone has discovered planets outside our galaxy,” Dai said.

    Of course, we haven’t seen the planets directly, and are unlikely to in the lifetime of anyone alive today. But being able to detect them at all is an incredible testament to the power of microlensing, not to mention being evidence that there are planets in other galaxies.

    Of course, common sense would dictate that planets are out there – but evidence is always nice.

    “This is an example of how powerful the techniques of analysis of extragalactic microlensing can be,” said Guerras.

    “This galaxy is located 3.8 billion light years away, and there is not the slightest chance of observing these planets directly, not even with the best telescope one can imagine in a science fiction scenario.

    “However, we are able to study them, unveil their presence and even have an idea of their masses. This is very cool science.”

    The research was published in The Astrophysical Journal.

    See the full article here .


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  • richardmitnick 12:33 pm on March 1, 2018 Permalink | Reply
    Tags: , , , Can Strongly Lensed Type Ia Supernovae Resolve One of Cosmology’s Biggest Controversies?, , , gravitational microlensing, ,   

    From LBNL: “Can Strongly Lensed Type Ia Supernovae Resolve One of Cosmology’s Biggest Controversies?” 

    Berkeley Logo

    Berkeley Lab

    March 1, 2018
    Linda Vu
    (510) 495-2402

    This composite of two astrophysics simulations shows a Type Ia supernova (purple disc) expanding over different microlensing magnification patterns (colored fields). Because individual stars in the lensing galaxy can significantly change the brightness of a lensed event, regions of the supernova can experience varying amounts of brightening and dimming, which scientists believed would be a problem for cosmologists measuring time delays. Using detailed computer simulations at NERSC, astrophysicists showed that this would have a small effect on time-delay cosmology. (Credit: Danny Goldstein/UC Berkeley)

    Gravitational Lensing NASA/ESA

    NERSC Cray XC40 Cori II supercomputer

    LBL NERSC Cray XC30 Edison supercomputer

    The Genepool system is a cluster dedicated to the DOE Joint Genome Institute’s computing needs. Denovo is a smaller test system for Genepool that is primarily used by NERSC staff to test new system configurations and software.


    PDSF is a networked distributed computing cluster designed primarily to meet the detector simulation and data analysis requirements of physics, astrophysics and nuclear science collaborations.

    In 1929 Edwin Hubble surprised many people – including Albert Einstein – when he showed that the universe is expanding. Another bombshell came in 1998 when two teams of astronomers proved that cosmic expansion is actually speeding up due to a mysterious property of space called dark energy. This discovery provided the first evidence of what is now the reigning model of the universe: “Lambda-CDM,” which says that the cosmos is approximately 70 percent dark energy, 25 percent dark matter and 5 percent “normal” matter (everything we’ve ever observed).

    Until 2016, Lambda-CDM agreed beautifully with decades of cosmological data. Then a research team used the Hubble Space Telescope to make an extremely precise measurement of the local cosmic expansion rate. The result was another surprise: the researchers found that the universe was expanding a little faster than Lambda-CDM and the Cosmic Microwave Background (CMB), relic radiation from the Big Bang, predicted. So it seems something’s amiss – could this discrepancy be a systematic error, or possibly new physics?

    Astrophysicists at Lawrence Berkeley National Laboratory (Berkeley Lab) and the Institute of Cosmology and Gravitation at the University of Portsmouth in the UK believe that strongly lensed Type Ia supernovae are the key to answering this question. And in a new The Astrophysical Journal paper, they describe how to control “microlensing,” a physical effect that many scientists believed would be a major source of uncertainty facing these new cosmic probes. They also show how to identify and study these rare events in real time.

    “Ever since the CMB result came out and confirmed the accelerating universe and the existence of dark matter, cosmologists have been trying to make better and better measurements of the cosmological parameters, shrink the error bars,” says Peter Nugent, an astrophysicist in Berkeley Lab’s Computational Cosmology Center (C3) and co-author on the paper.

    CMB per ESA/Planck


    “The error bars are now so small that we should be able to say ‘this and this agree,’ so the results presented in 2016 [ApJ] introduced a big tension in cosmology. Our paper presents a path forward for determining whether the current disagreement is real or whether it’s a mistake.”

    Better Distance Markers Shed Brighter Light on Cosmic History

    But last year an international team of researchers found an even more reliable distance marker – the first-ever strongly lensed Type Ia supernova [Science]. These events occur when the gravitational field of a massive object – like a galaxy – bends and refocuses passing light from a Type Ia event behind it. This “gravitational lensing” causes the supernova’s light to appear brighter and sometimes in multiple locations, if the light rays travel different paths around the massive object.

    Because different routes around the massive object are longer than others, light from different images of the same Type Ia event will arrive at different times. By tracking time-delay between the strongly lensed images, astrophysicists believe they can get a very precise measurement of the cosmic expansion rate.

    “Strongly lensed supernovae are much rarer than conventional supernovae – they’re one in 50,000. Although this measurement was first proposed in the 1960’s, it has never been made because only two strongly lensed supernovae have been discovered to date, neither of which were amenable to time delay measurements,” says Danny Goldstein, a UC Berkeley graduate student and lead author on the new Astrophysical Journal paper.

    After running a number of computationally intensive simulations of supernova light at the National Energy Research Scientific Computing Center (NERSC), a Department of Energy Office of Science User Facility located at Berkeley Lab, Goldstein and Nugent suspect that they’ll be able to find about 1,000 of these strongly lensed Type Ia supernovae in data collected by the upcoming Large Synoptic Survey Telescope (LSST) – about 20 times more than previous expectations.


    LSST Camera, built at SLAC

    LSST telescope, currently under construction on the El Peñón peak at Cerro Pachón Chile, a 2,682-meter-high mountain in Coquimbo Region, in northern Chile, alongside the existing Gemini South and Southern Astrophysical Research Telescopes.

    These results are the basis of their new paper in The Astrophysical Journal.

    “With three lensed quasars – cosmic beacons emanating from massive black holes in the centers of galaxies – collaborators and I measured the expansion rate to 3.8 percent precision. We got a value higher than the CMB measurement, but we need more systems to be really sure that something is amiss with the standard model of cosmology, “ says Thomas Collett, an astrophysicist at the University of Portsmouth and a co-author on the new Astrophysical Journal paper. “It can take years to get a time delay measurement with quasars, but this work shows we can do it for supernovae in months. One thousand lensed supernovae will let us really nail down the cosmology.”

    In addition to identifying these events, the NERSC simulations also helped them prove that strongly lensed Type Ia supernovae can be very accurate cosmological probes.

    “When cosmologists try to measure time delays, the problem they often encounter is that individual stars in the lensing galaxy can distort the light curves of the different images of the event, making it harder to match them up,” says Goldstein. “This effect, known as ‘microlensing,’ makes it harder to measure accurate time delays, which are essential for cosmology.”

    But after running their simulations, Goldstein and Nugent found microlensing did not change the colors of strongly lensed Type Ia supernova in their early phases. So researchers can subtract the unwanted effects of microlensing by working with colors instead of light curves.

    Gravitational microlensing, S. Liebes, Physical Review B, 133 (1964): 835

    Once these undesirable effects are subtracted, scientists will be able to easily match the light curves and make accurate cosmological measurements.

    They came to this conclusion by modeling the supernovae using the SEDONA code, which was developed with funding from two DOE Scientific Discovery through Advanced Computing (SciDAC) Institutes to calculate light curves, spectra and polarization of aspherical supernova models.

    “In the early 2000s DOE funded two SciDAC projects to study supernova explosions, we basically took the output of those models and passed them through a lensing system to prove that the effects are achromatic,” says Nugent.

    “The simulations give us a dazzling picture of the inner workings of a supernova, with a level of detail that we could never know otherwise,” says Daniel Kasen, an astrophysicist in Berkeley Lab’s Nuclear Science Division, and a co-author on the paper. “Advances in high performance computing are finally allowing us to understand the explosive death of stars, and this study shows that such models are needed to figure out new ways to measure dark energy.”

    Taking Supernova Hunting to the Extreme

    When LSST begins full survey operations in 2023, it will be able to scan the entire sky in only three nights from its perch on the Cerro Pachón ridge in north-central Chile. Over its 10-year mission, LSST is expected to deliver over 200 petabytes of data. As part of the LSST Dark Energy Science Collaboration, Nugent and Goldstein hope that they can run some of this data through a novel supernova-detection pipeline, based at NERSC.

    For more than a decade, Nugent’s Real-Time Transient Detection pipeline running at NERSC has been using machine learning algorithms to scour observations collected by the Palomar Transient Factor (PTF) and then the Intermediate Palomar Transient Factory (iPTF) – searching every night for “transient” objects that change in brightness or position by comparing the new observations with all of the data collected from previous nights. Within minutes after an interesting event is discovered, machines at NERSC then trigger telescopes around the globe to collect follow-up observations. In fact, it was this pipeline that revealed the first-ever strongly lensed Type Ia supernova earlier this year.

    “What we hope to do for the LSST is similar to what we did for Palomar, but times 100,” says Nugent. “There’s going to be a flood of information every night from LSST. We want to take that data and ask what do we know about this part of the sky, what’s happened there before and is this something we’re interested in for cosmology?”

    He adds that once researchers identify the first light of a strongly lensed supernova event, computational modeling could also be used to precisely predict when the next of the light will appear. Astronomers can use this information to trigger ground- and space-based telescopes to follow up and catch this light, essentially allowing them to observe a supernova seconds after it goes off.

    “I came to Berkeley Lab 21 years ago to work on supernova radiative-transfer modeling and now for the first time we’ve used these theoretical models to prove that we can do cosmology better,” says Nugent. “It’s exciting to see DOE reap the benefits of investments in computational cosmology that they started making decades ago.”

    The SciDAC partnership project – Computational Astrophysics Consortium: Supernovae, Gamma-Ray Bursts, and Nucleosynthesis – funded by DOE Office of Science and the National Nuclear Security Agency was led by Stan Woosley of UC Santa Cruz, and supported both Nugent and Kasen of Berkeley Lab.

    NERSC is a DOE Office of Science User Facility.

    See the full article here .

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  • richardmitnick 9:25 am on February 4, 2018 Permalink | Reply
    Tags: , gravitational microlensing, ,   

    From Universe Today: “For the First Time, Planets Have Been Discovered in ANOTHER Galaxy!” 


    Universe Today

    3 Feb , 2018
    Matt Williams

    Using the microlensing metthod, a team of astrophysicists have found the first extra-galactic planets! Credit: NASA/Tim Pyle

    Gravitational microlensing, S. Liebes, Physical Review B, 133 (1964): 835

    The first confirmed discovery of a planet beyond our Solar System (aka. an Extrasolar Planet) was a groundbreaking event. And while the initial discoveries were made using only ground-based observatories, and were therefore few and far between, the study of exoplanets has grown considerably with the deployment of space-based telescopes like the Kepler space telescope.

    As of February 1st, 2018, 3,728 planets have been confirmed in 2,794 systems, with 622 systems having more than one planet. But now, thanks to a new study by a team of astrophysicists from the University of Oklahoma, the first planets beyond our galaxy have been discovered! Using a technique predicting by Einstein’s Theory of General Relativity, this team found evidence of planets in a galaxy roughly 3.8 billion light years away.

    The study which details their discovery, titled Probing Planets in Extragalactic Galaxies Using Quasar Microlensing, recently appeared in The Astrophysical Journal Letters. The study was conducted by Xinyu Dai and Eduardo Guerras, a postdoctoral researcher and professor from the Homer L. Dodge Department of Physics and Astronomy at the University of Oklahoma, respectively.

    See the full article here .

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  • richardmitnick 8:19 am on December 15, 2017 Permalink | Reply
    Tags: , , , , , gravitational microlensing, Rogue One: The First Einstein Ring Measurements of A Free-Floating Planet,   

    From astrobites: “Rogue One: The First Einstein Ring Measurements of A Free-Floating Planet” 

    Astrobites bloc


    Dec 14, 2017
    Mara Zimmerman

    Title: A Free-Floating Planet Candidate from the OGLE and KMTNET Surveys
    Authors: Przemek Mróz, Y.-H. Ryu, J. Skowron, et al.
    Lead Author’s Institution: Warsaw University Observatory

    1.3 meter OGLE Warsaw Telescope at the Las Campanas Observatory in Chile, over 2,500 m (8,200 ft) high,

    Status: Submitted to The Astrophysical Journal

    A free-floating, or rogue, planet is simply a planet that is not gravitationally bound to any star. Given that current planetary detection methods, such as the transiting method and radial velocity measurements, highly depend on the properties of the host star, planets without accompanying stars have proven more difficult to detect.

    Planet transit. NASA/Ames

    However, there still have been detections of these objects, mainly due to microlensing surveys.

    Gravitational microlensing, S. Liebes, Physical Review B, 133 (1964): 835

    The microlensing effect is shown in detail below in Figure 1. These kinds of events are rare, but when they are detected they reveal a lot of information about the planet creating the lens.

    Figure 1: The microlensing process in stages, from left to right. The lens, either planet or star, moves in front of the source, another star far behind the lens, which creates a microlensing event. The characteristic spikes in the light curve are formed when the planet around the lens adds its own effect. This same basic process holds true for the detection of rogue planets, but the lens in that case is just the planet itself. (Image from Planetary Society website)

    See the full article here .

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    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 3:09 pm on December 5, 2017 Permalink | Reply
    Tags: , , , , , , gravitational microlensing   

    From astrobites : “Planet Frequencies in the Galactic Bulge” 

    Astrobites bloc


    5 December 2017
    Elisabeth Matthews

    Artist’s impression of an icy exoplanet found via gravitational microlensing. [ESO]

    Title: Towards a Galactic Distribution of Planets. I: Methodology & Planet Sensitivities of the 2015 High-Cadence Spitzer Microlens Sample
    Authors: Wei Zhu, A. Udalski, S. Calchi Novati et al.
    First Author’s Institution: Ohio State University

    Status: Published in ApJ

    I don’t know if you’ve heard, but astronomers have found quite a few exoplanets in the last couple of decades. However, most of these are clustered in our tiny corner of the galaxy. For the 2,043 planets with stellar distance listed on exoplanets.org today (yes, I know this article will be out of date in a week…) the average distance from to the host star from Earth is 624 pc. The center of the galaxy, meanwhile, is ~8,000 pc away. That’s further than even the furthest known exoplanet, OGLE-05-390L b, which is 6,500 pc from us.

    And we’d really like to have a better understanding of the exoplanets in the galactic bulge, because their presence — or lack thereof — helps us to understand planet formation. Planet formation is believed to be affected by several external factors such as the host star’s metallicity, the stellar mass, the stellar multiplicity, and the stellar environment. That final category is what we’re going to consider today: does the presence of a large number of nearby stars interrupt the formation of planets? The galactic bulge, as the part of the galaxy with the highest number density of stars, is an ideal place to test this — if only we could detect enough planets out there…

    1.3 meter OGLE Warsaw Telescope at the Las Campanas Observatory in Chile, over 2,500 m (8,200 ft) high,

    Any readers particularly clued-up on exoplanet surveys might have recognised the phrase ‘OGLE’ in the name of planet ‘OGLE-05-390L b’. OGLE is the Optical Gravitational Lensing Experiment, a microlensing project run by Warsaw University. Although the mission was initially designed for dark-matter surveys, it has also made several serendipitous exoplanet discoveries. This astrobite describes microlensing for exoplanet detection in more detail, but for today all we really need to know is that sometimes nearby stars and distant stars happen to be really well aligned on the sky for a short time.

    Gravitational microlensing, S. Liebes, Physical Review B, 133 (1964): 835

    See the full article here .

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    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 11:36 am on November 10, 2017 Permalink | Reply
    Tags: , , , , gravitational microlensing, ,   

    From Science Alert: “Astronomers Are Puzzled by a Huge Object at The Centre of Our Galaxy” 


    Science Alert

    10 NOV 2017

    (Nostalgia for Infinity/Shutterstock)

    Planet? Dead star? It’s so massive!

    The Universe is full of oddball objects that simply don’t sit neatly into categories. Take a hint, Pluto.

    Astronomers have used the light-warping effects of gravity to spot a massive object that could be a huge planet or a failed star, right in the centre of our galaxy.

    Gravitational Lensing NASA/ESA

    Not only is it a fun astronomical puzzle, but it’s also pushing the limits of the tools we have for watching space.

    NASA’s Spitzer space telescope has been following Earth’s orbit around the Sun since 2003, using its infrared camera to capture stunning images of the heavens.

    NASA/Spitzer Infrared Telescope

    One task for astronomers has been to use Spitzer’s images to find exoplanets; a goal nobody had considered when it launched. The more ‘traditional’ approach is to watch for the dimming of a star as a planet passes in front of it.

    Planet transit. NASA/Ames

    But Spitzer has another trick up its sleeve – microlensing.

    Gravitational microlensing, S. Liebes, Physical Review B, 133 (1964): 835

    Gravity is the warping of space, which means a massive object can bend space into what is effectively a lens. Spitzer has been used to find a few exoplanets this way.

    But this one takes the cake. If not the whole buffet. (That is, if it’s a planet at all.)

    Its name is OGLE-2016-BLG-1190Lb, and this beast is a whopping 13 times the mass of Jupiter and orbits a star about 22,000 light years away, in the busy neighbourhood of the Milky Way’s centre.


    OGLE might not quite as big as the record-breaking behemoth DENIS-P J082303.1-491201 b, which is 29 times the mass of Jupiter. But it’s up there.

    Before we get too excited, it could still be a brown dwarf star – a boring wannabe that isn’t even big enough to spark a serious nuclear furnace. While tiny stars aren’t unknown, OGLE’s mass puts it at the lower limit of what’s needed to get the party started.

    So why should we care?

    The interesting thing is OGLE sits on the edge of what’s known as the brown dwarf desert – a range of orbits described as a zone devoid of failed stars.

    Astronomers have noticed there’s a distinct lack of brown dwarfs within 5 AU of other stars. For perspective, the distance from Earth to the Sun is 1AU, or about 150 million kilometres.

    OGLE has an orbit roughly 5 AU from its companion star that takes about three years to complete. If it is a planet, it’s grown to mammoth proportions.

    If it’s a small brown dwarf, the fact it sits on the border could help us understand more about the ways cosmic objects grow into stars.

    More information is clearly needed, and microlensing as a technique is still in its infancy. But it could be powerful, identifying details about stars, planets, and even galaxies other methods can’t.

    By perfecting processes that can pull more details from the warped light, especially viewed using different satellites from different positions, we should be able to gain a better understanding of the relationship between stars and their orbiting family members.

    So here’s to you, OGLE. Whatever the hell you are.

    This research has been submitted to The Astronomical Journal

    See the full article here .

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  • richardmitnick 12:47 pm on June 7, 2017 Permalink | Reply
    Tags: , , , , gravitational microlensing, , White dwarf star Stein 2051 B   

    From Hubble: “Hubble Astronomers Develop a New Use for a Century-Old Relativity Experiment to Measure a White Dwarf’s Mass” 

    NASA Hubble Banner

    NASA/ESA Hubble Telescope

    NASA/ESA Hubble Telescope

    June 7, 2017

    Donna Weaver
    Space Telescope Science Institute, Baltimore, Maryland

    Ray Villard
    Space Telescope Science Institute, Baltimore, Maryland

    Kailash Sahu
    Space Telescope Science Institute, Baltimore, Maryland

    Release type: American Astronomical Society Meeting

    Astronomers have used the sharp vision of NASA’s Hubble Space Telescope to repeat a century-old test of Einstein’s general theory of relativity. The Hubble team measured the mass of a white dwarf, the burned-out remnant of a normal star, by seeing how much it deflects the light from a background star.

    This observation represents the first time Hubble has witnessed this type of effect created by a star. The data provide a solid estimate of the white dwarf’s mass and yield insights into theories of the structure and composition of the burned-out star.

    First proposed in 1915, Einstein’s general relativity theory describes how massive objects warp space, which we feel as gravity. The theory was experimentally verified four years later when a team led by British astronomer Sir Arthur Eddington measured how much the sun’s gravity deflected the image of a background star as its light grazed the sun during a solar eclipse, an effect called gravitational microlensing.

    Astronomers can use this effect to see magnified images of distant galaxies or, at closer range, to measure tiny shifts in a star’s apparent position on the sky. Researchers had to wait a century, however, to build telescopes powerful enough to detect this gravitational warping phenomenon caused by a star outside our solar system. The amount of deflection is so small only the sharpness of Hubble could measure it.

    Hubble observed the nearby white dwarf star Stein 2051 B as it passed in front of a background star. During the close alignment, the white dwarf’s gravity bent the light from the distant star, making it appear offset by about 2 milliarcseconds from its actual position. This deviation is so small that it is equivalent to observing an ant crawl across the surface of a quarter from 1,500 miles away.

    Using the deflection measurement, the Hubble astronomers calculated that the white dwarf’s mass is roughly 68 percent of the sun’s mass. This result matches theoretical predictions.

    The technique opens a window on a new method to determine a star’s mass. Normally, if a star has a companion, astronomers can determine its mass by measuring the double-star system’s orbital motion. Although Stein 2051 B has a companion, a bright red dwarf, astronomers cannot accurately measure its mass because the stars are too far apart. The stars are at least 5 billion miles apart – almost twice Pluto’s present distance from the sun.

    “This microlensing method is a very independent and direct way to determine the mass of a star,” explained lead researcher Kailash Sahu of the Space Telescope Science Institute (STScI) in Baltimore, Maryland.

    Gravitational microlensing, S. Liebes, Physical Review B, 133 (1964): 835

    “It’s like placing the star on a scale: the deflection is analogous to the movement of the needle on the scale.”

    Sahu will present his team’s findings at 11:15 a.m. (EDT), June 7, at the American Astronomical Society meeting in Austin, Texas.

    The Hubble analysis also helped the astronomers to independently verify the theory of how a white dwarf’s radius is determined by its mass, an idea first proposed in 1935 by Indian American astronomer Subrahmanyan Chandrasekhar. “Our measurement is a nice confirmation of white-dwarf theory, and it even tells us the internal composition of a white dwarf,” said team member Howard Bond of Pennsylvania State University in University Park.

    Sahu’s team identified Stein 2051 B and its background star after combing through data of more than 5,000 stars in a catalog of nearby stars that appear to move quickly across the sky. Stars with a higher apparent motion across the sky have a greater chance of passing in front of a distant background star, where the deflection of light can be measured.

    After identifying Stein 2051 B and mapping the background star field, the researchers used Hubble’s Wide Field Camera 3 to observe the white dwarf seven different times over a two-year period as it moved past the selected background star.

    NASA/ESA Hubble WFC3

    The Hubble observations were challenging and time-consuming. The research team had to analyze the white dwarf’s velocity and the direction it was moving in order to predict when it would arrive at a position to bend the starlight so the astronomers could observe the phenomenon with Hubble.

    The astronomers also had to measure the tiny amount of deflected starlight. “Stein 2051 B appears 400 times brighter than the distant background star,” said team member Jay Anderson of STScI, who led the analysis to precisely measure the positions of stars in the Hubble images. “So measuring the extremely small deflection is like trying to see a firefly move next to a light bulb. The movement of the insect is very small, and the glow of the light bulb makes it difficult to see the insect moving.” In fact, the slight movement is about 1,000 times smaller than the measurement made by Eddington in his 1919 experiment.

    Stein 2051 B is named for its discoverer, Dutch Roman Catholic priest and astronomer Johan Stein. It resides 17 light-years from Earth and is estimated to be about 2.7 billion years old. The background star is about 5,000 light-years away.

    The researchers plan to use Hubble to conduct a similar microlensing study with Proxima Centauri, our solar system’s closest stellar neighbor.

    The team’s result will appear in the journal Science [advance online paper ] on June 9.


    NASA, ESA, and K. Sahu (STScI)

    See the full article here .

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    The Hubble Space Telescope is a project of international cooperation between NASA and the European Space Agency. NASA’s Goddard Space Flight Center manages the telescope. The Space Telescope Science Institute (STScI), is a free-standing science center, located on the campus of The Johns Hopkins University and operated by the Association of Universities for Research in Astronomy (AURA) for NASA, conducts Hubble science operations.

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    NASA image

  • richardmitnick 11:55 am on March 2, 2017 Permalink | Reply
    Tags: , , , , , gravitational microlensing, , Primordial black holes,   

    From IAC: “A new look at the nature of dark matter” 


    Instituto de Astrofísica de Canarias – IAC

    Mar. 2, 2017
    Evencio Mediavilla (IAC)
    +34 922 605 318

    A new study suggests that the gravitational waves detected by the LIGO experiment must have come from black holes generated during the collapse of stars, and not in the earliest phases of the Universe.

    The nature of the dark matter which apparently makes up 80% of the mass of the particles in the universe is still one of the great unsolved mysteries of present day sciences. The lack of experimental evidence, which could allow us to identify it with one or other of the new elementary particles predicted by the theorists, as well as the recent discovery of gravitational waves coming from the merging of two black holes (with masses some 30 times that of the Sun) by LIGO the Laser Interferometer Gravitational Wave Observatory) have revived interest in the possibility that dark matter might take the form of primordial black holes with masses between 10 and 1000 times that of the Sun.

    LIGO bloc new
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo Hanford, WA, USA installation
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA
    Caltech/MIT Advanced aLigo detector installation Livingston, LA, USA

    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project
    Cornell SXS, the Simulating eXtreme Spacetimes (SXS) project

    Primordial black holes, which would have originated in high density fluctuations of matter during the first moments of the Universe, are in principle very interesting. As opposed to those which form from stars, whose abundance and masses are limited by models of stellar formation and evolution, primordial black holes could exist with a wide range of masses and abundances. They would be found in the halos of galaxies, and the occasional meeting between two of them having masses 30 times that of the Sun, followed by a subsequent merger, might have given rise to the gravitational waves detected by LIGO.

    “Microlensing effect”


    If there were an appreciable number of black holes in the halos of galaxies, some of them intercept the light coming towards us from a distant quasar. Because of their strong gravitational fields, their gravity could concentrate the rays of light, and cause an increase in the apparent brightness of the quasar. This effect, known as “gravitational microlensing” is bigger the bigger the mass of the black hole, and the probability of detecting it would be bigger the more the presence of these black holes. So although the black holes themselves cannot be directly detected, they would be detected by increases in the brightness of observed quasars.

    On this assumption, a group of scientists has used the microlensing effect on quasars to estimate the numbers of primordial black holes of intermediate mass in galaxies. The study, led by the researcher at the Instituto de Astrofísica de Canarias (IAC) and the University of La Laguna (ULL), Evencio Mediavilla Gradolph, shows that normal stars like the Sun cause the microlensing effects, thus ruling out the existence of a large population of primordial black holes with intermediate mass.

    Computer simulations

    Using computer simulations, they have compared the rise in brightness, in visible light and in X-rays, of 24 distant quasars with the values predicted by the microlensing effect. They have found that the strength of the effect is relatively low, as would be expected from objects with a mass between 0.05 and 0.45 times that of the Sun, and well below that of intermediate mass black holes. In addition they have estimated that these microlenses form roughly 20% of the total mass of a galaxy, equivalent to the mass expected to be found in stars. So their results show that, with high probability, it is normal stars and not primordial intermediate mass black holes which are responsible for the observed microlensing.

    “This study implies “says Evencio Mediavilla, “that it is not at all probable that black holes with masses between 10 and 100 times the mass of the Sun make up a significant fraction of the dark matter”. For that reason the black holes whose merging was detected by LIGO were probably formed by the collapse of stars, and were not primordial black holes”.

    Astronomers participating in this research include Jorge Jiménez-Vicente and José Calderón-Infante (University of Granada) and José A. Muñoz Lozano, and Héctor Vives-Arias, (University of Valencia).

    Article: Limits on the Mass and Abundance of Primordial Black Holes from Quasar Gravitational Microlensing, by E. Mediavilla et al. Published in The Astrophysical Journal Letters. Reference: E. Mediavilla et al 2017 ApJL 836 L18.

    See the full article here.

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    The Instituto de Astrofísica de Canarias(IAC) is an international research centre in Spain which comprises:

    The Instituto de Astrofísica, the headquarters, which is in La Laguna (Tenerife).
    The Centro de Astrofísica en La Palma (CALP)
    The Observatorio del Teide (OT), in Izaña (Tenerife).
    The Observatorio del Roque de los Muchachos (ORM), in Garafía (La Palma).

    These centres, with all the facilities they bring together, make up the European Northern Observatory(ENO).

    The IAC is constituted administratively as a Public Consortium, created by statute in 1982, with involvement from the Spanish Government, the Government of the Canary Islands, the University of La Laguna and Spain’s Science Research Council (CSIC).

    The International Scientific Committee (CCI) manages participation in the observatories by institutions from other countries. A Time Allocation Committee (CAT) allocates the observing time reserved for Spain at the telescopes in the IAC’s observatories.

    The exceptional quality of the sky over the Canaries for astronomical observations is protected by law. The IAC’s Sky Quality Protection Office (OTPC) regulates the application of the law and its Sky Quality Group continuously monitors the parameters that define observing quality at the IAC Observatories.

    The IAC’s research programme includes astrophysical research and technological development projects.

    The IAC is also involved in researcher training, university teachingand outreachactivities.

    The IAC has devoted much energy to developing technology for the design and construction of a large 10.4 metre diameter telescope, the ( Gran Telescopio CANARIAS, GTC), which is sited at the Observatorio del Roque de los Muchachos.

    Gran Telescopio  Canarias at the Roque de los Muchachos Observatory on the island of La Palma, in the Canaries, SpainGran Telescopio CANARIAS, GTC
    Gran Telescopio CANARIAS, GTC

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