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  • 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” 

    ScienceAlert

    From Science Alert

    23 DEC 2018
    MICHELLE STARR

    1
    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
    lvu@lbl.gov
    (510) 495-2402

    1
    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.

    NERSC PDSF


    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


    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


    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

    Universe Today

    3 Feb , 2018
    Matt Williams

    1
    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

    astrobites

    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.

    1
    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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    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 3:09 pm on December 5, 2017 Permalink | Reply
    Tags: , , , , , , gravitational microlensing   

    From astrobites : “Planet Frequencies in the Galactic Bulge” 

    Astrobites bloc

    astrobites

    5 December 2017
    Elisabeth Matthews

    1
    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” 

    ScienceAlert

    Science Alert

    10 NOV 2017
    MIKE MCRAE

    1
    (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.

    2
    http://www.truepatriot.net/tag/ogle-2016-blg-1190lbogle-2016-blg-1190lb/

    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
    410-338-4493
    dweaver@stsci.edu

    Ray Villard
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4514
    villard@stsci.edu

    Kailash Sahu
    Space Telescope Science Institute, Baltimore, Maryland
    410-338-4930
    ksahu@stsci.edu

    1
    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.

    Credits

    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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  • 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” 

    IAC

    Instituto de Astrofísica de Canarias – IAC

    Mar. 2, 2017
    Evencio Mediavilla (IAC)
    emg@iac.es
    +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”

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    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.

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    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

     
  • richardmitnick 10:08 am on January 30, 2017 Permalink | Reply
    Tags: Active supermassive black holes forming accretion disks, , , , BLR - broad line regions, gravitational microlensing, Larger accretion disks for quasars, Pan-STARRS survey, Sloan Digital Sky Survey (SDSS)   

    From astrobites: “Larger accretion disks for quasars” 

    Astrobites bloc

    Astrobites

    Jan 30, 2017
    Suk Sien Tie

    Title: Detection of time lags between quasar continuum emission bands based on Pan-STARRS light-curves
    Authors: Yan-Fei Jiang, Paul J. Green, Jenny E. Greene, and others
    First Author’s Institution: Kavli Institute of Theoretical Physics, University of California, Santa Barbara
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    Status: Submitted to ApJ (open access)

    Active supermassive black holes, also known as quasars, are “active” because they continuously feed on materials that spiral into them, forming accretion disks. These accretion disks light up the surrounding of the black holes and make them visible (see the featured image for a very realistic rendering of an accretion disk from the movie Interstellar). Intuitively then, how luminous and massive a quasar grows to be must somehow depend on the size and structure of its disk. The properties of the quasar are then believed to affect the evolution of its host galaxy, as suggested by various black hole and host galaxy relations such as the MBH-σ and MBH-Mbulge relations.

    But alas, most quasars are simply too far away and their accretion disks far too small for our current telescopes to resolve (i.e. take sharp images of). The handful of size measurements of quasar disks we currently have come mostly from gravitational microlensing, which requires years of monitoring and significant amount of (good) modeling. An alternative and more direct approach to probe the quasar disks is by extracting information from the quasar variability in luminosity.

    Quasars are known to vary in an irregular and non-periodic manner (i.e. stochastically or randomly), where their variability is believed to be driven by the innermost region of the disk close to the black hole. As the inner disk experiences instability and varies in luminosity, the variability would need some time to propagate to the outer disk, causing the variability in the outer regions to lag behind that of the inner regions. The time delay is set by the size of the disk and the speed of light. Therefore, by measuring the time delay of the variability between the outer and inner disk, we can constrain the size of the disk. This is the core idea behind the technique of reverberation mapping, commonly applied to map out the sizes of the quasars broad line regions (BLR; see this very helpful schematic), which are then used to measure black hole masses.

    Compared to reverberation mapping of the BLR, where the lags are measured between the continuum light curve (emitted by the accretion disk) and the broad emission lines light curve (emitted by gases in the BLR), reverberation mapping of accretion disk measures the lags between the continuum light curves at different wavelengths of light. Since continuum emission originates from the disk, this directly probes the structure the disk itself. As temperature varies between different disk annuli, different wavelengths of light are emitted; UV light is emitted closer to the inner disk while optical light further out.

    2
    Fig. 1 – Variability lags (in unit of days) between the r-, i-, and z-bands and the g-band of the two hundred or so quasars in this study. Top panel shows the observational results, compared with theoretical predictions on the bottom panel. Notice the broader (as well as negative) lag distributions in the top figure compared with the bottom figure. [Figure 10 in the paper]

    In this paper, the authors measured the optical lags of more than two hundred quasars using four years of data from the Pan-STARRS survey.

    2
    2
    The Pan-STARRS1 data archive home page

    This is a significant jump in numbers as, due to the intensive monitoring required, reverberation mapping of quasar disks has only been done on tens of quasars. The quasar sample in this paper consists of sources that the Sloan Digital Sky Survey (SDSS) classifies as quasars and are located at redshifts around 0.3 and 1.

    SDSS Telescope at Apache Point, NM, USA
    SDSS Telescope at Apache Point, NM, USA

    4
    The Sloan Digital Sky Survey: Mapping the Universe

    These redshifts are where emission lines from the BLR are least likely to be redshifted into the optical wavelengths to contaminate the continuum light curves. The authors used an algorithm based on modeling quasar variability, known as JAVELIN, to measure the lags between the continuum light curves in different photometric filters (or different bands). The top figure in Figure 1 shows the observed distributions of variability lags in the r, i, and z band from the g-band variability for the whole sample, while the bottom figure shows the predicted lag distribution from standard accretion disk theory, which posits that accretion disk is geometrically thin, optically thick, and radiatively efficient. As seen from the figure, the mean lags increase from shorter to longer wavelengths, while also having two to three times larger values compared to theoretical estimates. These larger lags imply longer light travel times and so larger accretion disks, which also agree with findings using gravitational microlensing.

    While there seems to be a general increase of lags towards longer wavelengths, a number of quasars show negative g-r lags, as shown by the topmost panel in Figure 2. After ruling out factors such as observing cadence and technicalities of the JAVELIN code as contributors, the authors believe these negative lags to be real, possibly indicating some off-centered and inward-traveling disturbances that arise at the outer disk where light of longer wavelengths is emitted. To tease out the sources of these off-centered variabilities would require, as you may have guessed, more work and more data. But this statistical study of hundreds of quasars lends support to the gradually emerging picture that quasars might harbor larger cookie jars, well, accretion disks, than we initially believe.

    3
    Fig. 2 – Distribution of lags as a function of the quasar apparent luminosity for a subsample of quasars with clear lag detections. The points are color-coded according to the black hole mass. Some quasars have negative g-r lags (topmost panel), where points lie below the dashed horizontal line. [Figure 12 in the paper]

    See the full article here .

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    STEM Icon

    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 2:18 pm on December 15, 2016 Permalink | Reply
    Tags: , gravitational microlensing, Lake Tekapo, , , New Zealand, University of Canterbury Mt John Observatory   

    From Goddard: “Microlensing Study Suggests Most Common Outer Planets Likely Neptune-mass” 

    NASA Goddard Banner

    NASA Goddard Space Flight Center

    Dec. 15, 2016
    Francis Reddy
    francis.j.reddy@nasa.gov
    NASA’s Goddard Space Flight Center in Greenbelt, Maryland

    A new statistical study of planets found by a technique called gravitational microlensing suggests that Neptune-mass worlds are likely the most common type of planet to form in the icy outer realms of planetary systems. The study provides the first indication of the types of planets waiting to be found far from a host star, where scientists suspect planets form most efficiently.


    Neptune-mass worlds are likely the most common type in the outer realms of planetary systems
    Credits: NASA’s Goddard Space Flight Center

    1
    University of Canterbury Mt John Observatory, Lake Tekapo, New Zealand

    “We’ve found the apparent sweet spot in the sizes of cold planets. Contrary to some theoretical predictions, we infer from current detections that the most numerous have masses similar to Neptune, and there doesn’t seem to be the expected increase in number at lower masses,” said lead scientist Daisuke Suzuki, a post-doctoral researcher at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and the University of Maryland Baltimore County. “We conclude that Neptune-mass planets in these outer orbits are about 10 times more common than Jupiter-mass planets in Jupiter-like orbits.”

    Gravitational microlensing takes advantage of the light-bending effects of massive objects predicted by Einstein’s general theory of relativity.

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

    It occurs when a foreground star, the lens, randomly aligns with a distant background star, the source, as seen from Earth. As the lensing star drifts along in its orbit around the galaxy, the alignment shifts over days to weeks, changing the apparent brightness of the source. The precise pattern of these changes provides astronomers with clues about the nature of the lensing star, including any planets it may host.

    2
    This graph plots 4,769 exoplanets and planet candidates according to their masses and relative distances from the snow line, the point where water and other materials freeze solid (vertical cyan line). Gravitational microlensing is particularly sensitive to planets in this region. Planets are shaded according to the discovery technique listed at right. Masses for unconfirmed planetary candidates from NASA’s Kepler mission are calculated based on their sizes. For comparison, the graph also includes the planets of our solar system.
    Credits: NASA’s Goddard Space Flight Center

    “We mainly determine the mass ratio of the planet to the host star and their separation,” said team member David Bennett, an astrophysicist at Goddard. “For about 40 percent of microlensing planets, we can determine the mass of the host star and therefore the mass of the planet.”

    More than 50 exoplanets have been discovered using microlensing compared to thousands detected by other techniques, such as detecting the motion or dimming of a host star caused by the presence of planets. Because the necessary alignments between stars are rare and occur randomly, astronomers must monitor millions of stars for the tell-tale brightness changes that signal a microlensing event.

    However, microlensing holds great potential. It can detect planets hundreds of times more distant than most other methods, allowing astronomers to investigate a broad swath of our Milky Way galaxy. The technique can locate exoplanets at smaller masses and greater distances from their host stars, and it’s sensitive enough to find planets floating through the galaxy on their own, unbound to stars.

    NASA’s Kepler and K2 missions have been extraordinarily successful in finding planets that dim their host stars, with more than 2,500 confirmed discoveries to date.

    NASA/Kepler Telescope
    NASA/Kepler Telescope

    This technique is sensitive to close-in planets but not more distant ones. Microlensing surveys are complementary, best probing the outer parts of planetary systems with less sensitivity to planets closer to their stars.

    “Combining microlensing with other techniques provides us with a clearer overall picture of the planetary content of our galaxy,” said team member Takahiro Sumi at Osaka University in Japan.

    From 2007 to 2012, the Microlensing Observations in Astrophysics (MOA) group, a collaboration between researchers in Japan and New Zealand, issued 3,300 alerts informing the astronomical community about ongoing microlensing events. Suzuki’s team identified 1,474 well-observed microlensing events, with 22 displaying clear planetary signals. This includes four planets that were never previously reported.

    To study these events in greater detail, the team included data from the other major microlensing project operating over the same period, the Optical Gravitational Lensing Experiment (OGLE), as well as additional observations from other projects designed to follow up on MOA and OGLE alerts.

    1.3 meter OGLE Warsaw Telescope at the Las Campanas Observatory in Chile1.3 meter OGLE Warsaw telescope interior
    1.3 meter OGLE Warsaw Telescope at the Las Campanas Observatory in Chile”

    From this information, the researchers determined the frequency of planets compared to the mass ratio of the planet and star as well as the distances between them. For a typical planet-hosting star with about 60 percent the sun’s mass, the typical microlensing planet is a world between 10 and 40 times Earth’s mass. For comparison, Neptune in our own solar system has the equivalent mass of 17 Earths.

    The results imply that cold Neptune-mass worlds are likely to be the most common types of planets beyond the so-called snow line, the point where water remained frozen during planetary formation. In the solar system, the snow line is thought to have been located at about 2.7 times Earth’s mean distance from the sun, placing it in the middle of the main asteroid belt today.

    3
    Neptune-mass exoplanets like the one shown in this artist’s rendering may be the most common in the icy regions of planetary systems. Beyond a certain distance from a young star, water and other substances remain frozen, leading to an abundant population of icy objects that can collide and form the cores of new planets. In the foreground, an icy body left over from this period drifts past the planet.
    Credits: NASA/Goddard/Francis Reddy

    A paper detailing the findings was published in The Astrophysical Journal on Dec. 13.

    “Beyond the snow line, materials that were gaseous closer to the star condense into solid bodies, increasing the amount of material available to start the planet-building process,” said Suzuki. “This is where we think planetary formation was most efficient, and it’s also the region where microlensing is most sensitive.”

    NASA’s Wide Field Infrared Survey Telescope (WFIRST), slated to launch in the mid-2020s, will conduct an extensive microlensing survey.

    NASA/WFIRST
    NASA/WFIRST

    Astronomers expect it will deliver mass and distance determinations of thousands of planets, completing the work begun by Kepler and providing the first galactic census of planetary properties.

    NASA’s Ames Research Center manages the Kepler and K2 missions for NASA’s Science Mission Directorate. The Jet Propulsion Laboratory (JPL) in Pasadena, California, managed Kepler mission development. Ball Aerospace & Technologies Corporation operates the flight system with support from the Laboratory for Atmospheric and Space Physics at the University of Colorado in Boulder.

    WFIRST is managed at Goddard, with participation by JPL, the Space Telescope Science Institute in Baltimore, the Infrared Processing and Analysis Center, also in Pasadena, and a science team comprising members from U.S. research institutions across the country.

    For more information on how NASA’s Kepler is working with ground-based efforts, including the MOA and OGLE groups, to search for planets using microlensing, please visit:

    https://www.nasa.gov/feature/ames/kepler/searching-for-far-out-and-wandering-worlds/

    See the full article here.

    Please help promote STEM in your local schools.

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    NASA’s Goddard Space Flight Center is home to the nation’s largest organization of combined scientists, engineers and technologists that build spacecraft, instruments and new technology to study the Earth, the sun, our solar system, and the universe.

    Named for American rocketry pioneer Dr. Robert H. Goddard, the center was established in 1959 as NASA’s first space flight complex. Goddard and its several facilities are critical in carrying out NASA’s missions of space exploration and scientific discovery.

    NASA Goddard campus
    NASA/Goddard Campus
    NASA image

     
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