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  • richardmitnick 2:28 pm on January 12, 2019 Permalink | Reply
    Tags: Astronomers find signatures of a ‘messy’ star that made its companion go supernova, , , , , , It takes many astronomers and a wide variety of types of telescopes working together to understand transient cosmic phenomena, , SN 2015cp, Type Ia supernova, ,   

    From University of Washington: “Astronomers find signatures of a ‘messy’ star that made its companion go supernova” 

    U Washington

    From University of Washington

    January 10, 2019
    James Urton

    An X-ray/infrared composite image of G299, a Type Ia supernova remnant in the Milky Way Galaxy approximately 16,000 light years away.NASA/Chandra X-ray Observatory/University of Texas/2MASS/University of Massachusetts/Caltech/NSF

    NASA/Chandra X-ray Telescope

    Caltech 2MASS Telescopes, a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center (IPAC) at Caltech, at the Whipple Observatory on Mt. Hopkins south of Tucson, AZ, Altitude 2,606 m (8,550 ft) and at the Cerro Tololo Inter-American Observatory at an altitude of 2200 meters near La Serena, Chile.

    Many stars explode as luminous supernovae when, swollen with age, they run out of fuel for nuclear fusion. But some stars can go supernova simply because they have a close and pesky companion star that, one day, perturbs its partner so much that it explodes.

    These latter events can happen in binary star systems, where two stars attempt to share dominion. While the exploding star gives off lots of evidence about its identity, astronomers must engage in detective work to learn about the errant companion that triggered the explosion.

    On Jan. 10 at the 2019 American Astronomical Society meeting in Seattle, an international team of astronomers announced that they have identified the type of companion star that made its partner in a binary system, a carbon-oxygen white dwarf star, explode. Through repeated observations of SN 2015cp, a supernova 545 million light years away, the team detected hydrogen-rich debris that the companion star had shed prior to the explosion.

    “The presence of debris means that the companion was either a red giant star or similar star that, prior to making its companion go supernova, had shed large amounts of material,” said University of Washington astronomer Melissa Graham, who presented the discovery and is lead author on the accompanying paper accepted for publication in The Astrophysical Journal.

    The supernova material smacked into this stellar litter at 10 percent the speed of light, causing it to glow with ultraviolet light that was detected by the Hubble Space Telescope and other observatories nearly two years after the initial explosion. By looking for evidence of debris impacts months or years after a supernova in a binary star system, the team believes that astronomers could determine whether the companion had been a messy red giant or a relatively neat and tidy star.

    The team made this discovery as part of a wider study of a particular type of supernova known as a Type Ia supernova. These occur when a carbon-oxygen white dwarf star explodes suddenly due to activity of a binary companion. Carbon-oxygen white dwarfs are small, dense and — for stars — quite stable. They form from the collapsed cores of larger stars and, if left undisturbed, can persist for billions of years.

    Type Ia supernovae have been used for cosmological studies because their consistent luminosity makes them ideal “cosmic lighthouses,” according to Graham. They’ve been used to estimate the expansion rate of the universe and served as indirect evidence for the existence of dark energy.

    An image of SN 1994D (lower left), a Type Ia supernova detected in 1994 at the edge of galaxy NGC 4526 (center).NASA/ESA/The Hubble Key Project Team/The High-Z Supernova Search Team.

    NASA/ESA Hubble Telescope

    Yet scientists are not certain what kinds of companion stars could trigger a Type Ia event. Plenty of evidence indicates that, for most Type Ia supernovae, the companion was likely another carbon-oxygen white dwarf, which would leave no hydrogen-rich debris in the aftermath. Yet theoretical models have shown that stars like red giants could also trigger a Type Ia supernova, which could leave hydrogen-rich debris that would be hit by the explosion. Out of the thousands of Type Ia supernovae studied to date, only a small fraction were later observed impacting hydrogen-rich material shed by a companion star. Prior observations of at least two Type Ia supernovae detected glowing debris months after the explosion. But scientists weren’t sure if those events were isolated occurrences, or signs that Type Ia supernovae could have many different kinds of companion stars.

    “All of the science to date that has been done using Type Ia supernovae, including research on dark energy and the expansion of the universe, rests on the assumption that we know reasonably well what these ‘cosmic lighthouses’ are and how they work,” said Graham. “It is very important to understand how these events are triggered, and whether only a subset of Type Ia events should be used for certain cosmology studies.”

    The team used Hubble Space Telescope observations to look for ultraviolet emissions from 70 Type Ia supernovae approximately one to three years following the initial explosion.

    “By looking years after the initial event, we were searching for signs of shocked material that contained hydrogen, which would indicate that the companion was something other than another carbon-oxygen white dwarf,” said Graham.

    In the case of SN 2015cp, a supernova first detected in 2015, the scientists found what they were searching for. In 2017, 686 days after the supernova exploded, Hubble picked up an ultraviolet glow of debris. This debris was far from the supernova source — at least 100 billion kilometers, or 62 billion miles, away. For reference, Pluto’s orbit takes it a maximum of 7.4 billion kilometers from our sun.

    In 2017, 686 days after the initial explosion, the Hubble Space Telescope recorded an ultraviolet emission (blue circle) from SN 2015cp, which was caused by supernova material impacting hydrogen-rich material previously shed by a companion star. Yellow circles indicate cosmic ray strikes, which are unrelated to the supernova. NASA/Hubble Space Telescope/Graham et al. 2019.

    By comparing SN 2015cp to the other Type Ia supernovae in their survey, the researchers estimate that no more than 6 percent of Type Ia supernovae have such a litterbug companion. Repeated, detailed observations of other Type Ia events would help cement these estimates, Graham said.

    The Hubble Space Telescope was essential for detecting the ultraviolet signature of the companion star’s debris for SN 2015cp. In the fall of 2017, the researchers arranged for additional observations of SN 2015cp by the W.M. Keck Observatory in Hawaii, the Karl G. Jansky Very Large Array in New Mexico, the European Southern Observatory’s Very Large Telescope and NASA’s Neil Gehrels Swift Observatory, among others. These data proved crucial in confirming the presence of hydrogen and are presented in a companion paper lead by Chelsea Harris, a research associate at Michigan State University.

    Keck Observatory, Maunakea, Hawaii, USA.4,207 m (13,802 ft), above sea level,

    NRAO/Karl V Jansky Expanded Very Large Array, on the Plains of San Agustin fifty miles west of Socorro, NM, USA, at an elevation of 6970 ft (2124 m)

    ESO VLT at Cerro Paranal in the Atacama Desert, •ANTU (UT1; The Sun ),
    •KUEYEN (UT2; The Moon ),
    •MELIPAL (UT3; The Southern Cross ), and
    •YEPUN (UT4; Venus – as evening star).
    elevation 2,635 m (8,645 ft) from above Credit J.L. Dauvergne & G. Hüdepohl atacama photo, with an elevation of 2,635 metres (8,645 ft) above sea level,

    NASA Neil Gehrels Swift Observatory

    “The discovery and follow-up of SN 2015cp’s emission really demonstrates how it takes many astronomers, and a wide variety of types of telescopes, working together to understand transient cosmic phenomena,” said Graham. “It is also a perfect example of the role of serendipity in astronomical studies: If Hubble had looked at SN 2015cp just a month or two later, we wouldn’t have seen anything.”

    Graham is also a senior fellow with the UW’s DIRAC Institute and a science analyst with the Large Synoptic Survey Telescope, or LSST.

    LSST telescope, currently under construction 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, altitude 2,663 m (8,737 ft),

    “In the future, as a part of its regularly scheduled observations, the LSST will automatically detect optical emissions similar to SN 2015cp — from hydrogen impacted by material from Type Ia supernovae,” said Graham said. “It’s going to make my job so much easier!”

    Co-authors are Harris; Peter Nugent at the University of California, Berkeley and the Lawrence Berkeley National Laboratory; Kate Maguire at Queen’s University Belfast; Mark Sullivan and Mathew Smith at the University of Southampton; Stefano Valenti at the University of California, Davis; Ariel Goobar at Stockholm University; Ori Fox at the Space Telescope Science Institute; Ken Shen, Tom Brink and Alex Filippenko at the University of California, Berkeley; Patrick Kelly at the University of Minnesota; and Curtis McCully at the University of California, Santa Barbara and the Las Cumbres Observatory. The research was funded by the National Science Foundation, NASA, the European Research Council and the U.K.’s Science and Technology Facilities Council.

    See the full article here .


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  • richardmitnick 2:30 pm on December 1, 2018 Permalink | Reply
    Tags: , , , , Kepler Space Telescope’s K2 Supernova Cosmology Experiment, Kepler telescope captures extraordinary observations of a star's death throes, SN 2018oh, Type Ia supernova,   

    From UC Santa Cruz: “Kepler telescope captures extraordinary observations of a star’s death throes” 

    UC Santa Cruz

    From UC Santa Cruz

    November 30, 2018
    Tim Stephens

    Unprecedented images of a Type Ia supernova, from the moment of explosion through the rise and fall of the light curve, show an unexpected early rise in brightness.

    The supernova—known as SN 2018oh—is located in a spiral galaxy called UGC 4780 in the constellation Cancer at a distance of more than 170 million light years.

    An exploding star in another galaxy has been documented with unprecedented precision thanks to the Kepler Space Telescope’s K2 Supernova Cosmology Experiment, one of the telescope’s final missions before running out of fuel late last month.

    Kepler’s observations of the supernova known as SN 2018oh showed an unexpected fast rise in brightness that may be an important clue to understanding the progenitors of Type Ia supernovae, which cosmologists use to study the expansion of the universe and dark energy.

    An international team led by astronomers at the University of California, Santa Cruz, conducted an analysis of SN 2018oh focusing on the first week after the explosion. Their paper, accepted for publication in Astrophysical Journal Letters, is one of a series of papers analyzing SN 2018oh.

    Kepler’s observations of the supernova known as SN 2018oh showed an unexpected fast rise in brightness that may be an important clue to understanding the progenitors of Type Ia supernovae, which cosmologists use to study the expansion of the universe and dark energy.

    “This is an incredibly exciting discovery,” said Georgios Dimitriadis, a postdoctoral researcher at UC Santa Cruz who led the analysis. “When I downloaded the data and started looking at it in detail, my jaw dropped.”

    “The observations are exquisite, because we have images from Kepler every 30 minutes, starting from before the explosion all the way past its peak brightness. And it’s scientifically interesting because the increase in brightness deviates from the expected behavior,” said Ryan Foley, assistant professor of astronomy and astrophysics at UC Santa Cruz.

    The supernova was also extensively monitored by ground-based facilities which provided important complementary observations, including the Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1) at Haleakala Observatory, Hawaii, and the Dark Energy Camera (DECam) at Cerro Tololo Inter-American Observatory in Chile.

    Pannstars telescope, U Hawaii, Mauna Kea, Hawaii, USA

    Dark Energy Survey

    Dark Energy Camera [DECam], built at FNAL

    NOAO/CTIO Victor M Blanco 4m Telescope which houses the DECam at Cerro Tololo, Chile, housing DECam at an altitude of 7200 feet

    The light curve of the supernova shows how its brightness changed over time. A typical supernova gets steadily brighter for almost three weeks, then gradually fades away. SN 2018oh, however, brightened very quickly right after explosion before settling into the normal progression. Because of the fast brightening, SN 2018oh was about 3 times brighter than a typical supernova a few days after explosion.

    “This early bump in the light curve requires an extra source of light, and the question is where does that come from,” Foley said.

    Dimitriadis said the team investigated three possible explanations.

    “We know a Type Ia supernova results from the explosion of a white dwarf that acquires extra mass given to it from a companion star,” he explained. “But we don’t know what kind of star donates this extra mass.”

    One possibility is that the white dwarf accretes matter from a star like our sun. This scenario could give rise to extra light (the bump in the light curve) when the shock wave from the exploding white dwarf runs into the companion star. As the supernova flows around the companion star, it creates an area of extremely hot material on the star which emits light in addition to the light from the supernova.

    “In that scenario, we would expect the observation of excess light to be very dependent on the viewing angle, which may explain why it has not been seen in all supernova observations,” Foley said.

    Another prediction of this scenario is that the excess light would be blue, because of the high shock temperatures. The researchers obtained critical color information for SN 2018oh from ground-based observations. “We observed blue colors at the time of the flux excess, a key clue in understanding what was causing the extra light,” Dimitriadis said.

    The scenario where the supernova runs into its nearby companion star should produce blue light similar to what was seen from the ground. However, the researchers did not rule out other possible explanations. The light from a supernova comes from the radioactive decay of heavy elements such as nickel–56, which tend to be in the center of the star. If nickel accumulates on the surface during the explosion, however, its radioactive decay could also generate excess light at an early stage of the supernova. It could even produce a “double detonation” in which a small explosion on the surface triggers a second explosions that consumes the entire star.

    Another possibility is excess light being emitted when the shock wave from the supernova heats a large shell of material just above the surface of the star. According to Foley, the color information from early ground-based images is critical to distinguishing between these different scenarios.

    “The blue color, in particular, agrees with the scenario in which the supernova interacts with a companion star, and is harder to explain with either nickel on the surface or the heating of circumstellar material,” he said.

    This is significant because it favors one of the two general models for Type Ia supernovae that astrophysicists have been debating for decades. In the “single-degenerate” model, the white dwarf accretes matter from a normal companion star until it reaches a certain limit and explodes. In the “double-degenerate” model, the excess mass results from the merger of two white dwarfs.

    “The interaction with a companion star is a prediction of the single-degenerate model, whereas the other two scenarios for the excess light could fit with either model,” Foley said. “This supernova is consistent with the single-degenerate model, but there are other supernovae where there is strong evidence against a normal companion star, so it remains an open question.”

    Dimitriadis adds that his team continues to observe the supernova, searching for additional clues about how it exploded. He says, “This is an important problem, and we will keep chipping away at it.”

    SN 2018oh is located in a spiral galaxy called UGC 4780 in the constellation Cancer at a distance of more than 170 million light years. This galaxy was included as a target for monitoring by NASA’s Kepler Space Telescope as part of the K2 Supernova Cosmology Experiment. The supernova was discovered in February 2018 by the All Sky Automated Survey for Supernovae (ASAS-SN). Early images were obtained by the Pan-STARRS1 telescope and the CTIO Mayall telescope with DECam.

    “This study was a large collaborative effort involving 150 scientists from a wide range of specialties,” Dimitriadis said. “A lot of credit goes to the people who worked on the Kepler telescope and gave it extra life with the K2 mission. Kepler was not designed to observe supernovae, and we had important contributions from exoplanet scientists because they know the instrument best.”

    The coauthors of the paper include scientists from more than 50 institutions, including UC Santa Cruz, Space Science Telescope Institute, and UC Berkeley. This work was supported in part by NASA, the Gordon and Betty Moore Foundation, the Packard Foundation, the National Science Foundation, and the Heising-Simons Foundation.

    See the full article here .


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    UCSC Lick Observatory, Mt Hamilton, in San Jose, California, Altitude 1,283 m (4,209 ft)


    UCO Lick Shane Telescope
    UCO Lick Shane Telescope interior
    Shane Telescope at UCO Lick Observatory, UCSC

    Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

    Lick Automated Planet Finder telescope, Mount Hamilton, CA, USA

    UC Santa Cruz campus
    The University of California, Santa Cruz, opened in 1965 and grew, one college at a time, to its current (2008-09) enrollment of more than 16,000 students. Undergraduates pursue more than 60 majors supervised by divisional deans of humanities, physical & biological sciences, social sciences, and arts. Graduate students work toward graduate certificates, master’s degrees, or doctoral degrees in more than 30 academic fields under the supervision of the divisional and graduate deans. The dean of the Jack Baskin School of Engineering oversees the campus’s undergraduate and graduate engineering programs.

    UCSC is the home base for the Lick Observatory.

    Lick Observatory's Great Lick 91-centimeter (36-inch) telescope housed in the South (large) Dome of main building
    Lick Observatory’s Great Lick 91-centimeter (36-inch) telescope housed in the South (large) Dome of main building

    Search for extraterrestrial intelligence expands at Lick Observatory
    New instrument scans the sky for pulses of infrared light
    March 23, 2015
    By Hilary Lebow
    The NIROSETI instrument saw first light on the Nickel 1-meter Telescope at Lick Observatory on March 15, 2015. (Photo by Laurie Hatch) UCSC Lick Nickel telescope

    Astronomers are expanding the search for extraterrestrial intelligence into a new realm with detectors tuned to infrared light at UC’s Lick Observatory. A new instrument, called NIROSETI, will soon scour the sky for messages from other worlds.

    “Infrared light would be an excellent means of interstellar communication,” said Shelley Wright, an assistant professor of physics at UC San Diego who led the development of the new instrument while at the University of Toronto’s Dunlap Institute for Astronomy & Astrophysics.

    Wright worked on an earlier SETI project at Lick Observatory as a UC Santa Cruz undergraduate, when she built an optical instrument designed by UC Berkeley researchers. The infrared project takes advantage of new technology not available for that first optical search.

    Infrared light would be a good way for extraterrestrials to get our attention here on Earth, since pulses from a powerful infrared laser could outshine a star, if only for a billionth of a second. Interstellar gas and dust is almost transparent to near infrared, so these signals can be seen from great distances. It also takes less energy to send information using infrared signals than with visible light.

    Frank Drake, professor emeritus of astronomy and astrophysics at UC Santa Cruz and director emeritus of the SETI Institute, said there are several additional advantages to a search in the infrared realm.

    “The signals are so strong that we only need a small telescope to receive them. Smaller telescopes can offer more observational time, and that is good because we need to search many stars for a chance of success,” said Drake.

    The only downside is that extraterrestrials would need to be transmitting their signals in our direction, Drake said, though he sees this as a positive side to that limitation. “If we get a signal from someone who’s aiming for us, it could mean there’s altruism in the universe. I like that idea. If they want to be friendly, that’s who we will find.”

    Scientists have searched the skies for radio signals for more than 50 years and expanded their search into the optical realm more than a decade ago. The idea of searching in the infrared is not a new one, but instruments capable of capturing pulses of infrared light only recently became available.

    “We had to wait,” Wright said. “I spent eight years waiting and watching as new technology emerged.”

    Now that technology has caught up, the search will extend to stars thousands of light years away, rather than just hundreds. NIROSETI, or Near-Infrared Optical Search for Extraterrestrial Intelligence, could also uncover new information about the physical universe.

    “This is the first time Earthlings have looked at the universe at infrared wavelengths with nanosecond time scales,” said Dan Werthimer, UC Berkeley SETI Project Director. “The instrument could discover new astrophysical phenomena, or perhaps answer the question of whether we are alone.”

    NIROSETI will also gather more information than previous optical detectors by recording levels of light over time so that patterns can be analyzed for potential signs of other civilizations.

    “Searching for intelligent life in the universe is both thrilling and somewhat unorthodox,” said Claire Max, director of UC Observatories and professor of astronomy and astrophysics at UC Santa Cruz. “Lick Observatory has already been the site of several previous SETI searches, so this is a very exciting addition to the current research taking place.”

    NIROSETI will be fully operational by early summer and will scan the skies several times a week on the Nickel 1-meter telescope at Lick Observatory, located on Mt. Hamilton east of San Jose.

    The NIROSETI team also includes Geoffrey Marcy and Andrew Siemion from UC Berkeley; Patrick Dorval, a Dunlap undergraduate, and Elliot Meyer, a Dunlap graduate student; and Richard Treffers of Starman Systems. Funding for the project comes from the generous support of Bill and Susan Bloomfield.

  • richardmitnick 5:24 pm on November 9, 2017 Permalink | Reply
    Tags: , , , , , , SN 2014J, Type Ia supernova   

    From Hubble: “Hubble Shows Light Echo Expanding from Exploded Star” 

    NASA Hubble Banner

    NASA/ESA Hubble Telescope

    NASA/ESA Hubble Telescope

    Nov. 9, 2017

    Donna Weaver
    Space Telescope Science Institute, Baltimore, Maryland

    Ray Villard
    Space Telescope Science Institute, Baltimore, Maryland

    Yi Yang
    Weizmann Institute of Science, Israel


    Light from a supernova explosion in the nearby starburst galaxy Messier 82 is reverberating off a huge dust cloud in interstellar space.

    The supernova, called SN 2014J, occurred at the upper right of Messier 82, and is marked by an “X.” The supernova was discovered on Jan. 21, 2014.

    The inset images at top reveal an expanding shell of light from the stellar explosion sweeping through interstellar space, called a “light echo.” The images were taken 10 months to nearly two years after the violent event (Nov. 6, 2014 to Oct. 12, 2016). The light is bouncing off a giant dust cloud that extends 300 to 1,600 light-years from the supernova and is being reflected toward Earth.

    SN 2014J is classified as a Type Ia supernova and is the closest such blast in at least four decades. A Type Ia supernova occurs in a binary star system consisting of a burned-out white dwarf and a companion star. The white dwarf explodes after the companion dumps too much material onto it.

    Over a period of two and a half years, NASA’s Hubble Space Telescope observed the “light echo” of supernova SN 2014J in galaxy Messier 82, located 11.4 million light-years away.
    Credits: NASA’s Goddard Space Flight Center

    The image of Messier 82 reveals a bright blue disk, webs of shredded clouds, and fiery-looking plumes of glowing hydrogen blasting out of its central regions.

    Close encounters with its larger neighbor, the spiral galaxy Messier 81, is compressing gas in Messier 82 and stoking the birth of multiple star clusters. Some of these stars live for only a short time and die in cataclysmic supernova blasts, as shown by SN 2014J.

    Located 11.4 million light-years away, M82 appears high in the northern spring sky in the direction of the constellation Ursa Major, the Great Bear. It is also called the “Cigar Galaxy” because of the elliptical shape produced by the oblique tilt of its starry disk relative to our line of sight.

    The Messier 82 image was taken in 2006 by the Hubble Space Telescope’s Advanced Camera for Surveys. The inset images of the light echo also were taken by the Advanced Camera for Surveys.

    The science team members are Y. Yang of Texas A&M University, College Station, and the Weizmann Institute of Science, Rehovot, Israel; P.J. Brown of Texas A&M University, College Station; L. Wang of Texas A&M University, College Station, and Purple Mountain Observatory, China; D. Baade, A. Cikota, F. Patat, and J. Spyromilio of the European Organization for Astronomical Research in the Southern Hemisphere, Garching, Germany; M. Cracraft and W.B. Sparks of the Space Telescope Science Institute, Baltimore, Maryland; P.A. Hoflich of Florida State University, Tallahassee; J. Maund and H.F. Stevance of the University of Sheffield, U.K.; X. Wang of Tsinghua University, Beijing Shi; and J.C. Wheeler of the University of Texas at Austin.

    The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy, Inc., in Washington, D.C.

    For images and more information about the light echo and Hubble, visit:



    Image credit: NASA, ESA, and Y. Yang (Texas A&M University and Weizmann Institute of Science, Israel)

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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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    AURA Icon

    NASA image

    • Greg Long 11:52 pm on November 9, 2017 Permalink | Reply

      I find the idea of this astounding. I mean, sure light would bounce, but it’s the scale that astounds


    • richardmitnick 10:11 am on November 10, 2017 Permalink | Reply

      Greg, thanks for your comment and your continued support.


  • richardmitnick 2:57 pm on January 20, 2017 Permalink | Reply
    Tags: , , , , , , iPTF16geu, Supernova Refsdal, Type Ia supernova, University of California Berkeley and Lawrence Berkeley National Laboratory   

    From AAS NOVA: ” The Search for Lensed Supernovae” 


    American Astronomical Society

    20 January 2017
    Susanna Kohler

    Supernova Refsdal, seen in quadruplicate in the inset of this Hubble image, is one of only two supernovae we’ve observed to have multiple images caused by gravitational lensing. The other (not shown) is a Type Ia supernova, iPTF16geu. A new study discusses the prospects for discovering more multiply-imaged Type Ia supernovae. [NASA/ESA/STScI/UCLA]

    Type Ia supernovae that have multiple images due to gravitational lensing can provide us with a wealth of information — both about the supernovae themselves and about our surrounding universe. But how can we find these rare explosions?

    Clues from Multiple Images

    An illustration of gravitational lensing. Light from the distant supernova is bent as it passes through a giant elliptical galaxy in the foreground, causing multiple images of the supernova to appear to be hosted by the elliptical galaxy. [Adapted from image by NASA/ESA/A. Feild (STScI)]

    Clues from Multiple Images

    When light from a distant object passes by a massive foreground galaxy, the galaxy’s strong gravitational pull can bend the light, distorting our view of the background object. In severe cases, this process can cause multiple images of the distant object to appear in the foreground lensing galaxy.

    Observations of multiply-imaged Type Ia supernovae (explosions that occur when white dwarfs in binary systems exceed their maximum allowed mass) could answer a number of astronomical questions. Because Type Ia supernovae are standard candles, distant, lensed Type Ia supernovae can be used to extend the Hubble diagram to high redshifts. Furthermore, the lensing time delays from the multiply-imaged explosion can provide high-precision constraints on cosmological parameters.

    The catch? So far, we’ve only found one multiply-imaged Type Ia supernova: iPTF16geu, discovered late last year. We’re going to need a lot more of them to develop a useful sample! So how do we identify the mutiply-imaged Type Ias among the many billions of fleeting events discovered in current and future surveys of transients?

    Absolute magnitudes for Type Ia supernovae in elliptical galaxies. None are expected to be above -20 in the B band, so if we calculate a magnitude for a Type Ia supernova that’s larger than this, it’s probably not hosted by the galaxy we think it is! [Goldstein & Nugent 2017]

    Searching for Anomalies

    Two scientists from University of California, Berkeley and Lawrence Berkeley National Laboratory have a plan. In a recent publication [citation below], Daniel Goldstein and Peter Nugent propose the following clever procedure to apply to data from transient surveys:

    From the data, select only the supernova candidates that appear to be hosted by quiescent elliptical galaxies.
    Use the host galaxies’ photometric redshifts to calculate absolute magnitudes for the supernovae in this sample.
    Select from this only the supernovae above the maximum absolute magnitude expected for Type Ia supernovae.

    Supernovae selected in this way are likely tricking us: their apparent hosts are probably not their hosts at all! Instead, the supernova is likely behind the galaxy, and the galaxy is just lensing its light. Using this strategy therefore allows us to select supernova candidates that are most likely to be distant, gravitationally lensed Type Ia supernovae.

    Redshift distribution of the multiply-imaged Type Ia supernovae the authors estimate will be detectable by ZTF and LSST in their respective 3- and 10-year survey durations. [Goldstein & Nugent 2017]

    A convenient aspect of Goldstein and Nugent’s technique is that we don’t need to be able to resolve the lensed multiple images for discovery. This is useful, because ground-based optical surveys don’t have the resolution to see the separate images — yet they’ll still be useful for discovering multiply-imaged supernovae.

    Future Prospects

    How useful? Goldstein and Nugent use Monte Carlo simulations to estimate how many multiply-imaged Type Ia supernovae will be discoverable with future survey projects. They find that the Zwicky Transient Facility (ZTF), which will begin operating this year, should be able to find up to 10 using this technique in a 3-year search.

    The Zwicky Transient Facility (ZTF) | Bryan Penprase

    The Large Synoptic Survey Telescope (LSST), which should start operating in 2022, will be able to find around 500 multiply-imaged Type Ia supernovae in a 10-year survey.

    LSST/Camera, built at SLAC
    LSST/Camera, built at SLAC
    LSST Interior
    LSST telescope, currently under construction 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.
    LSST telescope, currently under construction 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.


    Daniel A. Goldstein and Peter E. Nugent 2017 ApJL 834 L5. doi:10.3847/2041-8213/834/1/L5

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  • richardmitnick 12:56 pm on January 12, 2017 Permalink | Reply
    Tags: , , IC 3639, Monster black holes, , , NGC 1448, , Type Ia supernova,   

    From Space Science Laboratory at UC Berkeley: “NuSTAR – Black Holes Hide in our Cosmic Backyard” 

    UC Berkeley

    UC Berkeley

    SSL UC Berkeley

    Space Science Laboratory

    No image caption. No image credit.



    January 12, 2017
    Christopher Scholz

    Monster black holes sometimes lurk behind gas and dust, hiding from the gaze of most telescopes. But they give themselves away when material they feed on emits high-energy X-rays that NASA’s NuSTAR (Nuclear Spectroscopic Telescope Array) mission can detect. That’s how NuSTAR recently identified two gas-enshrouded supermassive black holes, located at the centers of nearby galaxies.

    “These black holes are relatively close to the Milky Way, but they have remained hidden from us until now,” said Ady Annuar, a graduate student at Durham University in the United Kingdom, who presented the results at the American Astronomical Society meeting in Grapevine, Texas. “They’re like monsters hiding under your bed.”

    Both of these black holes are the central engines of what astronomers call “active galactic nuclei,” a class of extremely bright objects that includes quasars and blazars. Depending on how these galactic nuclei are oriented and what sort of material surrounds them, they appear very different when examined with telescopes.

    Active galactic nuclei are so bright because particles in the regions around the black hole get very hot and emit radiation across the full electromagnetic spectrum — from low-energy radio waves to high-energy X-rays. However, most active nuclei are believed to be surrounded by a doughnut-shaped region of thick gas and dust that obscures the central regions from certain lines of sight. Both of the active galactic nuclei that NuSTAR recently studied appear to be oriented such that astronomers view them edge-on. That means that instead of seeing the bright central regions, our telescopes primarily see the reflected X-rays from the doughnut-shaped obscuring material.

    “Just as we can’t see the sun on a cloudy day, we can’t directly see how bright these active galactic nuclei really are because of all of the gas and dust surrounding the central engine,” said Peter Boorman, a graduate student at the University of Southampton in the United Kingdom.

    Boorman led the study of an active galaxy called IC 3639, which is 170 million light years away.

    IC 3639, a galaxy with an active galactic nucleus, is seen in this image combining data from the Hubble Space Telescope and the European Southern Observatory.

    This galaxy contains an example of a supermassive black hole hidden by gas and dust. Researchers analyzed NuSTAR data from this object and compared them with previous observations from NASA’s Chandra X-Ray Observatory and the Japanese-led Suzaku satellite.

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    JAXA/Suzaku satellite
    JAXA/Suzaku satellite

    The findings from NuSTAR, which is more sensitive to higher energy X-rays than these observatories, confirm the nature of IC 3639 as an active galactic nucleus that is heavily obscured, and intrinsically much brighter than observed.

    Researchers analyzed NuSTAR data from this object and compared them with previous observations from NASA’s Chandra X-Ray Observatory and the Japan-led Suzaku satellite. NuSTAR also provided the first precise measurement of how much material is obscuring the central engine of IC 3639, allowing researchers to determine how luminous this hidden monster really is.

    More surprising is the spiral galaxy that Annuar focused on: NGC 1448.

    NGC 1448 (also designated NGC 1457 and ESO 249-16) is a spiral galaxy located about 60 million light-years away in the constellation Horologium. It has a prominent disk of young and very bright stars surrounding its small, shining core. The galaxy is receding from us with 1168 kilometers per second.

    NGC 1448 has recently been a prolific factory of supernovae, the dramatic explosions that mark the death of stars: after a first one observed in this galaxy in 1983 (SN 1983S), two more have been discovered during the past decade.

    Visible as a red dot inside the disc, in the upper right part of the image, is the supernova observed in 2003 (Type II supernova SN 2003hn), whereas another one, detected in 2001 (Type Ia supernova SN 2001el), can be noticed as a tiny blue dot in the central part of the image, just below the galaxy’s core. If captured at the peak of the explosion, a supernova might be as bright as the whole galaxy that hosts it.

    A Type Ia supernova is a result from the violent explosion of a white dwarf star. This category of supernovae produces consistent peak luminosity. The stability of this luminosity allows these supernovae to be used as standard candles to measure the distance to their host galaxies because the visual magnitude of the supernovae depends primarily on the distance.

    A Type II supernova results from the rapid collapse and violent explosion of a massive star. A star must have at least 8 times, and no more than 40–50 times the mass of the Sun for this type of explosion. It is distinguished from other types of supernova by the presence of hydrogen in its spectrum. Type II supernovae are mainly observed in the spiral arms of galaxies and in H II regions, but not in elliptical galaxies.

    This image was obtained using the 8.2-metre telescopes of ESO’s Very Large Telescope. It combines exposures taken between July 2002 and the end of November 2003.

    ESO/VLT at Cerro Paranal, Chile, ESO/VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level
    ESO/VLT at Cerro Paranal, Chile, ESO/VLT at Cerro Paranal, with an elevation of 2,635 metres (8,645 ft) above sea level

    Credit: ESO

    The black hole in its center was only discovered in 2009, even though it is at the center of one of the nearest large galaxies to our Milky Way. By “near,” astronomers mean NGC 1448 is only 38 million light years away (one light year is about 6 trillion miles).

    Annuar’s study discovered that this galaxy also has a thick column of gas hiding the central black hole, which could be part of a doughnut-shaped region. X-ray emission from NGC 1448, as seen by NuSTAR and Chandra, suggests for the first time that, as with IC 3639, there must be a thick layer of gas and dust hiding the active black hole in this galaxy from our line of sight.

    Researchers also found that NGC 1448 has a large population of young (just 5 million year old) stars, suggesting that the galaxy produces new stars at the same time that its black hole feeds on gas and dust. Researchers used the European Southern Observatory New Technology Telescope to image NGC 1448 at optical wavelengths, and identified where exactly in the galaxy the black hole should be. A black hole’s location can be hard to pinpoint because the centers of galaxies are crowded with stars. Large optical and radio telescopes can help detect light from around black holes so that astronomers can find their location and piece together the story of their growth.

    “It is exciting to use the power of NuSTAR to get important, unique information on these beasts, even in our cosmic backyard where they can be studied in detail,” said Daniel Stern, NuSTAR project scientist at NASA’s Jet Propulsion Laboratory, Pasadena, California.

    NuSTAR is a Small Explorer mission led by Caltech and managed by JPL for NASA’s Science Mission Directorate in Washington. NuSTAR was developed in partnership with the Danish Technical University and the Italian Space Agency (ASI). The spacecraft was built by Orbital Sciences Corp., Dulles, Virginia. NuSTAR’s mission operations center is at UC Berkeley, and the official data archive is at NASA’s High Energy Astrophysics Science Archive Research Center. ASI provides the mission’s ground station and a mirror archive. JPL is managed by Caltech for NASA.

    See the full article here .

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