Tagged: UC Santa Cruz Toggle Comment Threads | Keyboard Shortcuts

  • richardmitnick 2:11 pm on July 26, 2016 Permalink | Reply
    Tags: , , Pacific Collegiate School student Spencer Cheleden, Soquel teen develops new technology for astronomical telescopes, UC Santa Cruz   

    From Santa Cruz Sentinel via UC Santa Cruz: “Soquel teen develops new technology for astronomical telescopes” 

    UC Santa Cruz

    UC Santa Cruz

    2
    Santa Cruz Sentinel

    07/25/16
    Ryan Masters

    1
    Pacific Collegiate School student Spencer Cheleden has developed a new way to coat the enormous astronomical telescope mirrors during his summer research at UC Santa Cruz with research astronomer mentor Andrew Phillips. (Dan Coyro — Santa Cruz Sentinel)

    While most teenagers play Pokémon Go this summer, Spencer Cheleden is discovering ways to improve the world’s most powerful astronomical telescopes.

    Under the mentorship of Andrew Phillips, who heads up the Advanced Coatings Lab at the University of California Observatories, Cheleden, began experimenting with silver-based reflective coatings on telescope mirrors in the fall of 2015 as part of UC Santa Cruz’s Science Internship Program.

    Optical coatings are thin films applied to mirror and lens surfaces to enhance reflection for mirrors. They can consist of one or multiple layers of various materials, and are roughly 200 to 400 nanometers in thickness — or 1/300 the diameter of a human hair.

    “Dr. Phillips outlined his research for me last summer and gave me a choice of projects. Silver-based reflective coatings had been sort of a dormant area of research and I became interested in improving the efficiency of the telescopes to create more light and more data,” said Cheleden, 17, who will be a senior at Pacific Collegiate School in the fall.

    Telescope mirrors traditionally have aluminum-based coatings, Cheleden said. Silver has been largely overlooked as a coating material because it tarnishes when exposed to oxygen. To protect the thin film of silver from oxidation, Phillips and Cheleden began experimenting with a variety of metal oxide, fluoride and nitride applications.

    “If you spray it clear over the silver, it maintains its reflecting properties and also protects from water and abrasion,” Cheleden said.

    This summer, Phillips and Cheleden have been creating composites using promising materials such as titanium oxide, hafnium oxide, silicon nitride and yttrium fluoride. To see which composite protects the silver reflecting surface longest and best, these coatings are being tested in a lab on the UCSC campus as well as in real-world situations such as a Lick Observatory telescope.

    Phillips and Cheleden already have co-published results in the Journal of Astronomical Telescopes, Instruments and Systems, a paper that Phillips also presented at a conference in Scotland. Cheleden says they hope to have a second paper published this year.

    In addition, Cheleden won first place in physics and astronomy at the 2016 California State Science Fair and received the Optics and Photonics Award from SPIE, the International Society for Optics and Photonics.

    His project was so outstanding that the University of Toronto’s engineering department selected him to attend a weeklong elite engineering summer camp in Toronto this year where he studied cleaner combustion engines for aerospace.

    Despite the accolades and success, Cheleden said he probably won’t pursue physics or astronomy in the future. While he dreams of attending Stanford University after high school, he doesn’t foresee a career in academia.

    “I see myself using applied mathematics in finance or consulting,” Cheleden said. “Maybe running a company offering computer-based solutions.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    UCO Lick Shane Telescope
    UCO Lick Shane Telescope interior
    Shane Telescope at UCO Lick Observatory, UCSC/em>

    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.

    Advertisements
     
  • richardmitnick 6:36 pm on July 7, 2016 Permalink | Reply
    Tags: , , Exploring a Frozen Extrasolar World, , UC Santa Cruz   

    From Gemini: “Exploring a Frozen Extrasolar World” 

    NOAO

    Gemini Observatory
    Gemini Observatory

    July 6, 2016
    Media Contacts:

    Peter Michaud
    Public Information and Outreach
    Gemini Observatory, Hilo, HI
    Email: pmichaud”at”gemini.edu
    Cell: (808) 936-6643

    Tim Stephens
    University of California, Santa Cruz
    Email: stephens”at”ucsc.edu
    Phone: (831) 459-4352

    Science Contacts:

    Andrew Skemer
    University of California, Santa Cruz
    Email: askemer”at”ucsc.edu
    Phone: (831) 459-5753

    Jacqueline Faherty
    Hubble Postdoctoral Fellow
    Carnegie Institution for Science
    Email: jfaherty17″at”gmail.com
    Cell: (201) 694-0807

    Sandy Leggett
    Gemini Observatory
    Email: sleggett”at”gemini.edu
    Phone: (808) 974-2604

    1
    Artist’s conception of how WISE 0855 might appear if viewed close-up in infrared light. Artwork by Joy Pollard, Gemini Observatory/AURA.

    University of California, Santa Cruz press release. [This is definitely worth reading, but, finding the Gemini article, I was bound to use it.]


    First Evidence for Water Ice Clouds Found outside Solar System
    Access mp4 video here .

    Astronomers have “cracked” a very cold case with the dissection of light from the coldest known brown dwarf. In fact, the brown dwarf, named WISE 0855, is billed as the most frigid discrete world yet discovered beyond our Solar System. The research also presents the strongest evidence yet for water clouds in the atmosphere of an extrasolar object.

    The history of “failed stars” having masses between that of a star and planet – called brown dwarfs – continues to blur. Now, that distinction is even more ambiguous with the confirmation that WISE 0855 shares more of a likeness with Jupiter than many exoplanets.

    New evidence for this comes from the first spectroscopy, or light fingerprint, of the object, performed at the Gemini North telescope in Hawai’i. The spectrum presents astronomers with the most definitive evidence ever for water vapor in the atmosphere of an object outside of our solar system. The research also confirms that temperatures dip to about 20 below zero Celsius (-10 degrees F) in its cold atmosphere.

    WISE 0855 was discovered by Kevin Luhman of Penn State in 2014 using data from NASA’s Wide-field Infrared Survey Explorer (WISE) satellite.

    NASA/Wise Telescope
    NASA/Wise Telescope

    WISE 0855’s relatively close proximity – it’s only about 7.2 light years away, the fourth closest extrasolar object to the Sun – provides an advantage in capturing the object’s miniscule glow; however, it is still remarkably difficult to observe.

    “It’s five times fainter than any other object detected with ground-based spectroscopy at this wavelength,” said Andy Skemer of the University of California Santa Cruz. “Now that we have a spectrum, we can really start thinking about what’s going on in this object. Our spectrum shows that WISE 0855 is dominated by water vapor and clouds, with an overall appearance that is strikingly similar to Jupiter.” Skemer is first author of a paper on the new findings to be published in Astrophysical Journal Letters and currently available online.

    “I think everyone on the research team really believed that we were dreaming to think we could obtain a spectrum of this brown dwarf because its thermal glow is so feeble,” said Skemer. WISE 0855, is so cool and faint that many astronomers thought it would be years before we could dissect its diminutive light into a spectrum. “I thought we’d have to wait until the James Webb Space Telescope was operating to do this,” adds Skemer.

    The spectrum, obtained using the Gemini North telescope on Hawaii’s Maunakea, was obtained over a period of 13 nights (about 14 hours of data collection). “These observations could only be done on a facility like Gemini North. This is due to its location on Maunakea, where there is often remarkably little water vapor in the air to interfere with the sensitive observations, and the technology on the telescope, like its 8-meter silver-coated mirror,” says Jacqueline Faherty of the Carnegie Department of Terrestrial Magnetism. “We pushed the boundary of what could be done with a telescope here on Earth. And the result is spectacular.”

    The resulting high-quality spectrum reveals water vapor and clouds in the object’s atmosphere, and opens opportunities to explore the atmosphere’s dynamics and chemistry. Gemini astronomer, and brown dwarf researcher, Sandy Leggett explains that the spectrum shows less phosphine than we see in Jupiter, “…suggesting that the atmosphere may be less turbulent, since mixing produces the phosphine seen in Jupiter’s atmosphere.”

    Results from previous observations of WISE 0855, published in 2014, provided hints of water clouds based on very limited photometric data (the relative brightness of specific wavelengths of light). Skemer, also a coauthor of the 2014 paper, adds that with spectroscopy scientists are able to separate the object’s light into a wide range of infrared wavelengths, and probe the body’s molecular composition. “If our eyes could see infrared light, which is redder than the reddest light we can see, the data would look like a rainbow of colors.” He adds, “The relative brightness of each color gives us a glimpse into the environment of the object’s atmosphere.”

    The coauthors of the study include graduate student Caroline Morley and professor of astronomy and astrophysics Jonathan Fortney at UC Santa Cruz; Katelyn Allers at Bucknell University; Thomas Geballe at Gemini Observatory; Mark Marley and Roxana Lupu at NASA Ames Research Center; Jacqueline Faherty at the Carnegie Institution of Washington; and Gordon Bjoraker at NASA Goddard Space Flight Center.

    Observations for this work were made using the Gemini Near-InfraRed Spectrograph (GNIRS) which is mounted on the Gemini North telescope on Maunakea in Hawai‘i.

    3
    Gemini Near-InfraRed Spectrograph (GNIRS)

    The research team, and Gemini staff, are grateful to be able to observe from Maunakea, Hawaii’s highest peak, where conditions are ideal for these types of observations.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Gemini North
    Gemini North, Hawai’i

    Gemini South
    Gemini South, Chile
    AURA Icon

    Gemini’s mission is to advance our knowledge of the Universe by providing the international Gemini Community with forefront access to the entire sky.

    The Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located on Mauna Kea, Hawai’i (Gemini North) and the other telescope on Cerro Pachón in central Chile (Gemini South); together the twin telescopes provide full coverage over both hemispheres of the sky. The telescopes incorporate technologies that allow large, relatively thin mirrors, under active control, to collect and focus both visible and infrared radiation from space.

    The Gemini Observatory provides the astronomical communities in six partner countries with state-of-the-art astronomical facilities that allocate observing time in proportion to each country’s contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the Canadian National Research Council (NRC), the Chilean Comisión Nacional de Investigación Cientifica y Tecnológica (CONICYT), the Australian Research Council (ARC), the Argentinean Ministerio de Ciencia, Tecnología e Innovación Productiva, and the Brazilian Ministério da Ciência, Tecnologia e Inovação. The observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.

     
  • richardmitnick 4:21 pm on June 8, 2016 Permalink | Reply
    Tags: , , Jennifer Burt, Lick APF, UC Santa Cruz,   

    From UCSC: Women in Science “The sky is no limit for planet-hunting grad student” 

    UC Santa Cruz

    UC Santa Cruz

    June 07, 2016
    Peggy Townsend

    Astronomy student Jennifer Burt helped write software that turned a powerful telescope at Lick Observatory into the first automated planet finder in the world.

    1
    Grad student Jennifer Burt, above, “played the linchpin role in writing the software that puts the ‘A’ in the APF (Automated Planet Finder) Telescope,” said Greg Laughlin, professor of astronomy and astrophysics. (Photo by Carolyn Lagattuta)

    Every night for a year, astronomy graduate student Jennifer Burt would settle into a small room on the UC Santa Cruz campus and begin her job as a planet hunter.

    While most people slept, Burt would examine weather, atmospheric conditions, and time of year before deciding which stars on a long list of possibilities would be the best targets for a powerful telescope located at Lick Observatory on Mount Hamilton. A run of fingers over computer keys would then start the telescope searching portions of the night sky for its prey: planets that orbited stars beyond our solar system.

    “After a year,” said the 28-year-old with a laugh, “I thought maybe we should automate this thing because I would like to sleep at night.”

    Which is exactly what the competitive ballroom dancer and former Cornell University grad did. She went to work helping write software that turned the $12 million telescope into a robotic version of herself. It became the first automated planet finder in the world.

    “Jenn played the linchpin role in writing the software that puts the ‘A’ in the APF (Automated Planet Finder) Telescope,” says Greg Laughlin, professor of astronomy and astrophysics at UC Santa Cruz. “With hard-won night after night of on-sky experience, she was able to gain a full understanding of all the nuances, subtleties, and contingencies that occur in the course of operations. She was then able to fully translate this intuitive understanding into the stark, fully defined logical structure that permits a computer to take over the night-to-night role of a human observer.”

    Soon, however, Burt will give up the redwoods of Santa Cruz for the historic streets of Cambridge, Mass., where she won a post-doc fellowship at the Massachusetts Institute of Technology and hopes to work on a NASA project aimed at discovering more about these so-called extrasolar planets or exoplanets. The project, dubbed TESS (Transiting Exoplanet Survey Satellite), is designed to determine the radii and orbits of the planets it detects. More than 3,000 have already been discovered.

    NASA/TESS
    NASA/TESS

    With nearby Harvard also taking part in the project, “it’s a cool place to be for someone like me,” Burt says. She notes however, the opportunity might not have happened without the guidance of her UC Santa Cruz mentors and a $10,000 scholarship from the Achievement Rewards for College Scientists (ARCS) Foundation.

    Tall, with long, dark hair and a way of explaining astronomy that can make even a science-phobe get excited about stargazing, Burt came to her career thanks to an old telescope set up at a family cabin in the Adirondacks and an energetic teacher who ran a NASA club at her high school in upstate New York. A club visit to Arizona State University, where NASA projects were being undertaken, sealed her fate.

    “That trip made it clear early on for me that astronomy was a viable career path,” Burt says.

    At Cornell, Burt’s attention was grabbed by the emerging field of exoplanet research, which led her to UC Santa Cruz and two professors of astronomy and astrophysics, Laughlin and Steve Vogt. Here, she began her nocturnal planet detecting with the result that her team was able to discover three different planetary systems using the APF telescope.

    UC Observatories Lick APF
    UC Observatories Lick APF

    The finding that most electrifies her was the detection of six planets orbiting a nearby star with the decidedly un-electrifying name of HD219134.

    “It’s especially exciting because the star is very bright so we can do a lot of follow-up studies,” Burt says. “The second thing that makes it cool is that at the same time we found six planets, another team in Switzerland found the same system but it had only seen the inner four planets.”

    Burt also is credited with locating a Neptune-sized planet orbiting a red dwarf star, and, while she admits there was nothing exceptional about this particular planet, the discovery showed the APF is designed perfectly for its job, which is to find even the most common planets.

    For Burt, who sports a star-shaped ring and a galactic-themed cell phone cover, the future holds the promise of discovering more about these exoplanets: their properties, their origin and, as always, whether there are other habitable Earth-sized planets out there.

    Delving into far-flung mysteries is exactly the place a sci-fi-loving scientist like Burt wants to find herself. But she wouldn’t have arrived, she says, without the ARCS scholarship—which allowed her to travel to meet prominent people in the field, resulting in a post-doctoral position—and also without the help of Laughlin and Vogt.

    Burt, who also coached the UC Santa Cruz ballroom dance team and designed a training program for teaching assistants on campus, says Vogt “taught me everything I know about finding planets” while Laughlin, a theorist, “taught me to look for the big science questions that were interesting.”

    “Any scientist’s eventual success is based, in part, on the people who supported them along the way,” Burt says. “I’ve been extremely fortunate to work with advisors who were always willing to share their knowledge, while also continually pushing me to become a better researcher.

    “That’s a huge advantage when you’re starting out.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    UCO Lick Shane Telescope
    UCO Lick Shane Telescope interior
    Shane Telescope at UCO Lick Observatory, UCSC/em>

    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.

     
  • richardmitnick 2:16 pm on May 14, 2016 Permalink | Reply
    Tags: , , , UC Santa Cruz   

    From UCSC: “Astronomer Sandra Faber to receive honorary degree from Amherst College” 

    UC Santa Cruz

    UC Santa Cruz

    May 13, 2016
    Tim Stephens

    1
    Sandy Faber

    Astronomer Sandra Faber will receive an honorary degree from Amherst College during its 195th commencement exercises on Sunday, May 22. Amherst President Biddy Martin will deliver the address during the ceremony, and Faber and the other honorees will speak in a series of public conversations.

    A professor emeritus of astronomy and astrophysics at UC Santa Cruz, Faber is known for her pioneering research on the formation and evolution of galaxies, distant galaxy clusters, and the large-scale structure of the universe. She is also a leading authority on telescopes and astronomical instrumentation and has been closely involved with both the Hubble Space Telescope and the W. M. Keck Observatory in Hawaii.

    NASA/ESA Hubble Telescope
    NASA/ESA Hubble Telescope

    Keck Observatory, Mauna Kea, Hawaii, USA
    Keck Observatory Interior
    Keck Observatory

    Among her many contributions to astronomy is the Faber-Jackson relation, the first known structural scaling law for galaxies—in this case, the relation between the mass of a galaxy and the speed of stars that orbit within it.

    3
    Velocity dispersion (y-axis) plotted against absolute magnitude (x-axis) for a sample of elliptical galaxies, with the Faber–Jackson relation shown in blue.
    Plot of the Faber-Jackson relation for elliptical galaxies, using data from the original paper by Faber & Jackson (1976)

    In addition, Faber’s work has uncovered huge irregularities in the expansion of the universe caused by the perturbing effects of gravity from superclusters of galaxies. With colleagues, she used the Hubble Space Telescope to penetrate the cores of galaxies, revealing massive black holes at their centers. She has led major efforts with both Hubble and Keck to survey thousands of distant galaxies to characterize and document the evolution of galaxies over the history of the universe.

    Faber, who joined the UCSC faculty in 1972, holds a bachelor’s degree in physics from Swarthmore and a Ph.D. in astronomy from Harvard. She has received many awards and honors in recognition of her accomplishments, including the National Medal of Science, the Franklin Institute’s Bower Award and Prize for Achievement in Science, and two awards for lifetime scientific achievement, the Bruce Medal of the Astronomical Society of the Pacific and the Russell Prize of the American Astronomical Society. She is a member of the National Academy of Sciences, American Academy of Arts and Sciences, and American Philosophical Society.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    UCO Lick Shane Telescope
    UCO Lick Shane Telescope interior
    Shane Telescope at UCO Lick Observatory, UCSC/em>

    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.

     
  • richardmitnick 2:38 pm on May 6, 2016 Permalink | Reply
    Tags: , , UC Santa Cruz   

    From UCSC: “Shallow slow-motion earthquakes detected offshore of New Zealand” 

    UC Santa Cruz

    UC Santa Cruz

    May 05, 2016
    Tim Stephens

    1
    An international team of scientists deployed a network of seafloor instruments, including seismometers and pressure gauges, offshore Gisborne, New Zealand, from the R/V Tangaroa. (Photo by Takeo Yagi, University of Tokyo)

    2
    The Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip (HOBITSS) detected a slow slip event at the Hikurangi subduction zone, where the Pacific Plate dives beneath New Zealand’s North Island. (Image credit: GNS Science/Laura Martin)

    Research published* in the May 6 issue of Science indicates that slow-motion earthquakes or “slow-slip events” can rupture the shallow portion of a fault that also moves in large, tsunami-generating earthquakes. The finding has important implications for assessing tsunami hazards. The discovery was made by conducting the first-ever detailed investigation of centimeter-level seafloor movement at an offshore subduction zone.

    “We’ve previously used land-based instruments to detect slow-slip events, but this is the first time we’ve been able to document slow slip in the shallow portion of an offshore subduction zone. With instruments on the seafloor right above the plate boundary, we now have very high-resolution mapping of where the slip occurred,” said coauthor Susan Schwartz, professor of Earth and planetary sciences at UC Santa Cruz.

    First author Laura Wallace, a research scientist at The University of Texas at Austin’s Institute for Geophysics, led an international team of researchers from the United States, Japan, and New Zealand in the collaborative research project. “These data have revealed the true extent of slow-motion earthquakes at an offshore subduction zone for the first time,” said Wallace, who earned her Ph.D. at UC Santa Cruz in 2002.

    Subduction zone

    The world’s most devastating tsunamis are generated by earthquakes that occur near the trenches of subduction zones, places where one tectonic plate begins to dive or “subduct” beneath another. Using a network of highly-sensitive seafloor pressure recorders, the team detected a slow-slip event in September 2014 off the east coast of New Zealand. The study was undertaken at the Hikurangi subduction zone, where the Pacific Plate subducts beneath New Zealand’s North Island.

    The slow-slip event lasted two weeks, resulting in 15 to 20 centimeters of movement along the fault that lies between New Zealand and the Pacific Plate, a distance equivalent to three to four years of background plate motion. If the movement had occurred suddenly, rather than slowly, it would have resulted in a magnitude 6.8 earthquake. The seafloor sensors recorded up to 5.5 centimeters (about 2 inches) of upward movement of the seafloor during the event.

    Slow-slip events are similar to earthquakes, but instead of releasing strain between two tectonic plates in seconds, they do it over days to weeks, creating quiet, centimeter-sized shifts in the landscape. In a few cases, these small shifts have been associated with setting off destructive earthquakes. The slow-slip event that the team studied occurred in the same location as a magnitude 7.2 earthquake in 1947 that generated a large tsunami. The study shows that the two types of seismic events can occur on the same part of a plate boundary.

    HOBITSS

    The link has been difficult to document in the past because most slow-slip monitoring networks are land-based and are located far from the trenches that host tsunami-generating earthquakes, Wallace said. The data for this study was recorded by HOBITSS, a temporary underwater network that monitored slow-slip events by recording vertical movement of the seafloor. HOBITSS stands for “Hikurangi Ocean Bottom Investigation of Tremor and Slow Slip.”

    “Our results clearly show that shallow, slow-slip event source areas are also capable of hosting seismic rupture and generating tsunamis,” said coauthor Yoshihiro Ito, a professor at Kyoto University. “This increases the need to continuously monitor shallow, offshore slow-slip events at subduction zones, using permanent monitoring networks similar to those that have been established offshore of Japan.”

    According to Schwartz, the demonstration that pressure sensors on the seafloor can be used to accurately measure the deformation associated with slow-slip events is an important proof of concept. “The ultimate goal is to map the mechanical properties of the shallow plate interface and understand what areas have the potential to slip in ways that produce damaging earthquakes, tsunami-generating earthquakes, or slow slip,” she said.

    Earthquakes are unpredictable events, Wallace said, but the linkage between slow-slip events and earthquakes could eventually help in forecasting the likelihood of damaging earthquakes. “To do that we will have to understand the links between slow-slip events and earthquakes much better than we currently do,” Wallace said.

    The research team installed the HOBITSS network in May 2014, which consisted of 24 seafloor pressure gauges, and 15 ocean bottom seismometers. The team collected the devices and data in June 2015.

    Additional participants included scientists from the University of Tokyo, Tohoku University, GNS Science, and the University of Colorado Boulder. The research was funded by the National Science Foundation; the Japan Society for Promotion of Science; Japan’s Ministry of Education, Culture, Sports, Science and Technology; and grants from participating universities and research institutions.

    *Science paper:
    Slow slip near the trench at the Hikurangi subduction zone, New Zealand

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    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.

     
  • richardmitnick 3:10 pm on April 8, 2016 Permalink | Reply
    Tags: , , , , UC Santa Cruz   

    From AAS NOVA: ” How Bright Can Supernovae Get?” 

    AASNOVA

    American Astronomical Society

    1
    Supernova remnant W49B. The highly distorted supernova remnant shown in this image may contain the most recent black hole formed in the Milky Way galaxy. The image combines X-rays from NASA’s Chandra X-ray Observatory in blue and green, radio data from the NSF’s Very Large Array in pink, and infrared data from Caltech’s Palomar Observatory in yellow. (X-ray: NASA/CXC/MIT/L.Lopez et al; Infrared: Palomar; Radio: NSF/NRAO/VLA)

    NASA/Chandra Telescope
    NASA/Chandra Telescope

    Caltech Palomar 200 inch Hale Telescope
    Caltech Palomar 200 inch Hale Telescope interior
    Caltech Palomar 200 inch Hale Telescope

    NRAO/VLA
    NRAO/VLA

    Supernovae — enormous explosions associated with the end of a star’s life — come in a variety of types with different origins. A new study has examined how the brightest supernovae in the Universe are produced, and what limits might be set on their brightness.

    Ultra-Luminous Observations

    Recent observations have revealed many ultra-luminous supernovae, which have energies that challenge our abilities to explain them using current supernova models. An especially extreme example is the 2015 discovery of the supernova ASASSN-15lh, which shone with a peak luminosity of ~2*1045 erg/s, nearly a trillion times brighter than the Sun. ASASSN-15lh radiated a whopping ~2*1052 erg in the first four months after its detection.

    How could a supernova that bright be produced? To explore the answer to that question, Tuguldur Sukhbold and Stan Woosley at University of California, Santa Cruz, have examined the different sources that could produce supernovae and calculated upper limits on the potential luminosities of each of these supernova varieties.

    Explosive Models

    Sukhbold and Woosley explore multiple different models for core-collapse supernova explosions, including:

    Prompt explosion
    A star’s core collapses and immediately explodes.

    Pair instability
    Electron/positron pair production at a massive star’s center leads to core collapse. For high masses, radioactivity can contribute to delayed energy output.

    Colliding shells
    Previously expelled shells of material around a star collide after the initial explosion, providing additional energy release.

    Magnetar
    The collapsing star forms a magnetar — a rapidly rotating neutron star with an incredibly strong magnetic field — at its core, which then dumps energy into the supernova ejecta, further brightening the explosion.

    They then apply these models to different types of stars.

    Setting the Limit

    2
    The authors show that the light curve of ASASSN-15lh (plotted in orange) can be described by a model (black curve) in which a magnetar with an initial spin period of 0.7 ms and a magnetic field of 2*1013 Gauss deposits energy into ~12 solar masses of ejecta. Click for a closer look! [Adapted from Sukhbold&Woosley 2016]

    The authors find that the maximum luminosity that can be produced by these different supernova models ranges between 5*1043 and 2*1046 erg/s, with total radiated energies of 3*1050 to 4*1052 erg. This places the upper limit on the brightness of a supernova at about 5 trillion times the luminosity of the Sun.

    The calculations performed by Sukhbold and Woosley confirm that, of the options they explore, the least luminous events are produced by prompt explosions. The brightest events possible are powered by the rotational energy of a newly born magnetar at the heart of the explosion.

    The energies of observed ultra-luminous supernovae are (just barely) contained within the bounds of the mechanisms explored here. This is even true of the extreme ASASSN-15lh — which, based on the authors’ calculations, was almost certainly powered by an embedded magnetar. If we were to observe a supernova more than twice as bright as ASASSN-15lh, however, it would be nearly impossible to explain with current models.
    Citation

    Tuguldur Sukhbold and S. E. Woosley 2016 ApJ 820 L38. doi:10.3847/2041-8205/820/2/L38

    Science Paper:
    THE MOST LUMINOUS SUPERNOVAE

    Science team:
    Tuguldur Sukhbold, S. E. Woosley

    Author affiliations
    Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA
    UC Santa Cruz Dept of Astronomy and Astrophysics

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

     
  • richardmitnick 11:07 am on March 11, 2016 Permalink | Reply
    Tags: , , Milky Way Halo of old stars, , UC Santa Cruz   

    From SKY & Telescope: “Galactic Archaelogy in the Milky Way Halo” 

    SKY&Telescope bloc

    Sky & Telescope

    March 10, 2016
    Monica Young

    MIlky Way Halo NASA ESA STScI
    Milky Way surrounded by halo of 13 old stars

    Thirteen lonely stars in the outer reaches of the Milky Way may hold clues to our galaxy’s formation. New research shows that they might be part of a shell-shaped relic that marks an ancient run-in with a dwarf galaxy.

    In the galactic disk, gas and stars circle the center in orderly orbits, but the same can’t be said of the cloud of stars that surround the Milky Way. Theorists think most of these so-called halo stars were born in a multitude of dwarf galaxies that were later devoured by our own. Now these stars follow orbits that take them in and out of our galaxy’s center rather than around it. At such great distances, these stars move in slow motion, just as Pluto moves far more slowly in its orbit than flighty Mercury, so their orbits “remember” their ancient origins.

    Digging Up Relics in Milky Way’s Halo

    Three years ago, Alis Deason (then at University of California, Santa Cruz) led a team in measuring the motions of halo stars across the sky. The team took advantage of a Hubble Space Telescope program that was observing the Andromeda Galaxy.

    NASA Hubble Telescope
    NASA/ESA Hubble

    Andromeda Galaxy

    Picking out a baker’s dozen of foreground stars that lie in front of Andromeda, Deason and colleagues watched their sideways motion over a period of five to seven years.

    Though exact measures of distance aren’t available, these stars are about 65,000 light-years from the center of the Milky Way: square in our galaxy’s halo, which extends out some 300,000 light-years.

    “Watching the motion of stars across the face of galaxies is analogous to watching human hair grow on the surface of the Moon as seen from Earth,” says Puragra Guha Thakurta (University of California, Santa Cruz). Yet, he notes, it’s doable.

    But the measurements from Deason’s team only gave stellar motions in two dimensions. This year, Emily Cunningham (University of California, Santa Cruz) took on the mantle, leading an effort to collect each star’s spectrum, looking for the shift in spectral lines that would reveal their motions along our line of sight.

    Cunningham’s team confirms that these 13 stars defy expectations: they’re not traveling along paths that take them straight into or out of our galaxy. Most likely, they’re part of a shell of stars that are piling up as they turn around in their in-and-out orbits.

    “If we are correct in our interpretation of a shell, this shell would be a relic from a past accretion event,” says Cunningham. This shell would be all that’s left of a dwarf galaxy, or perhaps even a group of dwarfs, that fell into the Milky Way’s gravitational grasp several billion years ago.

    The alternative is that the stars are actually forming out there, in the farthest corners of the Milky Way. But as James Bullock says, “It’s hard to imagine stars forming out there in regions of such low density.” Moreover, he adds, “cosmological models predict that shells like this should be out there.”

    The Future of Galactic Archaeology

    Ultimately, though, 13 stars is a pretty small sample with which to dig up our galaxy’s history. That’s why Cunningham, Deason, and colleagues are planning a much larger sample in a project known as HALO7D, which will contain information on hundreds of halo stars once observations are complete.


    HALO7D: Looking at and Through the Milky Way – Raja GuhaThakurta
    Access the mp4 video here .

    Bullock, whose simulations have outlined our galaxy’s formation history, is excited to see the results of this and other studies. “We aim to figure out what kinds of smaller galaxies fell into the Milk Way (How big were they? What kind of stars were they made of?), and also when those galaxies fell in.”

    But even the grandest cosmic implications can’t prevent more prosaic considerations. “We are completely at the mercy of the weather,” says Cunningham. Cloudy nights disrupted plans to finish collecting data last spring, so observing will continue this spring and next, with final results one to two years from now.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition

    Sky & Telescope magazine, founded in 1941 by Charles A. Federer Jr. and Helen Spence Federer, has the largest, most experienced staff of any astronomy magazine in the world. Its editors are virtually all amateur or professional astronomers, and every one has built a telescope, written a book, done original research, developed a new product, or otherwise distinguished him or herself.

    Sky & Telescope magazine, now in its eighth decade, came about because of some happy accidents. Its earliest known ancestor was a four-page bulletin called The Amateur Astronomer, which was begun in 1929 by the Amateur Astronomers Association in New York City. Then, in 1935, the American Museum of Natural History opened its Hayden Planetarium and began to issue a monthly bulletin that became a full-size magazine called The Sky within a year. Under the editorship of Hans Christian Adamson, The Sky featured large illustrations and articles from astronomers all over the globe. It immediately absorbed The Amateur Astronomer.

    Despite initial success, by 1939 the planetarium found itself unable to continue financial support of The Sky. Charles A. Federer, who would become the dominant force behind Sky & Telescope, was then working as a lecturer at the planetarium. He was asked to take over publishing The Sky. Federer agreed and started an independent publishing corporation in New York.

    “Our first issue came out in January 1940,” he noted. “We dropped from 32 to 24 pages, used cheaper quality paper…but editorially we further defined the departments and tried to squeeze as much information as possible between the covers.” Federer was The Sky’s editor, and his wife, Helen, served as managing editor. In that January 1940 issue, they stated their goal: “We shall try to make the magazine meet the needs of amateur astronomy, so that amateur astronomers will come to regard it as essential to their pursuit, and professionals to consider it a worthwhile medium in which to bring their work before the public.”

     
  • richardmitnick 3:13 pm on February 20, 2016 Permalink | Reply
    Tags: , , , UC Santa Cruz   

    From UCSC: “Astronomers plan science projects for powerful new space telescope” 

    UC Santa Cruz

    UC Santa Cruz

    February 18, 2016
    Tim Stephens

    NASA begins formal development of the Wide Field Infrared Survey Telescope (WFIRST), planned to launch in the mid-2020s

    NASA WFIRST New
    WFIRST


    Download mp4 video here .
    The Wide Field Infrared Survey Telescope (WFIRST) will image large regions of the sky in near-infrared light to answer fundamental questions about the structure and evolution of the universe and greatly expand our knowledge of planetary systems around other stars. (Credit: NASA’s Goddard Space Flight Center)

    A team of astronomers is beginning to plan projects and strategies for making the best use of a powerful new space telescope now under development by NASA.

    NASA announced the formal start of the Wide Field Infrared Survey Telescope (WFIRST) mission on February 18. Planned as the agency’s next major astrophysics observatory following the launch of the James Webb Space Telescope [JWST], WFIRST will survey large regions of the sky in near-infrared light to answer fundamental questions about the structure and evolution of the universe and to expand our knowledge of planetary systems around other stars.

    NASA Webb telescope annotated
    JWST

    Brant Robertson, associate professor of astronomy and astrophysics at UC Santa Cruz, leads the WFIRST Extragalactic Potential Observations (EXPO) Science Investigation Team, which will identify the most pressing and scientifically compelling projects for WFIRST beyond the primary survey projects already planned for the telescope.

    “There will be a huge amount of data from the surveys, and part of our job is to think about how we can make that data most useful for general astronomers in order to optimize the science payoffs,” Robertson said. “We are also helping to evaluate the design of the telescope, running simulations of how it will work and analyzing simulated images.”

    Wide Field Instrument

    WFIRST incorporates components from an existing telescope NASA acquired from another agency in 2012, including a 2.4-meter mirror of identical size and quality to the one used by the Hubble Space Telescope. The telescope’s Wide Field Instrument will give it the ability to capture a single image with the depth and quality of Hubble but covering 100 times Hubble’s field of view. WFIRST will also carry a Coronagraph Instrument designed to block the glare of individual stars and reveal the faint light of planets orbiting around them.

    “The design work is already well advanced, and it is a really impressive telescope,” Robertson said. “Its camera is about 200 times larger than Hubble’s, and this capability will enable astronomers around the world to use WFIRST to explore the deepest reaches of space over an area thousands of times larger than the size of the moon on the sky.”

    Guest investigators will be able to conduct their own investigations using data from the surveys, while guest observers can propose additional survey projects for the telescope. The WFIRST-EXPO team will evaluate guest investigator and guest observer projects to help maximize the scientific return of the WFIRST cosmological surveys and realize the full power of the telescope for extragalactic astronomy. The team, one of a dozen WFIRST science investigation teams, will receive $2.3 million to perform these studies over the next five years.

    Robertson leads the team of 11 astronomers, including world-wide experts in designing and executing space-based extragalactic survey programs, multi-object spectroscopic campaigns in optical and infrared wavelengths, and theoretical modeling of galaxy formation, exotic supernovae, and cosmic reionization. They include Piero Madau and Stan Woosley at UC Santa Cruz; Dan Marrone and Daniel Stark at the University of Arizona; Risa Wechsler at Stanford University; Jenny Greene at Princeton University; Steven Furlanetto and Alice Shapley at UCLA; Henry Ferguson at the Space Science Telescope Institute; and Mark Dickinson at the Association of Universities for Research in Astronomy.

    In addition to surveys of deep space beyond our galaxy, WFIRST’s sensitivity and wide field of view will enable a large-scale search for exoplanets by monitoring the brightness of millions of stars in the crowded central region of our galaxy. The survey will net thousands of new exoplanets, complementing the work started by NASA’s Kepler mission and the upcoming work of the Transiting Exoplanet Survey Satellite.

    Other wide-field surveys will enable astronomers to track how dark energy and dark matter have affected the expansion of the universe over the past 10 billion years or more. By measuring the distances to thousands of supernovae, astronomers can map in detail how cosmic expansion has increased with time. WFIRST can also precisely measure the shapes, positions and distances of millions of galaxies to track the distribution and growth of cosmic structures.

    Coronagraph

    The Coronagraph Instrument will enable detailed measurements of the chemical makeup of planetary atmospheres. Comparing this data across many worlds will allow scientists to better understand the origin and physics of their atmospheres and to search for chemical signs of environments suitable for life.

    “In addition to its exciting capabilities for dark energy and exoplanets, WFIRST will provide a treasure trove of exquisite data for all astronomers,” said Neil Gehrels, the WFIRST Project Scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “This mission will survey the universe to find the most interesting objects out there.”

    The James Webb Space Telescope (JWST), planned to launch in 2018, will see deeper into space and further back in time than WFIRST. With its larger mirror, JWST will be able to observe much fainter galaxies, but its field of view is much smaller.

    NASA Hubble mirror vs Webb mirror
    On the left, Hubble’s mirror; on the right JWST’s mirror

    “JWST will conduct very deep observations of a small area, while WFIRST will cover large areas at the same depth as Hubble,” Robertson said. “If they overlap and JWST is still operational when WFIRST launches, it will be a very powerful combination.”

    WFIRST is slated to launch in the mid-2020s. The project is managed at Goddard, with participation by the Jet Propulsion Laboratory in Pasadena, California, the Space Telescope Science Institute (STScI) in Baltimore, the Infrared Processing and Analysis Center (IPAC) in Pasadena, and a science team with members from U.S. research institutions across the country.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    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.

     
  • richardmitnick 10:06 am on January 26, 2016 Permalink | Reply
    Tags: , , , Superfast 'Cannonball' Star, UC Santa Cruz   

    From UCSC via SPACE.com: “Strange Superfast ‘Cannonball’ Star Likely Blasted from Supernova” 

    UC Santa Cruz

    UC Santa Cruz

    January 25, 2016
    Sarah Lewin, Staff Writer at SPACE.com

    dwarf carbon star SDSS J1128

    A star with an unusual history is racing through the galaxy at breakneck speed — most likely blasted away by a supernova and carrying traces of the exploded star.

    The strange runaway star, which is rocketing along at more than 960,000 miles per hour (1.54 million kilometers per hour), is stained in carbon even though it’s too immature to have created the stuff itself, scientists said.

    Kathryn Plant, a senior at the University of California, Santa Cruz (UCSC), presented the new observations earlier this month at the American Astronomical Society’s 227th meeting in Kissimee, Florida. She and her co-authors said the star’s tremendous speed and its carbon signal could be linked.

    “You’re looking at this very, very, very rare star that’s moving at cannonball velocity,” study co-author Bruce Margon, an astronomer at UCSC, told Space.com. “That got us thinking — maybe there’s something about it being a dwarf carbon star that has to do with it having this crazy-high speed.”

    Their top guess is that the speedy star was in a binary system with another star that imbued it with carbon before dying in a massive supernova explosion, shooting the first star out and away. The situation may be similar for several other “cannonball” candidates the researchers have identified.

    That unusual carbon content is the key “extra clue” to the speedy stars’ origin, said Plant, the new work’s lead author.

    “For many stars, we can look at them and see how they’re moving now, but we often don’t have a lot of clues to what they might have been doing in the distant past,” she told Space.com. “Since [the star] carries this material mark, we have a clue to what it was doing in the past.”

    Perplexing stars

    The star in question, called SDSS J112801.67+004034.6 (SDSS J1128 for “short”), was originally measured through the Sloan Digital Sky Survey [SDSS] in March 2000.

    SDSS Telescope
    SDSS telescope at Apache Point, NM, USA

    Along with about 500 others found so far, it seems to fall into the strange stellar category of “dwarf carbon stars.” Different than a “white dwarf,” the super-dense remnant left at the end of a star’s life cycle, a dwarf carbon star appears to be in an early stage of evolution but contains a high level of carbon. That’s odd, because carbon is usually found shrouding red giants, which are in a much later stage.

    “The mere existence of these stars is kind of perplexing, because they are adolescent stars — they are stars at about the same evolutionary stage as our sun,” Margon said. “There shouldn’t be such a thing as a dwarf carbon star, because there’s no way for that star to have created carbon given where it is in its life cycle.”

    Instead, researchers theorize that each of these stars once orbited together with another star, a companion, which was in a later part of its life cycle and had already produced carbon. If the binary stars orbited closely enough, one star’s carbon could transfer to the other.

    The transfer of mass could happen peacefully over time — “a gentle wind puffed off for millions of years,” Margon said — but the two stars’ association might end on much more violent terms when the more mature star explodes into a supernova.

    Smoking guns

    SDSS J1128 first came to the researchers’ attention because of how quickly it was speeding away from Earth, which researchers calculated based on distortion in the wavelengths of light it put out in that first measurement. They followed up by measuring the star with Hawaii’s Keck Observatory in April 2015, and found that it was still moving away at about the same speed.

    Keck Observatory
    Keck Observatory Interior
    Keck

    But not only that: After looking at the star’s location from surveys over many years (the earliest was in 1955), the research team realized that it was visibly sweeping across the sky as well, not just fleeing from Earth. That implied that the star was dimmer and close, rather than far away and very bright.

    Researchers know stars can pick up incredible speed by whipping around the supermassive black hole in the Milky Way’s center, so this was one of the first possible explanations for this star’s great velocity. But once the collaborators calculated its approximate location — between 3,000 and 10,000 light-years away — and its speed compared with the center of the galaxy, it became clear that the star was not on that type of trajectory.

    “Even though we don’t have one exact number, we can understand what it’s most likely doing,” Plant said. “We can rule out […] certain motions that are not possible, and that lets us conclude that it’s not coming from the center of the galaxy, which is one of the main questions we wanted to answer, and also lets us conclude that it is bound to the galaxy but it’s on an extremely eccentric orbit.”

    So they turned to the supernova possibility. Other stars’ speeds have occasionally been attributed to the driving force of a supernova, the researchers said, but evidence has not been conclusive.

    “This thing has a different set of smoking guns that are pointing towards that evidence,” Margon said. “It’s the thing science fiction emerges from: You have a peaceful star minding its own business, its companion goes ‘kerblooie’ and completely demolishes itself and shoots this thing off like a cannonball,” he added. “We’re advancing this as a candidate for that [scenario].”

    Not so alone

    To find out more about the high-speed star, researchers can take follow-up measurements to check for tiny variations in the speed at which it’s moving away from Earth, as well as more about its chemical composition. Ultimately, projects like Europe’s galaxy-mapping [ESA] Gaia mission could provide even more precise data about the star’s location, if it falls within the satellite’s view, the researchers said.

    ESA Gaia satellite
    ESA/Gaia

    The star is one of a few candidates the researchers found for this extreme motion — it had the fastest velocity of the bunch relative to Earth, but the others could prove even faster when measured in the context of the entire galaxy. Comparing the traits of all those “cannonball” stars could help solidify the supernova explanation or suggest another mechanism.

    “The fact that this is a super-high-velocity star isn’t going to go away,” Margon said. “The interpretation might change.”

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    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.

     
  • richardmitnick 8:41 pm on September 11, 2015 Permalink | Reply
    Tags: , , , UC Santa Cruz   

    From UCSC: “Study finds different ways for a black hole to swallow a star” 

    UC Santa Cruz

    UC Santa Cruz

    September 10, 2015
    Susanna Kohler (AAS) and Tim Stephens (UCSC)

    1
    In this simulated tidal disruption event, a star is pulled apart by the tidal forces of a black hole. (Image credit: NASA/S. Gezari, JHU/J. Guillochon, UCSC)

    In a tidal disruption event, an unfortunate star passes too close to a dormant supermassive black hole and gets torn apart by tidal forces, feeding the black hole for a short time. Astronomers use distinctive observational signatures to detect these events, but they are not seeing nearly as many tidal disruption events as theory says they should.

    A recent study by UC Santa Cruz researchers suggests that astronomers might be missing many of these events because of how the streams of shredded stars fall onto the black hole. James Guillochon, who earned his Ph.D. at UC Santa Cruz and is now at the Harvard-Smithsonian Center for Astrophysics, and Enrico Ramirez-Ruiz, professor and chair of astronomy and astrophysics, based their analysis on a series of computer simulations of tidal disruption events. They reported their findings in a paper published August 20 in the Astrophysical Journal.

    When a black hole tears a star apart, the star’s material is stretched out into what’s known as a tidal stream. That stream continues on a trajectory around the black hole, with roughly half the material eventually falling back on the black hole, whipping around it in a series of orbits. Where those orbits intersect each other, the material smashes together and circularizes, forming a disk that then accretes onto the black hole.

    Astronomers don’t observe anything until after the tidal streams collide and the material begins to accrete onto the black hole. At that point, they observe a sudden peak in luminosity, which then gradually decreases as the tail end of what’s left of the star accretes and the black hole’s food source eventually runs out.

    General relativity

    So why have astronomers only been observing about a tenth as many tidal disruption events (TDEs) as theory predicts they should see? By studying the structure of tidal streams in TDEs, Guillochon and Ramirez-Ruiz have found a potential reason, and the culprit is general relativity.

    “It is an effect of general relativity that is modulating the digestion process of the black hole, so the digestion rate depends strongly on the mass of the black hole,” Ramirez-Ruiz said.

    The researchers ran a series of simulations of tidal disruption events around black holes of varying masses and spins to see what form the resulting tidal streams take over time. They found that precession of the tidal stream due to the black hole’s gravitational effects changes how the stream interacts with itself, and therefore what astronomers observe. Some cases behave as expected for what’s currently considered a “typical” event, but some do not.

    For cases where the relativistic effects are small (such as black holes with masses less than a few million solar masses), the tidal stream collides with itself after only a few windings around the black hole, quickly forming a disk — but the disk forms far from the black hole, so it takes a long time to accrete. As a result, the observed flare can take 100 times longer to peak than typically expected, so these sources may not be identified as tidal disruption events.

    Furthermore, for cases where the black hole is both massive and has a spin greater than a certain value (about 20 percent of its maximum allowed spin), the tidal stream doesn’t collide with itself right away. Instead, it can take many windings around the black hole before the first intersection. In these cases, it may potentially be years after a star gets ripped apart before the material accretes and astronomers are able to observe the event.

    See the full article here .

    Please help promote STEM in your local schools.

    STEM Icon

    Stem Education Coalition
    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.

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