From UCSC: “Superluminous supernova marks the death of a star at cosmic high noon”

UC Santa Cruz

UC Santa Cruz

July 21, 2017
Tim Stephens
stephens@ucsc.edu

At a distance of 10 billion light years, a supernova detected by the Dark Energy Survey team is one of the most distant ever discovered and confirmed.

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The yellow arrow marks the superluminous supernova DES15E2mlf in this false-color image of the surrounding field. This image was observed with the Dark Energy Camera (DECam) gri-band filters mounted on the Blanco 4-meter telescope on December 28, 2015, around the time when the supernova reached its peak luminosity. (Observers: D. Gerdes and S. Jouvel)

The death of a massive star in a distant galaxy 10 billion years ago created a rare superluminous supernova that astronomers say is one of the most distant ever discovered. The brilliant explosion, more than three times as bright as the 100 billion stars of our Milky Way galaxy combined, occurred about 3.5 billion years after the big bang at a period known as “cosmic high noon,” when the rate of star formation in the universe reached its peak.

Superluminous supernovae are 10 to 100 times brighter than a typical supernova resulting from the collapse of a massive star. But astronomers still don’t know exactly what kinds of stars give rise to their extreme luminosity or what physical processes are involved.

The supernova known as DES15E2mlf is unusual even among the small number of superluminous supernovae astronomers have detected so far. It was initially detected in November 2015 by the Dark Energy Survey (DES) collaboration using the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory in Chile.

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

Follow-up observations to measure the distance and obtain detailed spectra of the supernova were conducted with the Gemini Multi-Object Spectrograph on the 8-meter Gemini South telescope.

Gemini Observatory GMOS on Gemini South


Gemini South telescope, Cerro Tololo Inter-American Observatory (CTIO) campus near La Serena, Chile

The investigation was led by UC Santa Cruz astronomers Yen-Chen Pan and Ryan Foley as part of an international team of DES collaborators. The researchers reported their findings in a paper published July 21 in the Monthly Notices of the Royal Astronomical Society.

The new observations may provide clues to the nature of stars and galaxies during peak star formation. Supernovae are important in the evolution of galaxies because their explosions enrich the interstellar gas from which new stars form with elements heavier than helium (which astronomers call “metals”).

“It’s important simply to know that very massive stars were exploding at that time,” said Foley, an assistant professor of astronomy and astrophysics at UC Santa Cruz. “What we really want to know is the relative rate of superluminous supernovae to normal supernovae, but we can’t yet make that comparison because normal supernovae are too faint to see at that distance. So we don’t know if this atypical supernova is telling us something special about that time 10 billion years ago.”

Previous observations of superluminous supernovae found they typically reside in low-mass or dwarf galaxies, which tend to be less enriched in metals than more massive galaxies. The host galaxy of DES15E2mlf, however, is a fairly massive, normal-looking galaxy.

“The current idea is that a low-metal environment is important in creating superluminous supernovae, and that’s why they tend to occur in low mass galaxies, but DES15E2mlf is in a relatively massive galaxy compared to the typical host galaxy for superluminous supernovae,” said Pan, a postdoctoral researcher at UC Santa Cruz and first author of the paper.

Foley explained that stars with fewer heavy elements retain a larger fraction of their mass when they die, which may cause a bigger explosion when the star exhausts its fuel supply and collapses.

“We know metallicity affects the life of a star and how it dies, so finding this superluminous supernova in a higher-mass galaxy goes counter to current thinking,” Foley said. “But we are looking so far back in time, this galaxy would have had less time to create metals, so it may be that at these earlier times in the universe’s history, even high-mass galaxies had low enough metal content to create these extraordinary stellar explosions. At some point, the Milky Way also had these conditions and might have also produced a lot of these explosions.”

“Although many puzzles remain, the ability to observe these unusual supernovae at such great distances provides valuable information about the most massive stars and about an important period in the evolution of galaxies,” said Mat Smith, a postdoctoral researcher at University of Southampton. The Dark Energy Survey has discovered a number of superluminous supernovae and continues to see more distant cosmic explosions revealing how stars exploded during the strongest period of star formation.

In addition to Pan, Foley, and Smith, the coauthors of the paper include Lluís Galbany of the University of Pittsburgh, and other members of the DES collaboration from more than 40 institutions. This research was funded the National Science Foundation, The Alfred P. Sloan Foundation, and the David and Lucile Packard Foundation.

The Dark Energy Survey is a collaboration of more than 400 scientists from 26 institutions in seven countries. Its primary instrument, the 570-megapixel Dark Energy Camera, is mounted on the 4-meter Blanco telescope at the National Optical Astronomy Observatory’s Cerro Tololo Inter-American Observatory in Chile, and its data are processed at the National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign. Funding for the DES Projects has been provided by the U.S. Department of Energy Office of Science, U.S. National Science Foundation, Ministry of Science and Education of Spain, Science and Technology Facilities Council of the United Kingdom, Higher Education Funding Council for England, ETH Zurich for Switzerland, National Center for Supercomputing Applications at the University of Illinois at Urbana-Champaign, Kavli Institute of Cosmological Physics at the University of Chicago, Center for Cosmology and Astro-Particle Physics at Ohio State University, Mitchell Institute for Fundamental Physics and Astronomy at Texas A&M University, Financiadora de Estudos e Projetos, Fundação Carlos Chagas Filho de Amparo à Pesquisa do Estado do Rio de Janeiro, Conselho Nacional de Desenvolvimento Científico e Tecnológico and Ministério da Ciência e Tecnologia, Deutsche Forschungsgemeinschaft, and the collaborating institutions in the Dark Energy Survey, the list of which can be found at http://www.darkenergysurvey.org/collaboration.

See the full article here .

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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

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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.

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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
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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.

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UCSC alumna Shelley Wright, now an assistant professor of physics at UC San Diego, discusses the dichroic filter of the NIROSETI instrument. (Photo by Laurie Hatch)

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.

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UCSC is the home base for the Lick Observatory.

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