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Researchers Detect Supernova, One of the Most Distant Ever Discovered and Confirmed

A rare superluminous supernova has been developed as an outcome of the death of a massive star in a distant galaxy 10 billion years ago. According to astronomers, this is considered to be one of the most distant that has ever been discovered.

The brilliant explosion, over three times as bright as the 100 billion stars present in the Milky Way galaxy combined, took place almost 3.5 billion years after the big bang during a period called "cosmic high noon," when the rate of star development in the universe touched its peak.

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)

Superluminous supernovae are considered to be 10 to 100 times brighter than a typical supernova that is the outcome of a massive star. However, Astronomers are still not aware of exactly what physical processes are involved or what kinds of stars result in their extreme luminosity.

The supernova called DES15E2mlf appears to look strange even in the midst of the small number of superluminous supernovae that have until now been detected by astronomers. Originally, it was detected in November 2015 by the Dark Energy Survey (DES) collaboration by using the Blanco 4-meter telescope at Cerro Tololo Inter-American Observatory in Chile. Follow-up observations for measuring the distance and attaining detailed spectra of the supernova were performed with the Gemini Multi-Object Spectrograph on the 8-meter Gemini South telescope.

UC Santa Cruz Astronomers Yen-Chen Pan and Ryan Foley headed this investigation as part of an international team of DES Collaborators. Their findings were reported in a paper published July 21st in the Monthly Notices of the Royal Astronomical Society.

The latest observations could offer clues to the nature of galaxies and stars during peak star formation. Supernovae play an important role in the evolution of galaxies since their explosions enhance the interstellar gas from which new stars develop with elements that are heavier than helium (which is called “metals” by Astronomers).

It's important simply to know that very massive stars were exploding at that time. 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.

Ryan Foley, an Assistant Professor of Astronomy and Astrophysics, UC Santa Cruz

Earlier observations of superluminous supernovae found they typically exist in dwarf or low-mass galaxies, which tend to be less enhanced in metals than several massive galaxies. However, the host galaxy of DES15E2mlf is a normal-looking, fairly massive 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.

Yen-Chen Pan, a Postdoctoral Researcher at UC Santa Cruz and First Author of the paper

Foley explained that stars made up of fewer heavy elements maintain a bigger fraction of their mass when they die and this could lead to a bigger explosion when the star exhausts its fuel supply and then 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. 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.

Ryan Foley, an Assistant Professor of Astronomy and Astrophysics, UC Santa Cruz

"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. A number of superluminous supernovae have been discovered by the Dark Energy Survey, which continues to observe more distant cosmic explosions explaining how stars exploded during the toughest period of star formation.

Besides Pan, Foley and Smith, the Co-authors of the paper include Lluís Galbany of the University of Pittsburgh, and other members of the DES collaboration from more than 40 institutions. The National Science Foundation, the Alfred P. Sloan Foundation, and the David and Lucile Packard Foundation funded this research.

The Dark Energy Survey is an association of more than 400 Scientists from 26 institutions in seven countries. Its key instrument, the 570-megapixel Dark Energy Camera, is placed 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.

The DES Projects were funded 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.

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