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Supernova Research Supports Measuring Pace at Which the Universe Expands

Saturday, January 7, 2017 16:25
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Type Ia supernovae are a key in measuring how fast the universe is expanding.  Type Ia Supernovas are among the very brightest cosmic explosions visible, signaling the death of stars, and their importance to cosmology cannot be understated.

A team of research scientists led by David Cinabro, professor of physics and astronomy in the College of Liberal Arts and Sciences at Wayne State University, recently published a paper marking the importance of Type Ia Supernovas in measuring the pace at which the universe expands. 

“Observations just before the turn of the century provided the first clear evidence of an accelerated expansion of the universe,” said Cinabro. “Subsequent observations combined with the clustering of galaxies and the cosmic microwave background further point towards this acceleration being caused by a mysterious anti-gravity-like force called Dark Energy.” 
Type Ia Supernovae 

The findings of the study – published in the Monthly Notices of the Royal Astronomical Society by Cinabro’s team at Wayne State University, Daniel Scolnic, a postdoctoral scholar at the University of Chicago’s Kavli Institute for Cosmological Physics, Rick Kessler, a senior researcher at the Kavli Institute, and undergraduate students Ashley Li and Jake Miller – support a theory that the expansion of the universe is accelerating and is attributable to a mysterious force known as dark energy – an unknown form of energy hypothesized to permeate all of space. The findings counter recent headlines that Type Ia Supernovae cannot be used as an accurate measure for the expansion of the universe.

According to Cinabro, these observations depend on the assumption that the light output of Type Ia Supernovas relatively near to the earth can be described in the same way as those that are much further away. The observations of two distinct types of Type Ia Supernovas with different amounts of light output by Peter Milne of the University of Arizona and his collaborators in 2015 called this underpinning assumption into question.

Checking this observation with publicly available observations of Type Ia Supernova is not so easy, commented Cinabro.

“Milne and his collaborators observed two peaks in the brightness of Type Ia Supernova in the ultraviolet part of the light spectrum using instruments on the Swift satellite,” said Cinabro. “Most of the existing Type Ia Supernova data have been observed with ground-based telescopes which have difficulty viewing in ultraviolet light due to the earth’s atmosphere, which would fuzzily smear together two ultraviolet peaks in the light from nearby Type Ia Supernova as claimed by Milne and collaborators.”

Based on the researcher’s observations, more distant supernova have their ultraviolet light red-shifted – or stretched into lower frequencies or longer wavelengths – into the visible. The high quality visible light observations of Type Ia Supernovas from the SuperNova Legacy Survey (SNLS) and the Sloan Digital Sky Survey (SDSS) for more distant explosions do not exhibit the two peak structure expected if the earlier results were correct.

“Rather we observe a single, broad distribution of Type Ia Supernova brightness in the ultraviolet agreeing with earlier assumptions and existing models of Type Ia Supernova explosions,” concluded Cinabro.

Contacts and sources: 

Julie O’Connor
Wayne State University

Citation: “Search for Type Ia Supernova NUV-Optical Subclasses,” by David Cinabro and Jake Miller (Wayne State University); and Daniel Scolnic and Ashley Li (Kavli Institute for Cosmological Physics at the University of Chicago); and Richard Kessler (Kavli Institute for Cosmological Physics at University of Chicago and the Department of Astronomy and Astrophysics at the University of Chicago). Monthly Notices of the Royal Astronomical Society, November 2016. DOI: 10.1093/mnras/stw3109


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