Research Supports Role of Supernovas in Measuring Pace at Which Universe Expands

The team led by David Cinabro, professor of physics and astronomy in the College of Liberal Arts and Sciences at Wayne State University, recently published their study in the Monthly Notices of the Royal Astronomical Society. Type Ia Supernovas are among the very brightest cosmic explosions visible, signaling the death of stars, and their importance to cosmology cannot be understated.

The findings of the study 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.

"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."

According to Cinabro, these observations depend on the assumption that the light output of Type Ia Supernovas relatively near to 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 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.