Supernova 2014J in the nearby galaxy M82 — less than 12 million light-years away — exploded January 14, 2014, and was the closest “standard candle” supernova in at least 42 years. An impressive coordinated observational effort orchestrated by the intermediate Palomar Transient Factory (iPTF) team and led by Ariel Goobar from the Oskar Klein Center (OKC) at Stockholm University provides important new clues into the nature of these explosions, as well as the environments where they take place. The proximity of SN2014J allowed the iPTF team to study this important class of stellar explosions known as type Ia supernovae over a wide wavelength range, starting just hours after the deduced explosion time.
Furthermore, Goobar and collaborators used pre-explosion images of the region of M82 where the supernova went off, both from the Hubble Space Telescope and from the Palomar Oschin Telescope, to search for a star in the location of the explosion or possible earlier nova eruptions. The lack of pre-explosion detections suggests that the supernova may have originated in the merging of compact faint objects, e.g., two white dwarf stars, the kind of Earth-sized stars that our Sun will evolve into once it runs out of nuclear fuel.
“Until very recently, the leading model for standard candle supernovae was thought to include a companion star from which material was stripped by the white dwarf until the accumulated mass could no longer be sustained by the outwards pressure, leading to a runaway thermonuclear explosion,” said Goobar. “The observations of SN2014J are challenging for this theoretical picture.”
Type Ia supernovae are among the best tools to measure cosmological distances. Thanks to their consistent peak brightness, these “standard candles” are used to map the expansion history of the universe. In 1998, distance measurements using supernovae led to a paradigm shift in cosmology and fundamental physics: The expansion of the universe is speeding up, contrary to the expectations from the attractive nature of gravitational forces — a mysterious new cosmic component, “dark energy,” has been invoked to explain this unexpected phenomenon. This discovery was awarded the 2011 Nobel Prize in physics.
“Since type Ia supernovae are very rare, occurring only once every several hundred years in a galaxy like ours, there have been very few opportunities to study these explosions in great detail,” said Rahman Amanullah, from OKC. “SN2014J in the nearby galaxy M82 is a very welcome exception.”
A better understanding of the physics behind type Ia supernovae and the material surrounding the explosion and dimming some of the light is crucial to further refine the measurements of the expansion history of the universe. “Many supernovae explode in clean environments, free of dust in the line of sight,” said Joel Johansson from OKC. “This is not the case for SN2014J, which gives us a unique opportunity to study both the properties of the supernova explosion but also of the intervening dust.”
The lessons learned by the studies of SN2014J may be very useful for the analysis of the large type Ia supernovae sample that scientists have collected over decades, especially the astrophysical corrections needed to make accurate distance estimates. Only then may we be able to tell what is causing the accelerated expansion of the cosmos.