Hopkins Astrophysicists Detect One of the Farthest Supernovae

By Lisa DeNike

HST HUDF ACS/WFC3 Image

A team of Johns Hopkins astrophysicists using NASA’s Hubble Space Telescope has detected a distant Type Ia supernova, the farthest stellar explosion that can be used to measure the expansion rate of the universe. The supernova is the remnant of a star that exploded 9 billion years ago. The sighting is the first finding of an ambitious survey that will help astronomers place better constraints on the nature of dark energy: a mysterious repulsive force that is causing the universe to fly apart ever faster.

The object, nicknamed SN Primo, belongs to a special class called Type Ia supernovae, which are bright beacons used as distance markers for studying the expansion rate of the universe. Type Ia supernovae most likely arise when white dwarf stars, the burned-out cores of normal stars, siphon too much material from their companion stars and explode.

The study was published in The Astrophysical Journal, and the results were presented in January at the American Astronomical Society meeting in Austin, Texas, by first author Steven Rodney, post-doctoral researcher in the Department of Physics and Astronomy. Teaming with Rodney was lead investigator Adam Riess, a professor of physics and astronomy at Johns Hopkins and a 2011 winner of the Nobel Prize in physics for his discovery that the expansion of the universe is accelerating, due to a mysterious force now known as “dark energy.”

According to Rodney, SN Primo is the farthest Type Ia supernova whose distance has been confirmed through spectroscopic observations. A spectrum splits the light from a supernova into its constituent colors. By analyzing those colors, astronomers can confirm its distance by measuring how much the supernova’s light has been stretched, or red-shifted, into near-infrared wavelengths due to the expansion of the universe.

The supernova was discovered as part of a three-year Hubble program to survey faraway Type Ia supernovae, enabling searches for this special class of stellar explosion at greater distances than previously possible. The remote supernovae will help astronomers determine whether the exploding stars remain dependable distance markers across vast distances of space in an epoch when the cosmos was only one-third its current age of 13.7 billion years.

Called the CANDELS+CLASH Supernova Project, the census uses the sharpness and versatility of Hubble’s Wide Field Camera 3 to look in regions targeted by two large Hubble programs: Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey (CANDELS) and the Cluster Lensing and Supernova Survey with Hubble (CLASH).

“In our search for supernovae, we had gone as far as we could go in optical light,” said Riess. “But it’s only the beginning of what we can do in infrared light. This discovery demonstrates that we can use the Wide Field Camera 3 to search for supernovae in the distant universe.”

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