NASA's Hubble Space Telescope has detected the weak glow of a star that exploded more than 9 billion years ago.
The stellar explosion, dubbed SN Primo, is part of a special class known as Type Ia supernovae, which are bright beacons used as distance markers for studying the expansion rate of the universe.
Astronomers believe Type Ia supernovae likely occur when white dwarf stars, the burned-out cores of normal stars, siphon too much material from their companion stars and explode.
SN Primo is the farthest Type Ia supernova - with its distance confirmed via spectroscopic observations.
In these types of 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 because of the expansion of the universe.
The above-mentioned supernova was discovered as part of a three-year Hubble program to survey faraway Type Ia entities.
According to Adam Riess of the Space Telescope Science Institute and The Johns Hopkins University in Baltimore, Md, remote supernovae can help astronomers determine whether exploding stars remain dependable cosmic yardsticks across vast distances of space in an epoch when the cosmos was only one-third its current age of 13.7 billion years.
Indeed, astronomers hope to determine the frequency of Type Ia supernovae during the early universe and glean insights into the mechanisms that detonated them.
"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 [Hubble's] Wide Field Camera 3 to search for supernovae in the distant universe."
As Riess notes, the supernova team's search technique involved taking multiple near-infrared images over a period of several months, looking for a supernova's faint glow. After astronomers spotted the stellar blast in October 2010, they used WFC3's spectrometer to verify SN Primo's distance and to decode its light, finding the unique signature of a Type Ia supernova. The team subsequently re-imaged SN Primo periodically for eight months, measuring the slow dimming of its light.
"If we look into the early universe and measure a drop in the number of supernovae, then it could be that it takes a long time to make a Type Ia supernova," said team member Steve Rodney of The Johns Hopkins University.
"Like corn kernels in a pan waiting for the oil to heat up, the stars haven't had enough time at that epoch to evolve to the point of explosion. However, if supernovae form very quickly, like microwave popcorn, then they will be immediately visible, and we'll find many of them, even when the universe was very young. Each supernova is unique, so it's possible that there are multiple ways to make a supernova."
If astronomers discover that Type Ia supernovae begin to depart from how they expect them to look, they might be able to gauge those changes and adjust dark energy measurements to make them more precise.