Seventeen years ago, astronomers saw a supernova going off in galaxy NGC 7424, 40 million light-years from Earth. Now, the Hubble Space Telescope has spotted its surviving companion star and researchers have discovered that this star harbors a secret. It stole material from its companion, making it unstable.
As reported in the Astrophysical Journal, supernova 2001ig, as it is named, was a Type IIb stripped-envelope supernova and spent millions of years stealing hydrogen from its companion star. Thanks to this process, the supernova experienced episodes where it blew off its outer layers, until the eventual catastrophe.
Observations in 2004 hinted at the presence of a companion but the system’s properties make it difficult to see with our instruments. Hubble’s capabilities were used and for the first time, the surviving companion star was photographed.
“We were finally able to catch the stellar thief, confirming our suspicions that one had to be there,” team member Alex Filippenko said in a statement. Filippenko first identified these types of supernova explosions back in 1987.
Originally, astronomers thought these supernovae were created by massive stars with stellar winds powerful enough to blow their outer layers into interstellar space. But when the astronomers started looking for these progenitor stars, they could not find many.
“That was especially bizarre, because astronomers expected that they would be the most massive and the brightest progenitor stars,” explained team member Ori Fox of the Space Telescope Science Institute in Baltimore. “Also, the sheer number of stripped-envelope supernovas is greater than predicted.”
A new explanation was necessary. Other types of supernovae require the interaction of two companions, so why not have two stars create the stripped-envelope type? This helps explain where most of the hydrogen disappears to before the star goes kaboom.
“We know that the majority of massive stars are in binary pairs,” lead author Stuart Ryder, from the Australian Astronomical Observatory (AAO) in Sydney, Australia, added. “Many of these binary pairs will interact and transfer gas from one star to the other when their orbits bring them close together.”
SN 2001ig was not completely stripped of hydrogen but about 90 percent stripped. The ones that are completely stripped have less shock interaction so they fade much more quickly. The companion is not visible until the supernova fades, so the team is planning to look for 100-percent-stripped supernovae, whose companions should become visible in just two or three years. They also hope to use the James Webb Space Telescope to continue the search.
