Two decades of searching has finally paid off for NASA’s Hubble Space Telescope, which has locked down a long-suspected companion star to a very rare type of supernova known as SN 1993J.
With a long-held theory that SN 1993J exploded when two stars locked in a binary system interacted with each other, this supernova is unlike any other that we know of. It’s a Type IIb, an unusual breed that has less hydrogen than is typical in your run-of-the-mill stellar detonation.
“A binary system is likely required to lose the majority of the primary star’s hydrogen envelope prior to the explosion,” says lead researcher Ori Fox of University of California, Berkeley, of SN 1993J, which now only continues to burn as a white-hot star packed with helium and no hydrogen in sight.
Knowing for sure if SN 1993J is a binary has been a bit tricky. “To date, direct observations of the predicted binary companion star have been difficult to obtain since it is so faint relative to the supernova itself,” Fox adds.
Discovered 21 years ago in spiral galaxy, M81, which rests some 11 million light years away in the constellation Ursa Major, astronomers knew that something was amiss when they got the very first detections of SN 1993J. Scrutinising the object under the steady gaze of Hawaii’s W.M. Keck Observatory on Mauna Kea, large amounts of ultraviolet radiation suggested a companion star in hiding.
So, in order to reveal if a so-called stellar hydrogen thief was really at work, Fox and his team combined optical light data with Hubble’s UV light images to put together a spectrum of what they would expect from a companion star.
And, with the help of the long-serving Hubble, this hypothesised light quickly became a real entity. “We were able to get the UV spectrum with Hubble, says the Space Telescope Science Institute’s Azalee Bostroem. “This conclusively shows that you have an excess of continuum emission in the UV, even after the light from other stars has been subtracted.”
“This is a crime scene, and we finally identified the robber,” concludes Alex Filippenko, also at UC Berkeley, triumphantly.