In some supernova cases, astronomers find no trace of the former star’s outermost layer of hydrogen. What happened to the hydrogen? Suspicions that companion stars are responsible — siphoning away their partners’ outer shell before a catastrophic explosion — are supported by Hubble’s identification of a surviving companion star on the scene of the Type Ib/c supernova (SN) 2013ge.
An artist’s illustration shows SN 2013ge, with its companion star at lower right. Image credit: NASA / ESA / Leah Hustak, STScI.
Astronomers detect the signature of various elements in supernova explosions. These elements are layered like an onion pre-supernova.
Hydrogen is found in the outermost layer of a star, and if no hydrogen is detected in the aftermath of the supernova, that means it was stripped away before the explosion occurred.
The cause of the hydrogen loss had been a mystery, and astronomers have been using the NASA/ESA Hubble Space Telescope to search for clues and test theories to explain these stripped supernovae.
The new Hubble observations provide the best evidence yet to support the theory that an unseen companion star siphons off the gas envelope from its partner star before it explodes.
“This was the moment we had been waiting for, finally seeing the evidence for a binary system progenitor of a fully stripped supernova,” said Dr. Ori Fox, am astronomer at the Space Telescope Science Institute.
“The goal is to move this area of study from theory to working with data and seeing what these systems really look like.”
Using data from Hubble’s Wide Field Camera 3 (WFC3) and the Barbara A. Mikulski Archive for Space Telescopes, Dr. Fox and colleagues studied SN 2013ge in ultraviolet light.
They saw the light of the supernova fading over time from 2016 to 2020, but another nearby source of ultraviolet light at the same position maintained its brightness.
This underlying source of ultraviolet emission is what they propose is the surviving binary companion to SN 2013ge.
This infographic shows the evolution astronomers propose for SN 2013ge. Panels (1-3) show what has already occurred, and panels (4-6) show what may take place in the future: (1) a binary pair of massive stars orbit one another; (2) one star ages into its red giant stage, getting a puffy outer envelope of hydrogen that its companion star siphons off with gravity; astronomers propose this is why Hubble found no trace of hydrogen in the supernova debris; (3) the stripped-envelope star goes supernova (SN 2013ge), jostling but not destroying its companion star; after the supernova, the dense core of the former massive star remains either as neutron star or black hole; (4) eventually the companion star also ages into a red giant, maintaining its outer envelope, some of which came from its companion; (5) the companion star also undergoes a supernova; (6) if the stars were close enough to each other not to be flung from their orbits by the supernova blast wave, the remnant cores will continue to orbit one another and eventually merge, creating gravitational waves in the process. Image credit: NASA / ESA / Leah Hustak, STScI.
In prior observations of SN 2013ge, the astronomers saw two peaks in the ultraviolet light, rather than just the one typically seen in most supernovae.
“One explanation for this double brightening was that the second peak shows when the supernova’s shock wave hit a companion star, a possibility that now seems much more likely,” Dr. Fox said.
“Hubble’s latest observations indicate that while the companion star was significantly jostled, including the hydrogen gas it had siphoned off its partner, it was not destroyed.”
“While additional confirmation and similar supporting discoveries need to be found, the implications of the discovery are still substantial, lending support to theories that the majority of massive stars form and evolve as binary systems.”
The team’s paper was published in the Astrophysical Journal Letters.
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Ori D. Fox et al. 2022. The Candidate Progenitor Companion Star of the Type Ib/c SN 2013ge. ApJL 929, L15; doi: 10.3847/2041-8213/ac5890
Source link: https://www.sci.news/astronomy/sn-2013ge-companion-star-10776.html
