The finding provides crucial insight into the binary nature of stars massive stars, as well as the possible prequel to the final merger of companion stars that would rock the universe like gravitational waves, ripples in the fabric of space-time itself.
Astronomers detect the signature of various elements in supernova explosions. These elements are layered like a pre-supernova onion. Hydrogen is found in the outermost layer of a star, and if no hydrogen is detected following the supernova, that means it was removed before the explosion occurred.
The cause of the hydrogen loss has been a mystery, and astronomers have been using Hubble to search for clues and test theories to explain these naked supernovae. The new Hubble observations provide the best evidence yet to support the theory that an unseen companion star strips away its companion star’s gas envelope before it explodes.
“This was the moment we had been waiting for, to finally see evidence of a completely naked supernova progenitor binary system,” astronomer Ori Fox of the Space Telescope Science Institute in Baltimore, Maryland, principal investigator of the program, said in a statement. of Hubble research. “The goal is to move this area of study from theory to working with data and see what these systems actually look like.”
Fox’s team used Hubble’s Wide Field Camera 3 to study the region of supernova (SN) 2013ge in ultraviolet light, as well as previous Hubble observations in the Barbara A. Mikulski Archive for Space Telescopes (MAST). Astronomers saw the light from the supernova fade over time from 2016 to 2020, but another nearby source of ultraviolet light in the same position maintained its brightness. This underlying source of ultraviolet emission is what the team proposes as the surviving binary companion of SN 2013ge.
Previously, scientists theorized that strong winds from a massive parent star might blow away its envelope of hydrogen gas, but observational evidence didn’t support this. To explain the disconnection, astronomers developed theories and models in which hydrogen is drawn by a binary partner.
“In recent years, many different lines of evidence have told us that naked supernovae are likely to form in binaries, but we have yet to see the companion. Much of the study of cosmic explosions is like forensic science: looking for clues and see which theories match up. Thanks to Hubble, we can see this directly,” said Maria Drout of the University of Toronto, a member of the Hubble research team.
In previous observations of SN 2013ge, Hubble saw two spikes in ultraviolet light, instead of the one normally seen in most supernovae. Fox said one explanation for this double brightness is that the second peak shows when the supernova shock wave hits a companion star, a possibility that now seems much more likely. Hubble’s latest observations indicate that while the companion star was pushed significantly, including the hydrogen gas it had siphoned away from its partner, it was not destroyed. Fox compares the effect to a bowl of jam being shaken, which will eventually return to its original shape.
While additional confirmation and similar supporting discoveries need to be found, Fox said the implications of the discovery remain substantial and support theories that most massive stars form and evolve as binary systems.
Unlike supernovae that have a puffy shell of gas to ignite, the progenitors of fully bare-enveloped supernovae have proven difficult to identify in pre-explosion images. Now that astronomers have been lucky enough to identify the surviving companion star, they can use it to work back and determine the characteristics of the star that exploded, as well as the unprecedented opportunity to see how the fallout plays out with the survivor.
As a massive star itself, SN 2013ge’s companion is also destined to supernovate. Its former companion is now likely to be a compact object, such as a neutron star or black hole, and the companion is likely to follow that path as well.
The closeness of the original companion stars will determine whether they stay together. If the distance is too great, the companion star will be kicked out of the system to wander our galaxy alone, a fate that might explain many seemingly solitary supernovae.
However, if the stars were close enough to each other before the supernova, they will continue to orbit each other as black holes or neutron stars. In that case, they would eventually spiral together and merge, creating gravitational waves in the process.
That’s an exciting prospect for astronomers, since gravitational waves are a branch of astrophysics that has only just begun to be explored. They are ripples or ripples in the fabric of spacetime itself, predicted by Albert Einstein in the early 20th century. Gravitational waves were observed directly for the first time by the Laser Interferometer Gravitational-Wave Observatory.