Researchers studying a new class of hot subluminous stars discovered that two of the weird stars they were looking at had atmospheres rich in carbon and oxygen, a situation that is weird. While carbon and oxygen are common enough elements, they are scarce in comparison to hydrogen and helium, and when we look at stars, we see atmospheres dominated by hydrogen and helium with only rare exceptions, and those exceptions are normal former stars. White dwarfs, the leftover cores of stars that are no longer undergoing nuclear burning, sometimes have carbon/oxygen atmospheres because their surfaces are what used to be the inner regions of a star where the elements were formed.

But hot subluminous stars are very much alive and do have nuclear burning going on. So how do you get a living star to look like a dead one? Apparently, through stellar resurrection.

This discovery was led by Klaus Werner and is published in a pair of papers in the Monthly Notices of the Royal Astronomica Society that are led by Werner and Miller Bertolami. The research team thinks that it’s possible that a carbon/oxygen white dwarf merged with a helium-rich white dwarf, and through their combined masses, these two dead stars combined into one living star capable of burning helium in its core. Maybe. As Bertolami puts it: Usually, white dwarf mergers do not lead to the formation of stars enriched in carbon and oxygen, but we believe that for binary systems formed with very specific masses, a carbon- and oxygen-rich white dwarf might be disrupted and end up on top of a helium-rich one, leading to the formation of these stars.

More modeling and more observations are needed to look at both what is possible and what is out there. No matter what is found, we can say the universe is more interesting than we knew yesterday.

More Information

Royal Astronomical Society press release

“An evolutionary channel for CO-rich and pulsating He-rich subdwarfs,” M M Miller Bertolami et al., 2022 January 7, Monthly Notices of the Royal Astronomical Society

“Discovery of hot subdwarfs covered with helium-burning ash,” Klaus Werner, Nicole Reindl, Stephan Geier, and Max Pritzkuleit, 2022 February 12, Monthly Notices of the Royal Astronomical Society