Rare collision of dead stars may give new life

Like the phoenix, some stars can explode with life and emerge from the 'ashes' of previously passed stars.

The researchers said in the journal Monthly Notices of the Royal Astronomical Society Letters: "two newly found fireballs have a flare hundreds of times brighter than the sun and are covered in carbon and oxygen." . This is considered a by-product of helium synthesis, belonging to a new class of stars.

A carbon and oxygen-rich star with a helium-burning core that can emerge from the merger of two dead stars is called a white dwarf (illustration).

Although these fiery orbs are not the first stellar objects found covered in carbon and oxygen, an analysis of the light emitted by the stars suggests they are the first to be discovered. found also has a helium-burning core.

Study co-author Nicole Reindl, an astrophysicist from the University of Potsdam (Germany), said: 'That combination has never been seen before. "That tells you the star must have evolved differently."

Stars can form from the merger of two white dwarfs, the remnant hearts of stars that have exhausted their fuel, one of which is rich in helium, while the other is rich in carbon and oxygen. . In the end, the helium-rich white dwarf devoured its counterpart, spewing carbon and oxygen all over its surface, like a messy child might have food on his face.

Tiara Battich, an astrophysicist from the Max Planck Institute for Astrophysics in Garching, says such a merger would create a stellar body covered in carbon and oxygen with enough mass to recombine. nuclear fusion in its core, Germany, and her colleagues.

To test this hypothesis, Battich and her colleagues simulated the evolution, death, and eventual merger of two stars. The team found that aggregating a carbon and oxygen-rich white dwarf into a star larger than helium could explain the surface composition of the two stars observed by Reindl and her colleagues.

"But this happens very rarely," Battich said.

In most cases, the opposite will happen - the carbon-oxygen white dwarf should cover itself with helium. That's because carbon-oxygen white dwarfs are usually more massive stars. In the rarer case, two stars slightly more massive than the sun must have formed at a moderate distance from each other. Furthermore, they then need to exchange matter at just the right moment before the two run out of nuclear fuel to leave behind a helium white dwarf with more mass than a carbon and oxygen counterpart.

Simon Blouin, an astrophysicist from the University of Victoria in Canada who was not involved in the study, says the origin story that Battich and her colleagues propose requires a set of situations. very specific and unusual. "But in the end, it makes sense." "Star mergers are complex and dynamic events that can play out in many ways," he said. "This is just another one."