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Astronomers Discover a New Class of Binary Star – "Astonishing, Missing Evolutionary Link"

Researchers at the Center for Astrophysics | Harvard & Smithsonian have discovered a type of binary star that had previously gone undetected by science. The discovery provides conclusive evidence for the formation and evolution of a type of star that is extremely rare in the universe.

Kareem El-Badry, a postdoctoral fellow at Lick Observatory in California, discovered the new class of stars with the help of data from several astronomical surveys and the Shane Telescope at Lick Observatory.

A new population of transitional binary stars has been discovered, according to El-Badry, and this is the first physical evidence for their existence. "This is extremely exciting because it identifies a previously unknown evolutionary link in binary star formation models," says the author.

A Different Kind of Star

It is estimated that when a star dies, it will most likely transform into a white dwarf, which is a small, dense object that has contracted and dimmed as a result of the exhaustion of its fuel.

On rare occasions, a star can degenerate into an extremely low mass (ELM) white dwarf, which is extremely rare. They are a conundrum because they have a mass less than one-third that of the Sun. If stellar evolution calculations are correct, all ELM white dwarfs appear to be more than 13.8 billion years old — older than the age of the universe and thus physically impossible to exist in the universe.

'The universe is simply too young to have produced these stars through normal evolution,' says El-Badry, who is a member of the Institute for Theory and Computation at the Center for Astrophysics in Tucson, Arizona.

As a result of their research, astronomers have come to the conclusion that the only way for an ELM white dwarf to form is with the assistance of a binary companion. Eventually, the gravitational pull of a nearby companion star can eat away at a star, causing it to collapse and become an ELM white dwarf (in less than 13.8B years).

The evidence, on the other hand, does not support this conclusion.

Astronomers have observed normal, massive stars similar to our Sun accreting onto white dwarfs — a process known as cataclysmic variable accretion — which is a process that occurs in the universe's early universe. They have also observed ELM white dwarfs coexisting with normal white dwarfs, which is an exciting discovery. Their observations did not include the transitional phase of evolution, also known as transformation in between: the point in time when a star has lost the vast majority of its mass, at which point it is on the verge of contracting and becoming an ELM white dwarf.

A Missing Evolutionary Link

A number of parallels between stellar astronomy and nineteenth-century zoology are frequently drawn by El-Badry.

"You set out into the jungle in search of a specific type of organism. Your description of its size and weight is followed by a move on to a different organism "He goes into detail. "You'll see a variety of different objects and will have to piece together how they're connected," says the game's creator.

El-Badry returned to the jungle in 2020 in search of the star that had eluded scientists for so long: the pre-ELM white dwarf. El-Badry was successful in his search, and the star was discovered (also referred to as an evolved cataclysmic variable).

El-Badry used new data from Gaia, the European Space Agency's space-based observatory, and Caltech's Zwicky Transient Facility to narrow down a pool of one billion stars to 50 potential candidates.

The astronomer emphasizes the critical role played by publicly available data from astronomical surveys in his research, which he considers to be of critical importance. It would not be possible to do this work without projects like the Zwicky Transient Facility and Gaia, which require hundreds of people to work behind the scenes, according to him.

El-Badry then conducted close examinations of 21 stars in the sky.

The strategy for selecting candidates was successful. According to him, "every single candidate was one of these pre-ELMs" that they were looking for. "They appeared to be inflated and bloated to a greater extent than ELMs. Aside from that, their spherical shape had been distorted by the gravitational pull of the other star, resulting in their egg-shaped appearance."

"We discovered a large number of binary stars and established an evolutionary link between two distinct classes of binary stars — cataclysmic variables and ELM white dwarfs," El-Badry continues.

13 stars continued to lose mass in relation to their companion, while eight stars appeared to have reached a point where they were no longer losing mass. Each of them, in addition, was significantly hotter than previously observed cataclysmic variables.

El-Badry intends to continue his research into pre-ELM white dwarfs, and he may also look into the 29 additional candidate stars that he discovered previously in his previous research.

He is astounded by the rich diversity of stars that can be produced by simple science, just as he is by the work of contemporary anthropologists who are filling in gaps in human evolution.

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