by Astronomers have witnessed for the first time a rare and important life event in the evolution of binary star couplings.
The team discovered a tight binary star surrounded by an expanding shell of material. This shell is matter left over from a stage in the evolution of stars called the common envelope phase.
This phase occurs when material from one star swells and engulfs the other in a cosmic ‘hug’. This results in a transfer of mass from the bloated star to its companion that can get out of control. The aftermath of this phase is something astronomers had not glimpsed until now.
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“The common envelope phase is a missing link in the long and complex chain of events that make up the lives of stars,” said Australian National University (ANU) associate professor Christian Wolf and part of the team that made the observations, in a study. . declaration. (opens in new tab) “Now we’re starting to fix that link.”
Half of all the stars in the universe come in binary pairs, and while the early stages of partnerships can be smooth, when a star runs out of hydrogen for nuclear fusion, things get interesting for the pairing.
The initial step in these events is the collapse of the star’s hydrogen-depleted core as its outer layers ‘explode’ – a process the sun will experience in about 5 billion years – creating a red giant star. But this is different for stars in binary pairs than for our lone star.
“When one of the stars transforms into a red giant, it doesn’t just claim more empty space the way a single star would,” Wolf said. “Instead, he ‘hugs’ or swallows his mate, and they appear like a star under an opaque envelope. That’s when things get really exciting.”
Wolf explains that the friction created in the envelope caused by the movement of stars within it has profound effects on the next step in the evolution of binary stars. “This not only causes heat, it slows the stars down, so they spiral into an increasingly tighter orbit; the envelope eventually overheats and is blown away,” he said.
As a result of this, stars can get more than 100 times closer together at the end of the common envelope phase than they were at the beginning, after the heat of the process causes surrounding matter to be expelled in a violent explosion. ‘
The explosion of the binary stars observed by Wolf and colleagues occurred about 10,000 years ago. The researchers predict that the binary stars they observed, now a white dwarf and a hot subdwarf that will eventually evolve into a white dwarf, will continue to spiral together eventually merging.
The team’s findings and the first glimpse into the consequences of the common envelope phase of stellar evolution could help other researchers identify more binary stars at a critical stage in their lives.
“It might be easier to recognize them now that we have a clearer idea of what to look for. There could be others that have been under our noses all along,” Wolf said, adding that the findings could also have ramifications for other cosmic unions. . “It may even help us better reconstruct gravitational wave events such as black hole mergers.”
The team’s research was published in the journal Monthly notices from the Royal Astronomical Society. (opens in new tab)
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