Astronomers have witnessed for the first time a rare and important event in the evolution of binary star pairings.
The team discovered a tight binary star surrounded by an expanding shell of matter. This shell is the material 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 “embrace.” This results in a transfer of mass from the inflated star to its companion which can get out of control. The consequences of this phase are something that astronomers had not glimpsed until now.
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“The common envelope phase is a missing link in the very long and complex chain of events that make up the life of stars,” said Christian Wolf, associate professor at the Australian National University (ANU), and part of the team that made the observations. statement. (opens in a new tab) “Now we’re starting to mend that bond.”
Half of all stars in the universe come in binary pairs and while the initial stages of partnerships may be uneventful, when a star runs out of hydrogen for nuclear fusion, things get interesting for pairing.
The first stage of these events is the collapse of the star’s hydrogen-depleted core as its outer layers “swell” – a process the sun will experience in about 5 billion years – creating a red giant star. But it happens differently for stars in binary pairs than for our lone star.
“When one of the stars becomes a red giant, it doesn’t just claim more empty space like a single star would,” Wolf said. “Instead, he ‘kisses’ or engulfs his mate, and they appear like a star under an opaque envelope. This is where things get really exciting.”
Wolf explains that the friction created in the envelope caused by the motion of the stars within has profound effects on the next stage of binary star evolution. “This not only causes heat, but slows the stars down, so that they wrap themselves in a tighter and tighter orbit; the envelope eventually overheats and is blown away,” he said.
As a result, stars can end up more than 100 times closer to each other at the end of the common envelope phase than they were at its beginning after the heat of the process causes the expulsion of surrounding matter in a violent “eruption”. ‘
The outburst of binary stars observed by Wolf and his colleagues occurred around 10,000 years ago. The researchers predict that the binary stars they observed, now a white dwarf and a hot sub-dwarf that will eventually evolve into a white dwarf itself, will continue to spiral together and eventually merge.
The team’s findings and the first insight into the consequences of the common envelope phase of stellar evolution could help other researchers spot more binary stars at the critical stage of their lives.
“It may be easier to recognize them now that we have a clearer idea of what to look for. There may be others that have been right under our noses the whole time,” Wolf said, adding that the findings could also have ramifications for other cosmic unions. . “It might even help us better reconstruct gravitational wave events, such as black hole mergers.”
The team’s research has been published in the journal Royal Astronomical Society Monthly Notices. (opens in a new tab)
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