Wednesday , December 8 2021

Fragmenting disc gives rise to binary star "odd couple"



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Astronomers using the Atacama Large Millimeter / Submillimeter Array (ALMA) have discovered that two young stars that form from the same swirling protoplanetic disc can be twins – in the sense that they came from the same parent cloud of star-forming material. In addition, however, they are shocking a little in common.

The main central star of this system, which is about 11,000 light years from the earth, is truly colossal – a whole 40 times more massive than the sun. The second star, as ALMA recently discovered just beyond the central star's disc, is a relatively uneven one-eight (1/80) this mass.

Their striking difference in size indicates that they were formed by following two very different ways. The more massive star took the more traditional way by collapsing under gravity from a dense "core" of gas. The less likely to follow the road less traveled – at least for stars – by accumulating mass from a part of the disc as "fragmented" away as it matures, a process that may have more in common with the gigantic planet's birth.

"Astronomers have long known that the most massive stars circle one or more other stars as partners in a compact system, but how they came there has been a subject of guesswork," says Crystal Brogan, an astronomer with the National Radio Astronomy Observatory (NRAO) in Charlottesville, Virginia, and a co-author of the study. "With ALMA, we now have evidence that the gas and dust discharges that feed and feed a growing massive star also produce fragments in early stages that can form a secondary star."

The main object, known as MM 1a, is a previously identified young massive star surrounded by a rotating disk of gas and dust. A weak protostellary companion to this object, MM 1b, was recently discovered by ALMA just outside the MM 1a protoplanetic disk. The team believes this is one of the first examples of a fragmented disk that can be detected around a massive young star.

"This ALMA observation opens new questions, such as" Does the secondary star have a disc? "and how fast can the secondary star grow? The amazing thing about ALMA is that we have not yet used its full capacity in this area, which will ever allow us to answer the new questions," said co-author Todd Hunter, who is also with NRAO in Charlottesville.

Stars form themselves within large clouds of gas and dust in interstellar space. When these clouds collapse under gravity, they begin to rotate faster and form a disk around them.

"In low-mass stars like our Sun, it's in these dishes that planets can form," says John Ilee, an astronaut at Leeds University in England, and leads the author of the study. "In this case, the star and the record we have observed so massively that, instead of witnessing a planet formed in the disc, we see that another star is born."

By observing the millimeter wavelength naturally transmitted by the dust and subtle shift in the light frequency from the gas, researchers could calculate the mass of MM 1a and MM 1b.

Their work is published in the Astrophysical Journal Letters.

"Many older, massive stars exist with nearby comrades," added Ilee. "But binary stars are often as big, and most likely formed as siblings. Finding a young binary system with an 80-to-1 mass ratio is very rare and proposes a completely different formation process for both objects."

The preferred formation process for MM Ib occurs in the outer areas of cold, solid discs. These "gravitationally unstable" discs can not stand up to their own gravity, collapse in one or more fragments.

The researchers find that the newly discovered young star MM 1b can also be surrounded by its own circumstellarious, which may have the potential to form planets in itself – but it must be quick.

"Stars that are massive like MM 1a only live for about a million years before they are exploited as powerful supernovae, so even though MM 1b may have the potential to form its own planetary system in the future, it will not be long," concluded Ilee.

Research Report: "TG11.92-0.61 MM1: A fragmented Keplerian disk surrounding a Proto-O star", J. Ilee., 2018, December 14, Astrophysical Journal Letters

Related links

National Radio Astronomy Observatory

Stellar chemistry, the universe and all within it



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