Astronomers spot young star forming in a really unexpected way

14 Dec 2018

An artist’s impression of the disc of dust and gas surrounding the massive protostar MM 1a, with its companion MM 1b forming in the outer regions. Image: Dr J D Ilee/University of Leeds

A star spotted in deep space was found to be forming in a rather unusual way, due in part to it actually being two stars, not one.

Once again, astronomers have been left surprised by something they have found in the outer reaches of the universe. This time around, a team from the University of Leeds captured one of the most detailed views of a young star to date, but something wasn’t quite right.

Upon further inspection, it was shown that the young star wasn’t solitary, but actually came with a companion. The main object, referred to as MM 1a, is a massive young star surrounded by a rotating disc of gas and dust that was the focus of the scientists’ original investigation.

Just beyond the disc, the team spotted the faint object dubbed MM 1b and believe this to be one of the first examples of a ‘fragmented’ disc to be detected around a massive young star.

“Stars form within large clouds of gas and dust in interstellar space,” said Dr John Ilee, who led the team.

“When these clouds collapse under gravity, they begin to rotate faster, forming a disc around them. In low-mass stars like our sun, it is in these discs that planets can form. In this case, the star and disc we have observed is so massive that, rather than witnessing a planet forming in the disc, we are seeing another star being born.”

‘An entirely different formation process’

Publishing its findings in the Astrophysical Journal Letters, the team went on to explain that by measuring the amount of radiation emitted by the dust, as well as the subtle shifts in the frequency of light emitted by the gas, it was able to calculate the mass of the two objects.

This showed that MM 1a weighs about 40 times the mass of our sun, while MM 1b is significantly smaller, at half that of our nearest star.

“Many older massive stars are found with nearby companions,” added Ilee. “But binary stars are often very equal in mass, and so likely formed together as siblings. Finding a young binary system with a mass ratio of 80:1 is very unusual and suggests an entirely different formation process for both objects.”

Additionally, the team think MM 1b could be surrounded by its own circumstellar disc, but it will need to form quickly as stars the size of MM 1a only last for approximately 1m years before exploding.

Colm Gorey was a senior journalist with Silicon Republic