Astronomers spot giant sun giving birth to new star

The moment a young “Mini-Me” star is born orbiting another giant sun has been spotted by astronomers.

Unusually the star is forming in the same way that our sun was, from a mass of swirling space debris in the orbit of a giant sun.

A disc of dust and gas surrounds the newly forming star and as it spins at high speed this material clumps together to form planets orbiting the sun.

But because the disc is so huge it’s actually creating a smaller star half the size of our sun which is orbiting another star 40 times as big as our sun.

The discovery was made as astronomers observed the young massive star MM 1a. The study was published in the Astrophysical Journal Letters.

They were investigating the surrounding rotating disc of gas and dust and detected a faint object, MM 1b, just beyond the disc in orbit around MM 1a.

The team believes this is one of the first examples of a “fragmented” disc to be detected around a massive young star.

Research Fellow Dr. John Ilee from the School of Physics and Astronomy at the University of Leeds explained: “Stars form within large clouds of gas and dust in interstellar space. 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.”

By measuring the amount of radiation emitted by the dust and subtle shifts in the frequency of light emitted by the gas, the researchers were able to calculate the mass of MM 1a and MM 1b.

MM 1a weighs 40 times the mass of our Sun while the smaller orbiting star MM 1b was calculated to weigh less than half the mass of our Sun.

Ilee added: “Many older massive stars are found with nearby companions. 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.”

The favored formation process for MM 1b occurs in the outer regions of cold, massive discs.

These “gravitationally unstable” discs are unable to hold themselves up against the pull of their own gravity, collapsing into one – or more – fragments.

Co-author Associate Lecturer Dr. Duncan Forgan from the Center for Exoplanet Science at the University of St Andrews, added: “I’ve spent most of my career simulating this process to form giant planets around stars like our sun.

“To actually see it forming something as large as a star is really exciting.”

The researchers note newly-discovered young star MM 1b could also be surrounded by its own circumstellar disc, which may have the potential to form planets of its own – but it will need to be quick.

Ilee said: “Stars as massive as MM 1a only live for around a million years before exploding as powerful supernovae, so while MM 1b may have the potential to form its own planetary system in the future, it won’t be around for long.”

The surprising discovery was made by using a unique new instrument situated high in the Chilean desert – the Atacama Large Millimetre/submillimetre Array (ALMA).

Using the 66 individual dishes of ALMA together in a process called interferometry, the astronomers were able to simulate the power of a single telescope nearly 4km across, allowing them to image the material surrounding the young stars for the first time.

The team has been granted additional observing time with ALMA to further characterize these exciting stellar systems in 2019. The upcoming observations will simulate a telescope that is 16km across – comparable to the area inside of the ring-road surrounding Leeds.

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