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For the first time, astronomers discover planet formation in another galaxy

In a significant breakthrough, astronomers have identified a rotating disc around a young star in the Large Magellanic Cloud, a galaxy in close proximity to the Milky Way. This is the first time that such a disc, akin to those that contribute to planet formation in our own galaxy, has been observed outside the Milky Way.

Finding the extragalactic rotating disc

The Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, an installation in which the European Southern Observatory (ESO) plays a significant role, was instrumental in this discovery. The observations disclosed a young, massive star in the process of growth, accumulating matter from its surroundings and forming a rotating disc.

Anna McLeod is an associate professor at Durham University in the UK and the study’s lead author. She expressed her astonishment at the discovery.

“When I first saw evidence for a rotating structure in the ALMA data I could not believe that we had detected the first extragalactic accretion disc, it was a special moment,” says McLeod. “We know discs are vital to forming stars and planets in our galaxy, and here, for the first time, we’re seeing direct evidence for this in another galaxy.”

McLeod highlighted the crucial role of discs in star and planet formation in our galaxy, emphasizing the importance of this discovery in another galaxy.

Follow-up observations

The Multi Unit Spectroscopic Explorer (MUSE) on ESO’s Very Large Telescope (VLT) previously observed a jet emanating from a forming star — named HH 1177 — within a gas cloud in the Large Magellanic Cloud.

McLeod noted, “We discovered a jet being launched from this young massive star, and its presence is a signpost for ongoing disc accretion.” However, to confirm the existence of a rotating disc, the team needed to analyze the movement of dense gas surrounding the star.

Rotating accretion discs

The process of matter accreting onto a growing star is complex. Rather than falling directly onto the star, it flattens into a spinning disc around it. The inner parts of the disc rotate faster than the outer regions, providing key evidence for the presence of an accretion disc.

Jonathan Henshaw is a research fellow at Liverpool John Moores University in the UK and co-author of the study. He explained how the frequency of light changes with the motion of the gas emitting it.

“The frequency of light changes depending on how fast the gas emitting the light is moving towards or away from us,” explains Henshaw. “This is precisely the same phenomenon that occurs when the pitch of an ambulance siren changes as it passes you and the frequency of the sound goes from higher to lower.”

ALMA’s precise frequency measurements allowed the researchers to detect the characteristic spin of a disc, confirming it was, indeed, the first discovery of a disc around an extragalactic young star.

Significance of massive stars

Massive stars, like the one observed in this study, form much more rapidly and have shorter lifespans than smaller stars like our Sun. They are usually difficult to observe in our galaxy due to the obscuring dust.

However, the Large Magellanic Cloud, situated 160,000 light-years away and having lower dust content, provided a clear view of the star and planet formation process.

McLeod concluded by emphasizing the rapid advancements in astronomical technology. “We are in an era of rapid technological advancement when it comes to astronomical facilities,” McLeod says. “Being able to study how stars form at such incredible distances and in a different galaxy is very exciting.”

This discovery marks a pivotal moment in our understanding of star and planet formation across the universe.

The full study was published in the journal Nature.

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