An extraordinary discovery in another galaxy. This is the first time something like this has been observed

The Large Magellanic Cloud is a galaxy neighboring ours. The disk discovered there is identical to the disks in which planets form in the Milky Way. The discovery was made using the Atacama Large Millimeter/submillimeter Array (ALMA) radio interferometer in Chile, in which the European Southern Observatory (ESO) is a partner.

– When I first saw evidence of rotating structure in the ALMA data, I couldn’t believe we had detected the first extrasolar accretion disk. It was a special moment, said Anna McLeod, professor at Durham University in the UK, first author of the research published on Wednesday in the journal Nature. “We know that disks are key to the formation of stars and planets in our galaxy, and now for the first time we see direct evidence that this is also the case in another galaxy,” she added.

This research expands on observations made with the Multi Unit Spectroscopic Explorer (MUSE) instrument on ESO’s Very Large Telescope, which spotted a jet from a forming star – in a system called HH 1177 – deep inside a gas cloud in the Large Magellanic Cloud.

– We discovered that a jet is being fired from a young massive star, and its existence heralds the ongoing disk accretion – McLeod points out. But to confirm that this type of disk was actually there, the research team needed to measure the movement of dense gas around the star.

As material is pulled towards a growing star, it does not fall directly onto it and instead flattens into a spinning disk around it. The closer to the center, the faster the disk rotates, and the difference in speeds is evidence that shows astronomers that an accretion disk exists.

– The frequency of light changes depending on how fast the gas emitting it is moving towards or away from us – explains Jonathan Henshaw, an intern at Liverpool John Moores University in the UK, co-author of the research. – This is exactly the same phenomenon that occurs when the tone of an ambulance siren changes as it passes us and the frequency of the sound decreases from higher to lower – he added.

Accurate frequency measurements with ALMA allowed the authors to distinguish the characteristic rotation of the disk, confirming the detection of the first disk around an extragalactic young star.

Massive stars like the one observed here form much faster and live much shorter than low-mass stars like the Sun. In our galaxy, massive stars are difficult to observe and are often obscured by the dust they form as the disk around them forms. However, in the Large Magellanic Cloud, a galaxy 160,000 years away light-years, the material from which stars are formed is fundamentally different from that of the Milky Way. Thanks to its lower dust content, HH 1177 is no longer obscured by its natal cocoon, giving astronomers a view of star and planet formation.

– In the case of astronomical infrastructure, we are in an era of rapid technological development – adds McLeod. “Being able to study how stars form at such incredible distances, and in another galaxy, is very exciting,” he added.