Detected the first extragalactic circumstellar disk around a massive young star outside of the Milky Way in the Large Magellanic Cloud

Artist's impression of the disk and jet in the young star system HH 1177 Credit: European Southern Observatory.

An international team of astronomers led by the Physics department of the Durham University, including astronomers at the UK Astronomy Technology Center, has reported the first detection of a rotating disc structure around a forming high-mass star outside of our Milky Way in another galaxy.

They used the AtacamaLarge Millimeter/submillimeter Array (ALMA) in Chile, the researchers observed motions in gas around a young stellar object in the Large MagellanicCloud consistent with a Keplerian accretion disc - the kind that feeds the growth of stars through infalling material.

The disc surrounds a young massive star is located in a stellar nursery called N180, residing in our own neighbouring dwarf galaxy, the famous Large Magellanic Cloud, which is located at a distance of 163,000 light years from Earth, so this makes it the most distant disk around a massive star ever to be directly detected.

    

    Digitized Sky Survey image around the HII region LHA 120-N 180B Credit: European Southern Observatory.

                        The HII region LHA 120-N 180B in the constellation Mensa. Credit: ALMA.

Evidence of star formation

As matter falls towards a growing star, conservation of angular momentum causes it to flatten into a spinning protoplanetary disc.

By detecting differences in rotational velocities within the disc, that is, the disk rotates faster to the centre, the researchers found clear evidence of its Keplerian nature - the smoking gun indicating ongoing star formation.

Lead author of the study, Dr. Anna McLeod from Center for Extragalactic Astronomy at Durham University said, "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 disk; it was a special moment."

"We know disks 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.

"We are in an era of rapid technological advancement when it comes to astronomical facilities."

"Being able to study how stars form at such incredible distances and in a different galaxy is very exciting."

Glimpse into the normally hidden process

Massive stars form more quickly and live shorter lives than stars like our Sun, and they are typically enshrouded by thick dusty envelopes that obscure the protostellar discs surrounding them.

But the circumstances in the of the Large Magellanic Cloud are different than in the Milky Way, our galactic neighbour has a low metal content, so it seems to make this disc more optically visible. This gives astronomers a chance to see the dynamics of the accretion disc, typically hidden behind veils of gas and dust.

This dazzling region of newly-forming stars in the Large Magellanic Cloud (LMC) was captured by the Multi Unit Spectroscopic Explorer instrument on ESO’s Very Large Telescope. The relatively small amount of dust in the LMC and MUSE’s acute vision allowed intricate details of the region to be picked out in visible light. Credit: ESO, A McLeod et al.

While this extragalactic disc shares many familiar traits with those in the Milky Way, some intriguing differences also emerge, likely linked to the lower metal abundance.

The detection significantly improves prospects for locating more such disks around distant massive stars using ALMA and other next-generation telescopes like the planned Next Generation Very Large Array (ngVLA).

Source: Durham University, Wikiedia, ESO, ALMA,

Read the full paper published in Nature: Anna McLeod, A probable Keplerian disk feeding an optically revealed massive young star, Nature (2023). DOI: 10.1038/s41586-023-06790-2. www.nature.com/articles/s41586-023-06790-2