First extragalactic exoplanet disc spotted outside of the Milky Way

First extragalactic exoplanet disc spotted outside of the Milky Way
by Staff Writers
Durham UK (SPX) Nov 30, 2023

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

The disc surrounds a young massive star located in a stellar nursery called N180, residing in a neighbouring dwarf galaxy called the Large Magellanic Cloud.

At a distance of 163,000 light years from Earth, this is the most distant disc around a massive star ever to be directly detected.

Using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile, in which the European Southern Observatory (ESO) is a partner, researchers observed motions in gas around a young stellar object in the Large Magellanic Cloud consistent with a Keplerian accretion disc - the kind that feeds the growth of stars through infalling material.

The team's findings have been published in the journal Nature.

As matter is pulled towards a growing star, it cannot fall directly onto it; instead, it flattens into a spinning disc around the star. Closer to the centre, the disc rotates faster, and this difference in speed is the smoking gun that shows astronomers an accretion disc is present.

Lead author of the study, Dr Anna McLeod from Centre for Extragalactic Astronomy, 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 disc; it was a special moment.

"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.

"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."

Massive stars, like the one observed here, form much more quickly and live far shorter lives than low-mass stars like our Sun.

In our galaxy, these massive stars are notoriously challenging to observe and are often obscured from view by the dusty material from which they form at the time a disc is shaping around them.

Unlike similar circumstellar disks in the Milky Way, this system is optically visible, likely due to the lower dust and metal content of its surrounding environment. This gives astronomers a peek into the dynamics of accretion that are typically hidden behind veils of gas and dust.

Analysis of the disc suggests an inner Keplerian region transitioning to infalling material at larger distances from the central star. The star is estimated to be around 15 times the mass of our Sun.

While bearing many familiar characteristics of Milky Way discs, some intriguing differences also emerge.

The low metal content typical of the LMC seems to make the disc more stable against fragmentation.

The successful detection of this extragalactic circumstellar disc boosts prospects for finding more such systems with ALMA and the upcoming Next Generation Very Large Array (ngVLA).

Studying star and disc formation across different galactic environments will help complete our understanding of stellar origins.

Research Report:A probable Keplerian disk feeding an optically revealed massive young star