Free Astronomy Magazine January-February 2024

JANUARY-FEBRUARY 2024 “When I first saw evidence for a ro- tating structure in the ALMA data I could not believe that we had de- tected the first extragalactic accre- tion disc, it was a special moment,” says Anna McLeod, an associate pro- fessor at Durham University in the UK and lead author of the study published in Nature . “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.” This study follows up observations with the Multi Unit Spectroscopic Explorer (MUSE) instrument on ESO’s Very Large Telescope (VLT), which spotted a jet from a forming star — the system was named HH 1177 — deep inside a gas cloud in the Large Magellanic Cloud. “We discovered a jet being launched from this young massive star, and its presence is a signpost for ongoing disc accretion,” McLeod says. But to confirm that such a disc was indeed present, the team needed to meas- ure the movement of the dense gas around the star. As matter is pulled towards a grow- ing 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 smok- ing gun that shows astronomers an accretion disc is present. “The frequency of light changes de- pending on how fast the gas emit- ting the light is moving towards or away from us,” explains Jonathan Henshaw, a research fellow at Liver- pool John Moores University in the UK, and co-author of the study. “This is precisely the same phenom- enon that occurs when the pitch of T his artist’s impression shows the HH 1177 system, which is located in the Large Magellanic Cloud, a neighbouring galaxy of our own. The young and massive stellar object glowing in the centre is collecting matter from a dusty disc while also expelling matter in powerful jets. Using the Atacama Large Millimeter/sub- millimeter Array (ALMA), in which ESO is a partner, a team of astronomers man- aged to find evidence for the presence of this disc by observing its rotation. This is the first time a disc around a young star — the type of disc identical to those forming planets in our own galaxy — has been discovered in another galaxy. [ESO/M. Kornmesser] W ith the combined capabilities of ESO’s Very Large Telescope (VLT) and the Atacama Large Millimeter/submillimeter Array (ALMA), in which ESO is a partner, a disc around a young massive star in another galaxy has been observed. Observations from the Multi Unit Spectroscopic Explorer (MUSE) on the VLT, left, show the parent cloud LHA 120-N 180B in which this system, dubbed HH 1177, was first observed. The image at the centre shows the jets that accompany it. The top part of the jet is aimed slightly towards us and thus blueshifted; the bottom one is receding from us and thus redshifted. Observations from ALMA, right, then revealed the rotating disc around the star, similarly with sides moving towards and away from us. [ESO/ALMA (ESO/NAOJ/NRAO)/A. McLeod et al.]