ALMA Spots Circumstellar Disk Around Young Star in Large Magellanic Cloud, First Planet-Forming Structure Detected Outside Milky Way

It is believed that the Earth and the other planets in our solar system were born from a giant disk of dust and gas around our sun. Dubbed circumstellar disks or protoplanetary disks, many planet-forming structures have been discovered in our Milky Way galaxy. A circumstellar disk was found around a massive young extragalactic star for the first time.

Star Formation in the Milky Way

Circumstellar disks are important in forming stars and planets in our galaxy. As matter is directed towards a growing star, it cannot fall directly onto it. Instead, it flattens into a spinning disk around the star. Near the center, the disk rotates faster, and this difference in speed signals the astronomers that an accretion disk is present.

Massive stars form at a much more rapid rate and live far shorter lives than less massive stars like our sun. In our Milky Way galaxy, these massive stars are challenging to observe since they are usually obscured from view by the dusty material from which they form at the moment a disk shapes around them.

Extragalactic Spinning Disk

An international team of experts from Durham University and the UK Astronomy Technology Center has reported the first detection of a spinning disk around a young high-mass star outside our host galaxy. The massive star is in a stellar nursery called N180, which resides in a nearby dwarf galaxy called Large Magellanic Cloud. At a distance of 163,000 light years from our planet, this is considered the most distant disk around a massive star ever to be detected.

The discovery was made possible with the help of the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile. While using this interferometer, the astronomers observed movements in gas around a young stellar object in the Large Magellanic Cloud, consistent with a Keplerian accretion disk.

Unlike similar protoplanetary disks in the Milky Way, this newly discovered system is optically visible, probably due to its surrounding environment's lower dust and metal components. This enables astronomers to peek into the dynamics of accretion, which are often hidden behind the veils of gas and dust. Further analysis of the rotating disk suggests that an inner Keplerian region transitions into infalling material at larger distances from the central star, estimated to be around 15 times the mass of our sun.

This new circumstellar disk bears many characteristics familiar to those found in the Milky Way, but there are also some intriguing differences. The low metal content typical of the Large Magellanic Cloud makes the spinning disk more stable against fragmentation. It shows that this planet-forming disk is common around stars in other galaxies besides ours.

The discovery of this extragalactic protoplanetary disk boosts the potential to find more similar systems using ALMA and the upcoming Next Generation Very Large Array (ngVLA). As experts study star and disk formation across various galactic environments, their findings could help us understand our stellar origins.

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