Astronomers have discovered the first example of a rotating disk of material feeding a young star in a galaxy outside the Milky Way. The disk is nearly identical to those found around baby stars in the Milky Way and shows that stars and planets form in other galaxies just as they do in our own.
The young star in question is located in the Large Magellanic Cloud, a neighboring galaxy 160,000 light-years away from the Milky Way, and its system, called HH 1177, is embedded in a huge cloud of gas.
The team behind this discovery observed the system with the Atacama Large Millimeter/submillimeter Array (ALMA), the world’s largest astronomy project, consisting of 66 antennas forming a single radio telescope in northern Chile.
“When I first saw evidence of a rotating structure in the ALMA data, I couldn’t believe we had detected the first extragalactic accretion disk. It was a special moment,” said study lead author and Durham University scientist Anna McLeod. he said in a statement. “We know that disks are vital to the formation of stars and planets in our galaxy, and here, for the first time, we see direct evidence of this in another galaxy.”
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McLeod and colleagues became aware of this system when the Multi-Unit Spectroscopic Explorer (MUSE) instrument on ESO’s Very Large Telescope (VLT) detected a jet emerging from a forming star. This device makes observations in the visible wavelength range while also measuring the wavelengths of light coming from an object, allowing scientists to tell what type of matter they are looking at.
“We discovered a jet ejected from this young, massive star, and its presence is a sign of ongoing disk accretion,” McLeod added. To confirm the presence of an accretion disk in HH 1177, scientists needed to measure the movement of dense gas around the star.
Accretion disks inside and outside the Milky Way
Such newly observed accretion disks form when matter falls towards a newborn star or other accreting object, such as a black hole or neutron star. The material carries angular momentum (spinal spin) as it falls on these objects, meaning it cannot go directly to that central body. Instead, this material forms a flattened rotating disk that gradually feeds the material into the central object.
Closer to the central object (in this case, a young feeding star), gas at the center of the accretion disk moves faster than matter at the outskirts of the disk, and it is this change in speed that is the “smoking gun.” This indicates the presence of an accretion disk.
“The frequency of the light changes depending on how fast the gas emitting the light is moving towards us or away from us,” said team member and Liverpool John Moores University research fellow Jonathan Henshaw. “This is exactly the same phenomenon that occurs when the ambulance siren changes pitch and the frequency of the sound decreases from high to low as it passes you.” (This phenomenon is known as redshift or blueshift, depending on whether the observed object is moving toward or away from the Earth.)
Astronomers have previously detected bright accretion disks around objects such as supermassive black holes in other galaxies; The immense gravity of these disks produced violent conditions that caused the gas and dust in these disks to shine brightly, often outshining the total light of every star in the galaxy surrounding them. . But the accretion disks around stars, from which planets eventually emerge, are much harder to detect, even in the Milky Way, in part because young stars are often still cocooned in the clouds of gas and dust from which they were born.
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The situation is somewhat different in the Large Magellanic Cloud, since the material that gives birth to young stars is less rich in dust. This means that HH 1177 has already escaped most of the “cocoon” in which it was born; This allows astronomers to observe its central star and possibly even watch the early stages of planet formation. Our own solar system would have been going through the same process about 4.5 billion years ago, when a protoplanetary disk surrounded the young sun in the process of giving birth to planets.
“We are in an era of rapid technological advancement when it comes to astronomical facilities,” says McLeod. “It’s very exciting to be able to study how stars form at such incredible distances and in a different galaxy.”
The team’s research is presented in a paper published in the journal. Nature On Wednesday, November 29.