New observations of the Small Magellanic Cloud show that it might actually be two galaxies disguised as one.
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The Small Magellanic Cloud is a nearby galaxy that is very familiar to astronomers — or so they thought. New research suggests that the satellite galaxy of the Milky Way, located around 199,000 light-years from Earth, seems to have been hiding a secret: It’s actually two galaxies, one behind the other.
To make the discovery, a team led by Claire Murray, an astronomer at the Space Telescope Science Institute in Maryland, tracked the movement of gas clouds and young stars being born within them around the Small Magellanic Cloud. They found that the small galaxy, which is around 18,900 light-years wide (or less than a fifth of the width of the Milky Way), contains two distinct stellar nurseries thousands of light-years apart.
The research has been accepted for publication in The Astrophysical Journal and is available as a preprint via arXiv.
A ‘trainwreck of a galaxy
Both the Small Magellanic Cloud and the Large Magellanic Cloud are dwarf galaxies that are gravitationally bound to the Milky Way and are being steadily drawn toward our galaxy for a collision and merger in the far future.
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While the Large Magellanic Cloud has a disk-like shape similar to that of the Milky Way, the Small Magellanic Cloud is more irregular. The Small Magellanic Cloud has only one-third the mass of the larger dwarf galaxy, which has a mass equivalent to around 7 billion times that of the sun.
Although the Small Magellanic Cloud was previously thought to consist of multiple components, it is somewhat obscured by interstellar clouds of gas and dust, meaning these features have been hard to distinguish.
Murray has previously determined that the Small Magellanic Cloud is a “trainwreck” of a dwarf galaxy, full of gas disrupted by gravitational interactions with the Milky Way and the Large Magellanic Cloud. For the new investigation of the Small Magellanic Cloud, she and her colleagues zoomed in on radio waves emitted by hydrogen gas in the dwarf galaxy using the Australian Square Kilometre Array Pathfinder radio telescope, which comprises 36 dish antennas. The team followed up these observations by using the European Space Agency‘s (ESA) Gaia spacecraft, which is currently building a 3D map of stars in the Milky Way, to track the speed and direction of thousands of stars in the Small Magellanic Cloud that are younger than 10 million years old.
