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One of the closest galaxies to the Milky Way almost got away with a theft!
Astronomers have discovered that a Large Magellanic Cloud (LMC) – one of the closest galaxies to the Milky Way – is stealing stars from its neighbour, the Small Magellanic Cloud (SMC).
The crucial evidence for “a crime of galactic proportions” came from surveys looking for something entirely different-dark objects on the outskirts of the Milky Way.
Astronomers have been monitoring the LMC to hunt for evidence of massive compact halo objects, or MACHOs.
MACHOs were thought to be faint objects, roughly the mass of a star, but their exact nature was unknown.
Several surveys looked for MACHOs in order to find out if they could be a major component of dark matter – the unseen stuff that holds galaxies together.
In order for MACHOs to make up dark matter, they must be so faint that they can’t be directly detected. However, astronomers looked for a phenomenon known as microlensing.
During a microlensing event, a nearby object passes in front of a more distant star. The gravity of the closer object bends light from the star like a lens, magnifying it and causing it to brighten.
The number of microlensing events observed by various teams was smaller than needed to account for dark matter, but much higher than expected from the known population of stars in the Milky Way.
This left the origin of the observed events a puzzle and the existence of MACHOs as exotic objects a possibility.
“We originally set out to understand the evolution of the interacting LMC and SMC galaxies,” said lead author Gurtina Besla of Columbia University.
“We were surprised that, in addition, we could rule out the idea that dark matter is contained in MACHOs.”
“Instead of MACHOs, a trail of stars removed from the SMC is responsible for the microlensing events,” says co-author Avi Loeb of the Harvard-Smithsonian Center for Astrophysics.
“You could say we discovered a crime of galactic proportions,” Loeb said in a statement.
Computer simulations showed that the most likely explanation for the observed microlensing events was an unseen population of stars removed by the LMC from its companion, the SMC.
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