Astronomers last year spotted a star leaving the Milky Way Galaxy. Later one or two more were detected. And today, researchers announced the discovery of yet two more outbound stars.
With so many outcasts on record, astronomers now see them as a new class of astronomical object, intergalactic stars exiled from their home galaxies.
The two newfound exiles are racing out of the galaxy at more than a million miles an hour, fast enough that the galaxy’s gravity will never reel them back in.
"These stars literally are castaways," said Warren Brown of the Harvard-Smithsonian Center for Astrophysics. "They have been thrown out of their home galaxy and set adrift in an ocean of intergalactic space."
Brown told SPACE.com that the same thing likely occurs in other galaxies, so intergalactic space is probably filled with wanderers.
Lots of them
Brown’s team found the first outcast last year. Two other intergalactic vagabonds were spotted by European astronomers; one of those may have come from another nearby galaxy called the Large Magellanic Cloud.
There might be a thousand Milky Way exiles-to-be lurking inside the galaxy and on outbound tracks. The galaxy contains about 100 billion stars, so finding the outcasts is no easy task. Knowing what to look for is the key.
To leave the galaxy, a star must somehow be accelerated outward. Here’s what astronomers figure can happen: A two-star system, called a binary, rounds the center of the galaxy where it is tugged apart by the tremendous gravity of the central supermassive black hole. One of the stars is captured, while the other is shot outward as if from a slingshot.
The scenario has been modeled on a computer. Finding the fast-moving stars is evidence that it actually happens.
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