Aliens from Other Galaxies
You know that town in Texas where the residents think they’re seeing alien UFOs (which turned out to be Air Force jets)? Well, they haven’t seen anything as alien as what the folks at the Carnegie Institution of Washington found when they did observations and analysis of a star called HE 0437-5439, a so-called “hypervelocity” star. It’s speeding away from the Milky Way, but it wasn’t born IN the Milky Way. So, astronomers studied its mass, age, and speed of the star, which is about nine times the mass of the Sun. It’s moving into intergalactic space at about 2.6 million kilometers per hour. That’s much too fast for it to have come from the Milky Way, but where DID it come from?
As it turns out, HE 0437-5439 was born in the Large Magellanic Cloud, a neighbor galaxy to the Milky Way. The Carnegie astronomers figured this out by looking at amounts of certain elements in the star. The “elemental abundances” they found point to a particular area in the Large Magellanic Cloud where similar amounts of the same elements exist. Hence the star more than likely formed in that region. So, what’s it doing speeding away from the LMC and the Milky Way? Stars don’t get up and flash out of their home galaxies just for the heck of it. They have to be kicked out by something.
The most likely scenario goes something like this: HE 0437-5439 formed as part of a binary system (a pair of stars orbiting a common center of gravity). As that pair of stars moved through space, they passed by a black hole that was about a thousand times the mass of the Sun. As we all know, black holes suck; that is, they have strong gravitational pulls. One star of the pair got pulled into the black hole, while the other got a gravitational kick that flung it out of the LMC. Now the surviving star (HE 0437-5439) is on its way to intergalatic space, leaving astronomers with an important clue that there’s at least one black hole in the Large Magellanic Cloud. Now they just have to find it. (Note: for more information, read this press release.)