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Moon and Spica

July 11, 2016

Giant galaxies probably become giant galaxies through acts of cannibalism — they gobble up smaller galaxies. Our own Milky Way, for example, is ingesting at least one smaller galaxy right now, and there’s evidence that it has swallowed others in the past.

Another possible example is the massive elliptical galaxy M87. It’s one of the most impressive galaxies around. It’s 10 times wider than the Milky Way, and it contains a trillion stars. And quite a few of those stars may represent the remains of a smaller galaxy that M87 ingested within the last billion years.

European researchers reported the possible act of cannibalism last year. They discovered that many of the stars in M87 are quite blue, which means they’re also quite young. But M87 itself is an old galaxy that’s giving birth to almost no new stars. So the blue stars probably came from outside M87.

The researchers also looked at dying stars on the fringes of M87. The motions of these stars indicate that something stirred up the galaxy fairly recently.

From these observations, the researchers concluded that M87 gobbled up a smaller spiral galaxy within the last billion years — adding to M87’s considerable heft.

This galactic giant is a member of a large cluster of galaxies in the constellation Virgo. And the Moon is passing through Virgo right now. Tonight, the constellation’s brightest star, Spica, stands quite close to the lower left of the Moon as darkness falls.

Script by Damond Benningfield

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