Sunday, May 6, 2012

Black-Eyed Galaxy

I haven't traditionally done a lot of galaxy images in the past, but today I have a picture of a slightly mysterious galaxy with a rather evocative name. Messier 64 is also known as “The Black Eye Galaxy” or “The Sleeping Beauty Galaxy”, and it's a really neat celestial sight. It is a spiral galaxy located in the constellation Coma Berenices (Berenice's Hair, named after the legend of Queen Berenice II of Egypt, her missing sacrificial hair, and a quick-thinking court astronomer. But you can read that story for yourself at the link up there).

Messier 64, the Black Eye Galaxy, in Coma Berenices.

M64 gets its name the Black Eye Galaxy from its appearance in a small telescope. This is mainly due to the massive clouds of dust circulating through it, especially the prominent band silhouetted in front of the bright galactic nucleus, which I've seen myself through a moderate-size telescope. If it weren't for the dust clouds in the outer regions of the galaxy blocking most of the light, M64 would be a lot brighter.

Surprisingly, given its large apparent size, the distance to M64 is not very well known. The best figures I could find suggested a distance of 17-19 million light-years, but there are estimates ranging from 12 to 40 million. Given its redshift and applying the Hubble Law would give a rough distance of about 16 million; however, M64 sits on the outskirts of the humongous Virgo Galaxy Cluster, which gives it an unknown extra component to its radial velocity that makes the Hubble Law only very roughly approximate. Since even 40 million light-years is essentially just down the block in the cosmic neighborhood, it's rather surprising that the distance isn't known more accurately, as the Cepheid variable stars used as standard candles for determining distance in nearby galaxies ought to be visible. One possible reason the distance isn't known better is that to date no supernovae have been observed in M64. One of those would definitely help pin down the distance.

M64 is about 80,000-90,000 light-years across, similar in size to (about 10% smaller) than our own Milky Way Galaxy (about 100,000 light-years across). One extremely interesting feature of this galaxy, however, is that the innermost 6,000 light-year-across region seems to be rotating in the opposite direction to the rest of the galaxy. This is quite unusual, and may hint at a possible galactic merger sometime in the galaxy's past. At the border, the differently spinning clouds of gas may be colliding with each other, possible spurring a wave of star formation. This certainly isn't your run-of-the-mill spiral galaxy. (Though to be fair, pretty much every spiral galaxy is unique in some way.)

2 comments:

  1. Nice shot! M64 is a fascinating galaxy indeed. It is a Seyfert, suggesting that a merger may be the reason for the differential rotation.

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  2. I agree. I was honestly quite surprised to discover that the distance is still relatively unknown. Sounds like a good research paper project.

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