Snickers
Published on Feb 28, 2006 at 12:17 pm.
2 Comments.
Filed under galaxies.
Don’t let anyone tell you that astronomers don’t have a sense of humor!
A case in point is a small satellite of the Milky Way. Our galaxy has a number of smaller galaxies orbiting it as satellites. The most well known of these are the Magellanic Clouds. However, there are a host of smaller bodies orbiting us. In 1975, Christian Simonson discovered one such body in radio survey using 21cm radiation. Neutral hydrogen in the interstellar medium can emit radio waves having wavelenth of 21cm. This discovery was deemed to be a satellite galaxy of our Milky Way. Our own galaxy is filled with dust and gas that blocks our view of what is beyond. In fact, if you were to plot extragalactic objects on a map of the sky, you’d notice a large swath wrapping around the sky with hardly any objects in it. This is called the zone of avoidance. Really, the extragalactic objects don’t avoid this zone — the ones in the zone are simply hidden by our own galaxy. Galaxies in this zone are difficult or impossible to detect except by radio or infrared emissions, and even then sometimes with difficulty. Simonson’s new satellite galaxy was square in the zone of avoidance, 55,000 lightyears away in the general direction of the constellation Auriga (where several really nice open star clusters lay). Well, since this new small galaxy was hidden right behind the Milky Way, it was nicknamed “Snickers.”Â
In truth, Snickers is a pretty sorry excuse for a galaxy, and recent observations call that designation into question. Snickers has a very low surface brightness, and may contain very few stars. The radio emission was from hydrogen gas, so Snickers may be mostly a large mass of gas orbiting the Milky Way. There are several such gas clouds, called high velocity clouds that appear to be mostly hydrogen gas of about the mass of a satellite galaxy, but without stars, or with only a few stars. Interestingly enough, the high velocity clouds may have more mass than can be accounted for with just the hydrogen gas, so they may contain copious amounts of dark matter, too. This would make these clouds effectively starless satellite galaxies. Unfortunately for Snickers, it is still difficult to see through the interstellar medium of our own Milky Way, so it may be some years before we really know what sort of object it is. Whatever it is, it appears to be about the size and mass of a small satellite galaxy and it is orbiting the Milky Way.
So, that’s your astronomical trivia for the day.
-Astroprof
Snickers on October 15, 2008 at 5:22 am: 1
I think sense of humour is probably a bit extreme!
Steve J. on May 14, 2010 at 10:50 pm: 2
Sounds like Snickers is just peanuts on the other side of the Milky Way.