The background image was taken by Michael Hilker of the University of Bonn using the 2.5-metre Du Pont telescope, part of the Las Campanas Observatory in Chile. The two boxes show close-ups of two UCD galaxies in the Hilker image. These images were made using the Hubble Space Telescope by a team led by Michael Drinkwater, at the University of Queensland.
Galaxies are collections of stars. Some are massive, with many more times the mass of our own Milky Way galaxy, while others just have a fraction of our mass. Let’s take a look at the mass of different kinds of galaxies, and compare that to the mass of the Milky Way.
So, just to give you a baseline, let’s look at the mass of our own Milky Way. Astronomers measure galaxy mass in terms of suns. One sun is the mass of our own Sun, 10 suns is the same as 10 times the mass of our Sun. The total mass of the Milky Way is about 200 billion suns; although some scientists estimate it might be as high as 600 million suns.
The smallest, least massive galaxies in the Universe are a newly discovered class of objects known as ultra-compact dwarf galaxies. UCDs are less that 1/1000th the diameter of the Milky Way, but much more dense. They still only have a galaxy mass of 200 million suns – 1/10th the mass of the Milky Way.
The most massive galaxies in the Universe are giant elliptical galaxies at the center of galaxy clusters. These monsters are known as giant diffuse galaxies, or brightest cluster galaxies, and they can be 100 times more massive than the Milky Way, and 10 times brighter. An example of a galaxy like this is the central galaxy in the cluster Abell 2029.
We have written many articles about the galaxies for Universe Today. Here’s an article on ultra-compact dwarf galaxies, and here’s more information on some of the most massive galaxies in the Universe.
If you’d like more info on galaxies, check out Hubblesite’s News Releases on Galaxies, and here’s NASA’s Science Page on Galaxies.
We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.
Comments on this entry are closed.