HubbleSite: Jurrasic Space

[bystander]

Jurassic Space: Ancient Galaxies Come Together After Billions of Years
Hubble Site: STScI-2010-08 - 2010 Feb 18

Imagine finding a living dinosaur in your backyard. Astronomers have found the astronomical equivalent of prehistoric life in our intergalactic backyard: a group of small, ancient galaxies that has waited 10 billion years to come together. These "late bloomers" are on their way to building a large elliptical galaxy.

These four dwarf galaxies waited billions of years to come together, setting off a fireworks show as thousands of new star clusters come to life. The distorted galaxies are quickly producing massive, hot, young stars that are pumping out ultraviolet radiation, heating up surrounding gas clouds, and causing them to glow.

Such encounters between dwarf galaxies are normally seen billions of light-years away and therefore occurred billions of years ago. But these galaxies, members of Hickson Compact Group 31, are relatively nearby, only 166 million light-years away.

In this composite image of the galaxy grouping, the bright, distorted object at middle, left, is actually two colliding dwarf galaxies. Myriad star clusters have formed in the streamers of debris pulled from the galaxies and at the site of their head-on collision. The cigar-shaped object above the galaxy duo is another member of the group. A bridge of star clusters connects the trio. A long rope of bright star clusters points to the fourth member of the group, at lower right. The bright object in the center is a foreground star. The image was composed from observations made by the Hubble Space Telescope's Advanced Camera for Surveys, NASA's Spitzer Space Telescope, and the Galaxy Evolution Explorer (GALEX).

Hickson Compact Group 31: Interacting Galaxies Aglow with Millions of Young Stars

[bystander]

Hubble sees ancient galaxies rejuvenating themselves
Discover | Bad Astronomy | 2010 Feb 19

Every now and again I think I’ve pretty much seen it all when it comes to astronomical images, and I’m getting jaded.

And then I see a picture like this: ...

The image shows what’s called the Hickson Compact Group 31, a small collection of galaxies. It’s a combination of images from Hubble (visible light, shown in red, green, and blue), Spitzer (infrared, shown as orange), and the Galaxy Explorer or GALEX (ultraviolet, seen here as purple).

If I saw this picture with no caption, I’d know I was seeing dwarf galaxies colliding; the shape and the glow from newly-forming stars is a dead giveaway. But I’d also guess that the galaxies were young; old galaxies tend not to have much gas in them, and there’s clearly plenty of that in those galaxies! But in fact the galaxies here are very old; there are globular clusters (spherical collections of perhaps a million stars each that tend to orbit outside of galaxies) in the group that can be dated to being 10 or so billion years old. That means these are old objects, reinvigorated by their collision.