Rotating Question Curious About Astronomy? Ask an Astronomer

How are galaxies formed?

I am sixth grader and I am doing a science project on galaxies. I wanted to know how galaxies are formed.

As you may know, galaxies are mainly of two kinds: spiral galaxies and elliptical galaxies (there are also irregular galaxies).

Spiral galaxies form from the collapse of a protogalactic cloud. Spiral galaxies consist of three components: a rotating disk, a bulge and a halo. When the protogalactic cloud collapses, the stars in the bulge and halo form first. These stars have rather random orbits around the galactic center. The remainder of the cloud forms a disk due to the conservation of angular momentum (the same effect as the spinning up of the dancer when she pulls her arms inside). The stars in the disk form later and thus the disk population of stars are younger than those in the bulge and the halo. Further, the stars in the disk rotate around the center of the galaxy in a collective, well defined way unlike the stars in the bulge and halo.

Elliptical galaxies are thought to be formed as a result of a merger of two disk galaxies. When two spiral galaxies merge, then the orbits of all the stars are randomized. As a result, all the stars in an elliptical galaxy have random orbits and there is not much collective motion of stars.

November 2001, Jagadheep D. Pandian (more by Jagadheep D. Pandian) (Like this Answer)

Still Curious?

Get More 'Curious?' with Our New PODCAST:

Related questions:

More questions about Galaxies: Previous | Next

How to ask a question:

If you have a follow-up question concerning the above subject, submit it here. If you have a question about another area of astronomy, find the topic you're interested in from the archive on our site menu, or go here for help.

Table 'curious.Referrers' doesn't existTable 'curious.Referrers' doesn't exist

This page has been accessed 76572 times since August 23, 2002.
Last modified: October 26, 2002 1:55:34 PM

Legal questions? See our copyright, disclaimer and privacy policy.
Ask an Astronomer is hosted by the Astronomy Department at Cornell University and is produced with PHP and MySQL.

Warning: Your browser is misbehaving! This page might look ugly. (Details)