Cartwheel Galaxy

This image shows the results of a rare and spectacular head-on collision between two galaxies. The bright blue ring around the galaxy reveals billions of new stars born because of the collision.

Galaxies

A galaxy is a giant assembly of gas, dust and millions or billions of stars. The Cartwheel Galaxy was once a normal galaxy similar to our home galaxy, the Milky Way, with pinwheellike spiral arms winding outward from the galaxy's center. The Cartwheel's spiral structure is beginning to reemerge as seen in the faint arms extending out from the bull's eye core to the outer ring. Some galaxies are found in great clusters, with dozens or even thousands of members that gravitationally jostle each other.

Colliding Galaxies

Galaxies travel through space at speeds approaching two million miles per hour. In clusters, the member galaxies are relatively close together. Inevitably, collisions occur. In the Cartwheel Galaxy, a smaller intruder galaxy, possibly one of the two galaxies on the right side of the image, careened through the galaxy's core. Like a rock tossed into a lake, the collision sent a ripple of energy into space, plowing gas and dust in front of it at 200,000 miles per hour. The great energy wave heated and compressed the galaxy's dust and gas, producing an expanding ring of several billion new stars. This is an unusual opportunity to study new stars, because that many stars would ordinarily take much longer to form.

Definitions

Cluster of Galaxies: a collection of galaxies containing a few to several thousand members.

Galaxy: a large assembly of gas, dust and millions or billions of stars; seen in different shapes including pinwheelshaped spirals, smooth round ellipticals, and irregulars having neither spiral arms nor round shape.

Light Year: the distance light travels in a year (5.9 X 10^12 or 5 trillion, 900 billion miles).

Near-infrared: electromagnetic radiation (light energy) of longer wavelengths than visible light; infrared radiation (heat energy) reveals clouds of dust and gas where stars are born.

Fast Facts

Age: The ring resulted from a collision that probably occurred 200 million years ago.

Location: The galaxy is in the southern hemisphere constellation Sculptor.

Distance from Earth: 500 million light years.

Size: 150,000 light years across.

Electronic Addresses

You can get images and other information about the Hubble Space Telescope using the Internet.

Using ftp or gopher, connect to ftp.stsci.edu and find files and directories in /pubinfo.

Using the World Wide Web (Mosaic, NetScape, Lynx, and other browsers), use URL http://www.stsci.edu/public.html and follow links from there.