June 9, 1999

NGC 1316--An Unusual Elliptical Galaxy

The giant elliptical galaxy NGC 1316* as viewed by NASA's Hubble Space Telescope in April of 1996 with the telescope's Wide Field and Planetary Camera 2. Galaxy NGC 1316 is located at a distance of 53 million light-years from Earth in the southern constellation Fornax.

Click on the image for an enlarged view.

Image Credits: Carl Grillmair (California Institute of Technology), Duncan Forbes (University of Birmingham), Rebecca Elson (University of Cambridge), Jean Brodie (University of California), and NASA.

This intriguing image, taken by NASA's Hubble Space Telescope (HST), is of the giant elliptical galaxy NGC 1316.

Galaxy NGC 1316 is unusual in two ways: It possesses plenty of gas and dust, as illustrated by the dark, smoky-looking, interconnected dust lanes that contrast ominously with the bright, star-rich, central region of the elliptical galaxy. Also, there are relatively few globular star clusters, which are spherical aggregates of hundreds of thousands to millions of very old stars bound together by their mutual gravitational forces. Instead, NGC 1316 possesses many faint, bluish, point-like star clusters, each containing only a few thousand stars. (The reddish and fuzzy-looking objects visible in the image are not part of NGC 1316, but are separate, more distant galaxies.)

Most elliptical galaxies possess very little gas and dust (in contrast to other types of galaxies, such as our own Milky Way, which is a spiral galaxy). Furthermore, most ellipticals are rich in globular star clusters and poor in the small star clusters seen in NGC 1316.

The international team of astronomers that took the above image, led by Carl Grillmair of the California Institute of Technology, interprets the data as follows: Roughly within the past 100 million years, a small, dust-rich galaxy collided with and was captured by NGC 1316. That's the origin of the gas and dust seen in the above image. This gas and dust is spiraling inward toward the center of NGC 1316, where the matter falls into the massive black hole that is believed to reside there, providing the energy for jets of material that shoot outward more than 250,000 light-years from the galaxy's center (these jets are not visible in the above image).

The many small, point-like star clusters seen in NGC 1316 either belonged to the galaxy that provided the gas and dust, or came from other galaxies that were captured earlier.

Galactic cannibalism as exhibited by NGC 1316 is thought to have been the principal mechanism by which today's large galaxies, including the Milky Way, acquired their mass. Such galactic collisions and mergers occurred far more frequently early in the universe's history, when galaxies were packed together more closely and, hence, collided more often than they do today.

* The acronym "NGC" stands for the New General Catalogue of Nebulae and Clusters of Stars, compiled at the end of the nineteenth century by the Danish astronomer Johan L. E. Dreyer.

More Cool Stuff

We obtained the above image and information from press release 99-06 of the Space Telescope Science Institute:

http://oposite.stsci.edu/pubinfo/pr/1999/06/pr.html

We have featured galactic collisions and mergers in earlier Web publications:

http://observe.ivv.nasa.gov/nasa/ootw/1998/ootw_980617/ob980617.html (Galactic Cannibalism)

http://observe.ivv.nasa.gov/nasa/ootw/1998/ootw_980128/ob980128.html (Galaxies under Construction)

http://observe.ivv.nasa.gov/nasa/ootw/1997/ootw_970507/ob970507.html (Galaxy Encounter Spawns New Galaxies)

http://observe.ivv.nasa.gov/nasa/ootw/1996/ootw_960904/ob960904.html (Cosmic Collision)

As part of its Learning Technologies Project (LTP), NASA supports a number of educational Web sites that have excellent material on the space sciences:

http://observe.ivv.nasa.gov/nasa/education/edu/edudocs/topic_space.html