Quasars in the Neighborhood

There seems to be more to quasars than anyone had ever thought.

By Sam Flamsteed|Sunday, March 01, 1992
There is nothing in the cosmos as dazzling as a quasar. Though smaller than our solar system, a quasar emits more light than an entire galaxy, sending out a beacon that can be seen 10 billion light-years away. Quasars are also thought to be uncommon, distant objects, typically found no closer than one billion light-years from Earth.

Now it appears possible that there may be more of these remarkable bodies than anyone had ever thought. The reason the quasars haven’t been spotted until now? They’re pointed the wrong way.

No one knows for certain just what a quasar is. It looks like a single point of light (the name quasar is derived from quasi-stellar object), yet most astronomers agree that it is probably a galaxy with a black hole sitting at its center. Gas and dust falling toward the hole, they believe, is intensely heated, creating a brilliant beam of light. Quasars have thus been classified as one species of a family of highly active galaxies. In addition to the spectacular quasars, the family includes Seyfert galaxies (which are essentially dimmer versions of quasars), galaxies that look normal but are exceptionally bright in radio emissions, and galaxies that emit enormous jets of particles from their cores.

Recently, however, Caltech astronomer Stan Djorgovski released new findings challenging this galactic pluralism. Djorgovski was never completely convinced that just because such active galaxies look different, they actually are different. Their varying appearance, he suspected, might be caused by the same ring of infalling material that makes them shine in the first place.

As galaxies spin, says Djorgovski, their gas and dust gets flattened into a doughnut shape. At its outer edges the ring is dense enough to act as a light shield that makes it impossible to see the glow of the inner ring unless it’s viewed from directly above or directly below.

To test this theory, Djorgovski decided to search for infrared radiation--also produced in abundance by a quasar--which has a wavelength that is long enough to pass relatively unmolested through galactic dust. A year ago Djorgovski and several colleagues attached an infrared camera to the 200-inch Hale telescope at Palomar Observatory and looked at eight nearby galaxies that belong to the quasar family--in this case, galaxies that are heavy in both dust and radio emissions. With even a quick glance, the astronomers believed they had hit pay dirt: five of the galaxies had infrared readings consistent with the intense energy output of a quasar.

If these galaxies were oriented differently, says Djorgovski, they would be intensely bright. I was convinced that what we had found were indeed quasars.

If Djorgovski is right, quasars may turn out not only to be more numerous than once thought but also closer. One of the galaxies he and his colleagues observed was only 750 million light-years from Earth; two were within 270 million light-years; and a fourth was at a distance of just 50 million light-years--practically a celestial neighbor.

That no quasars had ever been found this close before, Djorgovski believes, has less to do with astronomy than probability. Since quasars are relatively rare objects to begin with, the closer to home astronomers look, the smaller their celestial sample group. This means they’re likely to find very few quasars, and fewer still that are positioned exactly the right way. As astronomers look farther out in space, however, the overall number of quasars grows, and the number of correctly oriented ones grows along with them. Djorgovski now believes that future stargazers looking for quasars will not only have to explore different parts of the electromagnetic spectrum but different parts of the sky as well.

Astronomers have been talking for some time about a sort of grand unified theory of active galactic nuclei, says Djorgovski, but there had never been a lot of proof. Our infrared studies lend some needed support to it.
Comment on this article
ADVERTISEMENT

Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!

ADVERTISEMENT
ADVERTISEMENT
Collapse bottom bar
DSCDecCover
+

Log in to your account

X
Email address:
Password:
Remember me
Forgot your password?
No problem. Click here to have it emailed to you.

Not registered yet?

Register now for FREE. It takes only a few seconds to complete. Register now »