July 7, 1999

A New Class of Black Holes

1. Artist's concept of the accretion disk and bipolar jets of a black hole. The black hole itself lies within the bright, very hot, central region of the accretion disk and is not visible.

Astronomers have discovered a new class of black holes--objects that pack 100 to 10,000 times the mass of the Sun into volumes smaller than the Earth's moon.

Up to now, astronomers knew of only two other classes of black holes: Stellar and galactic black holes. The former are "lightweights," weighing in at a few times the mass of the Sun, and are believed to be stellar remnants of supernova explosions. Galactic black holes are true "heavyweights." They have masses of millions to more than a billion times that of the Sun and reside in the centers of many, if not all, galaxies. They are believed to represent the "engines" that power quasars and other active galaxies.

The newly discovered black holes are "middleweights," possessing masses between the lightweights and the heavyweights. Astronomers are not certain how middleweight black holes form. A good guess is that they are the result of repeated collisions and mergers of stellar black holes and neutron stars.

Black holes represent the most extreme form of matter in the universe. Gravity in their vicinity is superstrong and warps space-time so severely that nothing can escape from the holes' interiors, not even light. This is what makes them "black."

Furthermore, black holes try to gobble up everything that comes close to them. Matter that gets too close to a black hole becomes trapped by the extreme gravitational field and spirals inward to form an accretion disk around the hole (see image 1 above). In the process, the matter is accelerated to near the speed of light and heated to millions of degrees. Most of the matter is swallowed by the black hole, never to be seen again. The rest is tossed out at relativistic speeds in two narrowly-focused jets in opposite directions from the plane of the accretion disk.

Because no light nor anything else escapes from black holes, they cannot be seen directly. It is short-wavelength radiation, in particular, X-rays, given off by the hot ionized gas of the accretion disks of black holes that reveals their existence. Galaxies M 82 and NGC 1313 are two relatively nearby galaxies in which middleweight black holes have been discovered (images 2 and 3).

* M 82 is the 82nd entry in the Messier Catalogue, a catalogue of celestial objects compiled by the eighteenth-century French astronomer Charles Messier. The acronym NGC refers to 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

Additional information and images on middleweight black holes can be found in NASA press release 99-51 and at an image page of NASA's Goddard Space Flight Center (GSFC):

ftp://ftp.hq.nasa.gov/pub/pao/pressrel/1999/99-051.txt

ftp://PAO.GSFC.NASA.GOV/Newsmedia/HEAD/NBH/

We discuss stellar black holes and their formation in our article "Stellar Evolution and Death":

http://observe.ivv.nasa.gov/nasa/space/stellardeath/stellardeath_opening.html

In this article, see in particular:

http://observe.ivv.nasa.gov/nasa/space/stellardeath/stellardeath_3cii.html

We have also featured black holes in our Observations of the Week:

"Rotating Black Hole Drags Space-Time":

http://observe.ivv.nasa.gov/nasa/ootw/1997/ootw_971203/ob971203.html

"Supermassive Black Holes in Galaxies":

http://observe.ivv.nasa.gov/nasa/ootw/1997/ootw_970319/ob970319.html

"Quasars--The Enigma Deepens":

http://observe.ivv.nasa.gov/nasa/ootw/1997/ootw_970128/ob970128.html

"A Supermassive Black Hole":

http://observe.ivv.nasa.gov/nasa/ootw/1996/ootw_960327/ob960327.html

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