Don Savage
Headquarters, Washington, DC	January 13, 1997
(Phone: 202/358-1547)
Sender: owner-press-release
Precedence: bulk

Tammy Jones
Goddard Space Flight Center, Greenbelt, MD (Phone: 301/286-5566)

Ray Villard
Space Telescope Science Institute, Baltimore, MD (Phone: 410/338-4514)

RELEASE: 97-9

MASSIVE BLACK HOLES DWELL IN MOST
GALAXIES, ACCORDING TO HUBBLE CENSUS

Announcing the discovery of three black holes in three normal galaxies, an international 
team of astronomers suggests that nearly all galaxies may harbor supermassive black holes 
which once powered quasars (extremely luminous nuclei of galaxies), but now are 
quiescent.

This conclusion is based on a census of 27 nearby galaxies carried out by NASA's Hubble 
Space Telescope and ground-based telescopes in Hawaii, which are being used to conduct a 
spectroscopic and photometric survey of galaxies to find black holes which have consumed 
the mass of millions of Sun-like stars. 

The findings, being presented today at the 189th Meeting of the American Astronomical 
Society in Toronto, Canada, should provide insights into the origin and evolution of 
galaxies, as well as clarify the role of quasars in galaxy evolution. 

The key results are:

* Supermassive black holes are so common that nearly every large galaxy has one.

* A black hole's mass is proportional to the mass of the host galaxy, so that, for example, a 
galaxy twice as massive as another would have a black hole that is also twice as massive. 
This discovery suggests that the growth of the black hole is linked to the formation of the 
galaxy in which it is located. 

* The number and masses of the black holes found are consistent with what would have 
been required to power the quasars.

"We believe we are looking at 'fossil quasars' and that most galaxies at one time burned 
brightly as a quasar," says team leader Doug Richstone of the University of Michigan, Ann 
Arbor. These conclusions are consistent with previous Hubble Space Telescope 
observations showing quasars dwelling in a variety of galaxies, from isolated normal-
looking galaxies to colliding pairs. 

Two of the black holes "weigh in" at 50 million and 100 million solar masses in the cores 
of galaxies NGC 3379 (also known as M105) and NGC 3377 respectively. These galaxies 
are in the "Leo Spur," a nearby group of galaxies about 32 million light- years away and 
roughly in the direction of the Virgo cluster. 

Located 50 million light-years away in the Virgo cluster, NGC 4486B possesses a 500-
million-solar-mass black hole. It is a small satellite of the very bright galaxy M87 in the 
Virgo cluster. M87 has an active nucleus and is known to have a black hole of about two 
billion solar masses.

Though several groups have previously found massive black holes dwelling in galaxies the 
size of our Milky Way or larger, these new results suggest smaller galaxies have lower-
mass black holes, below Hubble's detection limit. The survey shows the black hole's mass 
is proportional to the host galaxy's mass. 

It remains a challenging puzzle as to why black holes are so abundant, or why they should 
be proportional to a galaxy's mass. One idea, supported by previous Hubble observations, 
is that galaxies formed out of smaller "building blocks" consisting of star clusters. A 
massive "seed" black hole may have been present in each of these protogalaxies. The larger 
number of building blocks needed to merge and form very luminous galaxies naturally 
would have provided more seed black holes to coalesce into a single, massive black hole 
residing in a galaxy's nucleus. 

An alternative model is that galaxies start at some early epoch with a modest black hole 
(not necessarily approaching the masses discussed here), but that the black hole consumes 
some fixed fraction of the total gas shed by the stars in the galaxy during their normal 
evolution. If that fraction is around one percent, the black holes easily could weigh as much 
as they do now, and naturally would track the current luminosity of the galaxy. 

Critical ground-based observations to identify candidates were obtained for all three of 
these objects by John Kormendy with the Canada-France-Hawaii Telescope (CFHT) on 
Mauna Kea, Hawaii. The NGC 4486b black hole detection also was based on CFHT 
spectra. 

Hubble's high resolution then allowed the team to peer deep into the cores of the galaxies 
with extraordinary resolution unavailable from ground-based telescopes, and measure 
velocities of stars orbiting the black hole. A sharp rise in velocity means that a great deal of 
matter is locked away in the galaxy's core, creating a powerful gravitational field that 
accelerates nearby stars. 

The team is confident their statistical search technique has allowed them to pinpoint all the 
black holes they expect to see, above a certain mass limit. "However, our result is 
complicated by the fact that the observational data for the galaxies are not of equal quality, 
and that the galaxies are at different distances," says Richstone.

One of the features of the February 1997 servicing mission to the Hubble will be the 
installation of the Space Telescope Imaging Spectrograph. This spectrograph will greatly 
increase the efficiency of projects, such as this black hole census, that require spectra of 
several nearby positions in a single object. This group will be continuing this census with 
the refurbished telescope.

The Space Telescope Science Institute is operated by the Association of Universities for 
Research in Astronomy, Inc. for NASA, under contract with the Goddard Space Flight 
Center, Greenbelt, MD. The Hubble Space Telescope is a project of international 
cooperation between NASA and the European Space Agency.

- end -

Image files in GIF and JPEG format and captions may be accessed on the Internet via 
anonymous ftp from ftp.stsci.edu in /pubinfo. 

					GIF			JPEG
PRC97-01 Black Hole Galaxies 	gif/bhgalxs.gif 	jpeg/bhgalx.jpg 

Higher resolution digital versions (300 dpi JPEG) of the release photograph are available in 
/pubinfo/hrtemp: 97-01.jpg (color) and 97-01bw.jpg (black/white).

GIF and JPEG images, captions and press release text are available via World Wide Web 
at:

http://www.stsci.edu/pubinfo/PR/97/01.html and via links in: 
http://www.stsci.edu/pubinfo/Latest.html or 
http://www.stsci.edu/pubinfo/Pictures.html.