Don Savage
Headquarters, Washington, DC                    January 13, 1997
(Phone:  202/358-1547)

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. 

                           -more-
                            -2-

       "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.

                          -more-
                            -3-

       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.