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EMBARGOED UNTIL: 12 NOON (EDT) September 2, 1999

PHOTO NO.: STScI-PRC99-31

A MINUET OF GALAXIES

This troupe of four galaxies, known as Hickson Compact Group 87 (HCG
87), is performing an intricate dance orchestrated by the mutual
gravitational forces acting between them. The dance is a slow,
graceful minuet, occurring over a time span of hundreds of millions of
years.

The Wide Field and Planetary Camera 2 on NASA's Hubble Space Telescope
(HST) provides a striking improvement in resolution over previous
ground-based imaging. In particular, this image reveals complex
details in the dust lanes of the group's largest galaxy member (HCG
87a), which is actually disk-shaped, but tilted so that we see it
nearly edge-on. Both 87a and its elliptically shaped nearest neighbor
(87b) have active galactic nuclei which are believed to harbor black
holes that are consuming gas. A third group member, the nearby spiral
galaxy 87c, may be undergoing a burst of active star formation. Gas
flows within galaxies can be intensified by the gravitational tidal
forces between interacting galaxies. So interactions can provide fresh
fuel for both active nuclei and starburst phenomena. These three
galaxies are so close to each other that gravitational forces disrupt
their structure and alter their evolution.

From the analysis of its spectra, the small spiral near the center of
the group could either be a fourth member or perhaps an unrelated
background object.

The HST image was made by combining images taken in four different
color filters in order to create a three-color picture. Regions of
active star formation are blue (hot stars) and also pinkish if hot
hydrogen gas is present. The complex dark bands across the large
edge-on disk galaxy are due to interstellar dust silhouetted against
the galaxy's background starlight. A faint tidal bridge of
stars can be seen between the edge-on and elliptical galaxies.

HCG 87 was selected for Hubble imaging by members of the public who
visited the Hubble Heritage website (http://heritage.stsci.edu) during
the month of May and registered their votes. The HST exposures of the
winning target were then acquired in July 1999 by the Hubble Heritage
Team and guest astronomers Sally Hunsberger (Lowell Observatory,
Flagstaff, Arizona) and Jane Charlton (Pennsylvania State University).

Image Credit: The Hubble Heritage Team (AURA/STScI/NASA).

NOTE TO EDITORS: For additional information, please contact
Sally Hunsberger, Lowell Observatory, 1400 West Mars Hill Road. Flagstaff, AZ 86001,
(phone) 520-774-3358 ext 264, (fax) 520-774-6296, (e-mail) sdh@lowell.lowell.edu.
or Jayanne English, STScI, 3700 San Martin Drive, Baltimore, MD 21218,
(phone) 410-338-4352, (fax) 410-338-5090, (e-mail) jenglish@stsci.edu.


Image files are available on the Internet at:
http://heritage.stsci.edu/
http://oposite.stsci.edu/pubinfo/pr/1999/31 or via links in
http://oposite.stsci.edu/pubinfo/latest.html and
http://oposite.stsci.edu/pubinfo/pictures.html

Higher resolution digital versions (300 dpi JPEG and TIFF)
are available at:
http://oposite.stsci.edu/pubinfo/pr/1999/31/pr-photos.html

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