NASA’s Hubble Space Telescope is witnessing a grouping of galaxies
engaging in a slow dance of destruction that will last for billions of
years. The galaxies are so tightly packed together that gravitational
forces are beginning to rip stars from them and distort their shapes.
Those same gravitational forces eventually could bring the galaxies
together to form one large galaxy.
The name of this grouping, Seyfert’s Sextet, implies that six galaxies
are participating in the action. But only four galaxies are on the dance
card. The small face-on spiral with the prominent arms [center] of gas
and stars is a background galaxy almost five times farther away than the
other four. Only a chance alignment makes it appear as if it is part of
the group. The sixth member of the sextet isn’t a galaxy at all but a
long “tidal tail” of stars [below, right] torn from one of the galaxies.
The group resides 190 million light-years away in the constellation
Serpens.
This densely packed grouping spans just 100,000 light-years, occupying
less volume than the Milky Way galaxy. Each galaxy is about 35,000
light-years wide. Three of the galaxies [the elliptical galaxy, second
from top, and the two spiral galaxies at the bottom] bear the telltale
marks of close interactions with each other, or perhaps with an
interloper galaxy not pictured here. Their distorted shapes suggest that
gravitational forces have reshaped them. The halos around the galaxies
indicate that stars have been ripped away. The galaxy at bottom, center,
has a 35,000 light-year-long tail of stars flowing from it. The tail may
have been pulled from the galaxy about 500 million years ago.
Although part of the group, the nearly edge-on spiral galaxy at top,
center, remains relatively undisturbed, except for the slight warp in
its disk. Most of its stars have remained within its galactic
boundaries.
Unlike most other galaxy interactions observed with the Hubble
telescope, this group shows no evidence of the characteristic blue
regions of young star clusters, which generally arise during galaxy
interactions.
The lack of star-forming clusters suggests that there is something
different about Seyfert’s Sextet compared with similar systems. One
example is Stephan’s Quintet, another congregation of interacting
galaxies observed with the Hubble telescope. The difference between the
two systems could be a simple one: astronomers may be seeing the sextet
at the beginning of its interaction, before much has happened. This will
not be the case for long, though. The galaxies in Seyfert’s Sextet will
continue to interact, and eventually, billions of years from now, all
four may merge and form a single galaxy. Astronomers have strong
evidence that many, if not most, elliptical galaxies are the result of
mergers.
Astronomers named the grouping Seyfert’s Sextet for astronomer Carl
Seyfert, who discovered the assemblage in the late 1940s. Seyfert
already suspected that one apparent member of the sextet was not a
galaxy but simply a tidal tail stripped off of one of the other members.
The image was taken on June 26, 2000, with the Wide Field and Planetary
Camera 2.
Image Credits: NASA, J. English (U. Manitoba), S. Hunsberger, S. Zonak,
J. Charlton, S. Gallagher (PSU), and L. Frattare (STScI)
Science Credits: NASA, C. Palma, S. Zonak, S. Hunsberger, J. Charlton,
S. Gallagher, P. Durrell (The Pennsylvania State University) and J.
English (University of Manitoba)
Electronic image files and additional information are available at:
