Dance of Destruction
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
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
Image Credit: NASA, J. English (U. Manitoba), S. Hunsberger, S. Zonak, J.
Charlton, S. Gallagher (PSU), and L. Frattare (STScI)
Science Credit: NASA, C. Palma, S. Zonak, S. Hunsberger, J. Charlton, S.
Gallagher, P. Durrell (The Pennsylvania State University) and J. English
(University of Manitoba)