Galaxies on a String
Galaxies
NGC 5216
(top) and NGC 5218 really do look like
they are connected by a string.
Of course, that string is
a
cosmic trail of gas, dust, and stars about 22,000 light-years long.
Also known
as
Keenan's system (for its
discoverer)
and Arp 104, the interacting galaxy pair is some 17 million
light-years away in the constellation Ursa Major.
The
debris trail that joins them, along with NGC 5218's comma-shaped
extension and the distorted arms of NGC 5216, are a consequence of
mutual gravitational tides.
The tides disrupt the galaxies as they repeatedly
swing close to one another.
Drawn out over billions of years,
the encounters will likely result in
their merger into a single galaxy of stars.
Such spectacular
galactic mergers are now understood to be a normal
part of the evolution of galaxies,
including
our own Milky Way.
