Densest galaxy ever discovered

Astronomers have discovered the
densest galaxy ever to be found - packed with an
extraordinary number of stars - about 54 million light
years from our own Milky Way.
The ultra-compact dwarf galaxy, dubbed M60-UCD1,
was found in what's known as the Virgo cluster of
galaxies, researchers said.
Imagine the distance between the Sun and the star
nearest to it - Alpha Centauri. That's a distance of
about 4 light years. Now, imagine as many as 10,000
of our Suns crammed into that relatively small space.
That is about the density of a galaxy discovered by an
international team of astronomers led by a Michigan
State University faculty member.
"This galaxy is more massive than any ultra-compact
dwarfs of comparable size and is arguably the densest
galaxy known in the local universe," said Jay Strader,
MSU assistant professor of physics and astronomy.
The galaxy was discovered in the Virgo cluster of
galaxies, a collection of galaxies located about 54
million light years from our own Milky Way.
What makes M60-UCD1, so remarkable is that about
half of its mass is found within a radius of only about
80 light years. This would make the density of stars
about 15,000 times greater than found in Earth's
neighbourhood in the Milky Way.
"Travelling from one star to another would be a lot
easier in M60-UCD1 than it is in our galaxy. Since the
stars are so much closer in this galaxy, it would take
just a fraction of the time," Strader said.
The discovery of ultra-compact galaxies is relatively
new - only within the past 10 years or so. Until then,
astronomers could see these "things" way off in the
distance but assumed they were either single stars or
very-distant galaxies.
Another intriguing aspect of this galaxy is the presence
of a bright X-ray source in its centre. One explanation
for this is a giant black hole weighing in at some 10
million times the mass of our Sun.
Astronomers are trying to determine if M60-UCD1 and
other ultra-compact dwarf galaxies are either born as
really jam-packed star clusters or if they are galaxies
that get smaller because they have stars ripped away
from them.
The possible massive black hole, combined with the
high galaxy mass and Sun-like levels of elements
found in the stars, favour the latter idea.
A giant black hole at the centre of M60-UCD1 helps tip
the scales against the scenario where this galaxy was
once a star cluster, since such large black holes are
not found in these types of objects.
The galaxy was discovered using NASA's Hubble Space
Telescope. Follow-up observations were done with
NASA's Chandra X-ray Observatory and ground-based
optical telescopes, including the Keck 10-metre
telescope in Hawaii.
The study was published in the Astrophysical Journal
Letters.