Astronomers
are rubbing their eyes after discovering that a galaxy assumed to have been a giant for
the past 23 years is in fact a dwarf,
according to new observations.
NGC 5011C,
a galaxy in the vicinity of the Milky
Way is located towards the Centaurus constellation, one of the largest constellations of the southern
hemisphere. Because of its low density of stars and absence of other features,
astronomers would normally classify such a galaxy as a dwarf elliptical--a small
faint galaxy with little gas and dust that mainly consists of old stars.
However,
for years scientists thought that NGC 5011C was located in the more distant Centaurus
cluster--located some 155 million light years away--close to the NGC 5011B galaxy,
its bright red companion. So they pinned it as a giant galaxy that was just far
away.
Most
galaxies--the basic units of the universe which contain stars, gas,
dust, and dark
matter bound together by one central gravitational force--are found in
gravitationally joined binary pairs or in groups. So it was no surprise that
the projection of NGC 5011C and NGC 5011B in the sky had astronomers believing
that they were cohorts at about the same distance from our own.
But new
data obtained with the 3.6-m ESO telescope,
revealed that the two galaxies have very different red shifts and are not
at the same distance as once believed. NGC 5011C is centered around the Centaurus
A galaxy group which is estimated to be about 13 million light years away from
our galaxy, while the NGC 5011B galaxy--a member of the Centaurus cluster--is about
12 times farther away.
The NGC
5011C galaxy lies outside of the Local
Group, a small group of around 30 galaxies that include our own Milky Way. Being
that the Universe is about 14
billion years old, observing NGC 5011C will giving us a small glimpse of the
universe as it was just yesterday--more than 95 percent of its current age.
The
astronomers then determined that NGC 5011C contains only about 10 million times
the mass of the Sun in stars. Therefore it's considered a dwarf
galaxy.
"Our
new observations with the 3.6-m ESO telescope thus confirm a new member of
the nearby Centaurus A group whose true identity remained hidden because
of coordinate confusion and wrong distance estimates in the literature for
the last 23 years," said Ivo Saviane, a
researcher from the European Southern Observatory.
advertisement
