A recent sky survey has turned up
eight new members in our Local Group of galaxies,
including a new class of ultra-faint "hobbit" galaxies and what might
be the smallest galaxy ever discovered.
The Local Group is a collection of
about 40 galaxies, of which the Milky
Way and Andromeda are the dominant members. The rest of the galaxies are mostly small satellites
known as "dwarf
galaxies" that are gravitationally bound to
these two galaxies. The Large and Small Magellanic
Clouds are two of the Milky Way's better
known dwarf galaxies.
The new galaxies [image]
were detected over the past two years as part of the Sloan Digital Sky Survey
(SDSS-II) and presented last week at the 209th meeting of the American
Astronomical Society in Seattle.
Seven of the new galaxies
are gravitationally bound to the Milky Way,
while the eighth appears to float freely in space, beyond our galaxy's grasp.
Hobbit galaxies
The new Local Group members are even
smaller and fainter than other known dwarf galaxies, with luminosities ranging
from only a thousand to at most a few hundred thousand times that of our Sun.
"They seem to be much fainter than
anyone suspected galaxies could be before," said study team member Daniel Zucker
of Cambridge University. "So rather than dwarf galaxies, we
should perhaps call them 'hobbit galaxies.'"
The dimness could be the result of
stellar age, as seven of the new galaxies contain mostly old stars.
Of these seven, two are located in the constellation Canes Venatici,
one in Bootes,
one in Leo,
one in Coma Berenices,
one in Ursa Major and one in Hercules.
The eighth and most recently spotted
galaxy is in many ways the most interesting. Dubbed Leo T, it is located about
1.4 million light-years away from Earth,
so far away that it floats freely in space, unperturbed by the Milky Way.
Unlike the other hobbit galaxies,
Leo T includes both old and young stars. It also contains large amounts of
neutral hydrogen gas--a prime ingredient of star
formation--suggesting it is still an active
stellar nursery.
Because of its great distance, Leo T [image]
is also the dimmest of the new hobbits. "This is basically the smallest,
faintest star-forming galaxy known, by orders of magnitude," Zucker said.
Current galaxy
formation theories predict our Milky Way should
be surrounded by a swarm of smaller satellite galaxies. But until the new
survey, only twelve had been identified. Astronomers have dubbed this issue the
"missing satellite problem."
The new galaxies could go a long way
toward solving this problem and might represent just the tip of a cosmic
iceberg, the researchers say.
"The Sloan Digital Sky Survey covers
only a fifth of the night sky, so there must be many more dwarfs out there,"
said study team member Wyn Evans, also of Cambridge University.
VOTE NOW: Most
Amazing Galactic Images Ever
Dwarf Galaxies Give
Universe a Breath of Fresh Oxygen
Milky
Way vs. Andromeda: Study Settles Which Is More Massive
advertisement
