Like a beautiful rose sprouting from a field of weeds,
a spectacular spiral galaxy has emerged near the edge of the
observable universe, where most galaxies are ragged blobs.
The newfound galaxy is the most distant spiral seen and
may offer clues to the origin of spiral structure in galaxies
elsewhere.
Today about two-thirds of all bright galaxies,
including the Milky Way and Andromeda, are spirals. These galaxies
have fast-spinning disks whose stars and gas clouds nevertheless
move slowly relative to their neighbours, a condition that favours
the formation of spiral patterns.
In the distant past, however, spirals were rare,
because stars and gas clouds moved fast relative to one another,
suppressing spiral structure; so as astronomers peer out at great
distances, they look back to a time before these glowing pinwheels
existed.
Astronomer David Law of the University of Toronto, St.
George, in Canada, and his colleagues used the Hubble Space
Telescope to examine 306 far-off galaxies.
"There was this one that just popped out, looking like
a spiral," said Law; the galaxy had three spiral arms. "We were
pretty astounded when we first saw it. We thought, 'Oh, we must
have the wrong distance'.''
But, as Law's team reports online in Nature, subsequent
observations confirmed the galaxy's great distance. Residing in the
constellation Pegasus and named Q2343-BX442, the surprise spiral
has a redshift of 2.18, which means it is 10.7 billion light-years
from Earth and therefore existed just 3 billion years after the big
bang.
With the Keck II telescope in Hawaii, the astronomers
then detected Doppler shifts from different parts of the galaxy's
disk, indicating it spins as fast as the Milky Way does.
The galaxy is 50,000 light-years across - less than
half the diameter of the Milky Way's stellar disk - but harbours
more gas and spawns far more new stars.
"It's surprising, and it's telling us something, but we
haven't quite understood everything it's telling us," said
astronomer Bruce Elmegreen of the IBM Research Division in Yorktown
Heights, New York, who was not involved in the discovery.
"It may be showing us a physical process that's really
very important, like how spiral arms push material toward a
galaxy's centre."
"It seems to me to be some kind of very interesting,
possibly even a new manifestation of spirality," adds astronomer
Joss Bland-Hawthorn of the University of Sydney, Camperdown, in
Australia, because the galaxy's stars and gas clouds move fast
relative to their neighbours, yet despite the turbulence the galaxy
has been able to form spiral arms.
Whatever the spiral's origin, the galaxy may no longer
be so beautiful today."I don't think we've ever found anything like
that in the local universe."
During the nearly 11 billion years that its light has
travelled to Earth, the galaxy may have collided with another large
galaxy that tore the spiral asunder, transforming it into a
featureless elliptical galaxy - a fate that likely awaits the Milky
Way after it smashes into the Andromeda galaxy billions of years
from now.
Science Now
