AUSTIN, Texas — A colossal cloud of gas is racing
toward a collision with our galaxy, and when it hits, the crash could trigger
an intense burst of star formation.
The
collision and stellar light show will occur in 20 million to 40 million years,
an astronomer announced here today at a meeting of the American Astronomical
Society.
The cloud,
dubbed Smith's Cloud after the astronomer who discovered it in 1963, is just
8,000 light-years from our galaxy's disk. Jam-packed with enough hydrogen to
make a million stars like the sun, it is 11,000 light-years long and 2,500 light-years
wide.
"My
guess is that this [gas cloud] is a remnant of the original formation of the
Milky Way in the way that comets and meteors are remnants of the formation of
the solar system," said Jay Lockman, of the National Radio Astronomy
Observatory (NRAO) in Green Bank, West Virginia.
If you
could see the cloud, it would span 30 times the width of the moon.
"From
tip to tail it would cover almost as much sky as the Orion constellation,"
Lockman said. "But as far as we know it is made entirely of gas — no one
has found a single star in it."
For decades
after the
cloud's discovery, scientists were puzzled over its allegiance
because the available images lacked any detail. They didn't know whether it
belonged to the Milky Way, or if the cloud was moving — either getting blown
out or falling into our galaxy.
Lockman and
his colleagues made their recent observations of the cloud with the National
Science Foundation's Robert C. Byrd Green Bank Telescope, the largest steerable
radio telescope. Since the cloud is made of cold gas, it emits only in the
radio wavelengths, Lockman said. It does not generate any visible light.
Results
showed Smith's Cloud is plunging into the Milky Way, not heading out. And it's
falling in at more than 540,000 mph (869,000 kilometers per hour).
"We
are able to see it rubbing up against the outer atmosphere of the Milky
Way," Lockman told SPACE.com. "It's not only coming in, it's
starting to push up gas in front of it."
He added,
"It is also feeling a tidal force from the gravity of the Milky Way and
may be in the process of being torn apart."
Tidal
forces of gravity, like the moon tugging on Earth, pull the front parts of an
object greater than the regions on the far side.
He said the
cloud would likely strike a region somewhat farther from the galactic center
than our solar system. The addition of new gas into our galaxy along with the
shock of the collision may trigger a burst of rapid
star formation.
"When
it hits, it could set off a tremendous burst of star formation," Lockman
said. "Many of those stars will be very massive, rushing through their
lives quickly and exploding as supernovae."
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