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Space Cloud to Collide With Our Galaxy

Space Cloud to Collide With Our Galaxy
Artist's conception of Smith's Cloud approaching, then colliding with, our own Milky Way Galaxy in approximately 40 million years. Sequence of images shows the approach and collision. Detail: Robert C. Byrd Green Bank Telescope radio image of Smith's Cloud.
(Image: © Bill Saxton, NRAO/AUI/NSF)

AUSTIN, Texas — A colossal cloud of gas is racingtoward a collision with our galaxy, and when it hits, the crash could triggeran intense burst of star formation.

Thecollision and stellar light show will occur in 20 million to 40 million years,an astronomer announced here today at a meeting of the American AstronomicalSociety.

The cloud,dubbed Smith's Cloud after the astronomer who discovered it in 1963, is just8,000 light-years from our galaxy's disk. Jam-packed with enough hydrogen tomake a million stars like the sun, it is 11,000 light-years long and 2,500 light-yearswide.

"Myguess is that this [gas cloud] is a remnant of the original formation of theMilky Way in the way that comets and meteors are remnants of the formation ofthe solar system," said Jay Lockman, of the National Radio AstronomyObservatory (NRAO) in Green Bank, West Virginia.

If youcould see the cloud, it would span 30 times the width of the moon.

"Fromtip 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 onehas found a single star in it."

For decadesafter thecloud's discovery, scientists were puzzled over its allegiancebecause the available images lacked any detail. They didn't know whether itbelonged to the Milky Way, or if the cloud was moving — either getting blownout or falling into our galaxy.

Lockman andhis colleagues made their recent observations of the cloud with the NationalScience Foundation's Robert C. Byrd Green Bank Telescope, the largest steerableradio telescope. Since the cloud is made of cold gas, it emits only in theradio wavelengths, Lockman said. It does not generate any visible light.

Resultsshowed Smith's Cloud is plunging into the Milky Way, not heading out. And it'sfalling in at more than 540,000 mph (869,000 kilometers per hour).

"Weare able to see it rubbing up against the outer atmosphere of the MilkyWay," Lockman told SPACE.com. "It's not only coming in, it'sstarting to push up gas in front of it."

He added,"It is also feeling a tidal force from the gravity of the Milky Way andmay be in the process of being torn apart."

Tidalforces of gravity, like the moon tugging on Earth, pull the front parts of anobject greater than the regions on the far side.

He said thecloud would likely strike a region somewhat farther from the galactic centerthan our solar system. The addition of new gas into our galaxy along with theshock of the collision may trigger a burst of rapidstar formation.

"Whenit hits, it could set off a tremendous burst of star formation," Lockmansaid. "Many of those stars will be very massive, rushing through theirlives quickly and exploding as supernovae."

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