An invisible cloud of gas is speeding toward our Milky Way galaxy at 700,000 miles per hour. But don't worry: It will take about 30 million years to get here.
It's a case of “what goes up must come down," according to Hubble Space Telescope astronomers who say the space cloud likely originated in our galaxy and is boomeranging back. When it returns, they predict "a spectacular burst of star formation, perhaps providing enough gas to make 2 million suns."
Astronomers are aware of many space clouds, but the Smith Cloud is unique because its trajectory is well-known.
“The cloud is an example of how the galaxy is changing with time,” said Andrew Fox of the Space Telescope Science Institute in Baltimore, Maryland. “It’s telling us that the Milky Way is a bubbling, very active place where gas can be thrown out of one part of the disk and then return back down into another.
Doctoral astronomy student Gail Smith discovered the Smith Cloud in the 1960s. Researchers believe it is 11,000 light-years long and 2,500 light-years across.
Fox and his team recently used the Hubble Space Telescope to learn about the cloud's chemical composition and origin.
The astronomers found that the Smith Cloud is as rich in sulfur as the Milky Way's outer disk, a region about 40,000 light-years from the galaxy's center (about 15,000 light-years farther out than our sun and solar system). This means that the Smith Cloud was enriched by material from stars. This would not happen if it were pristine hydrogen from outside the galaxy, or if it were the remnant of a failed galaxy devoid of stars. Instead, the cloud appears to have been ejected from within the Milky Way and is now boomeranging back.
How the space cloud was catapulted from the Milky Way in the first place -- and what has kept it together -- remain unknown. Only more research will tell.
The astronomers' findings appear in this month's edition of The Astrophysical Journal Letters.
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