A massive cloud of gas will crash into the Milky Way in about 30 million years, but there's no real danger to our home galaxy, NASA says. 

New observations by NASA's Hubble Space Telescope suggest that the gas, called Smith's Cloud, was cast from the Milky Way long ago. A new NASA video describes the cloud's discovery in 1963 and what researchers know.

"We don't fully understand the Smith Cloud's origin," Andrew Fox, an astronomer at the Space Telescope Science Institute who led the research, said in a statement from NASA. "There are two leading theories. One is that it was blown out of the Milky Way, perhaps by a cluster of supernova explosions. The other is that the Smith Cloud is an extragalactic object that has been captured by the Milky Way." Fox's team examined the cloud using Hubble's Cosmic Origins Spectrograph, and saw evidence of sulfur, which absorbs ultraviolet light from the cores of three galaxies lying beyond the cloud. The team found that the amount of sulfur in Smith's Cloud is the same as that found in the outer disk of the Milky Way, suggesting that both objects came from the same family. [Stunning Photos of Our Milky Way Galaxy (Gallery)]

"The cloud appears to have been ejected from within the Milky Way and is now falling back," Fox said. "The cloud is fragmenting and evaporating as it plows through a halo of diffuse gas surrounding our galaxy. It's basically falling apart. 

Smith's Cloud, a massive cloud of gas, will crash into the Milky Way in about 30 million years. New research suggests it was ejected from the Milky Way and is now returning.
Smith's Cloud, a massive cloud of gas, will crash into the Milky Way in about 30 million years. New research suggests it was ejected from the Milky Way and is now returning.
Credit: NASA

"This means that not all of the material in Smith's Cloud will survive to form new stars," he added. "But if it does survive, or some part of it does, it should produce an impressive burst of star formation."

It's still unclear what event tore this cloud from the Milky Way's disk and how it stayed together so long, NASA officials said in the statement. What is known, however, is that in roughly 30 million years, it will crash into our galaxy's Perseus Arm, one of the two major spiral arms in the Milky Way. When that happens, there will be a surge of star formation when clouds of gas in the spiral arm are compressed, NASA officials said.

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