Giant gas cloud headed straight for our galaxy

A giant gas cloud of hydrogen threatens to crash into our Milky Way galaxy, astronomers announced at the 211th meeting of the American Astronomical Society.

There’s no need to panic though, as the gas cloud is predicted to strike a spiral arm of the Milky Way 40,000 light years from Earth and in about 20 million years. For now, this discovery marks the first time a three-dimensional view of the gas cloud has ever been made as it moves through space.

“This cloud that we’re seeing today is a remnant of the formation of the Milky Way,” said Jay Lockman, leader of the science team that studied the gas cloud. Lockman is the principal scientist of the Greenbank Telescope at the National Radio Astronomy Observatory in West Virginia. He said that billions of years ago, the Milky Way galaxy was probably formed when a lot of objects like this gas cloud, or even bigger objects, clumped together.

“And so, this object, this cloud, is kind of left-over debris from the construction of the Milky Way, in the same way that the comets and asteroids are leftover debris from the building of the solar system,” said Lockman to Earth & Sky.

The Greenbank Telescope collected over 40,000 measurements of radio waves streaming from the object, called Smith’s Cloud, which was first discovered by Gail Beeger Smith in 1963.

It measures 11,000 light-years long and 2,500 light-years wide, and it’s moving towards the Milky Way at a supersonic speed of 150 miles every second. With it comes the equivalent of one million suns worth of hydrogen gas into a region of space ripe with the formation of new stars. “And so that gas is going to shock the local gas,” said Lockman to Earth & Sky. The shock might trigger formation of a whole cluster of new stars.

What’s more, Lockman said that this far-off region in the Perseus spiral arm of the Milky Way might have habitable planets. “So people who were living in the area would probably see the event as a series of shocks in interstellar gas and then subsequently a lot of new, big stars forming. It would really light up the sky.” To the local denizens, it might look something akin to an aurora, said Lockman’s collaborator and co-panelist Robert A. Benjamin, of the University of Wisconsin, Whitewater.