London, Jan 12 : New observations from the Green Bank Telescope in West Virginia, US, have indicated that a gas cloud weighing a million times the mass of the Sun, is on a collision course with the Milky Way in a timeline of 20 to 40 millions years.
According to a report in New Scientist, the cloud, known as "Smith's Cloud", is made mostly of hydrogen gas and is 11,000 light years long and 2500 light years wide, about the size of a dwarf galaxy.
Discovered in 1963, nothing was known about the cloud's motion towards our galaxy until now.
But after observations from the Green Bank Telescope, a team led by Felix Lockman of the National Radio Astronomy Observatory, made a detailed radio image of the cloud and measured its velocity to come up with the conclusion.
The new image shows the cloud's comet-like appearance as it ploughs into the gaseous "atmosphere" around our galaxy. The measurements also reveal the cloud is about 8000 light years away and is closing in on the Milky Way at 240 kilometres per second.
Exactly when it will impact is unclear because astronomers are not sure how much the drag from our galaxy's envelope of gas will slow it down.
But, based on its direction of motion, the cloud is expected to hit a region about a quarter of the way around the galaxy from the Sun, near the Perseus arm of the galaxy.
According to astronomers, the results will be spectacular when the cloud actually hits our galaxy.
"You have all these shock waves that go out - it's just like making a bomb go off in this area," said Lockman. "In the shock waves, you can trigger a ring or region of enhanced star formation. A few million years later, they'll start going off as supernovae," he further explained.
According to the report, the impact of the gas cloud itself poses no danger to any inhabited solar systems that might be present at the impact site. That's because despite its great mass, the cloud is spread out over such a wide area that it would have no direct effect on existing stars and planets.
"But the supernovae that go off a few million years later could be hazardous to life in solar systems unfortunate enough to be nearby," said Lockman.
Although the motions of other hydrogen clouds near our galaxy have not been measured as well, some are probably heading towards the Milky Way as well.
"Such clouds probably regularly fall into our galaxy and supply it with new material for forming stars," said Lockman. "I think we're seeing now that the Milky Way is under bombardment. There are still fragments of it coming in that are still arriving on the scene," he added.