Meet the Smith Cloud. It’s headed towards our galaxy at over 310KM (190 miles) per second.
There is a massive gas cloud known as the Smith Cloud that’s on a collision course with the Milky Way. It’s expected to touch down some 30 million years from now, and if it were visible in the night sky it would be 30 times larger than the full moon. When the Smith Cloud eventually pushes through the Milky Way, it’s expected to generate nearly 2 million new stars.
Recently, scientists have believe they may have discovered it’s origins, and they suspect they are much closer than we previously thought.
Using Hubble to determine the Smith Cloud’s composition, it was found that the cloud is rich in heavy elements similar to those found in our galaxy, indicating that it may have actually come from the Milky Way itself. The cloud itself does not emit light so to understand the composition scientists observed background galaxies; as light would pass through the cloud, some if it gets absorbed at certain wavelengths that correspond to different known elements. Looking at these results they could then determine how significant the absorption was for one specific element, in this case they looked for sulfur:
By measuring sulfur, you can learn how enriched in sulfur atoms the cloud is compared to the Sun.
Andrew Fox, Space Telescope Science Institute
Initially theorists believed that the cloud was composed of hydrogen and helium, indicating that it came from intergalactic space, but these new findings actually indicate that the Smith Cloud was ejected by the Milky Way 70 million years ago in a brilliant supernovae explosion that enriched it with sulfur. It’s orbit is bringing it right back.
Scientists have discovered where a giant gas cloud that’s on a collision course with the Milky Way comes from, and the answer is closer to home than you might think.
The 100 million year journey of the Smith Cloud
While it may seem arbitrary, this is a rather important discovery for the understanding of galaxy formation. It helps us to visualize how galaxies endlessly produce large numbers of stars for extremely long periods of time.
We have found several massive gas clouds in the Milky Way halo that may serve as future fuel for star formation in its disk, but, for most of them, their origins remain a mystery. The Smith Cloud is certainly one of the best examples that shows that recycled gas is an important mechanism in the evolution of galaxies.
Nicolas Lehner, University of Notre Dame
Image: NASA, ESA and A. Feild, Saxton/Lockman/NRAO/AUI/NSF/Mellinger