Space Telescope Science
The old adage "what goes up must come down" even applies to an immense cloud of hydrogen gas outside our Milky Way galaxy. First discovered in the 1960s, the comet-shaped cloud is 11,000 light-years long and 2,500 light-years across. If the cloud could be seen in visible light, it would span the sky with an apparent diameter 30 times greater than the size of the full moon. The cloud, which is invisible at optical wavelengths, is plummeting toward our galaxy at nearly 700,000 miles per hour. Hubble was used to measure the chemical composition of the cloud as a means of assessing where it came from. Hubble astronomers were surprised to find that the cloud, which is largely composed of hydrogen, also has heavier elements that could only come from stars. This means the cloud came from the star-rich disk of our galaxy. The Smith Cloud is following a ballistic trajectory and will plow back into the Milky Way's disk in about 30 million years. When it does, astronomers believe it will ignite a spectacular burst of star formation, perhaps providing enough gas to make 2 million suns.
Please join the scientists in a live discussion about the origin and conclusions of this research during the Hubble Hangout at 3pm EST today (Thurs., Jan. 28, 2016): http://hbbl.us/Baq .