Astronomers Say They Have Proof the Milky Way Galaxy Is Still Expanding—And No One Can Explain It
There are a couple tenets astronomers and cosmologists live by: light sets the speed limit for the universe, nothing can escape a black hole, and galaxies don't grow in size unless they run into something. These observations have held up for years, but the last one may come crashing down thanks to new research by the Royal Astronomical Society: according to their findings, the Milky Way is still expanding at a rate of about 500 meters per second, or one light year every 600,000 years.
This has come as a major surprise for astronomers, in part because the increase in size is apparently due to star formation on the outer edges of the galaxy, where there is far less dense gas.
New stars aren't rare—about one Sun's worth of stars are produced each year—but they usually form in the galactic plane or the central bulge of a galaxy, where large clouds of gas are more common. The edge of the galaxy has been mostly discounted as a potential star nursery for its lack of star-building material, but it looks like that was a mistake According to Martinez-Lombilla:
"The Milky Way is pretty big already. But our work shows that at least the visible part of it is slowly increasing in size, as stars form on the galactic outskirts. It won't be quick, but if you could travel forward in time and look at the galaxy in 3 billion years' time it would be about 5 percent bigger than today."
The old hypothesis was that a galaxy's radius only increases when it consumes more matter, ie smaller galaxies or other cosmic material. For galaxies like MCG+01-02-015, which is 100 million light years away from the closest neighboring galaxy, that would mean no growth would be possible. Now, however, new estimates show that even isolated galaxies should display small amounts of growth over the centuries.
Hopefully, the Milky Way's weight class gets bumped up before our inevitable collision with Andromeda—which should be happening in about four billion years.