If you feel bad that you have gained a bit of weight thanks to all the Easter chocolate, cheer up – our own galaxy is probably getting bigger too. While observing other spiral galaxies, researchers discovered that they tend to expand at about 500 meters (1,640 feet) per second.
The study focused on star formation at the edge of the galaxy. After new stars are born from giant gas clouds, they slowly move away from each other, making the galaxy bigger bit by bit. This has been predicted for the Milky Way, but since we are in it, we can't really observe this expansion. The findings are presented by lead author Cristina Martínez-Lombilla at the European Week of Astronomy and Space Science, which is happening this week in Liverpool.
The team used the extensive galaxy catalog from the Sloan Digital Sky Survey and combined it with observations from the ultraviolet space telescope GALEX and the infrared space telescope Spitzer. They measured the motion of stars at the edge of galaxies similar to the Milky Way. Thanks to these observations, they were able to estimate the expansion rate for the Milky Way.
“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," Martínez-Lombilla, who's a PhD student at the Instituto de Astrofísica de Canarias, said in a statement. "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."
This estimate has important implications for the shape of the Milky Way. As we mentioned, our understanding of our galaxy's shape is limited due to our position in it. The Milky Way is a flat disk 100,000 light-years in diameter that bulges in the middle. The flat disk is where the spiral arms are, which are filled with gas and young stars. The bulge is bar-shaped and filled with much older stars believed to have formed between seven and 11 billion years ago. The Sun is located in one of the spiral arms at about 8,000 light-years from the center of the Milky Way.
