All galaxies are going through some rate of star formation. New stars are being formed every year in the Milky Way. But some galaxies, classified as “starburst galaxies” are undergoing furious rates of star formation. Some are so active, they’re forming thousands of new stars every year.
So why do starburst galaxies form, when our own Milky Way has a relatively slow rate of new star formation? The most popular theory is that a galaxy is put into a starburst phase when it makes a close encounter with another galaxy. The gravitational interaction sends shockwaves through giant clouds of gas, causing them to collapse and form star forming regions. These create some of the most massive stars in the Universe; monster blue stars with more than 100 solar masses.
These massive stars live short lives and detonate as supernovae, blasting out more shockwaves into the galaxy. This creates a chain reaction that cascades through the galaxy. Within a few million years, the galaxy is forming stars at tens or even hundreds of times the rate of formation in a normal galaxy. And then when the gas is used up, within about 10 million years, the period of star formation ends.
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Starburst galaxies are rare today, but astronomers have found that they were very common in the early Universe, when galaxies were closer and interacted more.
Thousands of starburst galaxies have been discovered across the Universe. One of the best known starburst galaxies is M82, located about 12 million light-years away in the constellation Ursa Major. The Hubble Space Telescope imaged the galaxy in 2005, and found 197 massive clusters of star formation going off simultaneously in the starburst core. The changes in M82 are being driven by its gravitationally interaction with nearby M81 galaxy.
We have written many articles about galaxies for Universe Today. Here’s an article about the starburst galaxy M82.
We have also recorded an episode of Astronomy Cast about galaxies – Episode 97: Galaxies.