M81, the bright spiral galaxy at the center of this image, is the hub of a small cluster of galaxies, the M81 Group, centered roughly 12 million light-years from Earth. The group's other major members are M82, left of center, which we see edge-on, and NGC 3077, near bottom center. The three galaxies have passed so close to each other that they have pulled long streamers of stars out into space. The close encounters also have triggered the birth of millions of new stars in M82. [Skatebiker]
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The Milky Way belongs to a small cluster of galaxies known as the Local Group. It contains two giants — the Milky Way and Andromeda — and a whole bunch of little galaxies. But over the next few billion years, conditions in the Local Group will change, because Andromeda and the Milky Way will merge.
To see what the early stage of that process may entail, we can look to one of our closest neighboring galaxy groups, named for its most impressive member, M81.
The M81 Group contains about three dozen galaxies. It’s centered roughly 12 million light-years away, near the Big Dipper.
Three of the group’s major galaxies — M81, M82, and NGC 3077 — have passed so close to each other that they’re interacting. Their gravity has pulled streamers of stars and gas out of each galaxy.
Gravity also has triggered the birth of huge numbers of stars in M82 and NGC 3077. As the galaxies passed close together, gravity squeezed vast clouds of gas and dust. That caused the clouds to collapse and fracture, giving birth to new stars.
M82, in fact, is forming so many stars that it’s known as a starburst galaxy — the first one ever discovered. Dozens of clusters of young stars are sprinkled throughout the galaxy — especially in its busy core. Many of their newborn stars have exploded, blowing huge bubbles of hot gas out into space.
That same scenario is likely to play out as the Milky Way and Andromeda begin to merge — in several billion years.
Script by Damond Benningfield