Researchers at the University of Michigan have found that Andromeda, the closest nearby galaxy to the Milky Way, collided and merged with a massive galaxy about 2 billion years ago. Now, the scientists identified the disappeared galaxy as the “lost twin” of the Milky Way.
Even though it was mostly shredded, this massive galaxy had left a definite proof of its existence, in the form of a nearly inconspicuous halo of stars bigger than Andromeda’s.
This fragmented galaxy, known as M32p, was the third most significant component of the local galactic cluster, after Andromeda and the Milky Way. By using computer models, Richard D’Souza and Eric Bell, of the University of Michigan’s Department of Astronomy, could rebuild the proof of this lost galaxy, bringing to light this “lost twin” of the Milky Way in the Nature Astronomy journal.
With advanced computer simulations, researchers learned that even though Andromeda absorbed many of its companion galaxies, the majority of the stars in Andromeda’s dim external halo were brought in by the collision with a single massive galaxy.
The discovery of this “lost twin” of the Milky Way shed some light on Andromeda’s M32 satellite galaxy, as well
“It was a moment of ‘Eureka!’. We realized that we could use this information from Andromeda’s outer star halo to infer the properties of the massive galaxy destroyed,” said Richard D’Souza, a Ph.D. researcher at the University of Michigan.
Also, Bell, a fellow researcher and professor of astronomy at the University of Michigan, argues that it was “shocking” to discover that the Milky Way had an older “lost twin” that the science has never been aware of.
This “lost twin” of the Milky Way, which collided and merged with Andromeda galaxy, had been of about 20 times more massive than the one that crashed with our galaxy in its early history.
This study may also solve the mystery of the formation of the enigmatic Andromeda’s M32 satellite galaxy. Scientists argue that the compact and dense M32 is the still-living core of the “lost twin” of the Milky Way.
“M32 is a rare bug. It looks like a compact example of an ancient elliptical galaxy, but it actually has many young stars. It’s one of the most compact galaxies in the universe. There is no other galaxy like it,” said Bell.