Andromeda is not bigger than the Milky Way after all, study reports

A team of scientists discovered that the Milky Way and Andromeda galaxies are about the same size.
By Joseph Scalise | Feb 19, 2018
A group of international astronomers have discovered that, despite popular belief, the Andromeda galaxy is roughly the same size as the Milky Way, a new study in theMonthly Notices of the Royal Astronomical Society reports.

Previously, scientists generally believed that Andromeda was roughly two or three times the size of the Milky Way. They also believed that discrepancy would one day cause our galaxy to be overtaken by its neighbor. However, the new research shows both of those notions are not true.

Researchers think previous estimates were false because past studies simply overestimated the amount of dark matter Andromeda has.

"By examining the orbits of high-speed stars, we discovered that this galaxy has far less dark matter than previously thought, and only a third of that uncovered in previous observations," said lead author Prajwal Kafle, a researcher at the University of Western Australia, according toUSA Today.

The Milky Way and Andromeda are two giant spiral galaxies that sit roughly two million light-years apart. Andromeda is so close to us that it is one of only 10 galaxies that can be seen with the naked eye.

The research showed that the galaxies are roughly 800 billion times the mass of the sun. As they are so similar in size, many previously held beliefs about their interactions are likely false.

Even so,astronomers do think they will eventually collide. However, that event will not occur for roughly 4 billion years.While the galaxies will crash into each other, the stars will not. Rather, they will move into different orbits around a new galactic center.

The findings change the way researchers view Andromeda, which could significantly alter future research and lead to a better understanding of the universe as a whole.

"We had thought there was one biggest galaxy and our own Milky Way was slightly smaller but that scenario has now completely changed," added Kafle, in a statement. "It's really exciting that we've been able to come up with a new method and suddenly 50 years of collective understanding of the local group has been turned on its head."


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