The Andromeda galaxy, our nearest large neighbour, is roughly the same size as the Milky Way, astronomers have found, putting the “gravitational arms race to rest”. It had been thought that Andromeda was two to three times the size of the Milky Way, and that our own galaxy would ultimately be engulfed by our supposedly bigger neighbour.
However, the latest research evens the score between the two galaxies. The study found the weight of the Andromeda is 800 billion times heavier than the Sun, on par with the Milky Way.
“We had thought there was one biggest galaxy and our own Milky Way was slightly smaller but that scenario has now completely changed,” said Prajwal Kafle, astrophysicist from the University of Western Australia node of the International Centre for Radio Astronomy Research. “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.”
The study used a new technique to measure the speed required to escape a galaxy. “Our home galaxy, the Milky Way, is over a trillion times heavier than our tiny planet Earth so to escape its gravitational pull we have to launch with a speed of 550 kilometres per second. We used this technique to tie down the mass of Andromeda,” said Dr. Kafle.
The research suggests scientists previously overestimated the amount of dark matter in the Andromeda galaxy. “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,”he added.
The Milky Way and Andromeda are two giant spiral galaxies in our local universe, and light takes a cosmologically tiny two million years to get between them. With Andromeda no longer considered the Milky Way’s big brother, new simulations are needed to find out what will happen when the two galaxies eventually collide, researchers said.
Kafle used a similar technique to revise down the weight of the Milky Way in 2014, and said the latest finding had big implications for our understanding of our nearest galactic neighbours. “It completely transforms our understanding of the local group,” he said.