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Milky Way Measures up to Andromeda

It had been long 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 bigger neighbour, but new research published in Monthly Notices of the Royal Astronomical Society has found that Andromeda is 800 billion times heavier than the Sun, which is on par with the Milky Way.

Astrophysicist Dr Prajwal Kafle of The University of Western Australia node of the International Centre for Radio Astronomy Research said the study used a new technique to measure the speed required to escape a galaxy.

“When a rocket is launched into space, it is thrown out with a speed of 11 km/s to overcome the Earth’s gravitational pull,” he said. “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 km/s. We used this technique to tie down the mass of Andromeda.”

Kafle said the research suggests that 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 said.

The Milky Way and Andromeda are two giant spiral galaxies in our local Universe. 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.

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.