Milky Way's neighbouring galaxy is of same size, not bigger

Sydney, Feb 15 (IANS) In what could put a galactic arms race to rest, astronomers have discovered that our nearest big neighbour, the Andromeda galaxy, is roughly the same size as the Milky Way.

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 bigger neighbour.

But the new study, published in the journal Monthly Notices of the Royal Astronomical Society, evens the score between the two galaxies.

It found the weight of the Andromeda is 800 billion times heavier than the Sun, on par with the Milky Way.

The research suggests scientists previously overestimated the amount of dark matter in the Andromeda galaxy.

"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 from the University of Western Australia.

"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 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 per second 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 550km/s," Kafle said.

"We used this technique to tie down the mass of Andromeda," 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, suggests the study.

--IANS

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