The apparently inevitable death of our own galaxy as it is engulfed by it’s nearest galactic neighbour – the Andromeda galaxy – might be less inevitable than previously thought.
Astronomers have discovered that Andromeda is roughly the same size as the Milky Way. It had been thought that it was two to three times the size of the Milky Way, and that our own galaxy would ultimately be engulfed by our bigger neighbour.
Astrophysicist Dr Prajwal Kafle, from The University of Western Australia node of the International Centre for Radio Astronomy Research, used a new technique to measure the speed required to escape a galaxy. The results suggest the weight of the Andromeda is 800 billion times heavier than the Sun, on par with the Milky Way.
“When a rocket is launched into space, it is thrown out with a speed of 11km/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 550km/s. We used this technique to tie down the mass of Andromeda.”
By examining the orbits of high speed stars, the team also suggest that Andromeda has far less dark matter than previously thought – only a third of that uncovered in previous observations.
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. Dr 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.
“We had thought there was one biggest galaxy and our own Milky Way was slightly smaller but that scenario has now completely changed. 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.”
University of Sydney astrophysicist Professor Geraint Lewis said it was exciting to be at a time when the data was getting so good.
“We can put this gravitational arms race to rest,” he said.
The work is published in the Monthly Notices of the Royal Astronomical Society.