If you believe in the Mayan prediction that 2012 is the end of the world, stop reading and jog on. If you’re more science-minded, you’ll see we may have slightly more time before the Apocalypse.
NASA can now “predict with certainty” that our home galaxy, the Milky Way, will collide with our neighbours’ Andromeda, known in geeky circles as M31, now a modest 2.5 million light-years away.
The mutual pull of gravity between Milky Way and Andromeda – let’s call it their galactic tug of war – will land us in the next cosmic breaking news. “Our findings are statistically consistent with a head-on collision between the Andromeda galaxy and our Milky Way galaxy,” says Roeland van der Marel of the Space Telescope Science Institute (STScI).
When the collision happens only in four billion years, the Milky Way will get a major makeover, in which the sun will be flung into a new region of the galaxy, but the Earth – our Earth – and solar system will not be destroyed.
“After nearly a century of speculation about the future destiny of Andromeda and our Milky Way, we at last have a clear picture of how events will unfold over the coming billions of years,” according to Sangmo Tony Sohn of STScI. The results come from studies on measurements of Hubble Space Telescope of the motion of Andromeda.
Computer simulations derived from Hubble’s data show that it will take another two billion years after the encounter for the merger to settle and reshape into a single elliptical galaxy similar to what we know in our common, local universe. Stars will not collide with other stars because of the sheer distance, but they will be thrown into different orbits around the new galactic centre.The Andromeda Galaxy ESA release
The missing point in predicting whether the encounter will be a miss, glancing blow or head-on smash-up had come from astronomers’ inability to measure M31’s sideways motion in their efforts in the past century. Precise observations by the Hubble team over five to seven years have removed any doubt that M31 will collide with the Milky Way head-on.
“In the worst-case scenario simulation, M31 slams into the Milky Way head-on and the stars are all scattered into different orbits,” said Gurtina Besla of Columbia University in New York. “The stellar populations of both galaxies are jostled and the Milky Way loses its flattened pancake shape with most of the stars on nearly circular orbits. The galaxies’ cores merge, and the stars settle into randomised orbits to create an elliptical-shaped galaxy.”
Main picture: The sky seen at night just before the predicted merger between our Milky Way galaxy and the neighbouring Andromeda galaxy. NASA photo illustration