An imagined view of the night sky just before the predicted merger between our Milky Way galaxy and the neighboring Andromeda galaxy in about four billion years. Illustration: NASA, ESA, Z. Levay and R. van der Marel (the Space Telescope Science Institute), and A. Mellinger
An epic galactic embrace is in the making between our own Milky Way and the neighboring Andromeda galaxies. The merger of the two is expected some four billion years from now as part of what scientists are calling a straight head-on collision.
"Our findings are statistically consistent with a head-on collision between the Andromeda galaxy and our Milky Way galaxy," according to Roeland van der Marel of the Space Telescope Science Institute (STScI) in Baltimore, Maryland. Van der Marel worked with Sangmo Tony Sohn.
The Andromeda, which is also known as M31, is rushing toward the Milky Way at 250,000 per hour, which, as scientists point out, is fast enough for us to reach the moon in an hour. That may seem like a lot to us but when you consider that the Andromeda is 2.5 million light years away from us, you understand that it is just painfully dragging toward us.
The Milky Way with its close to 400 billion stars, including our own Sun, and the Andromeda with a trillion stars will come together in what is routine in the universal order of things. The sheer scale of such enormities necessarily means that they can only drag toward each other. Can you imagine watching this unfold from a distance?
Scientists say that this merger is unlikely to cause any damage to individual stars and planets because they are separated by large distances.
“Computer simulations derived from Hubble’s data show that it will take an additional two billion years after the encounter for the interacting galaxies to completely merge under the tug of gravity and reshape into a single elliptical galaxy similar to the kind commonly seen in the local universe,” said a press release by Hubble Site.
“Although the galaxies will plow into each other, stars inside each galaxy are so far apart that they will not collide with other stars during the encounter. However, the stars will be thrown into different orbits around the new galactic center. Simulations show that our solar system will probably be tossed much farther from the galactic core than it is today,” it said.
Eight years of meticulous observations and calculations using the Hubble Space Telescope between 2002 and 2010 have convinced the NASA scientists that the collision is a certainty. It has been known for about a century that the two galaxies are headed for each other but it is only now that very specific details have been worked out.
As scientists point out given the incomprehensibly enormous size of the merger it will take two billion additional years for the tumult to settle down, as part of which our own solar system may get relegated to a much more distant corner of the new galaxy. Currently the Milky Way is 26,000 light years away from the galactic center, which is rather close.
At the heart of this impending galactic embrace is, of course, gravity of the two systems. So while overall the universe is expanding, in the more immediate context galaxies can still be drawn toward each other by their own gravity. After all some 1.4 trillion stars with their improbably massive burning of their own core fuels, complex orbiting, inordinately large individual mass, velocities and everything else that attends them are bound to create their own local spectacle.
The thing that strikes me the most about the universe is that it does whatever it has to do as part of its natural evolution. If two galaxies have to merge, it just gets it done irrespective of the time and the resource it takes. It seems to me that the universe is not working to some grand cosmic plan but doing what universes do as a matter of light yearly routine—always work towards reaching some sort of equilibrium among its trillions of gigantic volatile pieces.
It is not as if it has a specific outcome in mind when the Milky Way and Andromeda galaxies eventually collide. It is essentially letting the chips fall where they might. If the in the process, large parts of its own self get destroyed or violently reordered, so be it. But then these two galaxies do not even constitute a very significant part of the universe. That’s the whole point. There are no uniquely significant parts in the universe. Everything is significant and nothing is. It’s just all there beyond a humanly defined and understood purpose. In that it is a purposeless universe.