Intergalactic collisions don’t take a matter of moments, they take billions of years. The effects are virtually imperceptible. In fact, the intergalactic smash that we are involved in at this very moment has been going on for such a long time and at such a slow speed, that nobody knew it was happening until 1994.
The galaxy which is colliding with us has been given the name the Sagittarius Dwarf Spheroidal Galaxy, which I’ll just shorten to Sagittarius galaxy for today (yes, astronomers among you, I do know there’s another galaxy far, far away with a similar name, but let’s keep things simple for today).
Before we move onto a theory proposed by a gay Canadian astronomer about how this Sagittarius galaxy has shaped the Milky Way, where it is in the sky? Obviously, it’s in the same part of the sky as the constellation of the same name. The Sagittarius galaxy, which is too far away to see without a telescope, loops around our Milky Way at almost 90 degrees above and below. The video below shows a speeded up computer simulation of what the collision might have looked like. It doesn’t matter if you don’t understand everything mentioned on screen – all you need to see is how the Milky Way and Sagittarius galaxy have collided.
As you can see the Sagittarius galaxy has looped around the Milky Way several times and is still doing so. The main part will arrive back in our area in about 10 million years time.
Astronomers think that the first collision 2 billion years ago helped to create the Milky Way’s spiral arms. That’s not certain, but what is certain is that the Milky Way isn’t as flat as you think, and that gay astronomer I mentioned above thinks that the Sagittarius galaxy is warping our own.
Imagine the Milky Way is a huge vinyl record with a bulge in the middle or a hat with a very wide brim. The edges are very slightly curved – up on one side and down on the other, just as if something was pulling them up and down. This warp was discovered in 1957, decades before the Sagittarius galaxy itself was discovered.
One scientist who is a specialist in researching how galaxies are formed is that gay astronomer, Dr. Jeremy Bailin, currently Associate Professor of Astronomy at the University of Alabama.
In 2003 Jeremy’s research into the Milky Way warp suggested that it was caused by the Sagittarius galaxy as it looped around. By analysing the angular momentum of the Sagittarius galaxy as it is now and the angular momentum of the warped edges on the Milky Way Jeremy theorised that the collision was the cause for the warp. Over the next billion years the warp will flatten out as the Sagittarius galaxy becomes absorbed into the Milky Way (if it ever does). Other astronomers have put forward other theories.
Beyond the outer edge of the Milky Way, as you can also see on the video, is a halo of material stretching out into space (I looks like an enormous M&M). Jeremy Bailin is also studying this halo. His research uses computer simulation like the one above, but the problem is that, at the moment, it’s difficult to create a computational model that accurately represents all the stars, interstellar material and their forces that actually exist. In simulations each star is represented as a “particle” There are billions of stars in a galaxy so a simulation has to use billions of particles to create something reasonably accurate. Jeremy has used supercomputers to develop a new modelling technique using just that – billions of particles.
Two years ago Jeremy was a member of the team involved in another project that compiled a map of our galaxy and its close neighbours as seen from Earth, what they call the full-sky survey. It shows where the hydrogen is located, hydrogen being the most common interstellar element. Just like maps of the Earth which are distorted when flattened out, this full-sky image is also distorted. Those bright blobs in the bottom right are the two Magellanic Clouds, satellite galaxies like the Sagittarius one but closer. They have also been suggested as the reason for the Milky Way warp. Below this image is a more familiar-looking picture of the full night sky.
One final thought. Other scientists have theorised that when the Sagittarius galaxy passes through or close by our Milky Way, as it has done several times, some stars will be pulled out of it and into our own. Our Sun is near the edge of our galaxy and very close to one of the Sagittarius loops. Could it be, those scientists postulate, that our Sun was one of the earliest stars plucked out of the Sagittarius galaxy? Dr. Jeremy Bailin’s research and computer simulation techniques may help to determine the true shape of our galaxy and its closest neighbours. Perhaps, one day, his research will also provide proof, one way or the other, if we are indeed from another galaxy.