Imagine living in one city for all of your life. After a while you get to thinking you had a pretty good grasp about where things are, what the streets look like and so on. Then one day you realize nearly everything you thought you knew about home needed to be redrawn. Turns out, your home city is much bigger, shaped differently, spinning faster and… um… more likely to collide with the next nearest city. Pretty disorienting huh? Ok so my city metaphor sort of breaks down there at the end. That being the case, what I just described is almost exactly what’s happened with our home galaxy, the Milky Way this last week.
A galaxy is a massive cluster of stars, many thousands of light years across, and they come in numerous different shapes and sizes. The most common kind of galaxy is elliptical in shape however the one we live in is more of a couple of spiraling arms with a bulge in the center. Because we don’t have the technology yet to travel outside the galaxy to map it, astronomers have had to infer its contours based on data that we could gather here on Earth. On Monday a team of astrophysicists announced that they’ve finished using infrared light to model the complete shape of the galaxy. The old debate as to whether our spiral galaxy has two or four arms can be settled, they’re both right. The galaxy starts out with two arms jutting out from the center of the galaxy, which then each split off into two arms. This is the first time this particular shape has been proposed.
At the same time, the American Astronomical Society is having their huge annual meeting in Long Beach California, so there have been a slew of new cosmic discoveries announced this week. There, another team of astronomers announced that the speed our Sun is orbiting around the galactic core is around 100,000 mph faster than previously measured. In order for it to be moving that quickly at this distance from the center, the galaxy itself is likely 50 percent more massive than previously thought.
The one snag is that this extra mass means we’ve got a stronger gravitational pull. This rather considerably boosts the odds of an eventual collision with our nearest neighbor, the Andromeda Galaxy. No worries though, the predicted collision is at least two billion years away, giving us plenty of time to duck and cover.