1. A 250-Million-Year Orbit
On Earth, a year is determined by the length of time it takes the planet to orbit the Sun. Every 365 days, we’re right back where we started, generally speaking. It makes sense then that our entire solar system is similarly orbiting the black hole at the center of the Milky Way. It just takes a little longer, to the tune of 250 million years for each rotation. In other words, we’ve made about a quarter of a single orbit since the dinosaurs died.
Descriptions of the solar system rarely mention that it’s spinning through space just like everything else. We’re actually traveling at about 792,000 kilometers (483,000 mi) per hour relative to the center of the Milky Way. To put that into a more easily relatable example, that speed would take you around the Earth in just over three minutes. Each time the Sun makes it all the way around the Milky Way, it’s known as the galactic year, or cosmic year. It’s estimated that there have been only 18 galactic years in the history of the Sun.
2.Twin Galaxies
While the Milky Way might be unique in many ways, it’s safe to say it’s not exactly rare. We already mentioned that spiral galaxies are one of the most common types in the universe; add to that the fact that there are around 170 billion visible galaxies, and it wouldn’t be a stretch to imagine that there could be a few galaxies out there very similar to our own.
But what about one that’s almost an exact replica of ours? In 2012, astronomers discovered a galaxy that shares a likeness with everything we know about the Milky Way. It even has two small satellite galaxies orbiting it, perfectly corresponding to our own Magellanic Clouds. And that’s rare—only 3 percent of spiral galaxies have companion galaxies like that, and they don’t last long. The Magellanic Clouds will probably dissipate in a couple billion years, a leisurely afternoon on the cosmic time scale. To find another barred spiral with a supermassive black hole center that also has two satellite galaxies the same size as our own is highly unlikely, to say the least.
The galaxy is named NGC 1073, and it’s so similar that astronomers are actually using it to learn more about our own galaxy. Since we’re too deeply embedded for any kind of perspective on the Milky Way, NGC 1073 gives us that top-down view that we’ve always needed to fully study our own neighborhood.
3.Cosmic Warping
Although the Milky Way is a spiral by definition, that’s not an entirely accurate way to think about it—there’s actually a bulge at the center of the galaxy, so the whole thing sort of looks like a pancake with a pile of whipped cream on each side. The warped section is the result of hydrogen gas molecules stretching away from the two-dimensional plane of the spiral.
For years, astronomers were mystified by the seemingly inexplicable warping. By all logic, the gas should be pulled toward the disk, not away from it. The more they studied it, the deeper the mystery ran—because the molecules in the warp are not only pulling away, they’re vibrating at a frequency of their own.
So what’s causing it? As far as we can tell, dark matter and a duo of small galaxies known as the Magellanic Clouds. When they’re put together, the Magellanic Clouds have about 2 percent of the Milky Way’s mass—not enough to affect it much. But when dark matter moves through the Clouds, it creates ripples that apparently affect their gravitational pull on the Milky Way. This strengthens the pull and entices the hydrogen away from the center of our galaxy.
And it gets even weirder. The Magellanic Clouds orbit the Milky Way, so as they make each revolution, the spiral arms of the Milky Way flap in response to their presence like a flag waving in the wind.