Have you ever looked up on a dark night and seen the edge of the Milky Way stretched across the sky? As beautiful as it is, it means that astronomers have a pretty hard time figuring out the structure of our galaxy. For one, the center of the galaxy is filled with gas and dust that make it nearly impossible for our optical telescopes to see the stars that live there from our location within the galaxy. In addition, in order to figure out the 3D structure, we need to know distances to objects, which is no small feat in astronomy.
Luckily, astronomers have some tricks up their sleeves. Using telescopes that detect infrared light, we can see through the gas and dust. Using an infrared telescope, astronomers observed 22 million red giant stars at the center of our galaxy. After determining the distances to these stars, they were able to make a 3D map of our galaxy's core and conclude that it looks peanut-shaped from the side, and like a bar from the top. They suspect that it started out as a flat bar, and then buckled in the center to form the peanut shape.