The observations of our galaxy throughout history have told us that our Milky Way is roughly 100,000 light years across. A number confirmed time and time again by scientists with better and better instruments. But recently a team from the Rensselaer Polytechnic Institute in New York, USA, published a paper challenged that idea, saying the galaxy is much bigger, up to 150,000 light years in diameter.
They used the Sloan Digital Sky Survey’s (SDSS) data to look at the distribution of stars outward from the centre of the galaxy, in reference the the galactic plane. They discovered that the stellar distributions oscillated above and below the galactic plane as they went further out.
“What we found is that the disk of the Milky Way isn’t just a disk of stars in a flat plane – it’s corrugated,” said Prof Heidi Newberg, the second author on the study. “As it radiates outward from the Sun, we see at least four ripples in the disk of the Milky Way.”
Astronomers have observed that as you move further from the centre of the galaxy, the star counts diminish rapidly around 50,000 light years, and then pick up again in a ring, which was previously considered separate from the galactic disk. The research team suggests that the ring is the outermost ripple in the structure of the galaxy, and is actually part of the disk.
“What we see now is that this apparent ring is actually a ripple in the disk. And it may well be that there are more ripples further out which we have not yet seen,” Says Yan Xu, lead author on the study.
The Milky Way is both the easiest and most difficult galaxy to study. It is easy because the stars, nebulae, molecular clouds, and other features are so close by, we can study them in detail. Yet it is incredibly difficult to determine the large scale structure of the Milky Way from the inside out. It requires detailed observations to get the proper distribution of matter, and since we can’t go outside and look back in, we have to use innovative methods to infer it’s shape.