Our galaxy could be larger than we thought, according to researchers studying data from the Sloan Digital Sky Survey. New estimates bring the size of the Milky Way from 100,000 light-years to 150,000 light-years across – a difference of 50 percent.
The study, which was published in the Astrophysical Journal as "Rings and Radial Waves in the Disk of the Milky Way," built on material from the 2002 survey. At that time, researchers had discovered the "Monoceros Ring," a density of stars off the edge of the galaxy.
They noticed that this strange ring bulged above the galactic plane. Scientists also saw another similar ring between that one and the sun, but were unable to research it then.
Now, nearly 13 years later, they've learned that these rings – which extend out from the galaxy's disk – are actually ripples.
"In essence, 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 Professor Heidi Newberg from the Rensselaer School of Science. "As it radiates outward from the sun, we see at least four ripples in the disk of the Milky Way. While we can only look at part of the galaxy with this data, we assume that this pattern is going to be found throughout the disk."
It's likely that even more ripples occur farther out, which would mean that the Milky Way could span an even greater size than 150,000 light-years across.
Researchers also found that the oscillations of the ripples line up with the galaxy's spiraling arms. These findings fall in line with other studies, including one positing that there's a lump of dark matter or a dwarf galaxy (which contains a lot of dark matter) passing through the Milky Way. That would create a rippling effect.
"If a dwarf galaxy goes through the disk, it would gravitationally pull the disk up as it comes in, and pull the disk down as it goes through, and this will set up a wave pattern that propagates outward," said Newberg. "If you view this in the context of other research that's emerged in the past two to three years, you start to see a picture is forming."
This discovery could provide us with another way of measuring dark matter in our galaxy, in addition to gauging its overall size. Dark matter has become the holy grail of astrophysics – the stuff that we can't see or prove, but we know is there.
