According to a new study led by Yan Xu of Rensselaer Polytechnic Institute in Troy, NY, our Galaxy is at least 50 percent larger than is commonly estimated.
A rippled Milky Way Galaxy may be 50 percent larger than previously estimated. Image credit: Rensselaer Polytechnic Institute.
The study, to be published in the Astrophysical Journal (arXiv.org preprint), revisits data from the Sloan Digital Sky Survey (SDSS) which, in 2002, established the presence of the Monoceros Ring, a bulging ring of stars beyond the known plane of the Galaxy.
“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, also of Rensselaer Polytechnic Institute.
“As it radiates outward from the Sun, we see at least four ripples in the disk of the Milky Way.”
Importantly, the new study shows that the features previously identified as rings are actually part of the galactic disk, extending the known width of the Milky Way from 100,000 light-years across to 150,000 light-years.
“Going into the research, astronomers had observed that the number of Milky Way stars diminishes rapidly about 50,000 light years from the center of the galaxy, and then a ring of stars appears at about 60,000 light years from the center,” Xu said.
“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.”
Prof Newberg, Xu and their colleagues used SDSS data to show an oscillating asymmetry in the main sequence star counts on either side of the galactic plane, starting from the Sun and looking outward from the galactic center.
In other words, when we look outward from the Sun, the mid-plane of the disk is perturbed up, then down, then up, and then down again.
“Extending our knowledge of our Galaxy’s structure is fundamentally important,” said Dr Glen Langston of NSF, who was not involved in the study.
“The NSF is proud to support their effort to map the shape of our galaxy beyond previously unknown limits.”
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Yan Xu et al. 2015. Rings and Radial Waves in the Disk of the Milky Way. ApJ, accepted for publication, arXiv: 1503.00257
