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Milky Way may be 50 Percent Bigger than previously estimated

The Milky Way galaxy is approximately 50 percent larger than is generally estimated, according to new research that shows that the galactic disk is contoured into numerous concentric ripples. The research, led by an international team, reconsiders astronomical data from the Sloan Digital Sky Survey which, in 2002, established the occurrence of an expanded ring of stars beyond the known plane of the Milky Way. Significantly, the findings show that the features earlier acknowledged as rings are essentially part of the galactic disk, ranging the known width of the Milky Way from 100,000 light years across to 150,000 light years, said Yan Xu, a scientist at the National Astronomical Observatories of China, former visiting scientist at Rensselaer, and lead author of the research paper.
An unlabeled view of the corrugated Milky Way Credit: Rensselaer Polytechnic Institute

Xu said “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. 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.” The study, supported in part by the National Science Foundation and titled “Rings and Radial Waves in the Disk of the Milky Way,” was issued recently in the Astrophysical Journal. Newberg, Xu, and their coworkers used data from the Sloan Digital Sky Survey (SDSS) to display an oscillating asymmetry in the sun like star counts on either side of the galactic plane, starting from the sun and looking outward from the galactic midpoint. In other words this means, when we look outward from the sun, the central-plane of the disk is perturbed up, then down, then up, and then down again.

National Science Foundation program manager Glen Langston said “Extending our knowledge of our galaxy’s structure is fundamentally important. The NSF is proud to support their effort to map the shape of our galaxy beyond previously unknown limits.”

This new study builds upon a 2002 finding in which Newberg recognized the presence of the “Monoceros Ring,” an “over-density” of stars at the external edges of the galaxy that swells above the galactic plane. At the time, Newberg detected indication of another over-density of stars, between the Monoceros Ring and the sun, but was incompetent to study further. With more data obtainable from the SDSS, scientists recently returned to the mystery.

When they reexamined the data, they found four variances: one south of the plane at 4-6 kpc , a third to the north at 8-10 kpc, one north of the galactic plane at 2 kilo-parsecs (kpc) from the sun and indication of a fourth to the south 12-16 kpc from the sun. The Monoceros Ring is linked with the third ripple. The scientists further found that the oscillations seem to line up with the positions of the galaxy’s spiral arms. Newberg said the outcomes support other recent research, counting a theoretical finding that a dwarf galaxy or dark matter bulge passing through the Milky Way would create a similar rippling effect. Actually, the ripples might eventually be used to measure the lumpiness of dark matter in our galaxy.

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