March 11, 2015
than is commonly estimated, according to new findings
that reveal that the galactic disk is contoured
into several concentric ripples.
The research, conducted by an international team led by Rensselaer Polytechnic Institute (RPI) Professor Heidi Jo Newberg, revisits astronomical data from the Sloan Digital Sky Survey which, in 2002, established the presence of a bulging ring of stars beyond the known plane of the Milky Way.
Importantly, the findings show 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, said Yan Xu, a scientist at the National Astronomical Observatories of China (which is part of the Chinese Academy of Science in Beijing), former visiting scientist at Rensselaer, and lead author of the paper.
in the Milky Way reveals a rippling contour.
Newberg, Xu, and their collaborators used data from the Sloan Digital Sky Survey (SDSS) 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.
The new research builds upon a 2002 finding in which Newberg established the existence of the "Monoceros Ring," an "over-density" of stars at the outer edges of the galaxy that bulges above the galactic plane.
At the time, Newberg noticed evidence of another over-density of stars, between the Monoceros Ring and the sun, but was unable to investigate further.
With more data available from the SDSS,
researchers recently returned to the mystery.
When they revisited the data, they found four anomalies:
The Monoceros Ring is associated with the third ripple.
The researchers further found that the oscillations appear to line up with the locations of the galaxy's spiral arms.
Newberg said the findings support other recent research, including a theoretical finding that a dwarf galaxy or dark matter lump passing through the Milky Way would produce a similar rippling effect.
In fact, the ripples might ultimately be used to measure the lumpiness of dark matter in our galaxy.