Stunned astronomers discover 50,000 bonus light-years in our galaxy

The galactic disk has concentric ripples that extend outwards.
By Andrew McDonald | Mar 11, 2015
In 2002, observations gathered by the Sloan Digital Sky Survey led to the recognition of a ring of stars concentric with the rest of the disk of our Milky Way galaxy, but protruding beyond the galactic plane. This ring, dubbed the "Monoceros Ring"

Now, a new study led by Professor Heidi Jo Newberg of Rensselaer Polytechnic Institute has found that there are several concentric protruding rings in the Milky Way's disk, indicating that our galaxy is at least 50 percent larger previously thought.

According to a Rensselaer statement, the researchers demonstrated that the numbers of main sequence stars on either side of the galactic plane have an oscillating asymmetry, describing the structure of concentric rings of stars bulging up relative to the plane, then down, then up, and then down.

The concentric dense rings of stars are situated in this alternative pattern: a ring north of the galactic plane at two kiloparsecs (kpc; one kiloparsec equals 3,262 light-years) from the Sun, another south of the plane at four to six kpc, another (corresponding to the Monoceros Ring) north of the plane at eight to ten kpc, and a fourth south of the plane at 12 to 16 kpc.

These oscillating rings seem to line up with the Milky Way's spiral arms. This ripple-like structure means that the Milky Way is around 150,000 light-years in diameter, rather than the previously proposed 100,000 light-years. The oscillations might be the result of a dwarf galaxy or body of dark matter interacting with the galaxy; if so, the oscillations could provide a means to indirectly measure the distribution dark matter in the Milky Way.

"It's very similar to what would happen if you throw a pebble into still water the waves will radiate out from the point of impact," Newberg explained. "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. 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."

The new findings were published on March 11 in the Astrophysical Journal.

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