Milky Way Galaxy May Be 50 Percent Bigger Than We Thought

Rings of stars thought to surround the Milky Way are actually

part of it, according to new research, meaning the galaxy is bigger

than previously believed.
The findings extend 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 and former

visiting scientist at Rensselaer who was the lead author of a paper

detailing the discovery in Astrophysical Journal.

“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.”
An international

team led by Rensselaer Polytechnic Institute Professor Heidi Jo

Newberg, came to this conclusion after revisiting astronomical data from

the Sloan Digital Sky Survey and finding that the galactic disk of the Milky Way is actually contoured into several concentric 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 Newberg, a

co-author of the paper. “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.”
But in this case, the pebble could be a dwarf

galaxy passing 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,” she explained. “As

it radiates outward from the sun, we see at least four ripples in the

disk of the Milky Way.”
She added that although the data only looks at part of the galaxy, it can be assumed that the pattern continues throughout.
The

new research builds upon a 2002 paper 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 Sloan survey, researchers

recently took another crack at it.
“I wanted to figure out what

that other over-density was,” Newberg said. “These stars had previously

been considered disk stars, but the stars don’t match the density

distribution you would expect for disk stars, so I thought, ‘Well, maybe

this could be another ring, or a highly disrupted dwarf galaxy.'”
Newberg said the findings support 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.

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Milky Way Galaxy May Be 50 Percent Bigger Than We Thought