As of: February 2, 2024, 11:28 a.m
By: Tanja Banner
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Stars in the outer reaches of the Milky Way move slower than they should.
A research team draws conclusions about the center of the galaxy.
Cambridge – Like most galaxies in the universe, the Milky Way spins like water in a whirlpool.
The rotation is partly driven by the matter contained in the galactic disk - but not only.
As early as the 1970s, research discovered that the rotation of galaxies could not only be explained by visible matter - researcher Vera Rubin was one of the first to discover evidence of dark matter.
Stars in the Milky Way behave strangely
Dark matter, which has not yet been clearly detected, apparently ensures that stars within a galaxy all have the same speed - it does not decrease with distance.
An invisible dark matter appears to give the more distant stars a “nudge,” according to the theory.
But what is it actually like in our galaxy, the Milky Way?
A research team from the Massachusetts Institute of Technology (MIT) measured the speed of stars in the Milky Way and came to interesting new findings.
The stars on the edge of the Milky Way behave differently than expected, a new study shows.
(Archive image) © IMAGO/imageBROKER/ncphoto
“It turns out that it is harder to measure a rotation curve when you are inside a galaxy,” Xiaowei Ou said in a statement.
Ou is one of the authors of the study, which was published in the journal
Monthly Notices of the Royal Astronomical Society
.
At the edge of the Milky Way, stars slow down - does it have to do with dark matter?
Using data from Europe's Gaia spacecraft and the Earth-based Apogee program, the research team determined the distances of more than 33,000 stars in the Milky Way.
This resulted in a three-dimensional map showing the distribution of stars in the Milky Way.
The team then generated a rotation curve that showed how fast the stars were moving at a given distance from the galaxy center.
“That's where the weirdness started,” recalls co-author Lina Necib, a physics professor at MIT.
“What really surprised us was that this curve stayed flat, flat, flat until a certain distance, and then it started to decline,” said the researcher.
“This means that the outer stars are rotating a little slower than expected, which is a very surprising result.”
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“The result is in tension with other measurements”
Instead of seeing a slight decline like previous rotation curves, the curve ended up falling more sharply than expected.
Using the new rotation curve, the research team was able to recalculate the distribution of dark matter in the Milky Way to understand how the outer stars might be moving slower than they should.
And indeed: The result showed that the Milky Way apparently has a lighter core than previously thought.
The center of our galaxy could be less dense and contain less dark matter than expected.
“This result is in tension with other measurements,” explains Necib.
“There's something fishy somewhere, and it's very exciting to figure out where that is in order to really have a coherent picture of the Milky Way.”
Milky Way continues to be explored
In further research, the team now wants to find answers to the questions the study raised.
“Truly understanding this result will have profound implications,” emphasizes Necib.
“It could lead us to find more hidden masses beyond the edge of the galactic disk or cause us to rethink the equilibrium state of our galaxy.”
Just recently, another research team showed that the Milky Way looks very different than previously thought.
And it's not just the Milky Way that surprises researchers, another galaxy is also surprising.
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