MIT physicists discover surprising twist in Milky Way’s core
MIT physicists have discovered a surprising twist in the Milky Way’s rotation curve that challenges our understanding of dark matter. By tracking the speed of stars across the galaxy, they’ve uncovered a potential deficit of dark matter at the galactic core.
Traditionally, astronomers believed that dark matter was responsible for the galaxy’s rotation. Still, the new analysis raises the possibility that the Milky Way’s gravitational center may be lighter in mass than previously thought.
Dark matter’s role
So, what is dark matter? Scientists believe it is a hypothetical substance in the universe because it explains why galaxies rotate as they do. Dark matter is thought to be made up of particles that don’t interact with light, which makes them impossible to see directly. The only way to detect dark matter is by its gravitational effects on visible matter, such as stars and galaxies.
The team analyzed data from Gaia and APOGEE instruments. Gaia is an orbiting space telescope that tracks the precise location, distance, and motion of more than 1 billion stars throughout the Milky Way galaxy, while APOGEE is a ground-based survey. The scientists analyzed Gaia’s measurements of over 33,000 stars, including some of the farthest in the galaxy, determining the circular velocity of each star given its distance from the galaxy’s center.
A lighter galactic core
They plotted each star’s velocity against its distance to generate a rotation curve representing how fast matter rotates at a given distance from the center of a galaxy. The team found that the outer stars rotate slightly slower than expected, indicating a lighter galactic core.
“What we were really surprised to see was that this curve remained flat, flat, flat out to a certain distance, and then it started tanking,” says Lina Necib, assistant professor of physics at MIT. “This means the outer stars are rotating a little slower than expected, which is a very surprising result.”
The team’s results are reported in the Monthly Notices of the Royal Astronomical Society Journal.
The rotation of the Milky Way is driven, in part, by all the matter that swirls within its disk. In the 1970s, astronomer Vera Rubin observed that galaxies rotate in ways that cannot be driven purely by visible matter. She concluded that some other type of invisible matter must be acting on distant stars to give them an added push. Since then, astronomers have observed similar curves in far-off galaxies, supporting dark matter’s presence. Only recently have astronomers attempted to chart the rotation curve in our galaxy with stars.
The team established the precise distances for more than 33,000 stars and generated a 3D map of the stars scattered throughout the Milky Way to about 30 kiloparsecs. They then incorporated this map into a model of circular velocity to simulate how fast any star must travel, given the distribution of all the other stars in the galaxy. They observed that the new curve dipped more strongly than expected at the outer end, suggesting that the Milky Way’s core may contain less dark matter than previously estimated.
“This result is in tension with other measurements,” Necib says. “Really understanding this result will have deep repercussions. This might lead to more hidden masses just beyond the edge of the galactic disk, or a reconsideration of the state of equilibrium of our galaxy. We seek to find these answers in upcoming work, using high resolution simulations of Milky Way-like galaxies.”
Source: Interesting Engineering
MIT physicists discover surprising twist in Milky Way’s core