A new study suggests the Milky Way contains less dark matter than previously thought

A new study has found that stars at the edge of the Milky Way travel more slowly than those closer to the centre. Their findings suggest that our galaxy’s gravitational core may be lighter in mass and contain less dark matter than previously thought.

A new study done by physicists at the Massachusetts Institute of Technology (MIT) found that stars at the edge of the Milky Way travel more slowly than those closer to the centre. Their findings suggest that our galaxy’s gravitational core may be lighter in mass and contain less dark matter than previously thought.

The Milky Way, which according to NASA is estimated to be 13.6 billion years old, spins like water in a whirlpool, rotating in part by all the matter that swirls within its disk. Astronomer Vera Rubin and her work in the 1970s was among the first pieces of evidence that galaxies cannot rotate just from visible matter, suggesting the existence of dark matter, an unknown entity that may outweigh all the stars and other visible matter in the universe.

Since then, researchers have observed similar flat curves in neighbouring galaxies, further supporting the existence of dark matter. But only recently have there been attempts in charting the rotation curves of the Milky Way.

“It turns out it’s harder to measure a rotation curve when you’re sitting inside a galaxy,” said Xiaowei Ou, a graduate student at MIT and the study’s first author.

In 2019, Anna-Christina Eilers, assistant professor of physics at MIT, began to analyze earlier data from the Gaia space telescope. It showed stars as far as 81,000 light years from the Milky Way’s centre. The data suggested a flat, yet mildly declining rotation curve from the galaxy, hinting at there being a high volume of dark matter at its core.

But new data released by the telescope that includes stars as far as 100,000 light years from the galaxy’s core led to the study’s researchers refining their analysis, using measurements from the Apache Point Observatory Galactic Evolution Experience (APOGEE), a ground-based survey.

“We feed all this information into an algorithm to try to learn connections that can then give us better estimates of a star’s distance,” Ou said. “That’s how we can push out to farther distances.”