Scientists announce the strongest evidence yet that dark matter is lurking in our galaxy — and maybe even our solar system

Dark matter
Simulation of dark matter in the universe. Argonne National Laboratory

Astronomers understand very little about dark matter, especially the dark matter that may exist in our home galaxy, the Milky Way. But now, a team of international scientists has helped solve an outstanding mystery regarding dark matter in our galaxy.

Their findings are the strongest evidence yet pointing to the possibility that dark matter is lurking nearby — which means that scientists should be able to pick it up using the technology already in use in today’s dark matter detectors.

What is dark matter?

The universe is aglow with billions of galaxies and trillions of stars, but all of that ordinary matter comprises less than 5% of the entire cosmos.

A lot of something else — something invisible and mysteriously elusive — is out there, including right in our cosmic backyard, according to a paper published on Monday in the journal Nature Physics.

Scientists call this elusive entity dark matter and estimate that it comprises about 26% of all of the matter in the universe — and plays an important role in how galaxies form and evolve.

Dark matter is different from ordinary matter because scientists can’t see it with any instruments on Earth and have yet to detect it, despite years of searching.

Dark matter lurking in our solar system

When American astronomer Vera Rubin first discovered dark matter in the 60s, she found evidence for a high concentration of it located at the fringes of galaxies, but not in the central regions. Ever since, astrophysicists have been studying how dark matter distributes itself throughout galaxies, from the central core to the outer edge.

A fish-eye mosaic of the Milky Way arching at a high inclination across the night sky, shot from a dark sky location in Chile. European Southern Observatory

Looking from an outsider’s perspective, it’s easy to measure this distribution in other galaxies. But calculating it from within the Milky Way is more difficult for the same reason why it’s harder to estimate the size of a crowd if you’re part of it: your vantage point is skewed and you cannot easily determine where the crowd ends or begins. Similarly, astronomers on Earth have a harder time studying dark matter distribution in the Milky Way than in other galaxies.

Using the same method that Rubin first used to discover dark matter, the team has shown that dark matter exists in the central regions of the Milky Way. And if that’s the case, then that means there’s a tiny amount of dark matter right here in our solar system, they report. (The amount of dark matter in the solar system is too small to have any significant impact on the orbits of planets.)

“It’s encouraging to have this evidence for dark matter,” Jürg Diemand — a professor at the University of Zurich who specialises in simulations of dark matter and galaxy formation — told Business Insider. “It’s one more benchmark that we have to meet now when we simulate galaxy formation.”

How to see the invisible

The way astronomers study dark matter is by its gravitational influence on ordinary matter. Rubin first discovered dark matter when she noticed that stars located along the outer edges of galaxies were moving faster than they should be, according to the laws of physics. Something with a strong gravitational force was pulling them through space, and that something was later dubbed dark matter.

In this latest study, the scientists studied all of the available data they could find on the speeds of stars in the inner regions of the Milky Way. They then used state-of-the-art physics models to predict how fast the stars should be moving if this region was empty of dark matter. Sure enough, the stars were moving faster than theory predicts, indicating the presence of dark matter.

An important issue to address is if the reason why dark matter detectors continue to come up empty handed is because there is no nearby dark matter to detect.

According to this latest paper, that is not the case.

“For experiments, this means keep doing what you’ve been doing and keep analysing your results,” Diemand said. “[Their results] don’t point to any changes in course.”