While the Milky Way might be our home in the universe, there is still an unfathomable amount of mysteries about our stellar neighborhood left to explain. For years, an unprecedented amount of gamma rays have been emanating from the center of our galaxy, a region known as the galactic bulge. The source of this cosmic signal has been a matter of contentious debate among scientists, until now.

On Tuesday, a team of astronomers at the Australian National University published a study in the journal Nature Astronomy that may have cracked the case. The source of the gamma rays is actually a group of 10 billion-year-old stars, rather than dark matter, as previously thought.

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Dr. Roland Crocker, a co-researcher on the study, explained that because of the distance of these stars their radiation merged into a signal that looked a lot like dark matter to astronomers. Instead thousands of rapidly spinning neutron stars — called millisecond pulsars — are the culprits.

An artist's impression of the Milky Way, with the Galactic bulge at the center.
An artist's impression of the Milky Way, with the Galactic bulge at the center.

“At the distance to the centre of our galaxy, the emission from many thousands of these whirling dense stars could be blending together to imitate the smoothly distributed signal we expect from dark matter,” Crocker says in a statement.

Crocker and his team came to this conclusion by examining data gathered by the Fermi Gamma Ray Space Telescope that has been orbiting Earth since 2008. This spacecraft allowed scientists to see that the signals they’ve been detecting mirrors the distribution of stars at the center of the Milky Way. That’s a whole lot more evidence than astronomers have in favor of the dark matter theory.

Dark matter is a hypothetical type of matter that doesn’t emit light or energy. Scientists have theorized that this is the substance that holds galaxies together as they spin through space, instead of having them scatter apart.

How dark matter might be holding galaxies together.
How dark matter might be holding galaxies together.

Previously astronomers thought the gamma ray signals they’ve been detecting were caused by dark matter particles smashing into each other.

“It is thought that dark matter is composed of Weakly Interacting Massive Particles, which would be expected to gather in the center of our galaxy,” explains Crocker in a press release. “The theory is that, very occasionally, these particles crash into each other and radiate light a billion times more energetic than visible light.”

But with the new evidence Crocker and his team provided, it’s likely that dark matter isn’t responsible for this galactic anomaly.

That’s a big step toward understanding the Milky Way, but a confusing turn for astronomers seeking to explain dark matter.

Right when scientists think they have the answer, a telescope beams over more data suggesting the contrary. But hey, no one said space science was easy — or predictable.