Scientists Find Mysterious Galaxies That Don't Have Any Dark Matter

A picture of a starry night sky.
We have never seen a speck of it, but scientists say the universe is oozing with dark matter. pixelparticle/Shutterstock

True to its name, dark matter has long been one of the universe's biggest mysteries. It is, after all, invisible, emitting no light whatsoever. And yet, we know it exists by the gravitational strings it pulls. Stars, literally, dance to the beat of dark matter.

"Motions of the stars tell you how much matter there is," Yale University researcher Pieter van Dokkum noted in 2016. "They don't care what form the matter is, they just tell you that it's there."

At the time, van Dokkum was hailing the discovery of a galaxy with unusually high levels of dark matter — a place that boasts 99.99 percent of the stuff. On average, dark matter is estimated to make up around 27 percent of the universe.

But now researchers have made a discovery that could shatter our existing theory about how the universe is formed: No less than 19 galaxies seem to be missing dark matter altogether. Instead, dark matter's nemeses, called baryons, seem to dominate these dwarf galaxies.

Baryonic matter, comprising protons and neutrons, is the stuff we're more accustomed to — the matter scientists can relatively easily detect and measure. These newly discovered galaxies may be entirely composed of ordinary, run-of-the-mill baryonic matter.

A spiral galaxy
Dark matter is typically detected by the influence of its gravity on stars. Vladimir Arndt/Shutterstock

In the research paper, published in the journal Nature Astronomy, measured the swirl of 19 galaxies. That swirl factor tells scientists how much dark matter a galaxy contains. More specifically, they looked at the H1 rotation factor in these galaxies. That's the motion of hydrogen atoms as they're being swished around under dark matter's inexorable influence.

And to their surprise, they found those hydrogen atoms were completely free from dark matter's sway. How is it possible that an ingredient so essential in the formation of galaxies could be missing? (Dark matter pulls atoms of gas together to form stars.)

Well, if their findings prove accurate, prevailing theories on how galaxies are formed from the interplay of dark and baryonic matter would need a complete reset.

And it wouldn't be the first time scientists noted a galaxy seemingly bereft of dark matter. Last year, Yale researchers detected a similar phenomenon in a faraway galaxy known as NGC 1052–DF2.

What does it all mean for astrophysicists? There are still plenty of variables that may have thrown off their findings. For one thing, measuring the H1 rotation of a distant galaxy is easily skewed if its angle from Earth isn't calculated just right.

Another wildcard could be the presence of a supernova, which can have a profound effect on a galaxy's rotation. But if their findings are confirmed, then that ever-elusive material known as dark matter may have once again thrown science for a loop — and forced us to rethink how the universe came to be in the first place.

Still a little in the dark about dark matter? This video may help: