Astronomers are baffled after discovering 19 galaxies that seem to be entirely missing dark matter.

The mysterious invisible substance that pulls on nearby space objects was previously thought to be a key ingredient for galaxies.

Dark matter is a strange and puzzling material that could make up almost a third of the known universe — and potentially up to 85 percent of all matter.

It has never been directly observed and reflects no light.

Astronomers only think it exists because of its effects on other objects, like gravitational pull. This is thought to be important for galaxy formation.

But scientists have now uncovered 19 dwarf galaxies that are missing their dark matter.

When we look at all the visible mass of a galaxy, we can calculate how fast it should swirl.

The presence of dark matter will make the galaxy swirl faster, giving an indication of its amount.

This is a common occurrence and is one of the best pieces of evidence for dark matter.

However, these 19 newly uncovered galaxies appear to be dominated by ordinary matter — with no dark matter present.

It’s a mystery that’s left the astronomers at the Chinese Academy of Science puzzled.

One possible answer is that these physicists have simply made a mistake.

Perhaps the angle of the galaxy from Earth was calculated incorrectly.

This could lead to further errors in determining the presence of dark matter.

And other events — like a supernova — can also have an effect on the rotation of a galaxy.

If scientists do discover that dark matter is missing from these galaxies, it means going back to the drawing board on galaxy formation.

Dark matter is key to how scientists think the universe and galaxies developed, so these dwarf galaxies potentially throw a wrench into the works.

This research was published in the Nature Astronomy journal.