Scientists are searching for hidden hair around black holes
Black holes might be hiding something from us.
According to Einstein’s theory of general relativity, a simple black hole is surprisingly easy to describe. It has just three main properties: its mass, how fast it spins and its charge. That’s why physicists say that a black hole has no hair; it has no features other than those three properties.
But some scientists have wondered whether black holes might have extra matter or other new physics surrounding them. Physicists sometimes call this possible extra structure a black hole’s hidden hair.
On September 7, 2026, a team led by researchers at Nagoya University in Japan said they have a new way to look for this hair. The researchers said they might be able to find the answer in the gravitational waves produced when black holes collide and merge.
The researchers published their peer-reviewed findings on September 7, 2026, in the Journal of Cosmology and Astroparticle Physics.
Merging black holes ring like a bell
What happens when two black holes merge in a violent, cataclysmic event? They send out gravitational waves, or ripples in space and time. So the collision produces an effect like a ringing bell.
The gravitational waves that the newly combined black hole produces have specific frequencies that fade over time. The decay rates of the vibrations could reveal properties of the black hole. Scientists call the change in the wave pattern as it fades the ringdown.
For an ordinary black hole, the ringdown should depend on three things: the black hole’s mass, spin, and charge. But, if something else is surrounding the black hole (say, extra matter), it could change the way the black hole rings. And that could give scientists a way to find the hidden hair.
How could scientists discover black hole hair?
To be clear, researchers aren’t saying they’ve found a hairy black hole. But they now think they have a plan for how to find one. The Nagoya University team used theoretical black holes to test how small amounts of surrounding matter could change their ringdown signals.
They found that the matter would affect two parts of the ringdown signal: its frequency and how quickly it fades away. And what’s important is those two things wouldn’t change in exactly the same way. So the difference between them can show if matter is present. And it can also show the change in pressure around a black hole.
Lead author Ariadna Uxue Palomino Ylla of Nagoya University said:
The ringdown waves may not only show that something extra is affecting the black hole; the way the signal changes could also give us clues about what this hidden matter is actually like.
Spinning black holes make things more complicated
The researchers also looked at spinning black holes. Near a spinning black hole, light can orbit in different ways depending on whether it travels in the same direction as the black hole’s spin or in the opposite direction.
The researchers said that possible hidden matter would affect the ringdown’s frequency and fade-out speed differently, depending on the direction of the spin. And looking at the specific pattern can help identify the type of matter that makes up the hair.
So, the next time researchers find two colliding black holes and register that they are ringing like a bell, they have a better idea of what to look for. Soon maybe they’ll be able to demonstrate if there is hidden matter or strange physics occurring in the vicinity of the newly melded black hole.
Bottom line: If black holes have extra matter around them – what astronomers call hidden hair – astronomers could find it by measuring the different characteristics of these ripples.
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