Dark matter may have been detected by accident seven YEARS ago, study claims

Dark matter has eluded scientists for decades, but researchers now say it might have been detected by accident seven years ago.

Despite making up as much as 85 per cent of the matter in the universe, dark matter is completely invisible to our telescopes.

However, an international team of scientists proposes that this mysterious substance might leave a subtle trace in the gravitational waves emitted by colliding black holes.

If black holes collide while shrouded in dark matter, the ripples they send across the cosmos could carry an ‘imprint’ of that environment.

In a new study, researchers say they have found this telltale imprint in the record of a black hole collision spotted all the way back in 2019.

Scientists say more observations are needed before they can claim to have ‘detected’ dark matter, but their new method could help find even more dark matter signatures.

Co-author Dr Katy Clough, a researcher at Queen Mary University of London, told the Daily Mail: ‘The evidence we found in the data isn’t sufficient to be sure of what we are seeing, and we need to check other possibilities.

‘However, it is an interesting hint that something might be going on, and because we expect more signals from black hole mergers over the coming years, if this is a true signature of dark matter, we will see it again.’

Scientists say that dark matter might have been spotted seven years ago, with its telltale signature hidden in the gravitational waves from two merging black holes (illustrated) 

When a pair of black holes (known as a binary) spiral towards each other, they create such intense gravitational forces that they whip up waves in the fabric of spacetime.

These ripples stretch and compress reality as they travel the length of the universe, creating tiny disturbances that specialised detectors can pick up on Earth.

Dr Clough explains that gravitational waves ‘encode information about the event that generated them, in the same way that sound waves encode information about the shape and size of an instrument that is being played.’

That means those ripples should look subtly different if the binary collided while inside a dense cloud of dark matter rather than empty space.

According to one theory of dark matter, this strange substance is made up of ‘light scalar’ particles that are many, many times smaller than an electron.

Although these particles don’t interact with the electromagnetic force, they still produce the gravitational effects that scientists have attributed to dark matter.

Importantly, while this type of dark matter normally behaves like a particle, it can also act like a coordinated wave when near a black hole.

When waves of dark matter collide with a rapidly spinning black hole, scientists predict that some of the black hole’s rotational energy will be transferred to the dark matter.

Dark matter is an invisible substance that makes up around 85 per cent of the matter in the universe. It can only be detected through its gravitational effects, such as the way it stretches light from distant galaxies (pictured) 

In a phenomenon known as ‘superradiance’, this will amplify the dark matter waves, whipping them up into extremely high densities like churning cream into butter.

‘The presence of a significant amount of dark matter around a black hole binary creates a drag force on their motion,’ says Dr Clough.

‘It means that the binaries lose energy faster and tend to inspiral towards each other and merge faster than they would without it.’

If the dark matter is dense enough, that will produce a measurable difference in the gravitational wave signature, which observatories should be able to spot.

In their new paper, scientists created a mathematical model to predict what gravitational waves should look like from two black holes colliding in empty space versus a cloud of dark matter.

Using this model, the team created simulations of various sizes of black hole colliding at different speeds and in different clouds of dark matter.

They then compared those simulations to the 28 best signals of black hole mergers collected by the LIGO-Virgo-KAGRA observatory network.

Of those, 27 clearly showed that they had been created in empty space, but one showed a promising hint of a dark matter imprint. 

When two black holes spiral together inside a field of dark matter (artist’s impression), the dark matter should leave an impression on the ripples they send out through the cosmos 

The signal GW190728, named for the date it was discovered on, came from a black hole binary with a mass about 20 times that of the sun.

With their model, the researchers showed that such a system could have merged through a dense cloud of dark matter and produced a similar gravitational wave to GW190728.

Co-author Dr Josu Aurrekoetxea, a researcher at the MIT Department of Physics, says: ‘We know that dark matter is around us. It just has to be dense enough for us to see its effects.

‘Black holes provide a mechanism to enhance this density, which we can now search for by analysing the gravitational waves emitted when they merge.’

However, the researchers stop short of claiming to have detected dark matter.

Instead, they say that this method is a way of screening gravitational-wave data for hints of dark matter, which physicists can then follow up and confirm with other techniques.

Co-author Soumen Roy, of the Royal Observatory of Belgium, says: ‘We now have the potential to discover dark matter around black holes as the LVK detectors keep collecting data in the coming years.

‘It is an exciting time to search for new physics using gravitational waves.’

WHAT ARE GRAVITATIONAL WAVES?

Scientists view the the universe as being made up of a ‘fabric of space-time’.

This corresponds to Einstein’s General Theory of Relativity, published in 1916.

Objects in the universe bend this fabric, and more massive objects bend it more.

Gravitational waves are considered ripples in this fabric.

Gravitational waves are considered ripples in the fabric of spacetime. They can be produced, for instance, when black holes orbit each other or by the merging of galaxies

They can be produced, for instance, when black holes orbit each other or by the merging of galaxies.

Gravitational waves are also thought to have been produced during the Big Bang.

Scientists first detected the shudders in space-time in 2016 and the discovery was hailed the ‘biggest scientific breakthrough of the century’.

Experts say gravitational waves open a ‘new door’ for observing the universe and gaining knowledge about enigmatic objects like black holes and neutron stars.