What is dark matter? All about the universe’s biggest mystery after scientists found possible signal in South Dakota gold mine

Dark matter has suddenly moved back into the spotlight after scientists reported an unusual particle interaction deep beneath the ground in South Dakota. The event, recorded by the LUX-ZEPLIN experiment, could be linked to a hypothetical dark matter particle, although researchers have stressed that they have not yet confirmed a discovery. So, what exactly is dark matter?

Also Read: Dark Matter detected: Scientists may have solved Universe’s biggest mystery as possible dark matter signal found deep underground in a South Dakota gold mine

It is one of the biggest unanswered questions in modern physics. Scientists cannot see dark matter directly, and they still do not know what it is made of. Yet there is strong evidence that something invisible is exerting gravity on the matter and light we can observe across the universe.

What is dark matter?

Dark matter is a form of matter that does not appear to emit, absorb or reflect enough light for telescopes to see it directly. That is where the word "dark" comes from. It does not mean that dark matter is simply black or hidden somewhere in space. Rather, it appears to interact extremely weakly with electromagnetic radiation, making conventional observation almost impossible.

Scientists estimate that dark matter accounts for about 27% of the universe, while ordinary matter, the material that makes up stars, planets, people and everything we can directly observe, accounts for roughly 5%. Most of the remaining universe is attributed to dark energy, a separate and equally mysterious phenomenon.

But if nobody can see dark matter, how do scientists know it exists? The answer is gravity.

How do scientists know dark matter is there?

Astronomers have repeatedly observed objects behaving as though much more mass is present than can be seen. One of the early clues came from galaxy clusters. In the 1930s, astronomer Fritz Zwicky noticed that galaxies within the Coma Cluster were moving so quickly that the visible matter alone could not provide enough gravity to keep the cluster together.

Decades later, astronomer Vera Rubin found another important clue while studying spiral galaxies. Stars far from the centre of galaxies were moving faster than expected. Based on the amount of visible matter, those stars should have been moving more slowly.

Something unseen appeared to be providing additional gravitational pull. That missing mass became known as dark matter.

Scientists have since gathered evidence in several ways, including observations of galaxy movements and gravitational lensing. When light from distant objects passes through regions containing large amounts of mass, gravity can bend the light. The amount of bending can reveal the presence of matter that cannot be seen directly.

Is dark matter the same as dark energy?

No. The names sound similar, but dark matter and dark energy are very different ideas. Dark matter is believed to provide additional gravitational mass and help shape structures such as galaxies and galaxy clusters.

Dark energy, meanwhile, is associated with the accelerated expansion of the universe. Scientists estimate that dark matter makes up around 27% of the universe and dark energy around 68%, with ordinary matter accounting for roughly 5%.

In simple terms, dark matter helps explain how cosmic structures hold together, while dark energy is linked to why the expansion of the universe is speeding up.

What is dark matter made of?

This is the part scientists still cannot answer. Dark matter may be made of particles that have not yet been discovered. Researchers have proposed several possibilities, including WIMPs, axions and other hypothetical particles.

One leading candidate is the WIMP, short for weakly interacting massive particle. WIMPs are theorised to interact very weakly with ordinary matter. That would make them extremely difficult to detect, but not necessarily impossible to find.

And that brings the mystery back to South Dakota.

Why are scientists looking for dark matter underground?

The LUX-ZEPLIN experiment, or LZ, is located about 1.6 kilometres underground at the Sanford Underground Research Facility in a former gold mine. Going deep underground helps shield the detector from cosmic rays and other background signals that could make an extremely rare particle interaction harder to identify.

The experiment uses liquid xenon as its detection material. Researchers are looking for the tiny signals that could be produced if a dark matter particle collides with a xenon atom.

In the recently reported event, scientists detected an interaction that could potentially fit the expected behaviour of a WIMP. The event produced a faint signal and a recoil of the xenon nucleus. But there is an important qualification.

Have scientists finally detected dark matter?

Not yet. The LZ researchers have reported only a single unusual event. While the signal is intriguing and difficult to explain using known background processes, one event is not enough to establish a scientific discovery.

The researchers themselves have urged caution and are continuing to investigate whether an unknown background process could explain the observation.

The distinction matters. A confirmed discovery would require much stronger statistical evidence and, ideally, additional observations that reproduce the same pattern. So for now, scientists have a fascinating clue, not a final answer.

Why would discovering dark matter be such a big deal?

Finding dark matter would solve a problem that has puzzled scientists for decades. At present, researchers can observe the gravitational effects associated with dark matter but cannot identify the substance responsible. Directly detecting a dark matter particle would give physicists the first opportunity to study its properties in detail.

It could reveal what makes up much of the matter in the universe and improve our understanding of how galaxies and other large-scale structures formed.

NASA describes dark matter as an important component in the structure of the cosmos, with evidence for its existence coming from its gravitational effects on visible matter.

Could dark matter be passing through us?

Possibly. If dark matter is made of particles that interact only extremely weakly with ordinary matter, enormous numbers could pass through Earth, and even through our bodies, without producing any noticeable effect.

That is one reason direct-detection experiments are so challenging. Scientists are essentially waiting for an extraordinarily rare interaction and trying to distinguish it from all the other particles and radiation that can produce similar signals.

What happens next?

The latest LZ result is likely to trigger even more scrutiny of the unusual event. Researchers will continue looking for alternative explanations and, more importantly, for additional events that could strengthen the dark matter interpretation.

Scientists are also pursuing the mystery through other methods. Astronomers study dark matter's gravitational influence on galaxies and light, while particle physicists search for possible dark matter candidates in underground detectors and particle accelerators.

For now, the central mystery remains. We know something invisible appears to be shaping the universe through gravity. We just do not yet know what that something is.

And the strange signal detected deep beneath South Dakota could be one more step toward finding out.