After many decades, physicists are still hot on the trail of a suspect in a detective story that could change our understanding of the universe: dark matter in the form of primordial black holes.
These are not the massive monsters formed from dying stars, but tiny black holes created in the first moments after the Big Bang that zoom around the universe, visiting our only solar system every ten years or so.
And if a new theory from MIT physicists is right, these ancient cosmic wanderers could be the missing link in the mystery of dark matter.
David Kaiser, a professor of physics and history of science at MIT, alongside his team, believes we might soon find proof of these elusive objects right here in our solar system.
Their study, published in Physical Review D, suggests that if these primordial black holes do exist, they should zoom through our solar system at least once every decade, potentially causing a slight “wobble” in the orbit of Mars — a wobble that today’s technology could actually detect.
Dark matter and primordial black holes
To understand why this theory is so compelling, we need to revisit what we know — or rather, what we don’t know — about dark matter.
Most of the physical universe, around 80 percent, isn’t made up of the visible stuff we can see and touch, like stars, planets, or your kitchen sink. The rest is a mysterious substance known as dark matter.
This invisible matter doesn’t interact with light or other electromagnetic radiation, which makes it notoriously hard to detect. But its gravitational effects are big enough to affect the motion of stars and galaxies.
For decades, scientists have been setting up detectors on Earth to try to capture a glimpse of dark matter particles, assuming it might be made of exotic particles that decay into detectable forms. But after countless experiments, those searches have come up empty.
So, if dark matter isn’t made of mysterious particles, what is it? Enter the primordial black holes — a theory first proposed in the 1970s but largely dismissed until recent years.
Unlike the black holes formed from collapsing stars, primordial black holes would have originated from incredibly dense regions of the universe in the first seconds after the Big Bang.
They could be as small as an atom but with the mass of an asteroid. It’s a wild thought, but it might just make sense.
Mars and microscopic black holes
Kaiser and his team began to think about what would happen if one of these microscopic black holes passed through the solar system. Initially, the idea seemed like a joke.
As Tung Tran, a graduate student at Stanford University and the lead author of the study, remembers, “Someone asked me what would happen if a primordial black hole passed through a human body.”
Tran did the math and found it would push a person about 20 feet away in a second if it passed within a meter. Not very comforting, but also incredibly unlikely.
But what if a primordial black hole flew by something much larger, like a planet? The team ran the numbers for Earth and the Moon but found the effects were too muddy — there are just too many other factors that could create similar movements.
Mars, however, was a different story. “Given that scientists have been tracking Mars with incredible accuracy, to within about 10 centimeters, we realized that any wobble caused by a black hole would be much easier to detect,” Kaiser explained.
They estimate that if a black hole were to come within a few hundred million miles of Mars, the planet’s orbit would shift by about a meter over a few years — a tiny movement, but one we could measure with current technology.
Primordial black holes and Mars
Why does Mars, out of all the planets, offer the best chance of detection?
Sarah Geller, a postdoctoral researcher at the University of California at Santa Cruz (UCSC) and one of the study’s co-authors, explains, “Primordial black holes don’t live in the solar system.
They’re zipping through the universe, doing their own thing. And the probability is, they pass through the inner solar system once every 10 years or so.”
The team simulated different scenarios where asteroid-mass black holes zoom through the solar system at speeds around 150 miles per second. Mars showed a consistent response — a potential “wobble” in its orbit.
“Unlike Earth or the Moon, Mars doesn’t have a lot of interference from other gravitational forces,” says Geller. “It’s like a clean slate where we can see the tiny effect of a passing black hole more clearly.”
How to prove this theory
Detecting a wobble in Mars’ orbit would be a significant hint, but it wouldn’t immediately confirm the presence of a primordial black hole.
“There’s still much work needed to distinguish the push from a passing black hole from that of an asteroid or some other mundane space object,” Kaiser points out.
Fortunately, scientists have been tracking these space rocks for decades, so they have a pretty good idea of what a normal orbit looks like. Comparing these known paths with the unusual trajectories a black hole might take could help narrow things down.
The researchers are considering new collaborations to simulate a larger number of objects, from planets to moons and rocks, over extended periods.
“We want to inject close encounter scenarios and study their effects with higher precision,” says Geller. The more they can refine their simulations, the better they can differentiate between ordinary objects and the extraordinary.
Mars, dark matter, and the future of cosmology
So, what does this all mean for our understanding of the universe?
If these wobbles can be detected and confirmed, it would provide strong evidence that primordial black holes make up a significant part of dark matter.
This would not only solve one of the biggest mysteries in physics but also open up new avenues of research into the early moments of the universe itself.
But even if this theory doesn’t pan out, the search for dark matter continues. “Science is like peeling an onion,” says Kaiser. “Each layer we peel back leads to new questions and new possibilities. And sometimes, you find something you never expected.”
So, keep an eye on Mars. The Red Planet might just hold the clues to unlock the universe’s biggest secrets.
And as Kaiser and his team are proving, sometimes the
answers lie not in what we can see, but in the tiny, invisible forces passing
right under our noses — forces that could help us understand what makes up most
of our universe.
The full study was published in the journal Physical Review D.
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