Like something out of a science-fiction thriller, a new theory proposes that black holes generate swirling clouds of planet-sized particles that could be the elusive dark matter thought to hold galaxies together, suggesting that the Standard Model, developed more than 30 years ago, which successfully describes phenomena from subatomic to galactic scales and have been experimentally tested to a precision of twelve decimals– is insufficient to account for everything physicists observe. Hopes that the discovery of the Higgs would be followed by hints of other particles that match the properties of dark matter have so far been dead ends.
“We tend to think about particles as being tiny but, theoretically, there is no reason they can’t be as big as a galaxy,” says Asimina Arvanitaki, The Aristarchus chair in theoretical physics at the Perimeter Institute for Theoretical Physics in Waterloo, Canada about solving the mystery of dark matter.
These dark matter candidates, known as macros, would form heavier particles some ranging from planet-to-bullet sized. While macros would be much rarer than weakly interacting massive particles WIMPs, any collisions with ordinary matter would be violent, leaving an obvious trace.
A new study by Glenn Starkman and Jagjit Singh Sidhu, theoretical physicists at Case Western Reserve University, explores what those traces might look like if macros hit human beings. They propose a surprising new sensor -one from the farside- human flesh where this particular dark matter particle (if it existed), would occasionally kill humans, passing through them like a bullet. Because no one has died from unexplained gunshotlike wounds, this type of dark matter does not exist, according to a new study.
Still, there are other ways to detect this particular type of dark matter and researchers should keep looking, says Katherine Freese, a theoretical physicist at the University of Michigan in Ann Arbor who wasn’t involved in the study but has studied the effects of dark matter on humans. “We don’t know what dark matter is, so we shouldn’t write things off,” she says.)
Sidhu and Starkmen were originally searching for traces of macros in granite slabs when a colleague made a suggestion. “Why can’t you just use humans as a detector?” quoting Robert Scherrer, a co-author and theoretical physicist at Vanderbilt University in Nashville. “The energies you’re talking about, these things would probably at best maim a person, at worst kill a person.”
“Our results open a new window on dark matter: the human body as a dark matter detector.” Their paper – titled “Death By Dark Matter” -on the pre-print website arXiv- although absurd, is not a sci-fi novel waiting a Hugo award.
The “farside” team modeled macros that would have a similar effect to a fatal shot from a .22 caliber rifle focusing on the millions of people living in Canada, the United States, and Western Europe over the past decade because researchers say these countries have more reliable data on how many people died and from what causes.
In this sample, scientists would expect to see a handful of reports of unexplained deaths from invisible dark matter “bullets.” But there were none, the researchers report this week on the preprint server arXiv. These deaths would not go unnoticed—they would leave victims dead or dying with a tubular wound where their flesh was vaporized.
This experiment doesn’t rule out heavy macro dark matter altogether, Scherrer says. It merely eliminates a certain range of them. Heavier macro dark matter would not occur frequently enough to measure, Freese notes, and other forms wouldn’t kill people.
“There is probably still room for very heavy dark matter,” says Paolo Gorla, a particle physicist at Italy’s underground Gran Sasso National Laboratory, who is not involved with the study.
The Case Western Reserve team, reports Science, “is not the only group of researchers trying to harness new ways to detect dark matter. Freese has developed Paleo-Detector experiments that would be sensitive enough to detect the traces of WIMPs in ancient minerals. However, rocks could also show signals of heavier dark matter—in more obvious ways. If macros collide with rock, they would shoot straight through, melting a cylinder of rock that would quickly resolidify into new forms. When light-colored granite is melted, for example, the melted rock hardens as a channel of dark obsidian-like stone.”
For now, Science summarizes, “the Case Western Reserve researchers will not be extending their human death calculations. This fall, they will search monuments, countertops, and graveyards for dark, elliptical patches that could be signs of macros hitting granite slabs. Next, they hope to identify characteristics for a range of macros and then train people to look for the marks on granite surfaces around the world. That, they say, would open up a whole new way to use humans as dark matter detectors.”