High-flying X-rays

“Dark lightning” sounds like something out of science fiction. It’s a high-energy bolt, practically invisible to the naked eye, striking roughly one time for every thousand discharges of what we know as lightning.

Its existence first arose theoretically, as a logical offshoot during a computer simulation. Then the physicist who discovered it, professor Joseph Dwyer of the Florida Institute of Technology, was able to detect actual bursts of dark lightning.

Dwyer, a Chico High graduate, has received national attention for his research, in particular for a finding that air passengers could be exposed to sizeable doses of radiation if dark lightning strikes their plane.

“If an aircraft happened to be inside a thunderstorm at exactly the wrong place and exactly the wrong time, when one of these dark-lightning flashes went off, then the radiation doses inside the plane, through all that aluminum, could be fairly elevated,” Dwyer explained in a recent phone interview from his office. “It would be comparable to the level of radiation you’d get in the upper end of medical procedures, like a full-body CT scan.”

Since it’s estimated that every plane gets hit by lightning an average of once a year, it’s plausible that dark lightning has struck aircraft.

However, lest anyone think Dwyer is ringing alarm bells, he’s quick to add a soothing disclaimer.

“The message is this is something interesting, something we need to pay attention to and figure out, but is not a reason to quit flying,” Dwyer said. “First of all, pilots already know to stay away from thunderstorms; thunderstorms are dangerous places you really don’t want to spend any time in. And dark lightning, we believe, is fairly rare.

“So no one should be staying up at night worrying about their flight the next day because of this.”

Besides, aircraft designers already take lightning strikes into account.

“Lightning is a concern; there’s a lot of current flowing that could damage electronics and cause problems,” Dwyer said. “The good news is people who design aircraft know all about these things, and for years they’ve been careful to design aircraft to keep the lightning from damaging the people or components within the aircraft.

“The dark lightning, there’s not a whole lot you can do about it. The radiation is so penetrating—it goes through so many materials—that it would not be practical to shield people from it. A much better plan is to learn where it’s likely to be and do your best to stay away from areas like that.”

This is where Dwyer’s ongoing research comes in. Not only is he studying where dark lightning emanates, he also is assessing dispersal patterns, both of the bolts themselves and the high-energy particles they deliver.

Dwyer, who is 49 years old, is one of three FIT professors focused on lightning. He’s as surprised as anyone that he’s in what’s known as the “Lightning Group”; when Dwyer came to FIT in 2000, he was an astrophysicist.

“We’re in central Florida, a bit south of the Kennedy Space Center, and this is the lightning capital of the United States,” he said. “I’d been working on space instrumentation for several years, and that’s what I was hired to do.

“But when I got down here, I realized lightning is really cool, and I looked into it a bit and found lightning is really an unsolved problem in science. Very few people are working on it, and there’s a whole bunch of big questions on it. Eventually I shifted over to lightning and did less and less space physics.”

That required a bit of “retooling”—taking his physics background and applying it to a new field with additional study. It took two years, and he slid into his new niche.

“I was lucky that what I was interested in doing was seeing if lightning would emit X-rays,” Dwyer said, “and the reason I wanted to do that was I had been working with X-ray detectors for space missions, doing X-ray and gamma-ray astronomy. … Just right off the bat we established that lightning emits X-rays, which wasn’t known before then, and it got me in the field with a big splash.”

The dark-lightning discovery came during later research, a few years ago, while he was working with computer simulations of thunderstorms.

“The software was working very nicely, but it started doing something unexpected,” Dwyer said. “We began seeing discharges that involved gamma rays and high-energy particles, electrons and positrons, all this exotic stuff.

“We eventually figured out this was explaining perfectly these gamma-ray bursts that had been seen from thunderstorms by spacecraft. … Then we had the additional revelation that this was producing some of the biggest discharges within thunderstorms, which people had measured with radio waves.

“So it started out as a theoretical idea that began fitting more and more of the observations, and it all kind of clicked together: Wow, this is a new form of lightning!”

The name “dark lightning” is modeled on the physics term “dark matter”—material in space that cannot be seen with telescopes and also first came to light, so to speak, as a theory.

Dwyer since has constructed detectors for dark lightning, and his research continues.

“It’s really amazing that something as common as thunderstorms could still be hiding something like dark lightning from us,” Dwyer said. “You have to wonder what else is up there that we don’t know about.”