Sparks created in a lab give off X-rays, scientists announced Monday.
Researchers at Florida Institute of Technology brought their equipment, which had detected X-rays in lightning, into the lab. Half the team expected to see X-rays and the other half did not.
In sparks of 1.5 million to 2 million volts, the researchers indeed recorded X-rays that were remarkably similar to those produced by lightning.
"This amazed us. It opens the door to answering really big questions about lightning by generating it in the lab," said team member Hamid Rassoul. "It also tells us that we have a lot to learn about how even small sparks work."
X-rays are a form of electromagnetic radiation, on a spectrum that runs from radio waves on the low end to gamma rays on the high end and includes visible light, too.
Scientists don't know why lightning spawns X-rays. They theorize it involves a "runaway breakdown" of the air, in which electrons escape their normal bonds and gain very large energies.
"We didn't think [X-rays] could be made so easily in the air," said study leader Joseph Dwyer. "The results should allow for the detailed laboratory study of runaway breakdown, a mechanism that may play a role in thunderstorm electrification, lightning initiation and propagation, and terrestrial gamma-ray flashes."
The discovery is published in the journal Geophysical Research Letters.