‘Black Hole’ Created by Strongest Ever X-Ray Laser

If you shine the world’s strongest X-ray laser at a small molecule, it will quickly destroy it. However, in the act of destruction, something fascinating happens: The radiation creates a runaway process where electrons are stripped away from neighboring atoms, in a bizarre phenomenon akin to a black hole, which scientists haven’t seen before.

As described in a study published May 31 in the journal Nature, physicists used the X-ray laser at the SLAC National Accelerator Laboratory in northern California to expose several molecules to a mighty beam of radiation. The power is hard to imagine, with an intensity 100 times more than what you would get if you took all the sunlight hitting the Earth and focused it on a spot the size of a thumbnail. In this instance, however, the X-ray laser was focused on a single iodine atom, bound to a molecule comprised of one carbon and three hydrogen atoms (a methyl group). This beam is tiny, roughly speaking one thousand times thinner than a human hair.

As expected, the physicists found, the X-rays began to strip away the iodine's electrons. This gave the atom a positive charge, as electrons are negatively charged. Then something surprising happened: The iodine atom, excited by the x-ray, began violently ripping electrons away from its attached methyl group. This is not something physicists have seen before, says Daniel Rolles, study co-author and assistant professor at Kansas State University.

molecular-black-hole Physicists have found that an intense X-ray beam knocks so many electrons out of an iodine atom (right) that it pulls in electrons from its attached methyl group (left), in a phenomenon akin to a molecular black hole. DESY/Science Communication Lab

The X-ray “generated a lot of charge inside the atom, and it sucks in everything around it,” Rolles says. “It doesn’t seem to stop” doing this, acting in a way like “a molecular black hole.”

In total, the X-ray lasered away 54 of the molecule's 62 electrons, giving it a charge 54 times what it would be in an unexcited state. This is the most extreme charge, or level of ionization, ever achieved using light, according to the researchers.

It should also be noted, though it can’t really be comprehended, that this happened within much less than a trillionth of a second, or 30 femtoseconds. To say “a blink of an eye” would be a gross error—the process could take place tens of billions of time before you could shut your eye and open it again. (As MIT News explains, one femtosecond is to one second as one second is to about 32 million years.)

The scientists note that the force exerted on the molecule’s electrons is larger than what would be experienced surrounding an astrophysical black hole of about 10 times the mass of the sun. Of couse, astrophysical black holes exert gravitional forces, whereas the phenomenon in this paper is electrochemical in nature, the researchers note.

"When, say, a star is close to a black hole, the gravitational pull of the black hole causes a transfer of matter [away] from the star," says Robin Santra, with the German Electron Synchrotron and professor at the University of Hamburg. "It is known that when this happens, not only is matter sucked into the black hole, but there is also the ejection of strong jets of matter away from the black hole. The situation we have observed is similar. The high-intensity x-ray pulse causes the iodine atom... to lose a considerable number of its electrons. The highly positively charged iodine atom now behaves like a black hole: It uses its extremely strong electric pull to suck in electrons from the rest of the molecule."

Rolles says the international team behind the study hope their work helps to better understand the molecular effects of the X-ray laser, which is used by other researchers to study the structure of proteins, viruses and other tiny things.

This is a useful and powerful technique, the only problem being that “when you do [it], you damage the structure you want to look at,” he adds. “Our study tries to quantify this radiation damage on the microscopic level.”

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