X-Ray Lasers Create ‘Atomic Black Hole’

An atom in a molecule has been transformed into an electromagnetic black hole by a super-bright X-ray pulse. The new findings are published in the journal Nature.

Intense X-ray pulse removing electrons from atoms, creating a molecular black hole. Photo credits: DESY/Science Communication Lab.

What is a ‘molecular black hole’? It is basically an atom that has been X-rayed—a simple atom forming part of a molecule, namely methyl iodide, also known as iodomethane (CH3I), turned into a ‘black hole’ with the free electron laser LCLS. The resulting product (the X-rayed atom) draws in electrons from its surroundings with its electrical charge just like its space counterpart does with matter. This causes the molecule to explode in the space of a fraction of a second.

The CH3I molecules were exposed to intense X-ray light whose pulses were of great intensity: 100 quadrillion kilowatts per square centimetre. The powerful X-rays removed 54 of the 62 electrons of the molecule, resulting in one with a positive charge 54 times its normal charge. The process whereby electrons are either lost or gained is known as ionisation, and the one achieved in this study is deemed to be of the highest level ever achieved using light, says co-author Robin Santra, a Deutsches Elektronen-Synchrotron (DESY) scientist working at the Center for Free-Electron Laser Science (CFEL).

The ionisation occurs in stages within the CH3I molecule; the latter consists of a carbon atom and 3 hydrogen atoms, forming the methyl group, and an additional iodine atom. The X-ray pulse first removed 5 or 6 electrons from the iodine atom which now bears a strong positive charge upon having lost so many electrons. This allows the iodine atom to snatch away electrons from the methyl group (CH3)—a phase that happens in an ‘atomic black hole’ manner—in less than trillionth of a second. During this time, the electrons are sucked in, and then catapulted in the opposite direction by the same pulse, which sets in motion a chain of reactions that cause 54 of the 62 electrons to be removed. The super-high positive charge that accumulates in a small space (a ten-billionth of a metre) ultimately rips the molecule apart, explains DESY’s Daniel Rolles (co-author).

According to the researchers, the force acting on the electrons is much larger than that existing around an astrophysical black hole of ten solar masses.

“The gravitational field due to a real black hole of this type would be unable to exert a similarly large force on an electron, no matter how close you brought the electron to the black hole,” says Santra.

The findings are believed to be pertinent to the analysis of biomolecules using X-ray lasers. The facilities accommodating for these experiments generate extremely high-intensity X-rays. Complex molecules are examined in X-ray free-electron lasers (XFEL), and one of the purposes of this field of research is to determine the atomic spacial structure of complex molecules—data that is hoped to help researchers like biologists to unveil the precise mechanism of processes involving biomolecules.

Iodomethane has been chosen for this study because it is a relatively simple molecule to be used as model to understand the damage radiation does to organic compounds, explains co-author Artem Rudenko.

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