When German physicist Wilhelm Röntgen pioneered the use of x-rays 115 years ago—as celebrated today with a 115th-anniversary Google doodle—he couldn't have imagined the uses they'd be put to a century later.
(See x-rays turned into art by photographer Nick Veasey.)
On November 8, 1895, Röntgen (also spelled "Roentgen") was experimenting with vacuum tubes when he produced and detected the previously unknown type of radiation.
A few days later Röntgen made the first medical x-ray image in history by taking a picture that clearly revealed the bones of his wife's hand.
Medical imaging is still the best known use of x-rays, but scientists and engineers have devised a host of new uses for this uniquely penetrating form of light.
Astronomers, for example, were quick to grasp the potential of x-rays in their field. But it wasn't until 1949 that scientists strapped small Geiger counters to a captured German V-2 missile—with a peak altitude of about 50 miles (80 kilometers)—and the field of x-ray astronomy was born.
"What made [x-ray astronomy] possible was the ability to put instruments in space, because x-rays get absorbed by the atmosphere and don't reach the ground," said Leon Golub, an astrophysicist at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.
In that first experiment, scientists confirmed that our sun, and by extension all stars, emit x-rays. Stellar x-rays are emitted by superheated gas in the stars' atmospheres, or coronas.
So far, more than a dozen telescopes that detect x-rays have been launched into space. With their aid, astronomers have discovered sources of x-rays far beyond our solar system, including distant galaxies composed of trillions of stars, dying stars known as supernovae, stellar corpses called neutron stars and white dwarfs, and black holes.
While black holes themselves emit no light, their immediate environments are often so turbulent that they shine brightly with x-rays.
"What seems to be happening is that black holes accumulate large disks of infalling matter around them," Golub explained. (Find out how x-rays are unlocking black hole mysteries.)
"As that matter swirls around the black hole and spirals towards its center, it heats up, and the gas gets so hot that it becomes like the corona [of a star] and it produces x-rays."
(Read more on what x-rays have done for astronomy.)
X-Rays Turned Into Lasers
Since Röntgen's days, scientists have also learned to manipulate x-rays in a variety of nonmedical ways.
For example, a new multimillion-dollar machine at the SLAC National Accelerator Laboratory at California's Stanford University can combine x-rays into a laser beam similar to visible-light lasers.
Unlike regular lasers, though, laser bursts made from x-rays are so bright and so brief that they should allow researchers to create ultrafast stop-motion movies of natural phenomena that have never before been seen clearly.
For example, until now the formation and breakage of molecular bonds by atoms was essentially a blur to scientists. But with x-ray lasers, biological reactions—such as photosynthesis, which plants use to convert sunlight into energy—could theoretically be visualized one step at a time.
"With x-ray lasers," said SLAC senior scientist Uwe Bergmann, "you can study things on the time scale of molecules and chemical reactions."
X-Rays Expose Invisible World
Scientists are also combining x-rays with microscopy to pioneer new ways of visualizing cellular structures and microorganisms.
A light microscope's resolution is dependent on the wavelength of the light being used.
Because x-rays have much smaller wavelengths than visible light, they can be used to image objects that are up to ten times smaller than what can be resolved using traditional microscopy, explained Martin Richardson, a professor of optics at the University of Central Florida, whose group has been helping to pioneer x-ray microscopy for biological studies since the early 1990s.
(Related pictures: "'Invisible' Ancient Bugs Seen by Hi-Tech X-Rays.")
"Although Röntgen discovered x-rays 115 years ago," Richardson said, "x-ray science is very far from a dead science."
More on X-Rays