EMBARGOED FOR 2 pScientists are puzzling over the source and behavior of visible light coming from very near a black hole, and suggesting that the light may be generated by a process similar to one used in laboratories to create computer chips.
Black holes may be dark, but when they eat, they do so with vigor and a certain degree of slovenliness, dishing out bright radiation that turns their surroundings into beacons of observability. Most of this radiation is in the form of X-rays, which are spewed when matter, mostly gas, is superheated as it swirls inward and approaches the speed of light.
The X-rays are coughed up right near a black hole's lips, actually a sphere of no return called the event horizon. Once matter passes through the event horizon, it is trapped. Nothing, not even light, can escape the object's intense gravitational grip.
Visible light and other emissions are also sometimes detected coming from the suburbs of intense activity that surround black holes. There is a theory that explains how this visible light might be created, but it can't explain the observations of a new study.
. The black hole siphons its meals from a companion star as the two objects wing their way through space locked in an age-old gravitational dance.According to theory, the light could be what are known as reprocessed X-rays. As matter swirls inward, a large, flat "accretion" disk develops. X-rays coming from near the event horizon irradiate, or light up, the gas in the disk. The gas is heated and sometimes begins to radiate ultraviolet and visible light itself.
Typically, about 1 percent of a black hole's X-ray emissions are converted to UV or optical light in this manner, scientists say. But XTE J1118+480 produced much more UV and visible light than that, according to Hendrik Spruit, lead researcher on the study from the Max Planck Institut in Germany.
And the rapid increase of visible light, on the heels of the X-rays, also does not fit the theory of reprocessed light, he said.
So what's going on?
In an e-mail interview, Spruit said the light could be generated by a "cyclotron" process similar to one used in particle accelerators, as well as in a method for constructing computer chips. In a cyclotron, radiation is given off by electrons that move at high speed through a magnetic field.
"The new generation of chip-making devices in the electronics industry use cyclotrons for producing the far-UV radiation needed to image masks onto silicon," Spruit said. "The amount of radiation given off increases with the strength of the magnetic field and the energy of the electrons."
In such a scenario, the light coming from near the black hole would not be directly related to the X-rays, he said, but there is a connection. The X-rays appear to originate from a region near the black hole where other energy is flowing outward. The optical light is then produced by this outflow, but at a greater distance from the black hole, hence the delay.
The visible light is likely generated about 12,430 miles (20,000 kilometers) from the black hole's event horizon.
The whole process is not well understood. "Much of the study of these kind of X-ray sources in general aims at finding out how it works," Spruit said. Similar observations have been made at least twice before, in 1981 and 1997. But the data contained a lot of "noise" and the results where not clear.
"What made our observations special is the very good timing accuracy, and the large amount of data -- 2.5 hours at millisecond resolution," he said. "The effects we see stand out like sore thumbs."
Editor's Note: The black hole XTE J1118+480 was recently in the news when another research team determined its likely path, a 7-billion-year-old
advertisement
advertisement
