More clues in the cosmic jet mystery
Traveling at near light speed, powerful jets shoot out of the centers of some galaxies. Astronomers think they are a primary way matter and energy are redistributed throughout the universe. They would love to know how these speedy wonders work. Speculation and computer simulations have yielded few clues. Now, with the help of sharp-eyed satellites, investigators are starting to find out what these jets are made of.
Earlier this month, Rita Sambruna of the Goddard Space Flight Center in Greenbank, Md., told a meeting of the American Astronomical Society in San Francisco that the jets appear to contain electrons and protons. A team from Goddard and Italy's Merate Observatory had used the Swift X-ray observing satellite to look down the throats of two such jets from objects 10 billion light-years away. Their work does not explain how the jets form. "But at least we now have a solid idea of what they're made of," Dr. Sambruna said.
Those electrically charged particles add up to a lot of matter. At any one time, the jet holds a mass equal to that of a planet the size of Jupiter. That is "an enormous amount of energy" being shot out of the galaxy, notes Fabrizio Tavecchio at Merate. What's more, "this is happening throughout the universe," he says.
That cosmic cannonade presents what Sambruna calls "one of the great paradoxes of astronomy." The jets are ejected from galaxy centers that harbor massive concentrations of material mass. Mostly these are black holes – objects so condensed that nothing that enters them can ever escape their strong gravity. How, then, can black holes with millions or even billions of times the mass of our sun be shooting planet-size masses hundreds of thousands of light-years into intergalactic space? That's the puzzle astronomers have finally begun to solve.
It is starting to look like a system in which magnetism is the guiding force. Two research teams – one centered at Yale University in New Haven, Conn., the other at Britain's University of Southampton – have used data from three NASA satellites and from ground-based radio telescopes to study one black-hole jet system. It's an object called 3C273. With that range of instruments, they studied the jet in radio, infrared, visible light, and X-ray radiation – virtually the entire electromagnetic spectrum. They found the jet's strong radiation is coming from electrically charged particles spiraling around lines of magnetic force. This can kick out material surrounding the black hole before the black hole can swallow it.
The picture that is emerging is one in which magnetic forces accelerate electrically charged particles and guide their flight. This process can produce a tightly collimated beam of near light-speed particles. A lab-size simulation of at least some aspects of such cosmic jets has been produced by Paul Bellan's team at the California Institute of Technology in Pasadena. The apparatus sends an intense electric current through a gas while it's surrounded by a magnetic field. Out shoots a tightly collimated filament.
After decades of speculation, astrophysicists now are beginning to get some hard facts and suggestive leads with which to pursue the cosmic jet mystery. Sherlock Holmes warned that it is a capital mistake to theorize before getting relevant facts. Cosmic jet sleuths now are in position to take his advice.