Powerhouse Astronomy: Blazing black hole from the early universe

A jet of matter and radiation shooting from a newly discovered black hole could provide new information about the radiation left over from the Big Bang and about the first galaxies. This monster black hole, one of the heaviest and most distant known, was already gargantuan when the universe was only a billion years old.

MONSTER JET. Artist’s depiction of a blazar spewing from a black hole. M. Weiss/CXC

Estimated to weigh as much as 10 billion suns and residing 12.5 billion light-years from Earth, the black hole powers the oldest known blazar, a rare class of quasar in which a jet of particles and light points toward Earth. Many blazars also generate high-energy radiation, but X rays and gamma rays from the newfound blazar would have special significance. Such energetic emissions would provide a novel searchlight on the early universe, says Roger W. Romani of Stanford University in Palo Alto, Calif. He and his colleagues describe their finding in an upcoming Astrophysical Journal Letters.

The astronomers found the blazar while using the Very Long Base Array, a continent-wide array of 10 radio telescopes, to search for telltale radio emissions. To determine the blazar’s distance, the team then took visible-light spectra with the Hobby-Eberly Telescope in Fort Davis, Texas.

The team proposes to use NASA’s Chandra X-ray Observatory to look for X rays beaming from the body, known as Q0906+6930. Theoretical models suggest that most of the X rays from this remote blazar are created when high-speed electrons in the jet collide with the sea of cosmic background photons left over from the Big Bang.

The collisions boost the photons’ energy up to X-ray levels. The intensity of the X rays depends on the density of cosmic background photons that existed a billion years after the Big Bang, Romani says.

By using cosmological models to estimate the density of the background photons from the X-ray data, researchers can deduce the composition and energies of the charged particles in the high-speed jet. They can also investigate how the black hole boosted the particles to such high energies.

Gamma rays from Q0906+6930 should tell yet another story, but it will have to wait for a telescope that’s scheduled for launch in 2007. Gamma rays that collide with lower-energy radiation sometimes vanish, leaving pairs of electrons and positrons in their wake. Because a gamma-ray spectrum reveals how much of this high-energy radiation is absorbed, it provides a tally of the lower-energy photons generated by all the galaxies that lie between the distant blazar and Earth, says Romani.

By comparing this spectrum with spectra from blazars that lie closer to Earth, astronomers can infer the brightness of galaxies around the time that the remote blazar formed, notes Richard Mushotzky of NASA’s Goddard Space Flight Center in Greenbelt, Md. That time is of special interest because some of the first galaxies lit up the cosmos then, notes Romani.

The remote blazar is also intriguing because its black hole dates back to just a billion years after the birth of the universe, he adds. Other teams, observing quasars that existed even earlier, have found black holes of similar mass. Theorists are paying close attention to these observations, and current models of black hole formation are consistent with the data so far, says Avi Loeb of Harvard University.

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