Black Hole's Secrets Revealed

Many galaxies have super-massive black holes at their core, which expel powerful jets of particles at nearly the speed of light. Using the National Radio Astronomy Observatory's very long baseline array, scientists recently confirmed the leading theory, according to which the particles are accelerated by tightly-twisted magnetic fields close to the black hole.

Just how the powerful particle jets are emitted from black holes was one of the big mysteries of astrophysics. The confirmation of the leading theory, according to which the particles are accelerated by magnetic fields, required an elusive close-up view of the particle jet's inner throat. Astronomers managed to observe the material winding in a corkscrew outward path thanks to the high resolution of the National Radio Astronomy Observatory's very long baseline array (VLBA), an observation that supports the magnetic field theory.

The international team studied a galaxy named BL Lacertae (BL Lac), situated some 950 million light-years away from Earth. BL Lac is a blazar, the most energetic type of black-hole-powered galactic core. Super-massive black holes in galaxies' cores power jets of particles and intense radiation in similar objects, including quasars and seyfert galaxies. The scientists chose to focus on the BL Lacertae Galaxy because of the high rate in which the phenomena occur in that region.

According to the theory, the phenomena occur in stages. When material is pulled inward towards the black hole, it forms a flattened, rotating disk, called an accretion disk. As the material moves from the outer edge of the disk inward, magnetic field lines perpendicular to the disk are twisted, forming a tightly-coiled bundle. Astronomers believe that this 'bundle' propels and confines the ejected particles. Closer to the black hole, space itself, including the magnetic fields, is twisted by the strong gravitational pull and rotation of the black hole, causing the emission of the particles.

Theorists have several predictions concerning material and light in these situations. The first speculation is that material moving outward in this close-in acceleration region will follow a corkscrew-shaped path inside the bundle of twisted magnetic fields. The second prediction is that light and other radiation emitted by the moving material will brighten when its rotating path is aimed most directly towards Earth.

When the team observed an outburst from BL Lac, Alan Marscher of Boston University, who led the team, said that: "That behavior is exactly what we saw." During the numerous observations, the astronomers noticed that as the material sped out from the neighborhood of the black hole, the VLBA could pinpoint its location. Other telescopes measured the properties of the radiation emitted from the knot. It appears that the theories are very precise: bright bursts of light, X-rays, and gamma rays occurred when the knot was at the exact locations predicted by the theories. In addition, the alignment of the radio and light waves (a property called polarization) rotated as the knot wound its corkscrew path inside the tight throat of twisted magnetic fields. According to Marscher, this observation gave the researchers an unprecedented view of the inner portion of one of these jets, and therefore, they gained information critical to the understanding of how these particle accelerators work.

Obviously, the researchers were excited about the new discovery. "We have gotten the clearest look yet at the innermost portion of the jet, where the particles actually are accelerated, and everything we see supports the idea that twisted, coiled magnetic fields are propelling the material outward," Marscher said. It is evident that this is a major advance in the understanding of a remarkable process which occurs throughout the Universe.

TFOT has reported on images of the Triangulum Galaxy, which were captured during over 11 hours of exposure time, and on the discovery of the building blocks of life in space, made using NASA's Spitzer Space Telescope. Other related TFOT stories are the detection of the largest known comet outburst and a new explanation of the way the Peruvian Meteorite made it to Earth, given by an expert in extraterrestrial impacts from Brown University.