Black Hole Jets

An artist's conception of the blazar BL Lacertae at it spurts out jets of charged particles accelerated by corkscrew magnetic field lines.

CREDIT: Marscher et al., Wolfgang Steffen, Cosmovision, NRAO/AUI/NSF


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While we may never know what it looks like inside a black hole, astronomers recently obtained one of the closest views yet. The sighting allowed scientists to confirm theories about how these giant cosmic sinkholes spew out jets of particles travelling at nearly the speed of light.


Ever since the first observations of these powerful jets, which are among the brightest objects seen in the universe, astronomers have wondered what causes the particles to accelerate to such great speeds. A leading hypothesis suggested the black hole's gigantic mass distorts space and time around it, twisting magnetic field lines into a coil that propels material outward.


Now researchers have observed a jet during a period of extreme outburst and found evidence that streams of particles wind a corkscrew path away from the black hole, as the leading hypothesis predicts.

Astronomers combined the power of nine radio telescopes scattered across Earth's southern hemisphere to take the most detailed image yet of the jets. The team works under the TANAMI (Tracking Active Galactic Nuclei with Austral Milliarcsecond Interferometry) project.


The new image shows an area less than 4.2 light-years across, or shorter than the distance between our sun and its nearest star. The image resolution allows researchers to make out radio-emitting features as small as 15 light-years across. [Gallery: Black Holes of the Universe]


"Advanced computer techniques allow us to combine data from the individual telescopes to yield images with the sharpness of a single giant telescope, one nearly as large as Earth itself," said Roopesh
Ojha at NASA's Goddard Space Flight Center in Greenbelt,
Md.

The active galaxies appear to require a compact energy source of enormous strength. The most plausible candidate is a rotating, supermassive black hole of order a billion solar masses at their center. Until recently there has been strong circumstantial evidence to support such a mechanism. In the past few years evidence of much more direct nature has emerged.

Evidence for a Supermassive Black Hole in M87

The left portion of the following Hubble Space Telescope photograph shows the center of the giant elliptical galaxy M87, which is the 87th entry in the famous Messier Catalog. This galaxy is believed to contain a supermassive black hole of several billion solar masses at its center. The observations indicate that approximately 3 billion solar masses are concentrated in a region at the galactic core that is only about the size of the Solar System. The diagonal line across the right image is a jet of high-speed electrons approximately 6500 light years long that is probably being ejected from the galactic nucleus by the black hole located there.












<><> <><> Material cannot fall directly onto a black hole all at once. An active black hole has a disk or torus (doughnut) of gas and dust surrounding it which feeds the hungry black hole. Sometimes, not all of that material goes in and in an energetic process that is not yet fully understood, some of that material is blasted away from the black hole as high-speed, thin jets.
David Garofalo and his collaborators looked at the different types of active galaxies, those that have strong jets, those that have weak jets, and those that have no jets at all. Their model shows that black holes that are spinning in the opposite direction to the spinning disk around them can create powerful jets. These systems have a gap between the black hole and disk where powerful magnetic field can form which help drive the jets.