miércoles, 2 de noviembre de 2011

Astrophysics - The Brightest Lights in the Universe --Black-Hole Powered Quasars


Movement of black holes power the persistent lights in the universe. Black holes not only spin, they can also move laterally across their host galaxy. And according to astrophysicists at Brigham Young University, both types of movement power massive jets of energy known as quasars. One black hole in the galaxy Centauras A propels radiation in a jet measuring 1 million light-years long.

These spectacular jets stream out of galaxies that contain discs of debris and gas, the remnants of stars ripped apart by the force from black holes.

"The black hole is like a generator spinning around in these magnetic fields," said BYU professor David Neilsen, lead author of the study. "The way the field lines get twisted around and pulled by the spinning black hole creates electromagnetic tension that gets turned into radiation and energy that goes out."

The spin of black holes has been believed to play a role since the idea was put forward in 1977. The new study confirms this theory while also introducing a totally new component: that a black hole's lateral movement also powers these jets.

"Rotational kinetic energy contributes, but the simple movement like a billiard ball can also contribute to this," said BYU professor Eric Hirschmann, a co-author of the study. "The two processes don't compete with each other, they combine with each other to give you the overall energy that streams away from the black hole."

In other words, the biggest and brightest quasars could come from black holes that both spin fast and traverse their host galaxy at high speeds.

The XMM-Newton satellite has produced a strong Gamma ray image of the Geminga neutron star just 500 light years beyond the Solar System shown at top of the page. This smallest imaged star is about 20 km (12 miles) in diameter and has a mass 1.5 times that of the Sun. It rotates at a speed of 4 revolutions per second. Its hot surface exudes strong X-rays and Gamma rays, some extending out as filaments (tails), being driven by its huge magnetic field. Electrons and positrons are also a part of the filament, the result of the electric field built by the rotation of the star within its magnetic field. The electrons accelerate outward but some evidence shows that the positrons are coaxed back to the star to settle into hot spots.
The image at top of page shows quasar 3C279, a nondescript, faint, starlike object in the visible sky. Yet, in June of 1991 a gamma-ray telescope onboard NASA's orbiting Compton Gamma Ray Observatory unexpectedly discovered that it was one of the brightest objects in the gamma-ray sky. Shortly after this image was recorded the quasar faded from view at gamma-ray energies, more than 10,000 times more energetic than visible light. Astronomers are still trying to understand what causes these enigmatic objects to flare so violently. Another quasar, 3C273, is faintly visible above and to the right of center.

Image credit: NASA, CGRO, EGRET team.

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