GAMMA RADIATION FROM RAPIDLY ROTATING BLACK HOLES

Image: This artist's impression illustrates how high-speed jets from supermassive black holes would look. These outflows of plasma are the result of the extraction of energy from a supermassive black hole’s rotation as it consumes the disc of swirling material that surrounds it. Credit: NASA, ESA, M. Chiaberge (STScI)

The radiation from an active galactic nuclei (AGN) is believed to be a result of accretion of mass by a supermassive black hole at the centre of its host galaxy.

In a recent paper (Hirotani et al., 2016 ApJ) the authors demonstrate that electrons and positrons created by photon collisions near a rotating black hole are accelerated in the opposite direction by the electric field present near the event horizon. This electric field acts as a particle accelerator (or gap) and dissipates a part of the hole’s rotational energy. The resultant gamma-ray luminosity increases with decreasing plasma accretion from the surroundings.

The authors show that in the case of extremely rotating supermassive black-holes, the gap can reproduce the very high energy (VHE) gamma ray flux observed is some active galactic nuclei.

▪ Hirotani & Pu, 2016 ApJ - Energetic gamma radiation from rapidly rotating black holes (arXiv)

▪ Supermassive black holes - HST

Comments

A SIGNIFICATIVE FRACTION OF BARYONS RESIDE IN THE FILAMENTS OF THE COSMIC WEB

(Credit: NASA, ESA, and E. Hallman (University of Colorado, Boulder) Observations of the cosmic microwave background indicate that baryons (protons, neutrons, etc., - the ordinary matter just to understand) occupies only 5% of the total energy content of the Universe (95% is dark matter and dark energy). However in the local universe approximately half of this "ordinary" matter it has never been observed.

A UNIVERSE WITHOUT A CENTER?

Image Credit: Eugenio Bianchi, Carlo Rovelli & Rocky Kolb. According to the standard theories of cosmology, there is no center of the universe. In a conventional explosion, material expand out from a central point and the instinct suggests that with the Big Bang happened something similar. But the Big Bang was not an explosion like that at all: it was an explosion of space, not an explosion in space . The Big Bang happened everywhere in the Universe.

A Sapphire Super-Earth

Twenty-one light years away, in the constellation Cassiopeia, a planet by the name of HD219134 b orbits its star with a year that is just three days long. With a mass almost five times that of Earth, it is what is known as a super-Earth. Unlike our planet, however, these super-Earths were formed at high temperatures close to their host star and contain high quantities of calcium, aluminum and their oxides – including sapphire and ruby. HD219134 b is one of three candidates likely to belong to a new, exotic class of exoplanets. These objects are completely different from the majority of Earth-like planets. They have 10 to 20 percent lower densities than Earth. Researchers looked at different scenarios to explain the observed densities. For example, a thick atmosphere could lead to a lower overall density. But two of the exoplanets studied, 55 Cancri e and WASP-47 e, orbit their star so closely that their surface temperature is almost 3,000 degrees and they would have lost this ...

SpaceTime

Search This Blog