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

BOUNCING BLACK HOLES

Image: Illustration of a dusty supermassive black hole. Credit: ESA/NASA, the AVO project and Paolo Padovani Black holes could be bouncing stars as a consequence of quantum gravity: when the density of matter becomes high enough, quantum gravity effects generate sufficient pressure to compensate the matter's weight, the collapse ends, and matter bounces out. In a black hole, matter's collapse could stop before the central singularity is formed.

A DARK MATTER HALO AS SOURCE OF GAMMA-RAYS?

Image: Illustration of a dark matter halo around the Milky Way. Credit: ESO/L. Calçada. The gamma-ray source 3FGL J2212.5+0703 shows evidence of being spatially extended. In a recent paper (Bertoni et al. 2016) the authors use a large sample of active galactic nuclei and other known gamma-rays sources as a control group, confirming, as expected, that statistically significant extension is rare among such objects. They argue that the most likely (non-dark matter) explanation for this apparent extension is a pair of bright gamma-ray sources that serendipitously lie very close to each other, and estimate that there is a chance probability of ~2% that such a pair would exist somewhere on the sky. If a gamma-ray source without detectable emission at other wavelengths were unambiguously determined to be spatially extended, it could not be explained by known astrophysics, and would constitute a smoking gun for dark matter particles annihilating in a nearby subhalo. The authors...

Atmospheric Beacons Guide NASA Scientists in Search for Life

Beacons of life could help researchers identify potentially habitable worlds. Credits: NASA’s Goddard Space Flight Center/Mary Pat Hrybyk Some exoplanets shine brighter than others in the search for life beyond the solar system. New NASA research proposes a novel approach to sniffing out exoplanet atmospheres. It takes advantage of frequent stellar storms — which hurl huge clouds of stellar material and radiation into space — from cool, young dwarf stars to highlight signs of habitable exoplanets. Traditionally, researchers have sought potential biosignatures as ways of identifying inhabited worlds: byproducts from life as we know it such as oxygen or methane that over time accumulate in the atmosphere to detectable amounts. But with current technology, according to Vladimir Airapetian, lead author of a Nature Scientific Reports study published on Nov. 2, 2017, identifying these gases on distant terrestrial exoplanets is time-consuming, requiring days of observation time. The ne...

SpaceTime

Search This Blog