Accretion is the process of accumulation of mass on an object. It is an important process in the understanding of the universe. Accretion takes place in young starts to supermassive black holes in the universe. When materials accrete onto massive energy, there is a creation of potential gravitational energy which is usually converted to radiation through magneto-hydrodynamic friction thus accretion is a source of energy. The accreting material often forms a rotating thin disk due to the angular momentum it conserves. Accretion is more efficient than nuclear fusion which powers stars like the sun. Accretion on compact objects like the black hole is greater than fusion as it is estimated to be more than 20 times greater than fusion. Maximum accretion rate is given by, Eacc=GMm/R.Energy realized through accretion increases with mass accumulated on an object comparing to the size of an object whereby the smaller the size of the object the greater the energy released. There is, however, a limit to how much radiation is released referred to as Eddington Limit where the inwards gravitational force must always be greater than the outward radiation pressure otherwise the whole accreted object blows up.
Accretion is most powerful on compact objects including the black hole and Neutron star. Black holes come in several ‘flavors.’There is black holes formed on supernovae called stellar-mass black holes, and there are those found at the center of galaxies called supermassive black holes. Accretion of gas onto a black hole can shine light from the central region which is usually referred to as Quasars.
Black holes are the center of all major galaxies. There are different galaxies containing blackholes. One of them is Stellar-Mass Black hole which forms in a supernova explosion as the life of massive star ends. It is usually found in a binary system where matter can be accreted from the companion star. Another black hole is neutrons starts which are mostly made of neutrons and may contain exotic matter at the center. Similar to the stellar mass black hole, the neutron can be found in binary systems, and it can also accrete matter from a companion star.
Accreting black holes can be seen from an electromagnetic spectrum in sky optic.X-ray, and optical studies show that, of all-sky X-ray images, the brightest X=ray sources in the sky are accreted black holes or neutrons.Cackett’s research uses x- ray observations with instruments like Chandra, Suzaku and Swift in studying the process of accretion of the black hole in the binary system. The black holes accretion observed include stellar-mass black holes or neutron stars and Active Galactic Nuclei. Further, the research uses an X-ray reverberation mapping. In this map, echoes of light map the inner regions of a supermassive black hole. The analogy used is tidal disruptions. When a star falls into a black hole, its life ends. Scientists catch stellar materials into the spinning disc formed outside the black hole. This behavior is observed using the new X-ray technology.
Accretion power has therefore been observed as the most powerful as compared to nuclear fusion something that has been proved by scientist through X-ray and optic studies as the only observable X-ray sources are those of accreted black holes. Time scales and energy dependence on reverberations of high frequency show that most signals originate from close to black holes objects. If these signals are studies in future, then X-rays reverberation mapping will be carried out closest to black holes.