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In astrophysics, accretion is the accumulation of particles into a massive object by gravitationally attracting more matter, typically gaseous matter, into an accretion disk. [ 1 ] [ 2 ] Most astronomical objects , such as galaxies , stars , and planets , are formed by accretion processes.
Accretion disk jets: Why do the disks surrounding certain objects, such as the nuclei of active galaxies, emit jets along their polar axes? These jets are invoked by astronomers to do everything from getting rid of angular momentum in a forming star to reionizing the universe (in active galactic nuclei), but their origin is still not well understood.
Walter Hendrik Gustav Lewin (born January 29, 1936) is a Dutch astrophysicist and retired professor of physics at the Massachusetts Institute of Technology.Lewin earned his doctorate in nuclear physics in 1965 at the Delft University of Technology and was a member of MIT's physics faculty for 43 years beginning in 1966 until his retirement in 2009.
The magnetorotational instability (MRI) is a fluid instability that causes an accretion disk orbiting a massive central object to become turbulent.It arises when the angular velocity of a conducting fluid in a magnetic field decreases as the distance from the rotation center increases.
The Blandford–Znajek process is a mechanism for the extraction of energy from a rotating black hole, [1] [2] introduced by Roger Blandford and Roman Znajek in 1977. [3] This mechanism is the most preferred description of how astrophysical jets are formed around spinning supermassive black holes.
These are cataclysmic variables both of whose components are white dwarfs; the accretion disc is composed primarily of helium, and they are of interest as sources of gravitational waves. SW Sextantis: These are like dwarf novae but have the accretion disc in a steady state, so do not show outbursts; the disc emits non-uniformly.
They likely arise from dynamic interactions within accretion disks, whose active processes are commonly connected with compact central objects such as black holes, neutron stars or pulsars. One explanation is that tangled magnetic fields are organised to aim two diametrically opposing beams away from the central source by angles only several ...
AGN research encompasses observational surveys to find AGN over broad ranges of luminosity and redshift, examination of the cosmic evolution and growth of black holes, studies of the physics of black hole accretion and the emission of electromagnetic radiation from AGN, examination of the properties of jets and outflows of matter from AGN, and ...