Download Accretion as a Source of Energy

Accretion as a Source of Energy
cataclysmic variables
accretion energy
For the nineteenth century physics, gravity was the only conceivable source of
energy in celestial bodies, but gravity was inadequate to power the Sun for its
known lifetime. In contrast, in the latter half of the twentieth century it is to
gravity that we look to power the most luminous object
Some simple order-of-magnitude estimates. For a body of mass M and radius
R* the gravitational potential energy released by the accretion of a mass m on
its surface:
For comparison, consider the energy extracted from the mass m by nuclear
fusion reactions (conversion of H into He):
Accreting Objects
It is useful to express the accretion luminosity in terms of typical orders of
magnitude:
where we have used
x-ray binaries
x-ray binary
The Emitted Spectrum
We can now make an order of magnitude estimate of the spectral range of
emission from compact objects:
Finally we define a temperature that the accreted material would reach of its
gravitational potential energy were turned entirely into thermal energy.
In general, the radiation temperature may be expected to lie between the
thermal and black body temperatures:
neutron stars
Accretion Powered Objects
accretion onto a magnetized star
white dwarfs
accretion onto a magnetized WD
stellar mass black holes
the role of viscosity
the role of viscosity
supermassive black holes
supermassive black holes
galactic center
galactic center
galactic center
Z.-Q. Shen and K. Y. Lo
he first 86 GHz VLBI image of Sgr A* made with the VLBA in November 20
mly weighted image (beam: 1.11 mas×0.32 mas at 9◦ ). Right: a super-resolu
circular restoring beam of 0.20 mas. Note the different scales.