Radiation Pressure

Minute pressure exerted by electromagnetic radiation (such as but not limited to light from the sunOur parent star. The structure of Sun's interior is the result of the hydrostatic equilibrium between gravity and the pressure of the gas. The interior consists of three shells: the core, radiative region, and convective region. Image source: http://eclipse99.nasa.gov/pages/SunActiv.html. The core is the hot, dense central region in which the) on everything it encounters. This can be thought of as the transfer of momentum from photons as they strike the surface of the object. In the environs of stars such pressure can become important given the vast quantities of photons emitted. Under the essentially blackbodyIdeal object that is a perfect absorber of light and also a perfect emitter of light. A perfect black body will absorb all radiation that falls on it, and will emit radiation that has a continuous spectrum determined only by the temperature of the black body: Where, T is the Click on Term to Read More conditions that exist inside a starSelf-luminous object held together by its own self-gravity. Often refers to those objects which generate energy from nuclear reactions occurring at their cores, but may also be applied to stellar remnants such as neutron stars., radiation pressure is proportional to the fourth power of temperature via the equation:

where T = temperature, σ = Stefan-Boltzmann constant, and c = speed of lightSpeed at which electromagnetic radiation propagates in a vacuum. Although referred to as the speed of light, this should be more properly called the 'speed of a massless particle’ as it is the speed at which all particles of zero mass (not only photons, but gravitons and massless neutrinos if. Consequently, a small increase in temperature results in a large increase in the radiation pressure.

Most main sequence stars, which have internal temperatures of millions of degrees, are primarily supported against gravityAttractive force between all matter - one of the four fundamental forces. Click on Term to Read More by gas pressure although radiation pressure does contribute a few percent. The internal temperatures of massive stars are hundreds of times higher and, at these extreme conditions, radiation pressure begins to dominate. In the most massive stars, the mass of the star is supported against gravity primarily by radiation pressure, which ultimately sets the upper limit for how massive a star can become.

Other astronomical objects are also influenced by radiation pressure. The pressure from solar photons creates the dust tails of comets within our Solar SystemThe Sun and set of objects orbiting around it including planets and their moons and rings, asteroids, comets, and meteoroids.. Radiation pressure plays a vital role in the formation of planetary nebulaeAn immense interstellar, diffuse cloud of gas and dust from which a central star and surrounding planets and planetesimals condense and accrete. The properties of nebulae vary enormously and depend on their composition as well as the environment in which they are situated. Emission nebula are powered by young, massive Click on Term to Read More: as the dying star contracts into a white dwarfRemnant of a star with mass <8 Msun. White dwarfs have masses <1.4 Msun (the Chandrasekhar mass) and are supported by electron degeneracy pressure. White dwarfs have radii ~Rearth (<0.02 Rsun) and densities ~105-6 g/cm3. No nuclear fusion or gravitational contraction occurs in white dwarfs, they shine by residual heat., it releases vast amounts of heat. This radiation pressure is so strong that the outer layers of the star are pushed out to form the surrounding gaseous nebulaAn immense interstellar, diffuse cloud of gas and dust from which a central star and surrounding planets and planetesimals condense and accrete. The properties of nebulae vary enormously and depend on their composition as well as the environment in which they are situated. Emission nebula are powered by young, massive Click on Term to Read More. Similarly, a giant star ejects material and gas into the interstellar mediumMaterial between the stars, consisting of gas, dust and cosmic rays (high energy charged particles moving at nearly the speed of light). It comprises ~10% of visible matter in the disk of our Galaxy (Milky Way). Until recently it was generally assumed that silicates in the ISM were amorphous, but Click on Term to Read More through radiation pressure.