Astrophysics (index)about


(quantum of light, i.e., light as a particle)

A photon is a particle of light (electromagnetic radiation), i.e., what you call such a particle if light is considered a stream of particles. It is the quantum of light, the minimum possible amount. The photon theory, i.e., the modern particle theory of light, is that the minimum amount of light depends upon the light's wave frequency. Dating from prior to photon theory, there has been a very successful theory that EMR consists of waves, as summarized by Maxwell's equations. Photon theory coexists because it is successful in modeling some light/matter interactions that the wave theory does not.

Photons are elementary particles (a type of boson) according to current particle physics, interacting with other particles. They naturally travel "the speed of light". As implied above, photon has an associated "light-wave frequency" and carries an amount of energy proportional to that frequency.

Phenomena successfully modeled with photon theory includes the interaction of light with atoms and electrons, such as absorption, emission and scattering. The first such instance for photon theory was the photoelectric effect, i.e., that ionization by incoming EMR does not simply depend upon the total light energy striking the atoms, but more basically on the light's frequency, which Einstein explained as suggesting only those quanta of light carrying sufficient energy to free an electron from the atom were successful ionizing such an atom.

(physics,quantum mechanics)

Referenced by:
astronomical quantities
atomic excitation
Balmer jump
baryon acoustic oscillations (BAO)
Bohr model
Bose-Einstein statistics
cosmic microwave background (CMB)
CMB lensing
CMB polarization
CNO cycle
column density
Compton scattering
continuous absorption
continuum emission
cooling function
cosmic rays (CR)
Cherenkov Telescope Array (CTA)
dark matter
dark matter annihilation
de Broglie wavelength
Doppler broadening
electron degeneracy
electron orbital
electron scattering
epoch of reionization (EOR)
escape fraction
gamma rays
High-altitude Water Cherenkov Observatory (HAWC)
ionized hydrogen (HII)
HII region (HII)
hydrogen (H)
line blanketing
Lyman series
Lyman-Werner photon
mean free path
neutrino (ν)
optical depth (τ)
oscillator strength
pair production
photodissociation region (PDR)
photon counting
photon noise
Planck constant (h)
power law
Poynting-Robertson effect
Poynting vector (S)
pressure integral
pulsar (PSR)
quantum mechanics (QM)
quantum number
random walk
Rayleigh scattering
equation of radiative transfer (RTE)
spectral energy distribution (SED)
superluminous supernova (SLSN)
spectral power distribution (SPD)
spin (ms)
synchrotron self-Compton (SSC)
standard model
state of excitation
Strömgren sphere
synchrotron radiation
Sunyaev-Zel'dovich effect (SZ effect)
thermodynamic equilibrium (TE)
Thomson scattering
ultra-high-energy gamma rays (UHEGR)
very-high-energy gamma rays (VHEGR)
vegetation red edge (VRE)
wave-particle duality