Light from our Universe Flashcards
Radiation from the Universe
Energetic sub-atomic particles or wave traveling outward from a source
Particle with mass
- Cosmic rays
Radiation with no mass
- Light: electromagnetic (EM)
- Gravitational waves
Light as Observed
Carrying energy: Sunlight warms up the Earth
Travel at a constant speed
Can be absorbed/emitted
Travel at a straight line
- can bend when going into water
- can reflect/diffract/interfere
Light as EM Wave
Travel at v= c in vacuum
Carrying Energy
Frequency: π= c/π
Used to describe low-energy radio, infrared radiation
Light as Particle - Photons
Carry quantized amount of energy
- E=hπ
- Higher frequency photons carry more energies
Can interact like particles
- elastic collision
- reflection/refraction
Used to describe higher energy radiations
- X-rays, gamma-rays
Propagation of light
Energy per unit area decreases as the square of the distance from the source
Spectral Lines
a dark or bright line in an otherwise uniform and continuous spectrum, resulting from emission or absorption of light in a narrow frequency range, compared with the nearby frequencies
Emission Lines
a bright line in the emission spectrum
Absrobtion Lines
dark lines, or lines of reduced intensity, on a continuous spectrum
Radiation Mechanisms Exploited in Astronomy
Neutral Hydrogen 21-cm Line
Blackbody Radiation
Synchrotron Radiation
Neutral Hydrogen 21-cm Line
Hydrogen is the most abundant element in the interstellar medium
Lie in microwave radio frequency, can penetrate interstellar dust which are opaque to visible light
Exceptionally sensitive tracer of tidal interactions between galaxies
Blackbody Radiation
thermal radiation
From an object that absorbs all radiations falling on it or from an object with thermal equilibrium with its environment
- e.g., cosmic microwave background
Dependent solely on the temperature of the emitter
Distinct spectrum: βhot stars are blue, cold stars are redβ
Synchrotron Radiation
non-thermal radiation
From relativistic charged particles, usually electrons, spiralling/accelerating in magnetic field
Each radiate in a range of wavelength
Synchrotron radiation is a sum of radiations of many electrons
Radio synchrotron radiation can be found in places with magnetic fields and electrons
- Pulsars, supernovae, and jets in active galaxy or near the black holes
