IB Physics – Astrophysics

The apparent magnitude a star would have if viewed from a distance of 10 parsecs.

The received energy per second per unit area of detector.

A relative logarithmic system classifying the brightness of stars seen from earth. An increase in apparent magnitude by 5 units implies a decrease in apparent brightness by a factor of 100.

The theory according to which space, time, matter and energy were created at a singular point 13-14 billion years ago.

Two stars orbiting a common centre.

A star whose luminosity periodically changes due to expansions and contractions of its surface. The period of variation and the peak luminosity are related to each other.

The largest mass a white dwarf can have – 1.4 solar masses.

Electromagnetic radiation in the microwave region of the spectrum that fills the universe, with a black-body spectrum corresponding to about 2.7 K. The remnant of the high temperatures at the time of the Big Bang.

The density of the universe at which the expansion of the universe continues at a slowing rate for ever, stopping after an infinite amount of time.

Matter that is too cold to radiate, and so cannot be seen.

A plot of stars according to luminosity (vertical axis) and temperature (horizontal axis, higher temperatures on left).

The slope of a graph of galaxy speed versus distance.

The inverse of the Hubble constant – giving an estimate for the age of the universe.

v = Hd
Galaxies are moving away from us with a speed which is proportional to their distance away from us.

The amount of energy radiated by a star per second, dependent on the surface temperature and the surface area of the star.

m – M = 5log(d/10)
m is apparent magnitude, M is absolute magnitude and d is distance in parsecs.

Stars undergoing fusion of hydrogen to helium.

L ∝ M^n
n is a number between 3 and 4.

A collapsed star composed almost entirely of neutrons whose degeneracy pressure balances the inward pressure due to gravity.

If there were an infinite number of stars in the universe and they lived forever, the night sky would be infinitely bright.

The largest mass a neutron star can have – 3-4 solar masses.

A method of measuring the distance to nearby stars (up to a few hundred parsecs) relying on the fact that a nearby star viewed from two different positions appears displaced relative to the background of distant stars.

The ejection of mass from an exploding red giant.

A rotating neutron star emitting radio waves.

A classification of stars according to surface temperature and colour.

A method for determining distance to a main sequence star, using the Wien displacement law to determine surface temperature from the star’s spectrum, the Hertzsprung-Russell diagram to determine luminosity and apparent brightness measurements to determine distance.

(it’s complicated – learn it)

The ejection of mass from an exploding supergiant star.

The final stage in the life cycle of a small star, where degeneracy pressure from electrons balances the inward pressure of gravity.

λ₀T = 2.90 × 10³ Km … λ₀ is the wavelength at which most energy from the star is emitted and T is the surface temperature.