Astrophysics study guide

in the solar system a planet is a celestial body which: (a) is in orbit around the sun, (b)h as sufficient mass to assume hydrostatic equilibrium (a nearly round shape), and (c) has “cleared the neighborhood” around its orbit

irregular objects a few kilometers across comprising frozen gases, rock, and dust. travel around the sun in sharp elliptical orbits with period of a few to thousands of year.

form when gravity causes the gas in a nebula to condense

cooler than the sun, higher luminosity than the sun, therefore have much more surface area and a much larger diameter

remnants of old stars and constitute about 9% of all stars. very hot with relatively low luminosity and small surface area. take billions of year to cool down

a celestial object of very small radius (typically 18 miles/30 km) and very high density, composed predominantly of closely packed neutrons. Neutron stars are thought to form by the gravitational collapse of the remnant of a massive star after a supernova explosion, that is insufficiently massive to produce a black hole

A black hole is a region of spacetime exhibiting such strong gravitational effects that nothing—not even particles and electromagnetic radiation such as light—can escape from inside it

two stars that rotate about a common centre of mass.

a set of gravitationally bound non-stellar objects in orbit around a star or star system

a pattern formed by stars that are the same general direction when viewed from earth. more historically significant than physically as many ancient societies attributed them with religious importance

group of starts positioned closely enough to be held together by gravity. contain a few dozen to millions of stars. all those of the same grouping were formed at the same time by the same nebula.

also know as stellar nurseries because stars are “born” out of them, they are regions of intergalactic cloud of dust and gas.

a creation of stars, gas, and dust held together by gravity and containing billions of stars

a group of galaxies with a few dozen to a few dozen members. regular clusters consist of a concentrated core and are spherical in shape where irregular clusters also exist with no apparent shape and usually with a lower concentration of galaxies

large group of galaxy clusters, among the largest-known structures in the cosmos

powers stars

because inward gravity and outward radiation pressure balance each other

total energy emitted by the star per second in watt

= (2.90 x (10^-3))/T

number that is a measure of a celestial object’s brightness as seen from earth. the brighter the object appears, the lower its value. sun is -27

measure of intrinsic brightness of a celestial object. the brighter the celestial object, the lower is value

the apparent shift in position of a nearby star against the background of distant objects

describes how the universe expanded from a very high density and temperature state to what it is now, and what it will expand to be

thermal radiation left over from the time of the recombination in big band cosmology

Hubble’s constant shows us how fast the universe is expanding. with relative knowledge of the size of the universe, we can then deduce how long ago the big bang was and hence how old the universe is

function of time which represents the relative expansion of the universe

type Ia supernovae are redshifted and by the doppler affect then seen to be accelerating

9.46 x E15 meters

average distance between the sun and earth, really only useful when dealing with the distances of planets from the sun
one of these = 1.50 x E11 meters ≈ 8 light mins

most commonly used unit of distance in astrophysics
one of these = 3.26 ly = 3.09 x E16 meters

5.67 x E-8 in W(m^-2)(K^-4)

about 500 km(s^-1)(Mpc^-1)
there is still uncertainty in the value of the Hubble constant

if z is large there is a large frequency shift and the object in question is moving away from the earth at a high rate of speed