Option D: Astrophysics definitions

• A black hole is a region in space where gravity is so strong that nothing, not even light, can escape.
• Cosmic microwave background radiation (CMB) is electromagnetic radiation left over from the Big Bang.
• Dark matter is a form of matter that does not interact with or emit, or absorb, any type of electromagnetic radiation but whose presence can be inferred from its gravitational effects on visible matter.
• Dark matter is an invisible form of matter which makes up most of the mass of galaxies.
• solar system


  a collection of planets, moons, asteroids, comets and other objects travelling in an elliptical orbit around the sun
• asteroids


  rocky and metal chunks in the asteroid belt
• comets


  dust, rocks, and ice
• binary stars


  two stars rotating about a common center of mass
• stellar cluster


  a group of stars that are positioned close enough to be held together by gravity
• open cluster


  cluster of stars that are younger than 10 billion years, contain some gas and dust, in out galaxy, lie on a single plane
• globular cluster


  cluster of stars older than 11 billion years, outside the galaxy is a spherical shape
• constellation


  a group of stars that appears to be near each other when viewed from earth and make a recognizable pattern
• nebulae


  intergalactic cloud of dust and gas, a stellar nursery
• galaxies


  a creation of stars, gas, and dust held together by gravity
• to be a planet

  -spherical

  -orbit a star

  -must clear its orbital path
• light year


  unit of measure for the distance light travels in one year
• astronomical unit


  unit of measure for the average distance from the earth to the sun, used to measure things in our solar system
• parsec


  most commonly used, equals 3.26 ly
• stellar parallax


  apparent shifting of an object's position relative to other objects in the background of your view
• limitations of stellar parallax


  can only be used to .01 arcsecond because of the absorption and scattering of light by the atmosphere and the turbulence of the atmosphere
• luminosity


  the total energy emitted by the star per second
• apparent brightness


  the total energy emitted by the star per square meter
• apparent magnitude


  m, how bright a star appears to be when viewed from earth and compared to other stars
• absolute magnitude


  M, how bright a star would actually be if moved 10 pc away from earth
• doppler effect


  the change in frequency of the wave for the observer relative to the source
• cepheid variable


  an extremely luminous star which undergoes changes in luminosity, continuous pulsation
• HR diagrams


  scatter-grams of luminositys of stars compared with their temperature
• mass-luminosity relationship


  high mass stars have shorter lifetimes because more fusion in the core will occur
• formation of a star

  -gravitational attraction of hydrogen nuclei

  -potential energy is lost and there is an increase in the gas temperature

  -gas become denser

  -when there is enough mass, fusion will begin
• life cycle of a low mass star

  proto star, main sequence, red giant, planetary nebula, white dwarf
• life cycle of a high mass star

  proto star, blue main sequence, red supergiant, supernova, neutron star or black hole
• Chandrasekhar limit


  impossible for white dwarfs to have mass > 1.4xmass of the sun
• neutron degeneracy pressure


  resists further collapse of the white dwarf
• Oppenheimer-Volkoff limit


  neutron degeneracy limit able to resist further collapse into a black hole in stars up to 1.5-3 solar masses
• black holes


  remnant of a supernova, nothing can escape
• redshift


  stars are moving away from the earth, so the stars have longer wavelengths, caused by the expansion of the fabric of space
• blueshift


  local phenomena, stars might be moving towards us
• Hubble's law


  suggests that everything must have been in the same place at one point
• big bang model


  if all galaxies are moving apart, they must have started close together
• Solar system


  a collection of major planets bound in elliptical orbits around the Sun