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ASTRON 0089: Exam 3
How does a white dwarf form?
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a low mass star is near the end of its life, core shrinks and cools, it is very dense and held together by electron degeneracy pressure
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What is the Chandrasekhar limit?
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1.4 solar masses
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How does a neutron star form?
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stars above 1.4 solar masses push the protons and electrons together to form neutrons, and it may explode with a type 2 supernova, and only neutrons remain, and it will begin to rotate faster and faster
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How do black holes form?
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if the remaining mass of a neutron star is greater than 2-3 solar masses, then it will collapse into a black hole
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What is a pulsar?
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a rapidly rotating neutron star, discovered by bell and hewish from observing repeating radio bursts
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What is the binary pulsar?
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a binary system with two pulsars that were tested and confirmed the GTR
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How was the GTR tested with the binary pulsar?
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it predicted the intense gravity would change orbital paths by 4 degrees each year,
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What is gravitational radiation/waves?
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-ripples through space-time with no mass and that travel at the speed of light; sudden change in the curvature of space (move a mass)
due to an acceleration of a mass |
How does an Xray binary form?
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material from a companion star is accreted and it causes the star to rotate faster and hot spots, which emit xrays
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What are millisecond pulsars?
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Very old neutron stars, believed to have very weak magnetic fields so they dont slow
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What is gravitational redshift?
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the redshift experienced by gravity acting on light escaping a white dwarf
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Why must a white dwarf be in a binary system to measure redshift?
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Gravitational redshift cant be discerned from doppler redshift, so we must know their velocities to account for GR
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Why are stars brighter than black holes?
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black holes' gravity is so powerful that light literally bends back into the infinitely small point
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What 3 properties describe a black hole?
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mass, rotation rate, electric charge
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What are the two regions of interest in a black hole?
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the singularity, where all the matter is contained, and the event horizon, the (schwarzchild) radius at which gravity is too strong for light to escape
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if the sun was a black hole what would happen to earth?
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nothing, the mass is the same so the earth's orbit would stay the same
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How can we observe black holes?
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1.gravitational lensing, deflects light produces multiple images
2. measurement of binary system mass
3. binary system accretions
4. measuring gravitational radiation |
What is the Spaghettification effect?
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The stretching out of your body as you enter a black hole that pulls your feet faster than your head
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How is the event horizon affected by mass?
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(it is directly proportional, double mass, double radius)
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What is the Angol Paradox?
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when the more evolved star in a binary system is less massive, due to mass transfer (gains mass ---> evolves faster, and vice versa)
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What is the difference between type 1 and 2 supernovae?
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type 2- hydrogen found in spectra
type 1- no hydrogen |
what is a "standard candle"?
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any object with an easily recognizable appearance and known luminosity which can be used in estimating distances
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how far is the sun from the galactic center?
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28,000 light years
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What are the parts of a spiral galaxy?
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halo, bulge, disk (arms)
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Where do pop II stars (older) lie in the MWG?
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halo bulge an globular clusters, orbits not bound to center
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Where do population I stars(younger) lie in the MWG?
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disk, orbit galactic center
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how old is the MWG?
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about 13.5 billion years
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What is the nuclear bulge in the MWG?
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center of galaxy with a massive black hole and densely packed pop II stars and ISD and gas
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What is the disk in the MWG?
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the lage pinwheel structure that orbits the galactic center, contains young stars and ISD and gas
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What is the halo in the MWG?
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the spherical region that surrounds the galaxy, contains dark matter and dust
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what are the contents of the MWG?
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1. ISD and gas 10% of mass
2. stars
3. open and globular clusters
4. emission, reflection and dark, nebs
5. dark matter |
What is barionic matter?
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tangible material, things made of protons neutrons and electrons
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What is in the outer halo of the MWG?
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non luminous matter, known because of its attraction to luminous matter
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What are reflection nebulae and dark nebulae?
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r - reflects light from nearby stars
d - thick nebs that have dust that inhibits view behind |
What is an H2 region?
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a region where hydrogen is ionized
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WHat is interstellar extinction?
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when dust diminishes the light from a star, also referred to as interstellar reddening because of wavelength shift
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what are the two forms of Interstellar extinction?
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scattering and absorption
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what is the interstellar medium?
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gas and dust between stars, not uniform, perfect vacuum
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what are molecular clouds?
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cool and dense regions containing dust, thought to be nurseries for star formation
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What is neutral hydrogen emission?
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when a neutral hydrogen atom emits 21 cm radiation due to a flip of electron spin from a collision
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what is the density wave?
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the theory that higher density regions will orbit more slowly as in the traffic demonstration
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what are the four kinds of galaxies?
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elliptical, spiral, lenticular, irregular
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what is the mass to light ratio?
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the ratio of ML in solar mass to solar light; hot stars are <1, cool stars are >1
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what is a radio galaxy?
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a galaxy that emits strong nonthermal radio radiation
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what is a seyfert galaxy?
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a spiral galaxy with a big ass nucleus
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what is a quasar?
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or QSO, a large and active galaxy
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what is the basic model?
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a model of a massive black hole with an accretion disk
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what is olber's paradox?
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the night sky should be bright if the universe is full of stars, but light would take to long to reach us and might be redshifted
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What is Hubble's law?
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An expression of the idea that more distant galaxies move away from us faster; the expansion of the universe
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What is the cosmological principle?
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The idea that matter in the universe is evenly distributed, without a center or an edge, homogeneous and isotropic
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What is CMBR!?
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microwave radiation filling the universe coming from radiation caused by the original explosion
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what is cosmic nucleosynthesis?
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fusion of protons and neutrons into elements after the big bang
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what is dipole anisotropy?
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the motion of the sun throughout the universe, measured by the CMBR
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What is interferometry?
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Have two telescopes look at same object and feed two signals together, tricking recorder into thinking it's one telescope
Allows for huge objective diameter. |