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Flashcards in Astronomy Fifth Test-Final Exam Deck (55)
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first theorized black hole

1916 by elder Swarzchild, applied einstein's equations to a collapsing star, predicted it would collapse to a point- despite not knowing about white dwarfs or even stellar fusion


photon sphere

where light waves orbit a black hole, similar to a planet going around the sun. about 1.5 swarzchild radii.


lowest possible EV

fired directly at zenith (straight up). otherwise, curvature of space-time increases EV as you go out.


exit cone

EV gets too great for an object (just light I guess) to escape the greater an angle you get from the zenith. The exit cone is where the EV is less than c, a cone around the zenith. Gets smaller and smaller the closer you get to a gravitationally huge object/the object gets bigger.


star becoming black hole

collapses on itself at end of stellar life- collapses past event horizon, from the outside you never see it finish collapsing due to strong gravitational time dilation around the hole. asymptotically gets smaller. .001 sec to get to asymptotic point, 10^-2.



A point where laws of physics become discontinuous- suddenly jump. In this case, super strong gravity causes this.


swarzchild radius

distance of event horizon from center of black hole.


event horizon

the "point of no return", nothing inside it can be detected. inside it are things like other universes. everything with mass technically has an EV, but everyday objects have them very small.


knowable properties of a black hole

measured from outside- mass, electric charge, angular momentum. Unknown if black holes have electric charge or angular momentum, which are quantizised.


if sun became a black hole

we'd get cold but orbit would not change- gravity is about mass, not density


jumping into a black hole

you'd get spaghettified, pulled apart into a long chain.


black hole with angular momemtum

would twist space as it "rotates", causing extreme frame dragging around it, curves around the photon sphere


swarzchild radii for different masses

10^6 tons - (big hill/small mountain) - 13x10^-9 angstroms (cosmic black holes)
Earth mass - 1/3 inch
10 Ms - typical stellar black hole, 18.4 miles
10^8Ms - galactic black hole, orbit of mars


cosmic black holes

tiny black holes formed after big bang, 10^6 tons, 13x10^-9 angstroms. would pass right through earth, almost non-existtant impact parameter. possibly detected through gamma emissions when hawking radiation evaporates them - NASA launched


hawking radiation

a rare bridge between quantum mechanics and general relativity. at the event horizon, light can leave due to quantum tunneling, the quantum probability of transportation. this causes the black hole to lose mass, eventually evaporating in a gamma ray burst. Light leaks faster and faster the smaller the black hole. these gamma ray bursts supposedly detectable but none found


stellar black holes

5-100 Ms- look for a binary star system, a red giant with a dark companion. the BH is bigger, died sooner, red giant has expanded past Lagrangian point and is being eaten by black hole. this stellar black hole would then have a ridiculous accretion disk that shoots X-rays and is easy to see.


detecting stellar black hole

look for X-rays from accretion disk. scientists launched "uhuru" satellite from africa, not a nasa mission. need to be in space cause atmosphere blocks X-rays.


galactic black hole

seen by doppler shift in orbiting material. must be at center of galaxy judging by how fast things orbit. one was measured at 10 million solar mass, now known to be 3 billion. really early and active ones are thought to be quasars. basically, find the smallest orbiting thing you can, the hole must be in there.


how relativistic jets happen

frame dragging (warping of space by rotation of massive object) causes magnetic field lines to spiral out, jet corkscrews out.


friend falling into BH with light

you'd never see the friend go in completely, time stops at event horizon. green flash becomes less frequent, gets redshifted. from his perspective, he'd blast right in


Penrose diagrams

Universe 1, 2, singularity is lines on outside. learn this through diagram. Different universes out each side of black hole. Same black hole in both. Inner lines are EVs.


kerr solution

a spinning black hole. Model 10Ms, non-zero angular momentum, charge not important. Has two event horizons, one of them round like normal and other one oblate. space between them is the ergosphere. Within the ergosphere, you are compelled to travel through space in a certain direction but not in time- reverses. Re-reverses within inner EH.


white hole

the opposite of a black hole, puts out material. big bang singularity is possibly a white hole? At the other end of a penrose from the black hole. No white holes seen.


negative space universe

sides of L penrose diagram. shrink something down from zero, repulsive gravity, put a - in equations and its the same basically. past singularities in penrose


local group

Our group of galaxies, 50-60 members. Some clusters have billions of galaxies.


"zoo" of galaxies

tons of different types (spiral, barred spiral, etc) all interacting with each other.


galaxy interactions

galaxies gravitationally influence each other. sometimes some pass through others, leaving only a ring and the core. they pull each other apart, merge. 6 billion years from now, milky way will merge with andromeda.


spiral arms of galaxies

not caused by frame dragging, and companions are not an automatic ticket to them. They are compression wave shock fronts, not at speed of sound due to gravity influence. They circle the galaxy, the shock front picks up more material and the higher grav holds onto this material for a while, sustaining them. they are started by companion galaxies


shock front

Past the speed of sound, stuff builds up ahead of object- think bullet > sound or bubble that forms in front of supersonic jet. This is the process that sustains shock fronts.


seeing our spiral arms

look for O+B stars out from earth in different lines of sight. position them, look for spiral-arm based shapes.