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67 Cards in this Set
- Front
- Back
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Correct Theory of Gravity |
Einstein's - General Theory of Relativity |
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Gravitational Instability |
The universe began mostly homogeneously, but did have small quantum fluctuations in temperature --> this slight fluctuation increased over time, eventually creating galaxies and stars |
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Escape Velocity Formula |
V^2 = (GM)/R = (4piGpR^2)/3 |
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Schwarzschild Radius |
The radius around a black hole from which light cannot escape. A black hole has no hard surface - a person just falls in. The point of no return, marks the Event Horizon |
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Black Holes |
- have an interior region that cannot be observed - masses of less than 3x10^3 mass of the sun are fatal for humans |
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Event Horizon |
The boundary that separates where light can escape from where light cannot escape Marked by the Schwarzschild Radius |
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Tidal Force (Stretching Force) |
- becomes stronger as you approach the center of the BH - difference in force at head and at toes - we can't survive if the tidal force is > 10^2 g Stretching Force: (GMh)/d^3 |
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Escaping a Black Hole |
- Fire engines away from the BH at speed [GM/d]^(1/2) - Fire the engines in a transverse direction at speed V (dmin = d(Vtrans/Vo)^2 |
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Fundamental Properties of a Black Hole |
Electrical Charge (usually 0) Mass Spin (angular momentum) - all other information is lost - all other properties are identical |
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Hawking Radiation |
Black holes radiate, and their spectrum is similar to that of a black body at a temperature that is proportional to the inverse of the black hole mass. - means that black holes are not forever T(radiation, in Kelvin) = 10^26/M |
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Lifetime of a Black Hole |
1. Luminosity = 4piR^2(sigma)T^4, proportional to 1/M^2 2. Energy in an object = Mc^2 3. Time (equal to evaporation time) = E/L |
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Radiation Levels That Will Kill You |
- BH the size of 1 gram -> 100 miles away - BH the size of 10^15 grams -> 1 mile away - BH the size of sun -> close to the Event Horizon |
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Kerr Black Holes |
Rotating, much more complex objects |
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Small Black Holes |
- Between 5 and 20 solar masses - A result of massive stars dying and turning into supernovae - Roughly 10^7 in our galaxy |
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Supermassive Black Holes |
- Masses to a million to a few billion suns - Mostly living in galactic centers - Very little understanding of how they are formed |
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Observational Evidence for Black Holes |
- may be 1-100 million BH's in the galaxy - none identified alone in space - look for sources that are very bright in the x-ray |
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X-Rays Produced by a Black Hole |
- NOT Hawking Radiation - Gas falls into the BH, increasing speed - Part of the kinetic energy is converted into thermal energy due to friction - Gas is very hot, radiates X-rays with a huge luminosity - Black Holes are the most efficient way of producing energy - 20% conversion |
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Cygnus X-1 |
- First big x-ray source discovered, 1970's by Uluru Satellite - First and most-famous stellar-mass binary black hole candidate |
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Arguments For the Presence of Black Holes in a Binary System |
- Only neutron stars and BH's have the high gravity necessary for intense x-rays - Use Kepler's Law to find the "unseen" partner - Maximum mass of a neutron star is 2 SM ---> Must be a black hole (Could be hiding a third star, but not likely in systems with small mass companions) |
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Number of Black Hole Systems Known |
About 45 |
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Best Evidence for Existence of a Supermassive Black Hole |
- observations of stellar velocities near the center of our galaxy - Second best: NGC 4258 |
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Newton's Law to Find the Mass of an Unseen Object |
M = V^2R / (2G) |
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Evidence that the Galactic Center Has a Black Hole |
1. The object is invisible 2. It has a radius much less than 120 AU 3. Based on Kepler's Third Law (M = D^2 / P^3), the mass is about 3.7x10^6 solar masses - we can only see the center with x-rays and infrared light- Genzel and Ghez found strange motion of stars at the center - radius of this BH about 1 light hour |
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Absolute Proof of a Black Hole |
We must see velocities of almost the speed of light near the surface of one (so far, only about 100,000 km/s, 1/3 speed of light) |
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Black Hole Mass and Bulge Mass |
The larger the mass of the black hole, the larger the mass of the galactic central bulge Every galaxy with a bulge has a SMBH at the center |
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Major Unanswered Questions (BH) |
- What is the origin of SMBHs? - Are there intermediate mass black holes? - How/why are SMBHs related to their host galaxies? - How do SMBHs merge when their host galaxies merge? |
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First Quasar |
Maarten Schmidt, 1963 - Most distant object known at the time - Energy requirements for powering quasars were the first compelling argument for black holes |
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Quasars |
Quasi-Stellar-Radio Source (strong radio emission) - Quasar Era was about 10 billion years ago - most big galaxies had one - ordinary galaxies with a lot of gas/mass falling into the central black holes |
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SMBHs in QSOs |
QSO = Quasi-Stellar-Object (quasars and active galaxies) - original reasoning: energy is coming from a region to small to be anything other than a SMBH - the energy comes from gravitational energy released as matter falls into the black hole |
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Qualities of a Quasar |
- very small (a few light-days - about size of the solar system)
- very, very bright (sometimes brighter than whole galaxies) - feed gas to black holes to create this energy - often have jets that feed lobes of radio waves |
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Why Jets Imply Black Holes |
1. Jets remember ejection directions for a long time (energy sources must be rotating) 2. Jets move at almost the speed of light (the source must have very strong gravity) |
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Terrestrial Planets |
Inner planets
Low mass Rocky surfaces Slow rotation Little H and He |
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Jovian Planets |
Outer planets High mass Gaseous/liquid Rapid rotion Mostly H and He |
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Evidence that Planet Formation is a Byproduct of Star Formation |
- Age of the sun and the age of the solar system are the same - Orbits of the planets are aligned with the orbits of the sun - Planetary systems are ubiquitous (not a result of a special event) - We see gas disks around other young stars |
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Direct Detection of Other Planets |
Discriminating light from the planet (or reflecting off of it) from the direct radiation of the star - have to overcome the turbulence of the Earth's atmosphere with "seeing" (adaptive optics) |
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Indirect Detection of Other Planets |
Detect effects of the planetary system on the light from the star - radial velocity measurement - astrometry - transit photometry |
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Astrometric Planet Detection |
Astrometry: measurement of the back and forth wobble of two objects rotating around their center of mass |
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Radial Velocity Detection |
Measure radial (line-of-sight) velocity variations of the star, using the Doppler shift- measure orbit and center of mass and infer the planet (VERY difficult) |
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Planetary Transits |
Planet will pass between us and the star every orbit, blocking some of the light. We must be near the orbital plane. (VERY difficult) Three characteristics: period of recurrence of the transit, fractional change in brightness of the star, duration of the transit |
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Kepler-444 |
- smaller parent star, five planets ranging in size from Mercury to Earth, very compact system - ancient planetary system (11.2 billion years old) |
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Needed to Maintain Life |
- a source of energy - a chemical framework that supports many other elements - a means of transport of the chemicals (like liquid water) |
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The Fermi Paradox |
Where are they? - where are the other civilizations, if it's so possible? - few, if any, exist - or do they, and we just can't find them? |
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TESS |
Transiting Exoplanet Survey Satellite - Two-year mission (2017) to explore stars, looking for Earth and super-Earth-sized planets around Sun-like stars |
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Eternal Inflation |
Bubble theory, new universes are born (inflated) in regions where quantum fluctuations add constructively |
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Chaotic Inflation |
The scalar field potential varies randomly, regions where energy density is large mean new universes |
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String Theory |
There are 10^5000 different universes with different physical constants. Only some of these can make stars and galaxies |
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The Multiverse and Anthropic Principle |
There are many 3D universes separated in hyperspace, and each universe has different physical constants. |
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F = q^2/r^2 |
Charges and radius, force |
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Potential Ends to the Universe |
Protons and neutrons decay (Hawking radiation), black holes evaporate, empty full of diluted radiation Could end in a "Big Rip" with atoms being pulled apart with the fabric of spacetime |
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Formation of a Black Hole |
If the object has a mass greater than 1.4 mass of the sun, gravity will win and it will collapse into a black hole when the gas density becomes too large. |
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Black Hole Compression Formula |
R = 2GM / c^2 |
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Formation of Stars |
- In giant molecular clouds: small high-density regions - dense parts collapse under their own gravity, become closer and hotter, until eventually nuclear reactions start and the star is formed |
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Main Sequence Stars |
Main sequence stars with masses less than or equal to the sun fuse Hydrogen through proton-proton reaction |
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Most Efficient Way of Converting Mass to Energy |
Nuclear fusion |
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The Sun's Future |
- will die in about 5 billion years - will turn into a red giant - start burning He - die and become a white dwarf star - will forever be a WD star in a planetary nebula |
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Star Evolution |
change their chemical composition - switch to different types of fuel way a star evolves depends almost completely on the mass |
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H-R Diagram |
Census of stars at all ages, mapped according to age and temperature |
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Radius/Luminosity Formula |
R(wd)/R(s) = (L(wd)/L(s))^1/2 Wd = white dwarf star S = ? *slide |
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White Dwarf Stars and Energy |
- smallest, most dense, least luminous - gravity is 1,000,000x stronger - the dimmest and densest of the stars White dwarf stars do not collapse because of the gravitational pressure due to the repulsive nature of elections (electron degeneracy pressure) |
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Degeneracy Pressure |
- Made by anti-social particles - Doesn't decrease with decreasing temperature (below 10^10 K), like other pressures |
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Uncertainty Principle |
Heisenberg - can't measure momentum and position precisely (Δx)(Δp) >= h |
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Pauli's Exclusion Principle
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No two identical particles can occupy the exact same state Causes electrons to move faster when you pack them all together (degeneracy pressure) - but only works up to the Chandrasekhar mass (1.4 mass of the sun), at which gravity wins |
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Chandrasekhar Formula |
Star is unstable if -potential energy > kinetic energy |
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Supernova Type IA |
- all galaxy types (in elliptical galaxies, the stars that explode are very old) - the star must be long-lived and not very massive, like a white dwarf |
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Supernova Type Ib, Ic and III |
- mostly occur in spiral galaxies, in arms where new stars are born - NEVER occur in elliptical galaxies - made of young, short-lived massive stars, collapse into neutron stars or black holes |
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Proton-Proton Reaction |
How main sequence stars (masses less than or equal to that of the sun) fuse Hydrogen into Helium |
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Neutrinos |
P-P Reaction in the sun's core produces only electron-type neutrinos, which pass through the sun and escape, only to turn into mu and tau type neutrinos also |
