Astronomy (Sun/Stars/Galaxy) – Flashcards
Unlock all answers in this set
Unlock answersquestion
Supernova
answer
an explosion of a star
question
What causes supernova explosions?
answer
1. Binary Star Systems You have two stars orbiting each other, and one star steals more matter from the other star and explodes 2. End of Star's Lifetime Lack of nuclear fuel = mass flows into core = core is too heavy to withstand gravitational force = collapse
question
Why are supernovae important?
answer
1. distribute elements throughout universe (to form new stars) 2. Exploded stars = molecular clouds w/ elements for star formation
question
Younger Stars and Density of Elements?
answer
Young stars = more heavy elements
question
Why do younger stars have heavier elements than old stars?
answer
Because young stars are formed from the explosions of other stars, and those stars build up layers over time and have these heavy elements in them. So when they explode, you mainly have those heavy elements in molecular clouds for stars to form out of those.
question
What is the order of element fusion?
answer
Hydrogen > Helium > Carbon > Oxygen > Neon > Magnesium > Silicon > Iron > EXPLOSION
question
What's the result of a supernova explosion?
answer
Neutron Stars and Black Holes
question
Neutron Star
answer
- result of a supernova explosion of a fairly massive star - i.e. mass of our sun compressed to size of Earth
question
Pulsars
answer
rotating neutron stars! varying amplitude (height) but stable period (time difference between the peaks)
question
Why do Neutron Stars have pulsars?
answer
They are compressed so small that they rotate crazy fast As they shrink it also compresses the Magnetic Field, causing it to jet out material that radiate light. These beams of radiation from the neutron stars come from the poles, sometimes sweep by Earth and we can see it!
question
Overtime, what happens to the rotation of a Neutron Star?
answer
they begin to slow down because the star is constantly pushing out material (losing rotational energy)
question
Can Neutron Stars be plot on the H-R diagram?
answer
No, they are TOO small, which = super low luminosity (below the chart)... like white dwarfs, eventually they cool and fade
question
How are Neutron Stars held up?
answer
By neutron degeneracy pressure
question
X-Ray Buster (in Binary System)
answer
Neutron star and another low mass star orbit each other Other star's Hydrogen flows into Neutron Star Neutron Star develops layers of Helium (fusing) Once critical mass of Helium has been reached on a Neutron Star, then it ignites explosively, releasing sudden bursts of X-Rays
question
Black Hole
answer
region of space where nothing can escape because the escape speed exceeds the speed of light
question
What happens when a very massive star can't be held up by Neutron or Electron Degeneracy Pressure?
answer
it continues to collapse (with increasing density) into a Black Hole
question
Escape Speed Properties
answer
1. More massive a planet, faster you need to go to escape 2. Smaller the planet is (with the same mass), faster you have to go to escape Escape speed increases as Mass increases Escape speed Decreases as Radius Increases
question
Einstein's Special Relativity
answer
1. Speed of Light never changes 2. Space and Time aren't independent; united by Spacetime
question
Time Dilation
answer
clocks in moving objects appear slower
question
General Relativity
answer
1. Matter warps spacetime around it; no matter means flat and straight (Gravity arises from curvature of Spacetime) Consequence: Light is distorted and bent (by presence of matter) Gravitational Lensing: Light rays are trapped in a well of gravity and bent when it comes back out.
question
How does General Relativity describe Orbits?
answer
Things naturally want to go on a straight line, but when matter is warped; the nature of that line gets distorted by matter. Orbits are just following the "natural" path (which has been distorted)
question
Schwarzschild Radius
answer
The radius of which the mass has to compress into to be a Black Hole i.e. Earth would need to compress to 1 cm Sun would need to compress to 3 km
question
What happens when you travel to a Black Hole?
answer
The differential force of Tides will tear you apart
question
differential force
answer
the front is being tugged and the back is also being tugged as it lags behind
question
Light Around Black Holes
answer
Energy is the capacity for motion. Light can't be slowed down by gravity, so instead Light's energy is determined by energy of photons. So it changes colors! (w/ Gravitational Red Shift)
question
Gravitational Red Shift
answer
decreased frequency of light as you decrease energy of light; makes the light more red. connected to Time Dilation Closer to Black hole means light will be fighting very hard = lots of red shift
question
How do you find black holes?
answer
1. Use Orbits By Kepler's III law, you can find total mass of the star and mystery mass and then subtract that with the mass of the star to find mystery mass! 2. Use Light Forming Black Holes have an accretion disk around it (x-ray radiation)
question
What's the result of a Black Hole formation?
answer
Gamma Ray Burst
question
Gamma Ray Burst
answer
bright flashes of gamma rays; associated with supernovae followed by an afterglow at other wavelengths
question
Types of Gamma Ray Burst
answer
1. Hypernovae (explosions of massive stars) "long" GRB; jets are pointed at us. 2. Neutron Stars Merging "short" GRB from 2 Neutron stars coming together
question
Basic Components of the Milky Way
answer
1. Stars (young and old) 2. Gas (mostly Hydrogen, then Helium/hot near bright stars/supernova and cold inside dark clouds) 3. Dust (tiny solid particles, detected by its affect on stars = red tint)
question
Structure of Milky Way
answer
Galactic Halo, Galactic Disk, Galactic Bulge
question
Galactic Halo
answer
contains stars and globular clusters NO GAS OR DUST; ONLY STARS random orbit
question
Galactic Disk
answer
contains young Population I stars LOTS OF GAS; ACTIVE STAR FORMATION Rotate together in same direction
question
Galactic Bulge
answer
contains both young and old stars more gas and dust towards the center mostly random orbits
question
Galactic Center
answer
if you want to see beyond the dust towards the center, you need to look through infrared light because the dust scatters short wave length light. lots of gas = lots of star formation electrons everywhere = strong magnetic field
question
How do we weigh the Milky Way's Black Hole?
answer
Kepler's III Law it weighs approx 4 million solar masses
question
Characteristics of Spiral Galaxy
answer
Flat Disk & Spiral arms Central Bulge w/ dense nucleus Halo w/ Old stars (globular Clustes)
question
Spiral Classification
answer
Sa -----> Sc large bulge/tight spiral/some gas -----> small bulge/loose spiral/lots of gas SPIRALS CLASSIFIED BY SIZE OF BULGES
question
Where did we get this spiral structure?
answer
1. Lots of stars outside Spiral Arm 2. Blue color comes from O and B stars 3. Lots of gas/dust in spiral arms = star formation 4. Differential Rotation
question
Differential Rotation
answer
outskirts of galaxy don't rotate as fast as the inside; so you get a spiral
question
Density Waves
answer
it's a structure; things PASS THROUGH the wave when things pass through they form the spiral arm at some point, a gas cloud hits the Density Wave then the Density Wave compresses the gas cloud = star formation! now things get clumped together; you have massive and small stars.
question
why do we see Spiral Arms in visible light?
answer
The massive stars (O B) form pretty much right where we see them, they die too fast to rotate all the way around galaxy. The old stars that are too faint for us to see can rotate all the way around and don't die.
question
Elliptical Galaxy Classification
answer
classified by how circular they are E0 > E7 (most circular > least circular)
question
Properties of Elliptical Galaxy
answer
NO GALACTIC DISK Density increases towards center stars orbit randomly little gas/dust (no young stars) Similar to Halo!
question
Intermediate Cases (lenticular)
answer
inbetween spiral and elliptical S0 or SB0 (barred) have bulges and disks, NO ARMS
question
Irregular Galaxies
answer
small/lots of young stars Irregular because often disturbed by gravity of other galaxies or star formation (i.e. Magellanic Cloud)
question
Hubble's Classification Theory
answer
galaxies start off elliptical, and collapse into spiral
question
How do galaxies actually evolve?
answer
they start as spirals and turn into ellipticals
question
How do we measure how big/massive the galaxy is?
answer
Kepler's III Law: if you use KIII Law with the Sun, you can infer the mass inside the sun's orbit. If you can do that, you can find the mass inside of other stars beyond the sun and map out the galaxy This measures the Galactic Rotation Curve
question
Measuring Galactic Rotation Curves
answer
you get velocity and distance Velocity from the amount of red/blue shift Distance from each section
question
Velocity
answer
Use velocity and distance and you can find how long it takes for the thing to orbit (P) we actually measure the velocity of orbits
question
What really happens beyond the edge of the galaxy?
answer
The velocity still increases, so we need more mass!
question
Dark Matter Hypothesis
answer
beyond the galaxy edge the mystery mass is made up of dark matter
question
Possibilities for Dark Matter
answer
black holes faint things (dwarfs) subatomic particles that don't do anything except exert gravity
question
MACHO Hypothesis
answer
massive compact halo objects easy to test b/c of gravitational lensing: macho objects moving in front of a star makes the star brighter it's not enough of them to make up dark matter tho
question
WIMP Hypothesis
answer
weakly interacting massive particles 1. Particle accelerator takes protons and accelerates them to speed of light until they smash (result is shower of particles) look for evidence of something missing basically, look for strange collisions
question
What consists of the Sun's atmosphere?
answer
Chromosphere & Corona
question
Chromosphere
answer
first layer right off of photosphere significantly cooler than photosphere (3000 K compared to 5800 K) the red glow comes from emission lines from hot gas, NOT temperature
question
Corona
answer
2nd layer; right after the chromosphere CRAZY HOT (so weird?) 3 million K B/c of low density, emission is in X-RAY (our eyes can't see low density) huge big holes (coronal holes) there is dynamic activity....
question
Sunspots
answer
bases of Magnetic Fields they are always in pairs; they have a cycle of 22 years: 11 years to go up, 11 years to go back down.
question
Why are sunspots dark?
answer
Because those spots are cooler than the surface of the sun When Magnetic Field erupts from the sunspots, it is carried away from the surface therefore leaving a cool area
question
Heat source of the corona?
answer
Magnetic Fields The sun has plasma (for ions to flow), and it's so hot that things CAN be ionized
question
What generates Sunspots?
answer
The sun's differential rotation: the equator moves faster than the poles, so the Magnetic Field lines get stretched out. When they're stretched out, weird things happen; like they pop through the sun spots. After 11 years, the magnetic field lines are so stretched that they SNAP back and start over; hence switching the direction of the poles, so you start over.
question
Solar Wind
answer
solar wind is the ions that follow the Magnetic Field lines When the Magnetic Field lines break free, it goes off into space and the ions follow it.
question
Solar wind affects
answer
aurorae, distorted ionosphere, radio interference
question
Solar Flares/Coronal Mass Ejections
answer
Coronal Mass Ejections are bigger Solar Flares When Magnetic Field goes from loop to extended into space, the gas goes EVERYWHERE Solar Flares is a result of UNSTABLE MAGNETIC FIELDS
question
Effects of Solar Flares/Coronal Mass Ejections
answer
bright aurora, satellite disruption, radio interference, power grid issues
question
Measuring the Distance of Stars
answer
stellar parallax find angle and baseline/ calculate distance
question
distance (parsec) =
answer
1/parallax (arcseconds)
question
Measuring Motion in Space (Velocity)
answer
Proper Motion: looking at a star and following it/watching it move Doppler Effect: used if star is moving towards/away from us more effective b/c easier
question
Measuring Luminosity
answer
Inverse Square Law: apparent brightness proportional to luminosity/distance^2 find the apparent brightness and distance to get luminosity
question
How is apparent brightness measured?
answer
Magnitude!
question
Magnitude Scale
answer
on this scale, brighter objects have smaller magnitude based on logarithmic 0 to 5 (Magnitude 5 star is 100x dimmer than Magnitude 0 star)
question
How do we measure temperature?
answer
Wien's Law (blackbody law) vs Spectra (absorption lines)
question
Measuring Temperature by Wien's Law
answer
basically black body, you have intensity (y axis) over wavelength (x axis) and graph location at peak will shift w/ intensity coolest will have higher wavelength
question
Measuring Temperature by Spectra
answer
more accurate than Wien's law As you change temperature, you change absorption lines Hot stars: electrons are stripped from hydrogen atoms (not much to absorb) Cool stars: electrons in ground state; cant absorb visible photons Intermediate stars: lots of hydrogen absorption
question
Measuring Composition of Stars
answer
despite the temperature, all stars have the same composition
question
What's the composition of stars?
answer
75% Hydrogen/ 25% helium/ rest are random stuff
question
How do we measure the Radius of Stars
answer
1. Take image & Directly Measure it difficult in practice because you need large stars which would have to be close by too (rare) 2. Indirect Way (also best way): Luminosity Luminosity proportional to radius^2 x Temperature^4 Find the luminosity and the temperature and you have radius!
question
How do we measure Mass of a Star?
answer
BINARY STARS!!!!!!!!!!!!!!! (Kepler's III Law) Visual Binaries > Spectroscopic Binary > Eclipsing Binary
question
Visual Binary
answer
easiest way to study because it's visible rare because they have to be close
question
Spectroscopic Binary
answer
what if they're orbiting away/towards us? We use this (it's a step up from visual binary) because we can use Doppler Effect; measure period and how fast it's going to find mass Disadvantage: we don't know the inclination
question
Eclipsing Binary
answer
when one star moves in front of each other dip in amount of light (2 dips) figure out the radii of 2 stars (because the dip has a shape to it)
question
Most important properties of a star?
answer
Luminosity and Temperature (HR Diagram)
question
What determines where a star lays on HR Diagram?
answer
Mass (cool and faint stars are small in mass and hot and bright stars are large mass)
question
Where do stars come from?
answer
gas and dust! Interstellar medium
question
How do we study Gas? Dust?
answer
Gas = infrared / Dust = Radio (too cold for infrared)
question
"Reddening"
answer
when the cloud of dust looks red because as a cloud of gas/dust goes inbetween us and a star, the light is scattered from that dust (the dust reflects the blue light away and lets the red light through); so all we see is red light
question
Nebulae
answer
generic term of gas and dust associated with star formation only reason why we can see nebulae is because of star formation (clumps)
question
Types of Nebulae
answer
Emission Nebulae, Reflecting Nebulae, Dark Clouds (Molecular Clouds)
question
Molecular/Dark Clouds
answer
cloud that has enough stuff that makes whatever it is behind it seem DARK prettttty dang cold (must be seen through Radio waves)
question
Emission Nebulae
answer
Hot gas that glows from spectral line The way it works: you have a bright star in the center that emits light, that light heats up the gas cloud and then the gas cloud emits emission lines
question
Reflecting Nebulae
answer
dusty cloud that reflects light towards us. It reflects blue light (well, we see blue light)
question
What are star clusters useful for?
answer
enables astronomers to see how star populations evolve
question
Open Clusters
answer
generally young star cluster where there is lots of star formation sits near dark clouds
question
Globular Clusters
answer
huge globs within small space generally old stars
question
Hydrostatic Equilibrium
answer
when inward force of gravity is balanced by outward force of pressure from the interior stable because of Solar Thermostat
question
Solar Thermostat
answer
it's what keeps the Sun so stable: When the temperature and pressure increases in the Sun, it therefore increases the fusion rate of Hydrogen to Helium. As the fusion rate increases, the sun EXPANDS, and as it expands, the sun COOLS, therefore balancing the original increase in temperature and pressure
question
What energy source do Main Sequence stars rely on for stability?
answer
Hydrogen Fusion
question
What happens when a Main Sequence star runs out of Hydrogen Fusion?
answer
It goes to Red Giant Phase
question
Helium Fusion
answer
Unlike Hydrogen Fusion, Helium Fusion requires 3 Heliums to fuse into Carbon (that's a new energy source)
question
Red Giant Stage (Red Giant Branch)
answer
1. Hydrogen Fusion in core runs out 2. Gravity is overwhelming the useless core, so core starts to contract 3. As core contracts, it activates the shell surrounding the core 4. This shell starts to fuse its Hydrogen to Helium (note that while this shell is fusing, the core is still contracting) 5. This fusion affects the outer layers of the star, but not the core because it's beneath it 6. The outer layers of the star begin to expand, making it big = GIANT 7. These expanding layers make the star cool = RED
question
Helium Flash
answer
1. The Helium core contracts until it reaches 10^8 K 2. At that temperature, Helium can finally fuse into Carbon 3. Once it goes, it goes super fast; like a FLASH 4. You end up on Horizontal Branch
question
Horizontal Branch
answer
1. 2 Layers of Fusion 2. You stay there as long as you fuse Helium to Carbon 3. But you use that energy much more quickly because you're more luminous than before
question
How do galaxy's grow up?
answer
Start scruffy and small...get bigger and settle as a disk...2 disks combine to make elliptical
question
Major Merger
answer
2 big disks merge with each other to make an elliptical (huge starburst that destroys the disk, so you get elliptical)
question
Minor Merger
answer
1 big disk eats all the little things
question
Hubble's Law
answer
velocity is proportional to distance redshift is proportional to distance recession velocity = H0 (constant) x Distance there is a relation with how far away a galaxy is and how redshifted it is! he figured out that the faster something is moving away from us, it is going to have more of a red shift
question
Cosmological Principle
answer
the universe is homogenous and isotropic homogenous: universe is the same everywhere isotropic: universe looks the same in every direction
question
What does the cosmological principle tell us?
answer
we are not special :(
question
What does Hubble's Law tell us about the Universe?
answer
The Universe is the thing that CAUSES Red shift, WITHOUT THE DOPPLER EFFECT because light is stretched out along with the universe, so inevitably the photons will stretch with it; blue light is shorter, and red light is longer.
question
Are galaxies expanding like the universe?
answer
nope
question
How do you measure the distance in the universe with Hubble's Law?
answer
recession velocity = H0 x Distance To find distance, you need to know the recession velocity (you already know the constant H0) To find the recession velocity you find the redshift in the spectra!
question
What consists of the Cosmic Web
answer
filaments of galaxies (strings) Empty Regions (bubbles) Galaxy Clusters (connected by filaments)
question
Olber's Paradox
answer
if the universe is infinite and static, then at any given angle from the Earth the line of sight will end at the surface of a star.... An infinitely old universe means that there has been plenty of time for the light from every star that has ever shined to reach our eyes so the night sky shouldn't be dark.
question
So...why is the night sky dark?
answer
The universe is not unchanging; it's birth was 14 billion years ago (the big bang) Because the universe has a finite age, one reason our night sky is dark is that many photons have not had time to reach us, those that have lie within our observable universe. (So, some stars haven't had time to reach us) ALSO! The galaxies are moving away from us based on expanding universe, so they are becoming MORE redshifted and we can't see them; the faster they move away from us the redder they become. THEY BECOME INFRARED and we can't see infrared with our naked eyes!
question
What is significant about geometry in spheres?
answer
The geometry in spheres are different
question
Flat Geometry
answer
Critical Universe
question
Closed Geometry
answer
(Spherical) Recollapsing Universe
question
Open Geometry
answer
(Saddle) Coasting Universe
question
General Relativity and our Universe
answer
Matter content of space determines how the universe is expanding and what kind of geometry it is So, if we can measure the matter, we can infer: 1. The FATE of the universe 2. The GEOMETRY of the universe
question
How do we measure matter in the past universe?
answer
Standard Candles - Type I Supernovae we know the luminosity; so out of that we can get the distance. We can also measure red shift which gives us the recessional velocty. Distance + velocity lets us test if it is a constant or not
question
What did we find out about the universe based on Standard Candles?
answer
Instead of the expected idea that the universe before us expanded FASTER (faster velocity b/c our matter decelerates expansion), we find out that the universe has been expanding SLOWER in the past SO, OUR UNIVERSE IS ACTUALLY ACCELERATING!
question
So, if the universe is accelerating when it is supposed/hypothesized to be decelerating, what is the cause for this acceleration?
answer
Dark Energy
question
Dark Energy
answer
cosmological constant: new energy that acts like anti-gravity fills up more space as the universe continues to expand = encourages acceleration
question
Dark Energy & Geometry
answer
it acts like normal geometry
question
What do we know about our Universe?
answer
1. Universe will expand forever, at an accelerating rate 2. Geometry of Universe is FLAT ( The density of the universe (including dark energy) is all added together to get the geometry of the universe. So far as we can tell, we have the critical density) 3. Dark Energy + Matter = Critical Density
question
What happens to the Universe if we go back in time?
answer
it gets hotter; so it was hotter, and denser, so that means radiate light as Black Body
question
What is the relic radiation from the Big Bang?
answer
Radio waves! Microwave Radiation
question
What does the Cosmic Microwave Radiation tell us about the Universe?
answer
In the first 50 million years of the Big Bang, almost all the energy was in Photons. Cosmic Microwave BG DETERMINES how the Universe is evolving!
question
Recombination
answer
the period when protons and electrons combine to make atoms, and photons can't break them because they don't have enough energy (after 400,000 years of Big Bang)
