Flashcards on Astronomy Final
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Anatomy of a spiral galaxy
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Halo, Bulge, spiral arms, disk
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Bulge contains...
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mostly old stars
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Disk contains mostly
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Young stars, gas&dust (Star formation)
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Halo contains
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most old stars and looks very empty
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Dark matter
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(cosmology) a hypothetical form of matter that is believed to make up 90 percent of the matter in the universe and does not give off any light
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How do we know Dark matter exists?
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Because Dark Matter has mass, so there is a gravitational force between Dark Matter and visible. This force increases the net force of gravity exerted on the stars and gas, causing faster orbital motions than if there wasn't dark matter
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In our solar system...which planets travel the fastest?
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The planets nearest to the sun because they feel the strongest force of gravity, and therefore orbit faster
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Why is this opposite from a merry go round?
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because a merry go round is a rigid disk, where as planets orbit independently of each other. the orbital speed of each planet depends on the force of gravity between the planet and the sun. This force weakens with distance.
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If a planet felt a weak gravitational force, but had a high orbital speed it would....
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leave the solar system
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If the sun was more massive...
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the planets would orbit faster
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In a spiral galaxy...where do the stars orbit most slowly?
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Near the center of the galaxy
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In a spiral galaxy... and in the outer parts of the galaxy..the orbital speeds of the stars and gas______with increasing distances from the center
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barely change because the rotation curve is flat in the outer region of the galaxy, indicating that all the stars and gas have roughly the same orbital speeds
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How long does it take for the stars and has in the outer region of the disk to complete just one orbit?
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hundreds of millions of years to complete just one orbit. Thus we cannot measure speeds of stars and gas by watching the stars move around in circles
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How then are rotation curves of spiral galaxies obtained?
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measure the doppler shifts of the hydrogen gas emission lines and determine the orbital speed of the gas
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Spiral galaxies and the solar system...
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have inverse rotation curves
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Gravity relationship between force and orbital radius
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inverse
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gravity relationship between total amount of mass lying inside the orbit (Encircled mass) and force
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proportional
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Mass is distributed _______ in a planetary system than in a galaxy
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very different
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The sun accounts for ____% of the solar system's mass
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99.9% Thus the encircled mass is essentially the same for all radii outside the sun
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In a spiral galaxy...
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most of the mass in the galaxy is distributed outside the central region (Unlike solar region)
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Bright region of spiral galaxy
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high density of stars and large stellar mass
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dim region
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low density of stars, small stellar mass
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Dark region
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no stars no stellar mass
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encircled stellar mass depends on ___
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the encircled luminosity most bright...more stars!
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the stellar mass of a galaxy is distributed differently from total mass. showing what?
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the existence of dark matter
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In which region does most of the mass of a spiral galaxy reside?
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beyond the disk (Dark matter)
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Why does the rotation curve of a spiral galaxy increase with increasing distance near the galaxy's center?
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the encircled mass increases so fast that gravity increases with the radius
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What is the evidence that there is dark matter beyond the disk of a spiral galaxy?
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the stellar mass distribution does not account for the rotation curve of galaxies
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What is the evidence there is little or no dark matter in our solar system?
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The rotation curve of the planets is consistent with nearly all the mass being due to the sun
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Hubble's Law
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States that the farther away a galaxy is, the faster it is moving away from us.
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The expansion of the universe is _____
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accelerating because of dark energy
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Escape velocity for the Earth
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11.2 km/sec
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If a planet has a higher mass than Earth, but the same radius, the escape velocity is:
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higher than Earth's
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what determines the strength of gravity?
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mass, size (Radius), and density aka the density of its mass
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The _____ the average density of mass in the universe the _____ the overall strength of gravity
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the higher the average density of mass in the universe, the greater the overall strength of gravity
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Critical Density
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The precise average density for the entire universe that marks the dividing line between a recollapsing universe and one that will expand forever. (The flat universe point)
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How does adding a small amount of Dark energy
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the expansion rate speeds up rather than slowing down
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IF the actual mass density of the universe is greater than the critical density and there is no dark energy, then the universe would
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eventually stop expanding and begin contracting
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for which model would the universe be recollapsing the soonest?
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a universe with no dark energy and two times the critical mass density
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How many light years is the sun away from the bulge of the milky way galaxy?
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28,000 Lys
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Where do stars form in a spiral galaxy?
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mostly in the disk of a galaxy
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Supernova & galaxies...
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they blow up and go above and below the disk, until they cool and then comes back to the disk
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What is at the center of the milky way and how massive is it
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a black hole that is 4 million solar masses
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What obscures our view of the rest of the milky way?
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the galactic center
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Definition of Cosmology
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Study of the structure and evolution of the universe comes from greek word Kosmos meaning harmony/order
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Light year dimensions of the milky way
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1,000 LYs thick 100,000 lys wide
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Structure of spiral arms
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individually moving around density wave that builds up
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How do stars orbit spiral galaxies in the disk verses the bulge?
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Disk: orbits like a carousel (Up and down) Bulge: random movement
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Elliptical Galaxies
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No Disk, just bulge Older, most numerous in the universe Spheroidal, not much star formation reddish evidence that there is a black hole in the center
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Lenticular Galaxies
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Central bulge, disk, but no spiral arm structure between elliptical and spiral
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Irregular Galaxies
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No shape Blue light active star formation no discernable structure appears disrupted by gravitational forces Gas and Dust and ongoing star formation
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Why are the arms of spiral galaxies typically blue in color?
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Stars are forming in the spiral arms so there are high mass, hot, blue stars in the arms.
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Spiral galaxies have ____ and ____ stars
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both O and M type stars
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Which galaxies have a lot of M stars?
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elliptical galaxies (Older)
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Group:
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up to a few dozen galaxies (Spirals)
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CLuster
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100s to 1,000s (Ellipticals)
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1st step of cosmic distances/astronomical rulers
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Radar: Used within our solar system measures out to ~100s Au's ~10^-3 LYs
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2nd step of Cosmic distances/astronomical rulers
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Parallax:~300 lys (326 to be exact) 100 parsecs use standard candles
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standard candles
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easily recognizable astronomical objects whose luminosities are confidently known
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3rd astronomical ruler
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Main sequence fitting: ~10^3-10^4 lys take parallax to near by cluster, and compare brightness of MSS
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4th astronomical ruler
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Cepheid variables: Linear relationship with period luminosity ~ millions of light years away foundation of Hubbell's work
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#5 astronomical ruler
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White Dwarf Super Novae: out to a billion lys temporarily outshines a galazy std candle all have the same mass
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2 explanations of hubble's law
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1)Milky way is at the center of the universe and everything else is expanding away 2)Universe is expanding: space itself is expanding
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Expanding baloon concept
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a,b,c,d, written on edge of the balloon...blow it up more....A and D move apart from each other much faster and farther than A and B
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The Universe has no ____
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has no edge, or center every point is the center of the universe and has 4 dimensions. 3 space and 1 time
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Cosmological principle
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No matter where you are, the universe looks the same on a large scale
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If our Universe is expanding, what are the implica6ons for the separa6on between two stars within our galaxy?
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The distance between the two stars is unaffected.
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Look back time
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The difference between the current of the universe and the age of the universe when the light left the object
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Cosmological Redshift
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as space expands, light waves are stretched. they appear redder (cooler) as time goes on and the universe expands.
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Cosmological horizon
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The boundary of our observable universe, which is where the lookback time is equal to the age of the universe. Beyond this boundary in spacetime, we cannot see anything at all. -Based on the speed of light -Changes on different galaxies
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How do we observe life cycles when we only exist in the moment?
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Snapshots of different aged galaxies -Then computer generation
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Models assume:
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Matter was generally evenly distributed originally -Small density variations clumped matter under force of gravity
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Halo stars
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.2-2% heavy elements mostly old form first
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Disk stars
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2% heavy elements all ages
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What makes an elliptical galaxy verses a spiral galaxy?
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Intial Density and initial spin Higher initial density: Ellipticals Higher initial spin: Spiral
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Protogalactic cloud
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A huge, collapsing cloud of intergalactic gas from which an individual galaxy formed.
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Distant Red Ellipticals
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have some of the oldest stars in the universe
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Retrograde
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spinning opposite way of orbit
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direct
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spinning same way of orbit
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Bigger mass of disrupting galaxy...
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steals more stars
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Old galaxies tend to
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look disturbed -Created when the universe was more dense...more disruptions
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Starbursts Galaxies
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Very active star formation in galaxies that are colliding -Look in infrared to see past dust -Hot young O stars...go super nova and make a galactic wind with extended gas and dust
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olber's paradox
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saying that the sky should not get dark at night because all lines of sight end on a star meaning that the night sky should be ablaze BUT the big bang, because the universe had a beginning, says that the sky gets dark because out in space, galaxies light hasn't had time to reach us.
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How many parsecs btw magellanic clouds and milky way
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50,000-60,000 parsecs
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What produced the cosmic web?
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Small density variations under influence of gravity and universe expansion produced the cosmic web
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Quasars
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most luminous type of AGNs (active galactic nuclei) 10^12 luminosity of the sun (1 trillion suns)
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AGNs Active Galactic Nuclei
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Center of distant galaxies that are extremely bright -size on the order of our solar system -Very red shifted -NOT stars -has a jet of radio waves off of it -Doesn't have bright hydrogen emission lines -Common in early times in the universe
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AGN wavelength strengths
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Weak radio Strong Gamma Strong visible Strong Infrared doesn't have peak wavelength like stars
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What can you conclude from the fact that quasars usually have very large redshifts?
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-They are generally very distant -They were more common early in time -Galaxy collisions might turn them on -Nearby galaxies might hold dead quasars
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Radio Galaxies
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-Massive: 500,000-1million light years across -Hide active galactic nuclei at the center -Ejects material 100,000 lys out by the AGN at speeds nearly the speed of light -Energy source: supermassive black holes with strong accretion of matter around disk -Spins and heats up, produces X-rays and gamma rays that would kill a human -Material spiraling around a creating disk...density bumps into each other and causes wobble motion, friction and therefore light
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True false:all radio galaxies must have supermassive black hole in them
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true
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True false: We know how AGNs are produced
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false, we do not know how they are produced
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What lies between us and Quasar? what does it do?
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Protogalactic clouds are between us and Quasars, which absorb some of its light as it passes through them
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In general, how does the velocity of a galaxy depend on its distance from earth?
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The greater the distance, the higher the velocity
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Slope of the line is _____
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Hubble's constant
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The beginning of the universe must have been ____,_____,and _____ than it is now.
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smaller, denser, and hotter
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Hubble's constant
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a number that expresses the current rate of expansion of the universe; designated Ho, it is usually stated in units of km/s/Mpc. the reciprocal of Hubble's constant is the age the universe would have if the expansion rate had never changed.
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True/False: a galaxy's expansion period is proportional to the galaxy's initial distance
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True. the farther it is...the more it moves
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The greater Ho is, the faster all the galaxies are receding, and so the faster the universe is expanding
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...
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The higher Ho is, the younger the universe is
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...
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1 AU equals....
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150,000,000 km
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A star's parallax angle increases as the star gets...
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closer to earth
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Roughly how far away is Sirius from us?
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9 Lys
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we can measure main sequence stars as long as they are no more than.....______ lys away
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100,000
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Roughly how far away is Andromeda from us?
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2,600,000 lys
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White dwarfs all have ...
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the same mass (1.4 solar masses) and same peak luminosity
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White dwarf super novas are...
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very rare
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There is a relationship between the luminosity of a galaxy and the orbiting speed of its outer stars is called
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the Tully-Fisher relation
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Hubble's law means....
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the distance to the galaxy can be determines solely by measuring how fast the galaxy is moving away from us. -Hubbles law is the least accurate method of determining distances, but is often the only option available
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which type of standard candle is the most appropriate for determining the distance to nearby galaxies like Andomeda>
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Cepheid variables
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For planets and stars... where is the highest force of gravity
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the surface
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why does a black hole strip a star of its gas?
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because the gas feels a stronger gravitational pull towards the black hole than its own star
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What is the main reason the star feels a stronger gravitational pull from the black hole then from the star? (in the red giant example)
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The star's expansion pushes its outer layers far from its own center but closer to the black hole
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true or false: The force of gravity at an object's surface decreases as radius increases
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true
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Cosmic microwave background
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snapshot of all radiation from big bang
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energy and matter were _____ @ earliest times in the universe
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interchangeable
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Particle _______ & Particle ________ in the hot dense early universe
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Particle creation and particle annihilation
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2 gamma ray photos collide and create _____ and this is called _______
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1 electron and 1 antielectron, which is called particle creation
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Anti electron and electron collide to create ______ which is called what
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2 gamma ray photons, which is called particle annihilation
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Beginning universe had____,_____,____
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radiation, particles, and antiparticles
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What do we assume about the early universe?
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we assume the laws of physics still apply
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What force governs astronomy?
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Gravity governs astronomy, which is ironic because it is the weakest force
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The 4 fundamental forces of nature
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1. Gravity (weakest) 2. Weak Force 3.Electromagnetism 4. Strong force (strongest)
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Gravity
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10^0 -Interaction between masses -Weakest force
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Weak force
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10^25 governs radioactive decay
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Electromagnetism
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10^36 Interaction between electorally charged particles
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Strong force
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10^38 keeps nucleus together
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What would happen if these had different levels of strength?
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our world would be very different
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What prevents us from falling through the earth?
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electromagnetism
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Name the 8 eras of the universe
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Planck Era, GUT Era, Electroweak Era, Particle Era, Era of Nucleosynthesis, Era of Nuclei, Era Atoms, Era of Galaxies
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Planck Era
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We have no idea what this was like TOE forces
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TOE
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Theory of everything (All forces together)
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Grand Unified theory
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When Electromagnetic forces, strong forces and weak forces are all equal (Gravity Breaks away)
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GUT Era
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Inflation rapid expansion 10^-43 sec
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Electroweak Era
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Weak force and electromagnetic (Strong force breaks away) -Particles, antiparticles, and radiation -10^-38
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Particle Era
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All 4 forces separate -Universe filled with equal matter and antimatter -10^-10
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Era of Nucleosynthesis
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He: 25% H: 75% Hot enough for fusion 10^-3
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Era of Nuclei
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Filled with He, H, and electrons Couldn't form atoms
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Era Atoms
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-380,000 year later -Cosmic Microwave background -Atoms and plasma
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Era of Galaxies
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1 billions years later -Stars, galaxies, and clusters made of atoms and plasma
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What is time?
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Quantity of distance from event
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What happened at the end of the Particle Era
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there was a slight increase in matter over antimatter -1 proton extra for every billion proton-antiproton pairs which caused a switch from radiation dominated to matter dominated
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@ Era of atoms what was light like?
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3,000k: visible and IR dominant, very bright
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What is the temperature of the universe
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2.73K everywhere (Homogeneous)
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Galaxies prove what
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that the universe is un-homogenous small differences from the beginning, became giant differences as time went on
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How is the universe homogenous
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particles all started at same spot, and cooled as they grew apart
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True false: the universe is infinitely full
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false
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Dark energy
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Unknown form of energy that is causing the universe expansion to accelerate -changes the slope
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Overall geometry of the universe is closely related to total density of matter and energy
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...
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What happens when density=critical density
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the geometry of the universe is flat
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When Density>Critical
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Spherical geometry
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Density<Critical
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Saddle shaped geometry
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What is the universe made out of?
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-Ordinary Matter: 4% Stars, gas, dust, neutrinos. Evidence: we can see them in the sky -Dark matter: 22%: Evidence: Rotation curves of galaxies, gravitational lensing -Dark Energy: 74%: Expansion is accelerating:Distance/brightness of WD super nova
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Gravitational Lensing
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This phenomenon occurs when light travels past a very massive object. According to Einstein's theory of general relativity, mass shapes spacetime and space is curved by massive objects. Light traveling past a massive object follows a "straight" path in the curved space, and is deflected as if it had passed through a lens. This can can cause stars to appear as rings as their light travels in a curved path past a massive object along the line of sight. We observe microlensing when an object such as a MACHO moves between the Earth and a star. The gravitational lens associated with the MACHO focuses the star' light, so we observe the star grow brighter then dimmer as the MACHO moves across our line of sight to the star. -Caused by dark matter
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Keplerian rotation
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Further you go out = slower movement. Our galaxy or orbital speed increases the closer you are to the sun
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Solid Body Rotation
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slower on the inside, faster on the outside
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MACHOs
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Massive Compact Halo Objects -Baryonic matter living in the halo of our galaxy that we don't see, brown dwarfs, dead stars, massive black holes
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WIMPS
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weak interacting massive particles Most likely cause of gravitational lensing
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What dark matter could possibly be made out of
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-MACHOs -WIMPs -Neutrinos -Or we could totally not understand gravity
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Great Attractor
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galaxies are drawn to large accumulation of mass that has theorized to exist, assumed to be dark matter
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3 options for fate of the universe
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1. eventually will collapse 2. Density of matter and energy in universe with =critical density 3. Accelerate growth over time *****
