New Deck Flashcards
high spin of protogalactic cloud during formation creates
spiral galaxy
low spin during of protogalactic formation creates
elliptical galaxy
Denser protogalactic clouds during formation creates
elliptical galaxies
less dense protogalactic clouds could create
a spiral galaxy
active galactic nucleus:
the center of a galaxy is unusually bright and dominates the luminosity of the rest of the galaxy. quasars are an exampleAll AGN activity (unusually high luminosities, small sizes, radio emission, broadband spectra) believed to be produced by accretion of gas onto a supermassive black hole
Dark Matter
matter that emits little or no light, but has significant gravity (common examples: planets, moons)
the milky ways rotation curve is (blank) compared to what it would be if the mass was concentrated in the center
flatter
what is dark matter made of
- 2 concepts
- Ordinary Dark Matter (MACHOS)
– Massive Compact Halo Objects:
dead or failed stars in halos of galaxies - Extraordinary Dark Matter (WIMPS)
– Weakly Interacting Massive Particles:
mysterious neutrino-like particles
Bound Universe
means that the galaxies will move apart (“expand”), then slow down, then stop, then reverse (“collapse”). Would expect to see a redshift, then no shift, then a blueshift (as all the galaxies begin to rush towards each other)
Unbound universe
means that the expansion will go on forever
positive/curved space vs expansion
Universe bounded, will recollapse (Gravity wins (C>1))
negative/saddle shaped space
Negative Curvature: Universe infinite, space curved, will expand forever (Gravity not sufficient to halt collapse) (C
The Casimir Effect
plates are pushed together due to the energy of virtual particles
Virtual particles in the vacuum of space constantly appear and disappear.
However between two conducting plates separated by a small
distance (L/d ~ 1million) some virtual particles are excluded
This means the pressure of the particles on the outside of the
plates is greater than on the inside
nucleosynthesis
the process of creating new atomic nuclei from pre-existing nucleons (protons and neutrons). It is thought that the primordial nucleons themselves were formed from the quark–gluon plasma from the Big Bang as it cooled below two trillion degrees. lasted three minutes and created, hydrogen, helium and trace amounts of lithium and beryllium
inflation
Inflation proposes that a tiny region of the Universe grew exponentially for a short period of time shortly after the big bang
true or false, A protogalactic cloud with slow star formation is more likely to form a spiral galaxy than an elliptical galaxy
true
How did Edwin Hubble measure the distance to the Andromeda Galaxy?
He applied the period-luminosity relation to Cepheid variables.
What is a quasar?
the extremely bright center of a distant galaxy, thought to be powered by a massive black hole
what is inflation
a sudden expansion of the universe after the strong force froze out from the GUT force
Where are most of the Milky Way’s globular clusters found?
the halo
Which of these forms of radiation passes most easily through the disk of the Milky Way?
infrared
In which of these galaxies would you be least likely to find an ionization nebula?
elliptical
The luminosity of a quasar is generated in a region the size of
solar system
The primary source of a quasar’s energy is
gravitational potential energy
fast star formation will produce what kind of galaxy
elliptical
What is interstellar reddening?
Interstellar dust absorbs more blue light than red light, making stars appear redder than their true color.
Which kind of object is the best standard candle for measuring distances to extremely distant galaxies?
a white dwarf supernova
When the ultraviolet light from hot stars in very distant galaxies finally reaches us, it arrives at Earth in the form of
visible light
Why do virtually all the galaxies in the universe appear to be moving away from our own?
Observers in all galaxies observe a similar phenomenon because of the universe’s expansion.
What would your estimate be for the age of the universe if you measured Hubble’s constant to be 11 kilometers per second per million light-years?
28 billion years
The flat part of the Milky Way Galaxy’s rotation curve tells us that stars in the outskirts of the galaxy
travel in straight, flat lines rather than elliptical orbits.
A photograph of a cluster of galaxies shows distorted images of galaxies that lie behind it at greater distances. This is an example of what astronomers call
gravitational lensing
Why can’t current theories describe what happened during the Planck era?
We do not yet have a theory that links quantum mechanics and general relativity.
Why does the Big Bang theory predict that the cosmic background radiation should have a perfect thermal radiation spectrum?
The background radiation came from the heat of the universe, with a peak corresponding to the temperature of the universe.
Helium originates from
mostly from the Big Bang with a small contribution from stellar nucleosynthesis
What are the two key observational facts that led to widespread acceptance of the Big Bang model?
the cosmic background radiation and the high helium content of the universe
Which of the following observations is not a piece of evidence supporting the Big Bang theory?
Relative motions of galaxies in the Local Group
In the 1960s, Maarten Schmidt determined that quasars were very distant objects by
determining their redshifts.
How is the energy that powers radio galaxies, quasars, and other active galactic nuclei produced?
by gravity, which converts potential energy of matter falling toward a central black hole into kinetic energy, which is then converted to thermal energy by collisions among the particles of matter
The most active galactic nuclei are usually found at large distances from us; relatively few nearby galaxies have active galactic nuclei. What does this imply?
Active galactic nuclei tend to become less active as they age.
If we represent the Milky Way Galaxy as the size of a grapefruit (10-cm diameter), the distance to the Andromeda Galaxy would be about
3cm
Star burst galaxies
currently forming stars at a rapid rate. They represent a state of evolution that many galaxies may have gone through at least once in their lives. Since the rates of star formation in starbursts are unsustainable, it is most likely a temporary phase. They must return to a normal state after they run out of gas
Star burst galaxies
currently forming stars at a rapid rate. They represent a state of evolution that many galaxies may have gone through at least once in their lives. Since the rates of star formation in starbursts are unsustainable, it is most likely a temporary phase. They must return to a normal state after they run out of gas
Active galactic nuclei
galactic centers with extreme amount of radiation and sometimes powerful jets of material
Quasars
the brightest active galactic nuclei, extremely luminous. 1000x luminous milky way. They are temporary stages in galaxy evolution. They were common a billions of years ago (young galaxies). • The energy output of quasars comes from a gigantic accretion disk surrounding a massive supermassive black hole
how many galaxies are there
100 billion
Lenticular galaxies
a spiral galaxy that lacks spiral arms
most common type of galaxy in the universe
small elliptical
Hubble’s Galaxy class system
looks like a tuning fork. elliptical on the left (handle) the larger the number the flatte it is. fork is spirals with bulge size decreasing from a to c
Active galactic nuclei
galactic centers with extreme amount of radiation and sometimes powerful jets of material
Quasars
the brightest active galactic nuclei, extremely luminous. 1000x luminous milky way. They are temporary stages in galaxy evolution. They were common a billions of years ago (young galaxies). • The energy output of quasars comes from a gigantic accretion disk surrounding a massive supermassive black hole
how many galaxies are there
100 billion
Lenticular galaxies
a spiral galaxy that lacks spiral arms
most common type of galaxy in the universe
small elliptical
Hubble’s Galaxy class system
looks like a tuning fork. elliptical on the left (handle) the larger the number the flatte it is. fork is spirals with bulge size decreasing from a to c
main sequence fitting
we know the distance of hyades star cluster from parallax, so we compare the apparent brightness of its main sequence stars to those of the main sequence in star clusters in other galaxies
the technique of determining distances by comparing main sequences in different star cluster. We just need the spectral type and brightness. hyades was historically used, but it doesnt contain every type of star. uses parallax. works well within our galaxy
Cepheid variable stars
they are bright stars that follow the• Period-luminosity relationship- The longer the period between peaks in light, the more luminous the cepheid’s luminosities
calculating distances by methods
- With each link in the distance chain, our measurements become more uncertain
- Radar ranging- measure earth sun distance by boucing radio waves off planets and using geometry
- Parallax
- Main sequence fitting- we know the distance of hyades star cluster from parallax, so we compare the apparent brightness of its main sequence stars to those of the main sequence in star clusters in other galaxies
- Celpheid variables- use its period luminosity relationship. We can determine its luminosity by measuring the period between its peaks in brightness
- Distant standards- using the period of galaxies and the luminosities of supernova
shapley
said that spiral nebulae must be relatively nearby because an observed nova in the Andromeda galaxy had the same brightness as one that occurs in our galaxy. He thought spiral nebulae were gas clouds internal to the milky way. He thought the universe was made up of only our galaxy
Shapley was arguing in favor of the Milky Way as the entirety of the universe
curtis
Curtis said there were island universes
Andromeda and other such nebulae were separate galaxies, or “Island universes”
• Period-luminosity relationship
The longer the period between peaks in light, the more luminous the cepheid’s luminosities • They are pulsating variable stars
tully fisher relationship
luminosity and the rotation speed of a galaxy are related
how did hubble find the distance to the Andromeda galaxy
• After grad school he was offered a job at mount Wilson but he volunteered for WW1 instead. Did it after. 1919 started studying spiral nebulae. Discovered Cepheid stars in the Andromeda galaxy and used the period luminosity relation to estimate their distance from the inverse square law. He underestimated the distance by about half, but still showed that they the Andromeda nebula was in fact another galaxy
Cosmological Principle
matter in the universe is evenly distributed • The universe is expanding, but its not expanding into anything.. has no center and no edges
dark matter observations
mass to luminosity doesnt make sense.
rotation curves like ours are flat (instead of dropping off)
we use orbital speeds to calculate mas in spiral galaxies, and red shifts in elliptical ones
galaxy fraction of regular matter to dark matter
regular is 10% dark is 90%
evidence of dark matter
The evidence for dark matter in clusters comes from three ways of measuring stellar masses: measuring the speed of galaxies orbiting the center of the cluster, studying the X ray emission from hot gas between the cluster’s galaxies, and observing how clusters bend light through gravitational lensing
zwicky
the crazy looking guy, argued that clusters of galaxies held large amounts of a mysterious substance (dark matter). He was also one of the first to believe that galaxies existed within clusters • He measured cluster masses by observing galaxy motions and applying newton’s law of motion and gravity. He used redshifts to calculate the speed at which other galaxies are moving away from us. He determined the recession speed (the speed at which the universe is expanding away from us). Once he knew this speed, he could subtract it from the speeds of galaxies around us and find their orbiting speeds (could only tell us the radial speed, the speed they move away from us.) once he knew the average orbital velocity of galaxies, he could use newtons law of gravitation to estimate the clusters mass. Finally, he compared the clusters mass compared to its luminosity. Proportionally, he knew the mass was too large, so he concluded that it contains dark matter
baryonic matter
ordinary matter made of protons, neutrons and electrons (makes up a lot of dark matter)
Nonbaryonic material
extraordinary material. makes up part of dark matter. like neutrinos. cannot hold electrical charge
MACHOs
massive compact halo objects. failed stars that make up part of dark matter
WIMPs
weak interacting massive particles- hypothetical particles like neutrinos that are heavier. we think they comprise most of the dark matter and therefore most of the mass in the universe
what are the possible fate of the universe (2)
1) if gravity is strong enough, the expansion will someday halt and the universe will stop collapsing…
2) if expansion can overcome gravity, the universe will continue to expand forever, growing ever colder as its galaxies grow farther apart
critical density
marks the point between expansion and collapse
. Gravity can win the war over expansion if the density of the universe exceeds 10-29 grams per cubic centimeter. This density called the critical density marks the line between expansion and collapse
stars alone wont be able to reach this. we think we wont reach this even with dark matter
4 possible expansion patterns
recollapsing universe, critical universe, coasting universe, accelerating universe
recollapsing universe
if there is no dark energy and the matter density of the universe is larger than the critical density, then the collective gravity of all its matter will eventually halt the universe’s expansion and causing the great crunch, where the universe collapses in on itself. Final state like a sphere
critical universe
if there is no dark energy and the matter density of the universe equals the critical density, then the collective gravity of all its matter is exactly the amount needed to balance the expansion. The universe will expand more and more slowly. This is the critical density
coasting universe
if there is no dark energy and the matter density of the universe is smaller than the critical density, the collective gravity will not be able to stop the expansion. The universe will continue to expand with its rate remaining mostly unchanged
accelerating universe
if dark energy exerts a repulsive force that causes the expansion of the universe to accelerate with time, then the expansion rate will grow with time. Galaxies will separate from each other and the universe will become cold and dark more quickly than it would as a coasting universe
Ia supernova
Looking at a white dwarf supernova lets us see how far away and therefore how old it is. The amount redshift tells us how much the universe has expanded since then. The data tends to favor an accelerating universe
what do scientists think the fate of the universes expansion is
• We think the universe is doomed to expand forever and get cooler and cooler
What two observable properties of a Cepheid variable are directly related to one another?
the period between its peaks of brightness and its luminosity
Overall, what is our most accurate technique for measuring the distance to a nearby star?
stellar parallax.
You observe the peak brightnesses of two white dwarf supernovae. Supernova A is only ¼ as bright as Supernova B. What can you say about their relative distances?
Supernova A is twice as far away as Supernova B.
Telescopes designed to study the earliest stages in galactic lives should be optimized for observations in ______.
infrared light
The mass of a supermassive black hole thought to power a typical bright active galactic nucleus is roughly ______.
1 billion solar masses
Intergalactic hydrogen clouds are easiest to study by looking at ______.
absorption lines in quasar spectra
The best evidence for the existence of supermassive black holes is:
Very high orbital velocities in a very compact region.
What is a rotation curve?
a graph showing how orbital velocity depends on distance from the center for a spiral galaxy
What is the primary way in which we determine the mass distribution of a spiral galaxy?
We construct its rotation curve by measuring Doppler shifts from gas clouds at different distances from the galaxy’s center.
What do we mean when we say that particles such as neutrinos or WIMPs are weakly interacting?
They respond to the weak force but not to the electromagnetic force, which means they cannot emit light.
t or f The Big Bang predicts that one in four atoms in the universe is helium.
false
