AST201H1 Study Guide - Final Guide: Chief Operating Officer, Active Galactic Nucleus, Milky Way

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Interstellar medium absorbs visible ultraviolet and infrared light
Halo of our galaxy has globular clusters
The sun in 28000 light years from the center of the universe
Interstellar bubble are made from the winds of massive stars and supernovae
Most star formation occurs in the spiral arms
Elliptical galaxies are the most spherical in shape
Elliptical galaxies are redder and rounder
Cepheids are pulsating variable stars, and their pulsation periods are directly related to their true
luminosities. Hence, we can use Cepheids as "standard candles" for distance measurements
From the period-luminosity relation for Cepheids, he was able to determine the distance to
Andromeda and show that it was far outside the Milky Way Galaxy
stellar parallax is the most accurate way to determine the distance to a nearby star
parallax, main-sequence fitting, Cepheid variables, Tully-Fisher relation, Hubble's law
Observations at different distances show galaxies of different ages and therefore different stages of
Galaxies were closer together in the past because the universe was smaller.
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 **
How do we know that there are intergalactic clouds between a distant quasar and us? We see
hydrogen absorption lines at redshifts smaller than that of the quasar.
How do we know that there is much more mass in the halo of our galaxy than in the disk? Stars in the
outskirts of the Milky Way orbit the galaxy at much higher speeds than we would expect if all the mass
were concentrated in the disk
A large masstolight ratio for a galaxy indicates that on average, each solar mass of matter in the
galaxy emits less light than our Sun
gravitational lensing occur when masses distort space time, the fabric of the universe and massive
objects can act as gravitational lenses that bend light beams passing nearby
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Why isn't space expanding within systems such as our solar
system or the Milky Way: Their gravity is strong enough to hold them together against the expansion
of the universe
What kinds of atomic nuclei formed during the era of nucleosynthesis? hydrogen and helium and
trace amounts of lithium
Why did the era of nuclei end when the universe was about 300,000 years old? The universe had
expanded and cooled to a temperature of about 3,000 K, cool enough for stable, neutral atoms to
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
What are the two key observational facts that led to widespread acceptance of the Big Bang model? it
predicts the radiation that began to stream across the universe at the end of the era of nuclei should
still be present today and it predicts that some of the original hydrogen in the universe should have
fused into helium during the era of nucleosynthesis
Plasma tail points away from the sun
Why are Cepheid variables so important for measuring distances in astronomy? Their luminosity can
be inferred from their period.
Suppose you measure the parallax angle for a particular star to be 0.1 arcsecond. The distance to this
star is: 10 parsecs.
Which of the following sequences correctly describes the stages of life for a low-mass star? protostar,
main-sequence, red giant, white dwarf
After a supernova event, what is left behind? either a neutron star or a black hole
Compared to the star it evolved from, a red giant is cooler and brighter.
From an observational standpoint, what is a pulsar? an object that emits flashes of light several times
per second or more, with near perfect regularity
Which of the following is closest in size (radius) to a neutron star? A city
What types of stars end their lives with supernovae? stars that are at least several times the mass of the
Which of the following is closest in size (radius) to a white dwarf? the earth
When does a star become a main-sequence star? when the rate of hydrogen fusion within the star's
core is high enough to sustain gravitational equilibrium
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