midterm 2 Astro 102

What do we mean when we say that the Sun is in gravitational equilibrium?
There is a balance within the Sun between the outward push of pressure and the inward pull of gravity.
If you were to come to our Solar System 6 in 6 billion years, what might you expect to find?
a white dwarf
The first step in the proton-proton chain produces an anti-electron, or positron. What happens to the positron?
It is rapidly converted to energy when it meets an ordinary electron, resulting in matter-antimatter annihilation.
How do we know what happens at the event horizon of a black hole?
we don't know for sure: we only know what to expect based on the predictions of general relativity
What is a possible solution to the solar system problem?
the electron neutrinos created in the Sun change into another type of neutrino that we do not detect
The spectral sequence in order of decreasing temperature is
Which of the following is true about low-mass stars compared to high-mass stars?
low-mass stars are cooler and less luminous than high-mass stars
How does a black hole form from a massive star?
During a supernova, if a star is massive enough for its gravity to overcome neutron degeneracy at the core, the core will be compressed until it becomes a black hole.
Why do astronomers often measure the visible-light apparent brightness instead of the total apparent brightness of a star?
in order to measure the total apparent brightness of a star, you must measure its brightness in all WL's, and this is difficult to do. the only WL's you can measure from the surface of Earth are visible and radio WL's
The figure shows 4 H-r diagrams for different clusters of stars. which cluster is 10 billion yo?
A- (looks like a medium sized Z)
what happens to the visible radiation produced by new stars within a molecular cloud?
it is absorbed by dust grains and heats up the cloud
what is the closest temperature tot he core of the sun?
10 million K
What prevents the pressure from increasing as a cloud contracts due to its gravity?
thermal energy is converted to radiative energy via molecular collisions and released as photons
the H-r diagram in the figure shows the life track of a 1-solar mass star, with various stages labeled with roman numerals. which stage lasts longest?
iii. (on the main sequence)
the most distance stars we can measure stellar parallax are approximately
100 parsecs away
what is the difference between brown dwarfs and jupiter
brown dwarfs are more massive than jupiter
what is the range of timescales for star formation?
from 1 million years for the most massive stars up to 100 million years for the least massive stars
from a theoretical standpoint, what is a pulsar?
a rapidly rotating neutron star
the phase of matter in the sun is
no stars have been found with masses greater than 100 times the sun because
they would generate so much power they would blow themselves apart
which of the following statements about degeneracy pressure is NOT true
degeneracy pressure varies with the temp of the star
on the Hertz-sprung-Russell diagram, where would we find stars that are cool and dim
lower right
which of the following terms is given to a pair of stars that appear to chance positions in the sky, indicating they are orbiting one another?
visual binary
which of the following is the closest size (radius) to a neutron star?
a city
which is happening inside a star while it expands into a sub-giant?
it is fusing hydrogen into helium in a shell outside the core
the core of the sun is
hotter and denser than the surface
what happens to the core of a star after a planetary nebula occurs?
it becomes a white dwarf
look at
look at
why does a star grow larger after it exhausts its core hydrogen
hydrogen fusion in a shell outside the core generates enough thermal pressure to push the upper layers outward
consider the star to which the arrow in the H-R diagram above points. how is it currently generating energy?
by hydrogen shell burning around an inert helium core
suppose that, for some unknown reason, the core of the sun suddenly became hotter. which of the following best describes what would happen
higher temp would cause the rate of nuclear fusion to rise, which would increase the internal pressure, causing the core to expand and cool until the fusion rate returned to normal
what is a planetary nebula
the expanding shell of gas that is no longer gravitationally held to the remnant of a low-mass star
after a supernova event, what is left behind
either a neutron star or a black hole
what is the eventual fate of a brown dwarf
it gradually cools down and becomes even dimmer
you discover a binary star system in which one member is a 15 Msun main sequence star and the other star is a 10 Msun giant. how do we believe that a star system such as this might have come to exist?
the giant must once have been the more massive star but transfered some of its mass to its companion
which of the following may be caused by a protostellar disk
protostellar jets, protostellar winds, accretion of material onto a star, relatively slow protostellar rotation
you observe a star in the disk of the milky way, and you want to plot the star on the H-R diagram. You will need to determine all of the following EXCEPT the
rotation of the star
what is the ultimate fate of an isolated white dwarf
it will cool down and become a cold black dwarf
what type of star is our sun
a low mass star
what kind of pressure supports a white dwarf
electron degeneracy pressure
briefly describe what you would see if your friend plunged into a black hole
once he entered into the event horizon he would no longer be able to be seen.No light escapes and therefore time slows down for him and his body would be stretched and squeezed as he neared the singularity. time would move normal for you. it would be redshifted light
two stars, betty and wilma are both on the main sequence. Betty is more luminous than Wilma. which one has a hotter surface temp? which one is more massive? which one is bigger? if they both formed at the same time, which on will evolve off the main sequence first? draw and label a HR diagram to help you answer this Q
better has a higher surface temp, is more massive and bigger. Betty will evolve off the main sequence first and have a shorter lifetime since it has a higher fusion rate, even though it has more fuel. (look at diagram)
what are the 3 types of pressure that can push against the inward force of gravity? explain what causes each type and where it would be likely to occur?
degeneracy pressure- occurs in white/brown dwarfs and neutron stars. the electrons/neutrons are packed so tightly that they are moving at the speed of light and cant be compacted anymore. (chair ex)
thermal pressure- protostars, low mass stars. contraction causes the cores to heat up and expand pushing against gravity
radiative pressure- high mass stars. photons are radiated out causing the core to heat up and expand
briefly explain why high mass stars have shorter lifetimes than low mass stars
because they have higher fusion rates. even though they have more fuel, they use it a lot quicker than the low mass stars.