midterm 2 Astro 102

44 terms by mcguiregillan

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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

OBAFGKM

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

plasma

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.

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