astro test 3 pt 5
Which stellar spectral type has strong molecular absorption lines in its optical spectrum?
M
In the diagram above, which group represents stars of the largest radii?
e
If you were to come back to our Solar System in 6 billion years, what might you expect to find?
a white dwarf
What makes up the interstellar medium?
gas and dust
What eventually halts the gravitational collapse of an interstellar gas cloud that forms an object that is not massive enough to become a star?
the crowding of electrons in the core
In the diagram above, which group represents the most common type of stars?
d
What keeps the Sun's outer layers from continuing to fall inward in a gravitational collapse?
outward pressure due to super-heated gas
Of the four labeled stars in the diagram above, which one which one could represent the Sun's position in the galaxy?
1
The diagram on the right represents a star with an orbiting planet that, as seen from Earth, periodically transits across the face of the star and disappears behind the star. If you measure the brightness of this system, at which point would it be brightest?
1
You measure the parallax angle for a star to be 0.01 arcseconds. The distance to this star is
100 parsecs.
Of the four labeled stars in the diagram above, which one is located close to a place where evidence suggests we would find a several million solar mass black hole?
2
Of the four labeled stars in the diagram above, which one is located in the halo of the Milky Way galaxy?
4
What percentage of a star's total lifetime is spent on the main sequence?
90%
The figure on the right shows the abundance of elements in the galaxy relative to hydrogen. What is the general trend in elemental abundance?
A) Elements with more protons are less abundant. B) Elements with an odd number of protons are less abundant than neighboring elements. C) Elements with an even number of protons are less abundant than neighboring elements. D) both A and B (this) E) both A and C
Which of the following statements about apparent and absolute magnitudes is true?
A) The magnitude system that we use now is based on a system used by the ancient Greeks over 2,000 years ago that classified stars by how bright they appeared. B) A star with an apparent magnitude of 1 appears brighter than a star with an apparent magnitude of 2. C) The absolute magnitude of a star is another measure of its luminosity. D) A star's absolute magnitude is the apparent magnitude it would have if it were at a distance of 10 parsecs from Earth. E) All of the above are true. (this)
How can astronomers currently determine the temperature of an extrasolar planet?
A) estimate the temperature based on the planet's distance from the star B) measure the drop in total infrared light when the planet passes behind the star from our perspective C) use spectroscopy of the planet to identify the wavelength at which its emission peaks D) AandB (this) E) B and C
What is a geomagnetic storm?
An event initiated by a disturbance in the solar wind that includes radio blackouts, a depression of Earth's magnetic field, and an increase in the number of energetic particles in the solar wind.
What causes the radio pulses of a pulsar?
As the neutron star spins, beams of radio radiation sweep through space. If one of the beams crosses the Earth, we observe a pulse.
What happens to the core of a star after it ejects a planetary nebula?
It becomes a white dwarf.
Which of the following correctly describes how light will be affected as it tries to escape from a massive object?
Light escaping from a compact massive object, such as a neutron star, will be redshifted.
The galactic center lies in the direction of which constellation?
Sagittarius
You see two main-sequence stars with the same spectral type. Star 1 is dimmer in apparent brightness than Star 2 by a factor of 100. What can you conclude, assuming there is no absorption of either star's light by interstellar gas or dust?
Star 1 is 10 times more distant than Star 2.
Imagine comparing a 1.2 solar mass white dwarf to a 1.0 solar mass white dwarf. Which of the following must be true?
The 1.2 solar mass white dwarf has a smaller radius.
Why is there an upper limit to the mass of a white dwarf?
The more massive the white dwarf, the greater the degeneracy pressure and the faster the speeds of its electrons. Near 1.4 solar masses, the speeds of the electrons approach the speed of light, and no more mass can be supported.
Why do we believe that most of the mass of the Milky Way is in the form of dark matter?
The orbital speeds of stars far from the galactic center are surprisingly high, suggesting that these stars are feeling gravitational effects from unseen matter in the halo.
Observationally, how can we tell the difference between a white-dwarf supernova and a massive- star supernova?
The spectrum of a massive-star supernova shows prominent hydrogen lines, while the spectrum of a white-dwarf supernova does not.
Over time, what is the net effect of the star-gas-star cycle in the Milky Way?
The total mass in the galaxy's interstellar medium is gradually reduced, and the remaining gas is continually enriched in heavy elements.
Why are many of the newly detected extrasolar planets called "hot Jupiters"?
Their masses are similar to Jupiter but they are very close to the central star and therefore hot.
At the time the hypothesis was suggested, what major problem was identified with the idea that the Sun was powered by gravitational contraction?
This process would power the Sun for only about 25 million years, but geologists already had evidence the Earth was much older than that.
What is an "extrasolar planet"?
a planet that orbits a star that is not our own Sun
What is Sgr A∗?
a source of bright radio emission in the center of our galaxy
What is the solar wind?
a stream of charged particles flowing outward from the surface of the Sun
Degeneracy pressure stops the crush of gravity in all the following except
a very massive main-sequence star.
What are coronal holes?
areas of the corona where magnetic field lines project out into space, allowing charged particles to escape and form the solar wind
What produces the 21-cm radio line that we can be used to map the Milky Way Galaxy?
atomic hydrogen
In the diagram above, which group represents stars that are extremely bright and emit most of their radiation as ultraviolet light?
c
Order the interior layers of the Sun from the hottest to the coldest.
core, radiation zone, convection zone, photosphere
Which of the following methods has led to the most confirmed discoveries of massive planets orbiting near their parent stars?
detecting the gravitational effect of an orbiting planet by looking for the Doppler shifts in the star's spectrum
Which element has the lowest mass per nuclear particle and therefore cannot release energy by either fusion or fission?
iron
As a solar mass protostar moves on to the main sequence,
its surface temperature increases and its luminosity decreases.
Harlow Shapley concluded that the Sun was not located at the center of the Milky Way Galaxy by
mapping the distribution of globular clusters in the galaxy.
What is the transit method of finding extrasolar planets?
monitoring a star to detect periodic dips in its brightness from the planet passing in front of the star
By what process does the Sun generate energy?
nuclear fusion
Which of the following is the phase of matter in the Sun?
plasma
Sunspots are cooler than the surrounding gas in the photosphere because
strong magnetic fields slow convection and prevent hot plasma from entering the region.
The spectral sequence sorts stars according to
surface temperature.
What did Carl Sagan mean when he said that we are all "star stuff"?
that the carbon, oxygen, and other elements essential to life were created by nucleosynthesis in stellar cores
Which of the following quantities is equal to the energy per second generated by the Sun's nuclear reactions?
the luminosity of the Sun's photosphere
The depth of the dip in a star's brightness due to the transit of a planet depends most directly on
the planet's size.
A star's luminosity is the
total amount of energy that the star radiates each second.
