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AST EXAM 3
Terms in this set (99)
Can a cataclysmic variable star have more than one nova episode?
As more material is transferred to a neutron star from its binary companion, which of the following effects occurs?
- The neutron star starts spinning faster.
- The radius of the neutron star decreases.
- X-ray bursts are observed near the surface of the neutron star.
Which of the following qualities of Type Ia supernovae allow them to be used as "standard candles" or "standard bulbs" by astronomers for determining distances?
- There is little variation among their maximum luminosities.
- There is little variation in the way their light output initially increases and then slowly decreases over time.
Supernova 1993J was a Type Ia supernova observed with a peak apparent magnitude of about +10.5. Given that these events exhibit a peak absolute magnitude of about -19.5, how far away is/was this star?Express your answer in parsecs, rounded to the nearest 100,000 parsecs.
Match each element with the source that distributes the most significant amount of it throughout space.
- carbon = dying low mass stars
- sodium = exploding massive stars
- manganese = exploding white dwarfs
- gold =merging neutron stars
What is formed when gravity overcomes both electron degeneracy pressure and neutron degeneracy pressure?
a black hole
One way of detecting a black hole is by looking for a companion in a binary system that shines brightly in x-rays but not in visible light. Where do these x-rays originate?
the accretion disk
On May 29th, 1919 during a solar eclipse, observers saw a star that should've been behind the Sun appear to its side. How were they able to observe this star?
The Sun's gravity bent the path of the light coming from the star.
What is gravity?
the curvature of spacetime in the vicinity of a massive object
GPS relies on an array of 24 satellites orbiting the Earth, and at least 4 of them are visible from any spot on Earth. The combined effects of special and general relativity mean that the clocks on the Earth fall behind by a tiny amount each day compared to the clocks on board these satellites. By how much do clocks on the Earth tick slower each day? Express your answer in microseconds.
Light rays are bent substantially in the vicinity of a large mass like a neutron star. What is one consequence of this phenomenon?
We can see more than half of the surface of a neutron star from any angle.
If the entire mass of the Sun were compressed into a black hole, what would its Schwarzschild radius be?
Match the following phenomena with the terms describing them.
- light traveling away from the black hole becomes stretched to longer wavelengths = gravitational redshift
- as measured by an outside observer, time progresses more slowly closer to the event horizon = gravitational time dilation
- objects are stretched and ripped apart as they approach the black hole = spaghettification
(Select all that apply.) Otto journeys toward the event horizon of a black hole while Olivia stays at a distant space station to observe. What does Olivia see as she watches Otto's journey?
- Otto appears to change from orange to red and eventually fades to infrared.
- Otto is stretched and squeezed from a ball shape into a noodle shape.
- Otto's watch ticks much more slowly than Olivia's.
(Select all that apply.) What does Otto experience as he crosses the event horizon of a supermassive black hole?
He passes through, noticing only an increasing stretching force.
A black hole will inevitably suck up everything in the universe.
(Select all that apply.) How did astronomers discern the location and mass of the super massive black hole Sag A*?
- Astronomers observed radio waves and other light coming from the accretion disk around the black hole.
- Astronomers studied the orbits of stars orbiting Sag A*.
The supermassive black hole at the center of galaxy M87 has an estimated mass of 6 billion times the mass of the Sun. What is the approximate radius of its event horizon?
18 billion km
What would happen to the orbits of the planets in our solar system if the Sun were replaced with a 1 solar mass black hole?
Their orbits would be completely unaffected.
Which of the following statements about a black hole's Schwarzschild radius is correct?
- It corresponds with the event horizon for a non-rotating black hole.
- It is the distance within which the escape velocity is equal to the speed of light.
Which of the following statements about our Sun are true? (Select all that apply.)
- The Sun's Schwarzschild radius is 3 km.
- The Sun causes spacetime to curve in its viscinity.
In the far future, a starship becomes trapped inside the event horizon of a black hole. Although the crew discovers that their ship cannot out, they at least want to send a message to other ships in the area to stay away from the danger zone. If they send out a message in the form of a radio wave, what will be its fate?
The message will never emerge from the event horizon.
What is a key reason that gravitational waves are so much harder to detect than electromagnetic waves?
Gravitational waves are much weaker than electromagnetic waves and therefore require very, very precise equipment to detect.
In the first direct detection of gravitational waves by LIGO in 2015, the signal came from...
the merger of two black holes.
The first time that astronomers observed both gravitational waves and electromagnetic waves from the same event, the event they observed was...
the spiraling toward each other and merger of two neutron stars.
How do we know what the Milky Way looks like? (Select all that apply.)
- by mapping out the locations and distances of stars in the Milky Way
- by looking at other distant galaxies with structures similar to our own
How did Harlow Shapley deduce the location of the center of the Milky Way Galaxy?
He found the center of the distribution of globular clusters.
A globular cluster is observed to contain a Cepheid variable star with an average apparent magnitude of +10.8. Based on the period of variation of its magnitude, it's estimated to have an absolute magnitude of -4.9. How far away from the Sun is this globular cluster?
Match the following parts of the Milky Way Galaxy with their descriptions.
The Bulge: The dense collection of yellow stars at the center of the galaxy.
The Disk: The thin, swirling collection of gas, dust, and stars of various ages that orbit around the galactic center.
The Halo: The diffuse scattering of old stars and globular clusters above and below the galactic plane.
Where in the galaxy would the Sun have to be in order for us to view the Milky Way face-on (instead of a band of light circling the sky)?
in the halo, far away from the disk
Match the following galaxy types to their descriptions.
Elliptical Galaxy: A dense collection of stars mostly devoid of gas in a spherical or ellipsoidal shape.
Spiral Galaxy: A swirling galaxy of dust and stars, including a disk rotating around a dense central bulge.
Irregular Galaxy: A disorganized collection of stars and gas with no coherent shape or structure.
What property separates Barred Spiral Galaxies from regular Spiral Galaxies?
Regular Spiral Galaxies have a mostly spherical bulge, while Barred galaxies have a more elongated bulge.
Which of the following types of galaxies appears reddish orange?
Match each labeled part of this galaxy to the correct term for it.
c. globular cluster
Why do we tend to find open clusters in the disk but not in the halo?
Open clusters are young structures, and the dust needed to form them is only found in the disk.
Match the following galaxy images with the correct classification.
Which of the following statements applies to a "Fork Diagram" as made by Edwin Hubble?
Graphically organizes all of the majors types of galaxies except for irregular galaxies.
In which of the following would you find new star formation? (Select all that apply.)
Barred Spiral Galaxies
In which part of the Milky Way Galaxy can you find most new stars forming?
How do we think the Milky Way Galaxy developed into its present form?
Both (A) and (B)
Imagine viewing the Milky Way and Andromeda galaxies from very far away over the next several billion years. Sort the following into the order in which these two galaxies would appear from earliest (now) to latest (several billion years from now).
1. two large barred spiral galaxies approaching each other
2. two distorted spiral galaxies with emerging tidal streams
3. a "peculiar" galaxy with many H II regions and large amounts of star formation
4. an elliptical galaxy with a yellowish-white appearance
The Milky Way Galaxy is part of
the Local Group.
Which of the following are properties of Population I stars? (Select all that apply.)
-Located in the disk.
-A high proportion (1-4%) of heavy elements.
-Located in the disk.
-A high proportion (1-4%) of heavy elements.
Which of the following are properties of Population II stars? (Select all that apply.)
- Located mostly in the halo.
- Almost no or very few bright blue stars
In our solar system, most of the mass is concentrated in the Sun at the center of the solar system. How should the orbital speeds of the planets change with increasing distance from the Sun?
Their orbital speed should decrease, because the radius of each orbit is increasing while the mass inside each orbit isn't changing much.
Which star's orbit should you use to best measure the mass of the galaxy's bulge only?
How does the orbital speed of stars in the middle of the Milky Way Galaxy's disk compare to stars at the edge of the disk?
The stars in the middle of the disk orbit at close to the same speed as the stars at the edge of the disk.
The above graph shows our expectation for how the rotation curve of the Milky Way Galaxy should look based on the mass we are able to see (the dashed blue line) and the actual observed curve (the solid black line). What does this tell us about the mass in the galaxy?
Most of the mass is invisible.
What is dark matter?
the mass in galaxies that affects the orbits of stars, but does not emit or reflect any light
What is gravitational lensing?
the bending of light from a distant object by the curved spacetime of a closer, more massive object or objects
Which of the following is an example of the Doppler Effect?
A boat traveling across a lake creates tightly packed waves in front of it and loosely packed waves behind it.
You're sitting in front of your home when an ambulance passes by with its siren blaring. What do you hear?
A higher pitched siren as the ambulance approaches, a regular sounding siren as it passes by you, and a lower pitched siren as it drives away.
Each diagram shows a pair of absorption spectra with a set of spectral lines. The top spectrum always shows the lines as they appear in a spectrum created in a laboratory on Earth ("Lab") and the bottom spectrum shows the same set of lines from a distant star or galaxy. Which of these spectra corresponds to the celestial object moving with the greatest radial velocity (toward or away) relative to Earth?
Each diagram shows a pair of absorption spectra with a set of spectral lines. The top spectrum always shows the lines as they appear in a spectrum created in a laboratory on Earth ("Lab") and the bottom spectrum shows the same set of lines from a distant star or galaxy. Which of these spectra corresponds to the celestial object moving toward Earth the fastest?
Each diagram shows a pair of absorption spectra with a set of spectral lines. The top spectrum always shows the lines as they appear in a spectrum created in a laboratory on Earth ("Lab") and the bottom spectrum shows the same set of lines from a distant star or galaxy. Which of these spectra corresponds to the celestial object moving away from Earth the fastest?
An important emission line for Hydrogen is found at a wavelength of around 656.5 nm when the source is at rest. This emission line is observed in several different sources at the wavelengths listed below. Which source is moving towards the observer the fastest?
True or False? If light has been "blue shifted", it means the light now appears blue.
Which of the following describes a red shift of light? (Select all that apply.)
- A source emits a gamma ray. The observer sees an x-ray.
- A source emits blue light. The observer sees green light.
At rest in a lab, hydrogen has an emission line at a wavelength of 656.3nm. In a distant galaxy, the corresponding absorption line is found at a wavelength of 787.6nm. What is this galaxy's redshift, z? (Express your answer to two decimal places.)
A distant galaxy is observed to have a redshift of z = 0.2. What is the recession speed of this galaxy? (Express your answer in km/s, rounded to the nearest 1000 km/s.)
At rest in a lab, hydrogen has an emission line at a wavelength of 656.3nm. In a distant galaxy, the corresponding absorption line is found at a wavelength of 707.3 nm. What is this galaxy's redshift, z? (Express your answer to two decimal places.)
While studying the spectra of galaxies to measure their composition, Vesto Slipher found... (Select all that apply.)
- only a few of the galaxies he observed exhibited blueshifted absorption lines.
- the vast majority of the galaxies he observed were moving away from us.
- galaxies he observed have much higher Doppler shifts than stars he observed.
This graph plots the recession speed of distant galaxies against their distance away from us, determined using type Ia supernovae. What conclusion do we draw from this graph?
The recession speed of galaxies increases the farther away from us they are.
Which of the following questions could we answer using Hubble's Law?
Both (a) and (b).
a. Given a measurement of a galaxy's recession speed, how far away is it?
b. Given a measurement of a galaxy's distance, how fast is it receding?
As we survey the Doppler Shifts of galaxies, we find that...
Nearly every galaxy is red shifted, meaning almost all galaxies are moving away from us.
Hubble's Constant has been measured to have a value of H0 = 71 km/s/Mpc. If a galaxy is 2 Mpc away, what is its recession speed? (Express your answer in km/s.)
Hubble's Constant has been measured to have a value of H0 = 71 km/s/Mpc. If a galaxy's recession speed is determined to be 355 km/s, how far away is it? (Express your answer in megaparsecs, Mpc.)
What do we mean when we say that the Universe is expanding?
The distances between fixed points in space is expanding, making galaxies all move away from each other.
We observe the light of distant galaxies to be redshifted, even though we now know their apparent motion is almost entirely due to the expansion of the Universe. Why, then, do we observe a redshift?
The expansion of the Universe stretches out the light to longer wavelengths.
According to modern ideas and observations, what can be said about the location of the center of our expanding universe?
The universe does not have a center.
How do local forces and motion between nearby galaxies compare to the expansion of the universe?
On small scales, gravity dominates the relative motion of galaxies. On large scales, expansion dominates the relative motion of galaxies.
Order the following tools for measuring distances in the universe by the distances for which they are most appropriate from nearest (1) to farthest (4).
2. Cepheid varibles
3. Type Ia supernovae
An astronomer captures a supernova occurring in a galaxy far, far away with a telescopic survey. By observing it over a range of several days, they determine it peaked in brightness with an apparent magnitude of +13.7 and diminishged in brightness in a way that matches the behavior of Type Ia supernovae. Given that these supernova peak in absolute mangitude at about -19.5, how far away is the galaxy that hosted this supernova?
Order the following steps for conducting a redshift survey from first (1) to last (3).
1. Measure a distant galaxy's redshift.
2. Calculate a distant galaxy's recession velocity.
3. Infer a distant galaxy's distance from Hubble's law.
Estimate the distance to the galaxy which hosted the supernova shown above. (Blue is observational data while red is the theoretical light curve for a Type Ia supernova.) A straight line at the peak brightness lets you compare apparent and absolute magnitude.
Express your answer in megaparsecs (Mpc, or millions of parsecs).
The idea that free fall is indistinguishable from (and hence equivalent to) zero gravity is called...
the equivalence principle.
Which of the following helped to prove Einstein's general theory of relativity? (Select all that apply.)
- calculations of the changes to the orbit of Mercury
- the deflection of light paths near the Sun
When all the mass of a star's core collapses into a single point with zero volume and infinite density, we call this point...
A disturbance of spacetime created from any movement of matter is called
a gravitational wave
Which of the following helped Edwin Hubble make his first estimates about the distance between Earth and the Andromeda galaxy?
What type of galaxy appears disorganized with many undergoing relatively intense star formation activity?
Which of the following types of galaxies are places where many new stars can form? (Select all that apply.)
- Spiral galaxies
- Irregular galaxies
Which of the following standard bulbs has proven to be the most accurate?
Type Ia supernovae
Measurements taken from our galaxy and other galaxies support the conclusion that material that cannot presently be observed in any part of the electromagnetic spectrum accounts for ______ of the material in the universe.
Which of the following binary pairings are possible?
- A main-sequence star and a neutron star
- A red giant and a white dwarf
- Two main-sequence stars
- Two neutron stars
When stars in a binary star system are close enough together where material can flow from one star to the other, astronomers call this process:
When a white dwarf steals enough hydrogen from its binary companion to start fusion and the mass of the white dwarf stays below the Chandrasekhar limit, the explosion that results is called a:
Nova (new star)
A white dwarf is considered to have a mass over the Chandrasekhar mass limit when its mass exceeds ____ .
What type of remnant is left behind after a type Ia supernova?
No remnant is left behind
Which of the following are true about William Herschel's observations? (Select all that apply.)
- He made the first important discovery about the architecture of the Milky Way.
- He concluded that the stellar system to which the Sun belongs has the shape of a disk or wheel.
- His conclusions about the shape of the stellar system to which the Sun belongs were correct.
Match the following terms related to the structure of our galaxy to the correct descriptions.
halo: a spherical region of very old, faint stars that extends to a distance of at least 150,000 light-years from the galactic center
central bulge: a region of stars within about 10,000 light-years from the galactic center where stars are not confined to the disk
dark matter halo: an invisible region of unknown composition that extends at least 200,000 light-years from the galactic center
bar: an oblong or rectangular concentration of stars across the galaxy's central region
Determine whether the following characteristics are describing stars in the thin disk or stars in the stellar halo.
young stars: thin disk stars
orbit the galaxy's center at high speed: thin disk stars
old stars: stellar halo stars
low abundances of elements heavier than hydrogen and helium: stellar halo stars
have highly elliptical orbits randomly oriented in direction: stellar halo stars
What shape was the protogalactic cloud that formed our galaxy?
Which of the following describes Population II stars? (Select all that apply.)
- consists of all the stars in the halo and globular clusters
- consists of entirely old stars that formed very early in the history of the galaxy
Which of the following scientists was the first to discover that almost every galaxy (called spiral nebulae at the time) was moving away from us at incredible speeds?
The more distant the galaxy, the slower it is receding from us.
If a galaxy is 250 million light-years away from us, how fast is it receding from us?(Express your answer in km/s, but input only the numerical value. Use 22 kilometers per second per million light-years as the value for Hubble's constant.)
5500 bc 250*22=5500
Knowing a galaxy's recession velocity, Hubble's law can also allow us to determine the _____ remote galaxies.
As the Universe expands, which of the following also expands? (Select all that apply.)
- space itself
- the distance between us and a very distant galaxy
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