Astronomy Quizzes and Homework
According to our textbook, roughly what percent of the mass and energy contents of the universe is made up of dark matter plus dark energy?
95%
Let's imagine a cluster of stars that formed long ago. Say this cluster contains a wide range of stars with different characteristics that all formed at the same time. Eventually, all the stars will die and become some kind of remnant (star corpse). Please put the following stars in order of how long it takes them from birth to death, arranged in order from the shortest life to the longest life.
A star with 120 times the mass of our sun when it is born A star (without a companion) that will explode and become a neutron star when it dies A star with the mass of our sun when it is born A star with 70% the mass of our sun when it is born
Consider how we "Weigh Galaxies" Part (b) What have we learned about the total mass, its make-up, and its distribution?
We have learned that mass isn't just centered in one place. In fact, it is distributed through the halo of a galaxy which is dark matter
Consider how "we weigh" galaxies. Part (a) How can we use orbital properties of gas and stars to learn about the mass of the Galaxy?
Well, if we take the orbital period, and we have the radius we can use this information and Newton's version of Kepler 3rd law to determine the mass of a galaxy. We do this by observing a star and the speed at which the star is orbiting to help us determine mass
When a star too massive to make a white dwarf (but not massive enough to make a black hole) dies, its core becomes a ___________. The collapse of the core produces an object with a typical mass twice the mass of our Sun, but the diameter of _____________. At first astronomers did not think they could ever observe such a remnant, but then in the late 1960's, Jocelyn Bell and Antony Hewish discovered __________, which gave off rhythmic radio waves. The connection all came together when one of their objects was discovered at the center of the ___________, one of the best-known supernova remnants. The objects Bell and Hewish discovered produce beams of energy that we can observe when the beams happen to point in our direction. Astronomers think that the energy comes out in beams because these objects have a strong _________.
When a star too massive to make a white dwarf (but not massive enough to make a black hole) dies, its core becomes a NEUTRON STAR. The collapse of the core produces an object with a typical mass twice the mass of our Sun, but the diameter of THE SIZE OF A SMALL TOWN. At first astronomers did not think they could ever observe such a remnant, but then in the late 1960's, Jocelyn Bell and Antony Hewish discovered PULSARS, which gave off rhythmic radio waves. The connection all came together when one of their objects was discovered at the center of the CRAB NEBULA, one of the best-known supernova remnants. The objects Bell and Hewish discovered produce beams of energy that we can observe when the beams happen to point in our direction. Astronomers think that the energy comes out in beams because these objects have a strong MAGNETIC FIELD.
With modern telescopes, astronomers can observe galaxies that are, as the Star Wars movies say, "far, far away." They need large telescopes, because these distant galaxies appear very _____. One advantage of looking at galaxies really far away is that we see them far __________, allowing us to figure out the evolution of galaxies. Astronomers calculate the distance to a far-away galaxy by measuring its _______. For galaxies that are too far away to get a spectrum, they look at the galaxy's overall _____ to get a sense of what kind of stars it is dominated by. From its oldest constituents, astronomers estimate the age of the Milky Way Galaxy to be at least _________ years and other galaxies probably also started being formed that long ago.
With modern telescopes, astronomers can observe galaxies that are, as the Star Wars movies say, "far, far away." They need large telescopes, because these distant galaxies appear very FAINT. One advantage of looking at galaxies really far away is that we see them far BACK IN TIME, allowing us to figure out the evolution of galaxies. Astronomers calculate the distance to a far-away galaxy by measuring its RED-SHIFT. For galaxies that are too far away to get a spectrum, they look at the galaxy's overall COLOR to get a sense of what kind of stars it is dominated by. From its oldest constituents, astronomers estimate the age of the Milky Way Galaxy to be at least 13 BILLION years and other galaxies probably also started being formed that long ago.
Astronomers today know a lot about the size and shape of the Milky Way Galaxy. Which of the following common objects most resembles the shape of our Galaxy?
a CD or a DVD
Deep inside a black hole (and hidden from our view) is the compressed center, where all the "stuff" of the star goes. Astronomer call this central point
a singularity
From which of the following will a wave of light show the greatest gravitational redshift:
a white dwarf
In the very distant future, given our best model of the accelerating universe, what will the universe look like?
all the stars will die and the galaxies will be dark
Which of the following statements about dark matter is FALSE:
astronomers have a pretty good idea what the dark matter is made of
Astronomers have noticed that the visible filaments in the Crab Nebula are moving outward from a common center at great speed. How can they know about motions like this?
from the Doppler shift in the line radiation from the nebula
Where would you look for the youngest stars in the Milky Way Galaxy?
in the disk
The equivalence principle (principle of equivalence) says that
the effects of gravity are equivalent to the effects of acceleration
Edwin Hubble was able to show that (with the exception of our nearest neighbors) the farther a galaxy is from us, the
the faster it is moving away from us
According to Einstein's general theory of relativity, the stronger a star's gravity,
the slower time runs near it
When neutron stars were first predicted theoretically, no scientist expected to be able to detect one of them across interstellar distances. What enabled astronomers to find neutron stars in the late 1960's?
we found strongly magnetic neutron stars whose whirling beams of energy were detected as pulsars
Before you can use Hubble's Law to get the distance to a galaxy, what observation must you make of that galaxy?
you must take a spectrum of the galaxy and measure the red shift
According to our best theory of gravity, all the galaxies in the universe must be either going toward each other or ___________. Our theories and observations about cosmology today indicate that the universe began with a ________. According to Hubble's Law, the velocity (speed) of a galaxy is proportional to its ___________. If the universe has been obeying this simple law throughout its history, then its age is equal to the _________ time. If gravity and only gravity now plays a significant role in governing the motion in the universe, then we expect to see these motions experience ___________. But in fact, recent observations using supernovae, have shown that the universe is now experiencing __________.
According to our best theory of gravity, all the galaxies in the universe must be either going toward each other or EXPANDING AWAY FROM EATH OTHER. Our theories and observations about cosmology today indicate that the universe began with a BIG BANG. According to Hubble's Law, the velocity (speed) of a galaxy is proportional to its DISTANCE. If the universe has been obeying this simple law throughout its history, then its age is equal to the HUBBLE time. If gravity and only gravity now plays a significant role in governing the motion in the universe, then we expect to see these motions experience A DECELERATION. But in fact, recent observations using supernovae, have shown that the universe is now experiencing AN ACCELERATION.
Put the following in order of how abundant they are in the universe (how much of the universe they make up), starting with the least abundant to the most abundant.
Atoms in living things Matter inside stars Ordinary Matter Dark Matter Dark Energy
Edwin Hubble divided galaxies into types by their shape. Those galaxies that were flat and had arms or lanes of stars were called ________. Rounder, older galaxies were given the name __________, and galaxies whose shape did not fit an easy pattern and that were generally a bit less massive than the other two types were called __________. The galaxies that generally have almost no gas and dust in them are the _______________. But Hubble's classification scheme was done before the discovery of ____________, whose gravity may play a significant role in the evolution of galaxies, even though at present we can't see it.
Edwin Hubble divided galaxies into types by their shape. Those galaxies that were flat and had arms or lanes of stars were called SPIRALS. Rounder, older galaxies were given the name ELLIPTICALS, and galaxies whose shape did not fit an easy pattern and that were generally a bit less massive than the other two types were called IRREGULARS. The galaxies that generally have almost no gas and dust in them are the ELLIPTICALS. But Hubble's classification scheme was done before the discovery of DARK MATTER, whose gravity may play a significant role in the evolution of galaxies, even though at present we can't see it.
Consider a white dwarf supernova. Why are they useful for finding the distance to very remote galaxies? Answer in a few sentences.
They are useful for finding the distance to very remote galaxies because they act as a standard candle once you get really far out into space. They are really bright and sometimes even brighter than galaxies which means that they can be seen at very long distances.
Even in Newton's theory of gravity, scientists could see that if you compressed a star further and further, eventually it would become so small that the __________ became greater than the speed of light. In the general theory of relativity, as a star collapses at the end of its life, it is the ____________ that prevents light from escaping. The region around a black hole inside which light can no longer escape is called the _____________. The size of this region turns out to depend only on __________. Far away from the black hole, the gravity is _________ the gravity had been when the star that collapsed was still a regular star.
Even in Newton's theory of gravity, scientists could see that if you compressed a star further and further, eventually it would become so small that the ESCAPE VELOCITY became greater than the speed of light. In the general theory of relativity, as a star collapses at the end of its life, it is the CURVATURE OF SPACETIME that prevents light from escaping. The region around a black hole inside which light can no longer escape is called the EVEN HORIZON. The size of this region turns out to depend only on THE MASS INSIDE IT. Far away from the black hole, the gravity is THE SAME AS the gravity had been when the star that collapsed was still a regular star.
Put the following astronomical objects in order of size (diameter), from the smallest to the largest.
Neutron star White Dwarf Sun Red Giant Star Supernova remnant, 500 years after the explosion
Our best and most sophisticated theory of gravity is Einstein's ______________. The idea with which Einstein started, that free-fall is indistinguishable from gravity, is called the ______________. In his theory, the presence of mass bends or warps __________. This revolutionary idea was only accepted by scientists after experimental proof was found. Such evidence includes a small change in the orbit of the planet ______ from what Newton's theory of gravity predicts; the deflection of starlight by the Sun, observed during __________; and the increase in wavelength of radiation given off by objects with really strong gravity, which is called the ______________.
Our best and most sophisticated theory of gravity is Einstein's GENERAL THEORY OF RELATIVITY. The idea with which Einstein started, that free-fall is indistinguishable from gravity, is called the EQUIVALENCE PRINCIPLE. In his theory, the presence of mass bends or warps SPACETIME. This revolutionary idea was only accepted by scientists after experimental proof was found. Such evidence includes a small change in the orbit of the planet MERCURY from what Newton's theory of gravity predicts; the deflection of starlight by the Sun, observed during ECLIPSES; and the increase in wavelength of radiation given off by objects with really strong gravity, which is called the GRAVITATIONAL REDSHIFT.
Please put the following things that astronomers can observe in order of distance from the nearest to the farthest.
Pluto and its moon Charon The center of the Milky Way galaxy The Andromeda Galaxy (M31) The most distant Cepheid astronomer can observe The most distant galaxy which we have seen at Type la Supernova
Consider a white dwarf supernova. Can they be used to find the distance to any galaxy you might choose? Answer in a few sentences.
Probably not because each galaxy probably does not have a supernova in that galaxy right when you are trying to make your observations.
Some words are missing from the following paragraph.Stars that have starting masses of about 8 times the mass of the Sun are too massive to end up as white dwarfs. Because the star's core has more mass, it can reach higher temperatures later in the life of the star, making possible the _________ of heavier elements. That allows the star's core to continue generating energy. However, this process stops when the star reaches the element _______, which requires energy instead of giving off energy when it is turned into a heavier element. When energy is being drained from the core, at the same time that gravity wants it to collapse, the core undergoes a catastrophic collapse and becomes a ____________. The process of forming such a really compressed remnant from the star's core includes the emission of a huge number of ____________. The rest of the star explodes violently; astronomers call such an explosion a ___________. These explosions are so energetic, that in them some of the heaviest elements in nature can be created.
Some words are missing from the following paragraph.Stars that have starting masses of about 8 times the mass of the Sun are too massive to end up as white dwarfs. Because the star's core has more mass, it can reach higher temperatures later in the life of the star, making possible the FUSION of heavier elements. That allows the star's core to continue generating energy. However, this process stops when the star reaches the element IRON, which requires energy instead of giving off energy when it is turned into a heavier element. When energy is being drained from the core, at the same time that gravity wants it to collapse, the core undergoes a catastrophic collapse and becomes a NEUTRON STAR. The process of forming such a really compressed remnant from the star's core includes the emission of a huge number of NEUTRINOS. The rest of the star explodes violently; astronomers call such an explosion a SUPERNOVA. These explosions are so energetic, that in them some of the heaviest elements in nature can be created.
Recent observations indicate that the universe is expanding faster today than it was a few billion years ago (that, in other words, the expansion of the universe is accelerating.) What kind of observations have led astronomers to this surprising conclusion?
The measurement of galaxy distances using type Ia supernovae
One of the most important observations in the history of astronomy was the one by Edwin Hubble that established that there are other galaxies, quite removed from the Milky Way. How did Hubble show this?
by observing a Cepheid variable in a nearby galaxy and using it to get the distance
