Exam 4 Astronomy

 B. from a disk of material around the black hole (material that has been pulled from the companion star and is falling toward the black hole)

 When one member of a binary star system is a black hole, and astronomers detect flickering X-rays coming from the system, where are these X-rays usually coming from?

C. the message will never emerge from the event horizon

 In the far future, a starship becomes trapped inside the event horizon of a black hole. Although the crew discovers that their ship cannot escape, 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?

 E. the spiraling toward each other of two neutron stars

 The first time that astronomers observed both gravitational waves and electromagnetic waves from the same event, what they were observing was:

 D. by observing starlight coming close to the Sun during an eclipse

 When Einstein proposed his General Theory of Relativity, he suggested some pretty strange ideas about space, time, and gravity. How did scientists in 1919 show that Einstein's theory described the behavior of the real world and wasn't just a crazy hypothesis?

 C. equal to zero – you would be weightless

 If you are in a freely falling elevator near the top of a tall building, as the elevator falls, your weight would be:

. an O-type star

 What type of main sequence star is most likely to become a black hole?

mass

 To predict whether a star will ultimately become a black hole, what is the key property of the star we should look at?

the merger of two black holes

In the first direct detection of gravitational waves by LIGO in 2015, the waves came from:

causes a curvature (or warping) of spacetime

According to the general theory of relativity, the presence of mass:

at the center of the Milky Way Galaxy, where matter is more crowded

Astronomers have concluded that growing supermassive black holes (which have millions of times the Sun’s mass or more) is pretty unlikely at our location in the Milky Way Galaxy. Where do they think is the most likely place in the Milky Way for such a supermassive black hole?

It was on a collision course with the Milky Way and would be swallowed by it eventually

What was especially noteworthy about the Sagittarius Dwarf Galaxy when it was discovered among the small galaxies near the Milky Way?

Globular clusters

 What objects did Harlow Shapley use as "signposts" to figure out the extent of the Milky Way Galaxy and the location of its center?

Spiral

 Our Milky Way Galaxy is what type of galaxy?

The Hubble Space Telescope has shown us a visible-light image of an accretion disk at the center of the Galaxy

Which of the following is NOT part of the growing chain of evidence that makes many astronomers suspect there is a black hole at the very center of the Milky Way Galaxy?

A cloud of gas or star that is further from the center will generally take more time to orbit

 Objects orbiting around the center of the Milky Way obey Kepler's 3rd Law. Therefore:

The observation of long moving streams of stars that continue to orbit through our Galaxy’s halo

 Which of the following is evidence that the formation process of our Galaxy may have included collisions with smaller neighbor galaxies?

Find a variable star (Cepheid or RR Lyrae) in the cluster

 An astronomer needs to measure the distance to a globular cluster of stars that is part of a neighboring galaxy nearby the Milky Way Galaxy. What method should she try to use to find the distance?

The dust that extends throughout the disk of the Galaxy only allowed Herschel to see the small part of the Milky Way that surrounds us

 William Herschel thought that the Sun and Earth were roughly at the center of the great grouping of stars we call the Milky Way. Today we know this is not the case. What was a key reason that Herschel did not realize our true position in the Milky Way?

In the disk

Where would you look for the youngest stars in the Milky Way Galaxy?

An invisible halo made of what astronomers are calling “dark matter”

 Astronomers now know that surrounding the main body of our Galaxy (which our various kinds of telescopes have shown to us) and our fainter halo of stars, there is:

the 100-inch reflector on Mount Wilson

The new instrument that made it possible for Edwin Hubble to demonstrate the existence of other galaxies in the early 1920s was:

they are very bright, and generally reach the same peak luminosity

The reason type Ia supernovae are useful to astronomers for determining distances to other galaxies is that:

the faster it is moving away from us

Edwin Hubble was able to show that (with the exception of our nearest neighbors) the farther a galaxy is from us, the:

you must take a spectrum of the galaxy and measure the red shift

 Before you can use Hubble’s Law to get the distance to a galaxy, what observation must you make of that galaxy?

elliptical

Which type of galaxy is observed to contain mostly older stars?

 they are (for galaxies) very close to us, so they are easy to study

 Among irregular galaxies, what makes the Large and Small Magellanic Cloud especially useful for astronomers?

 finding the redshift and using Hubble's Law

What method would astronomers use to find the distance to a galaxy so far away that individual stars are impossible to make out (resolve)?

collisions and mergers between galaxies can sometimes change a galaxy’s type (shape)

Which of the following statements about the different types (shapes) of galaxies is correct?

Finding Cepheid variables and measuring their periods

 One of the main projects being carried out by the Hubble Space Telescope is to measure the distances of galaxies located in groups dozens of millions of light-years away. What method do astronomers use with the Hubble to find such distances?

obtain the speed at which stars or gas near the outer regions of the galaxy are moving around

A graduate student in astronomy needs to measure the mass of a spiral galaxy she is studying for her PhD thesis.  Which of the following observations would be important for her to make?

The energy we see from quasars comes from regions where matter is falling in; these regions are still outside the event horizon

 A science fiction fan says nothing can escape a black hole, so how can one power a quasar?

very powerful and compact sources of energy at the centers of distant galaxies

After decades of observation, astronomers have concluded that quasars are:

to simulate galaxy collisions on a large computer and watch what the simulation predicts

One important way astronomers learn about galaxy collisions is:

a lot of dark matter would affect the motions (orbits) of our spacecraft as they move through the solar system, and we see no such effect

 How do astronomers know there isn’t significant dark matter in our solar system?

compared to the size of a star, the stars are very far apart; but compared to the size of a galaxy, galaxies are close together

 Why do galaxies collide, while stars almost never do?

a quasar

 A Congressman wants to see the object with the biggest redshift. What should astronomers show him?

it must have had an entire generation of stars that was born, lived, and died

 A spectrum from a distant galaxy shows carbon, silicon, and sulfur. This tells astronomers:

 Quasars are active supermassive black holes at the centers of galaxies

 How are galaxies and quasars related?

Their spectral lines were hard to recognize, then turned out to have large redshifts

 If quasars often resemble little blue stars, what surprised astronomers when they were discovered?

from the collision and merger of many smaller fragments

 Astronomers believe large elliptical galaxies formed:

the globular cluster M-13

Which of the following is the Earth not located in?

the extra helium was made during the first few minutes of the Big Bang, when the entire universe was hot enough for fusion to occur briefly

 How do astronomers explain the extra helium in the universe?

the 3-degree cosmic microwave background radiation

Which of the following is pretty good evidence that the universe began with a Big Bang?

 all the stars will die and the galaxies will be dark

 In the very distant future, what will the universe look like?

everywhere at once

 Where in space did the expansion of the universe begin?

some very massive early stars formed

Which of the following did NOT happen during the first few minutes after the Big Bang?

the dark energy makes up just a little less than 70% of the density of the universe, making it the most significant constituent of the mass-energy

According to recent CMB measurements, what makes up most of the universe's energy content?

astronomers have a pretty good idea what the dark matter is made of

 Which of the following statements about dark matter is FALSE?

a few hundred thousand years

 After the Big Bang, how soon did it become cool enough for neutral atoms to form?

about 13.8 billion years

What is the current best estimate for the age of the universe?