E3 Homework 4

Which of the following objects do many astronomers believe is a black hole?

Cygnus X-1

The first, indirect detection of gravitational waves in the 1970s involved

a pulsar that was in a binary star system with a neutron star

Deep inside a black hole (and hidden from our view) is the compressed center, where all the "stuff" of the star goes. Astronomers call this central point

a singularity

From which of the following will a wave of light show the greatest gravitational redshift:

a white dwarf

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

an O-type star

Suppose each of the following objects could collapse into a black hole. Each black hole would have a sphere around it that is the limit for escape -- once you are inside this region, you cannot get away. For which object would this region be the largest in diameter?

an entire galaxy of stars (with about a billion stars in it)

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?

by observing starlight coming close to the Sun during an eclipse

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

causes a curvature (or warping) of spacetime

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

equal to zero - you would be weightless

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?

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)

A handsome, rich, but vain movie star notices that he is starting to age, and consults you as his astronomy expert, to see if you can find an astronomical way to slow down his aging. Putting aside practical considerations (such as the fact that we cannot travel to other stars), which of the following strategies would IN THEORY allow him to age more slowly than the rest of humanity?

he should travel to a black hole, and spend some time in orbit just above the event horizon

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

mass

Wearing a very accurate watch, you volunteer to go on a mission to a black hole in a spaceship that has powerful rockets. You are able to orbit the black hole and stay a little distance outside of the event horizon. Compared to watches on Earth, your watch near the black hole will run:

more slowly

Far away from a black hole (at the distance of another star), which of the following is a possible way to detect it?

search for flickering x-rays being given off from an accretion disk around the black hole, as it "eats" part of a neighbor star

In 1959, Pound and Rebka did an experiment to test the prediction of Einstein's general theory of relativity about the relationship between the pace of time and the strength of gravity. They did this by measuring the frequency of emitted gamma rays at the top and bottom of a laboratory tower, where the frequency acted like a "clock". When these two 'clocks' were compared,

the "clock" on the ground floor ran a tiny bit slower

When astronauts aboard the International Space Station (ISS) in space let go of an orange, it just floats there. Why is that?

the ISS is falling around the Earth, and in free fall, things feel no weight

The region around a black hole where everything is trapped, and nothing can get out to interact with the rest of the universe, is called

the event horizon

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

the merger of two black holes

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

Which of the following statements about the way the mass of a white dwarf affects spacetime is correct?

the white dwarf mass will curve spacetime; light has to follow that curvature