Astronomy Test 3 Flashcards

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Questions and Answers

What does the Schwarzschild radius of a black hole depend on?

Only the mass of the black hole

What would happen if a 1.5-solar-mass neutron star appeared in your hometown?

Earth would explode

The neutron star would disappear

Nothing would happen

The entire mass of Earth would become a thin layer over the neutron star (correct)

How do we know that pulsars are neutron stars?

No massive object, other than a neutron star, could spin as fast as we observe pulsars spin.

From an observational standpoint, what is a pulsar?

An object that emits flashes of light several times per second or more, with near perfect regularity. Signup and view all the answers

Sort the statements about black holes based on their accuracy. Which statements are true?

A black hole can have the mass of a star in a space less than a few kilometers across. Signup and view all the answers

Why is the statement 'a 3-solar-mass black hole may be hidden between Jupiter and Saturn' not true?

An object of that mass would disrupt the orbits of the planets in our solar system. Signup and view all the answers

Why is the statement 'the singularity of a black hole has infinite density' classified as unknown?

General relativity and quantum mechanics give different answers about the nature of singularity. Signup and view all the answers

Why is the statement 'black holes make up 1% of the mass of the Milky Way Galaxy' classified as unknown?

We cannot detect all black holes and therefore don't know the percentage of the galaxy's mass they make up. Signup and view all the answers

Which statements about gravitational waves are true?

Two orbiting neutron stars will gradually spiral toward each other due to energy loss from gravitational waves. Signup and view all the answers

What is the Schwarzschild radius of a 2×10^8 solar-mass black hole in the center of a quasar?

6.0×10^8 km Signup and view all the answers

What is the Schwarzschild radius of a 5 solar-mass black hole that formed in a supernova?

15 km Signup and view all the answers

What is the Schwarzschild radius of a mini-black hole with the mass of the Moon?

0.11 mm Signup and view all the answers

Estimate the Schwarzschild radius for an object weighing 50 kg.

7×10^−29 km Signup and view all the answers

What happens to time on the other rocket as it falls toward the event horizon of the black hole?

Time runs increasingly slower as the rocket approaches the black hole. Signup and view all the answers

What would an observer in the orbiting rocket see as the falling rocket approaches the event horizon?

The falling rocket slows down as it approaches the event horizon and never actually crosses it. Signup and view all the answers

Why will the in-falling rocket eventually disappear from view?

Its light will become so redshifted that it will be undetectable. Signup and view all the answers

If you were inside the rocket that falls toward the event horizon, you would notice your own clock to be running __________.

at a constant, normal rate as you approach the event horizon Signup and view all the answers

If you were inside the rocket that falls toward the event horizon, from your own viewpoint you would __________.

accelerate as you fall and cross the event horizon completely unhindered Signup and view all the answers

What is the Schwarzschild radius of a 100 million-solar-mass black hole?

300 million km Signup and view all the answers

How does the gravity of an object affect light?

Light coming from a compact massive object, such as a neutron star, will be redshifted. Signup and view all the answers

Rank these locations in the Milky Way Galaxy based on their distance from the center, from farthest to closest:

A globular cluster in the outskirts of the halo = Farthest A cloud of gas and dust in the outskirts of the disk = Far Our solar system = Closer The edge of the central bulge = Closest Signup and view all the answers

Study Notes

Black Holes

The Schwarzschild radius is determined solely by the mass of a black hole.
A 1.5-solar-mass neutron star would compress the entire mass of Earth into a thin layer about 1 cm thick on its surface.
A black hole can contain a stellar mass in a space less than a few kilometers across, and it can form during a supernova explosion.
Claims about black holes include:
- True: black holes can merge and emit gravitational waves; material from a binary companion can create an X-ray-emitting accretion disk; black holes are smaller than their Schwarzschild radii.
- Not true: black holes will not suck in any binary companion star, and the assertion about squashing at the event horizon is incorrect.
- Unknown: the exact percentage of the Milky Way’s mass that is made up of black holes remains unclear due to detection limitations.

Pulsars

Pulsars are observed as regular flashes of light several times per second, indicating high rotation speeds.
The rapid rotation of pulsars is characteristic of neutron stars, confirming their identity.

Gravitational Waves

The LIGO observatory announced the first direct detection of gravitational waves in 2016.
Merging black holes produce gravitational waves, as predicted by Einstein’s general relativity.
Two orbiting neutron stars or black holes spiral towards each other due to energy loss from gravitational waves.

Schwarzschild Radius Calculations

A black hole with 2×10^8 solar masses has a Schwarzschild radius of 6.0×10^8 km.
A 5-solar-mass black hole has a Schwarzschild radius of 15 km.
A mini-black hole with the mass of the Moon has a Schwarzschild radius of 0.11 mm.
A theoretical mini-black hole from a 50 kg mass would have a Schwarzschild radius of 7×10^−29 km.
A 100 million solar-mass black hole would have a Schwarzschild radius of 300 million km.

Observational Effects Near Black Holes

From the viewpoint of an observer in an orbiting rocket, time appears to run slower for an in-falling rocket as it nears the black hole.
Observers will never see the falling rocket actually cross the event horizon, as it appears to slow down and fade from view due to extreme redshift.
Individuals inside the falling rocket would experience time normally and would cross the event horizon without impediments.

Light and Gravity

Light emitted from compact massive objects, like neutron stars, experiences redshift due to intense gravitational forces.

Distances within the Milky Way

Locations in the Milky Way can be ranked from farthest to closest to the center:
- Farthest: globular cluster in the outskirts of the halo
- Cloud of gas and dust in the outskirts of the disk
- Our solar system
- Edge of the central bulge

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Description

Test your knowledge of black holes and neutron stars with these flashcards. Learn about the Schwarzschild radius and the extreme effects of neutron stars on their surroundings. Perfect for students preparing for astronomy exams.