a few questions

M

mstarry

Registered Member
Hi, I am doing a quiz (not homework, just to help understand astronomy)
I have a few questions that I am not sure about but I am fairly positive that I am right. Just wondering if you could help me out and give your opinions!

A spaceship cannot travel at the speed of light because
a. Objects with mass cannot travel at the speed of light?
b. Its mass would become infinitely small.
c. The pilot would not be able to see the destination.
d. We don't know how big the engine would need to be.

A spaceship moving at 250,000 km/s would measure the speed of light coming from a star to be
a. 50,000 km/s.
b. 300,000 km/s?
c. 250,000 km/s.
d. 550,000 km/s.

If a black hole is spinning, it must
a. Emit pulses of electromagnetic radiation.
b. Distort space-time near it?
c. Have a larger event horizon.
d. Be a Schwarzschild black hole.

Black holes are easier to detect if they are
a. Hot?
b. Spinning.
c. At the edge of a galaxy.
d. In a close binary system.

Mercury does not follow Kepler's laws of planetary motion because
a. It is too massive.
b. It is too close to the Sun?
c. Kepler didn't know about Mercury when he formulated the laws.
d. It is moving too fast.
 
umm spaceship would see light at speed of light, doesnt matter what speed the spaceship is goin.

Also the blackhole question, are u sure blackhole emits heat? I mean I thought wouldnt it be easier for a black hole to be seen if it was close to binary system, because we would see effects of black hole on a binary system, such as gravitational attraction, I mean the only thing i know that blackholes emit are x-rays...thats it...and they can be detected by distortion on star pictures and of course unusual gravitational pull...
 
You have them right with the possible exception of number 2. Sorry but I have not switched to metric. The speed of light (C) is a constant and always moves at 186,000 miles per second. If you are on a space ship moving 50,000 mph and fired a lazer (light) foward and aft, both beams would be moving at 186,000 mps.
 
Also #3 might be A & B. Hawking has suggested the a black hole might release radiation of some type which has come to be called 'Hawking radiation"
 
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Sorry, I moderate another board and that takes a bit of time.
First realize that we have not observed a black hole to date. We are just discussing theory. Yes black holes are believed to emit a very great deal of heat. they would have to. Crushing vast amounts of matter into a tiny, tiny area must release heat.
 
but emm...isnt black hole known for for the fact that it absorbs everything? and heat what is it? isnt heat just a movement of atoms or molecules, and if everything gets absorbed how can there be heat?
 
We are still talking theory but it seems to me that matter starts collapsing before it enters the black hole. I am sure that most physicists agree with the idea that black holes do emit hawking radiation.
 
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Snake River, please explain to us how the heat you suggest is emitted by a black hole manages to escape from said black hole, in theory, or in practice. What gives this particular form of electromagnetic radiation the ability to do what no other form of electromagnetic radiation can do? Are you suggesting that heat can travel faster than light?
More briefly, I shall state what dragon has been to polite to state: you are mistaken. [Although dragon, you also appear to be mistaken. Strictly speaking a black hole does not emit x-rays: they are emitted from this side of the event horizon.]
 
Ophiolite said:
Are you suggesting that heat can travel faster than light?
Click to expand...
if i understand the concept of a black hole correctly, even speeds faster than light are not gaurenteed to escape.
 
Snake River Rufus, Hawking radiation isn't related to the collapse of objects before they cross the event horizon though is it? It's because of quantum effects occuring next to the event horizon.
 
The answers:

#1: A
#2: B

For the third question, I am not positive. However we can rule out D because a Schwarzschild black hole has no spin. B would happen even if it didnt spin, thats why I dont like that answer. A just sounds funky... it can have magnetic field lines but thats with an accretion disk... and it can have a charge but pulses of electromagnetic radiation? No, because that would be light. Therefore I would say C.

#4: D

#5: B
 
Tristan, yes.

For #3 B already is true as you say, but maybe the question is asking about frame dragging? The event horizon as far as I know is determined solely by the mass of the hole. It's shape is determined by spin or lack thereof.

As for BH's emitting heat, if Hawking is correct, then all BH's radiate due to quantum uncertainty. BUt it is very, very small for macroscopic BH's. It only becomes significant for very small holes that are approaching evaporation (in a burst of gamma rays).
 
Yes, but hawking radiation wouldnt be considered electromagnetic radiation.... Its something else entirely. And I dont think the question is geared towards frame dragging. Thats more complicated than the question and answer would allow.
 
Hawking radiation was proposed to be the half of pair production, PARTICLES, which happened to be accidentally aimed away from the hole, opposed to the unlucky half which were aimed toward the hole and therefore fell in.
 
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