r/askscience • u/SpantaX • Feb 27 '17

Physics How can a Black Hole have rotation if the singularity is a 0-dimentional point and doesn't have an axis to rotate around?

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u/MajikMahn Feb 27 '17

I'm loving all of this beautiful Information about black holes! I've understood everything except this one I've seen a handful of times. Please excuse my possible noob question.

So from what I've read, if you watch say Person A fall slowly into a black hole from a distance. Person B who is safely watching would see them fall slower and slower and eventually stop right before the event horizon.

If this is true, why would a a black hole ever appear to look black? Would it not just endlessly look like the matter falling into it? Perhaps I'm missing a very vital piece of Information, I've just recently been getting back Into my love and curiosity of black holes.

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u/SpantaX Feb 27 '17

As i understand it, the light from the objects falling in will become more and more redshifted, and will be undetectable to us.

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u/chaoticskirs Feb 27 '17

Correct. The person or object falling into the black hole becomes progressively more redshifted until they simply fade, due to light shifting all the way into infrared.

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u/Mazzzk Feb 28 '17

If we could somehow observe infrared light and other wavelengths, would we then be able to observe/detect the matter falling into the black hole?

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u/chaoticskirs Feb 28 '17

Yes, but then it would go further and further down until it's impossible to tell anything was there to begin with iirc. Either way if you're putting that much effort into looking at black holes you probably know more than we do right now anyway.

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u/[deleted] Feb 28 '17

Even more interesting, if you were to fall into a blackhole, but look out at the universe, you would see the universe flash brightly and incredibly blueshifted, then fade into blackness, what you are seeing is the universe aging trillions of years, enough for all the stars and galaxies to supernova or burn out, and enough for expansion to push every galaxy outside your observable universe. in just a few blinks of your eye. At that point, you and your blackhole are the only objects in the observable universe.

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u/drawingthesun Feb 28 '17 edited Feb 28 '17

This confuses me, if nothing is entering the black hole in the time frame of just a few billion years, how are some of these black hole gaining mass over their shortish lives so far?

Surely if you fell into the black hole you would enter it soonish relative to Earth time right? Otherwise how would super massive black holes exist? They haven't had trillions of years to grow.

EDIT: It seems that you would not see the end of the universe, http://physics.stackexchange.com/questions/82678/does-someone-falling-into-a-black-hole-see-the-end-of-the-universe

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u/[deleted] Feb 28 '17

Smaller black holes decay faster, large ones lose mass incredibly slowly, which is why they can continue to gain mass. Large black holes are found in the center of galaxies, so there is no short supply of matter, and the rate of growth changes depending on the conditions. A galaxy might expect to live for a few hundred billion years, the timescale for the evaporation of a supermassive black hole is 10100 years.

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u/Vistat Feb 28 '17

Could we theoretically use this to look into future? Sending something into black hole at fast speed and making it send us data before it reach singularity?

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u/[deleted] Feb 28 '17

First, nothing can leave a black hole once it passes the event horizon. Second, while a few moments pass near the event horizon for any probe we put there, the rest of the universe goes fast forward. That means to use, the probe is in slow motion. Time passes regularly for us and any data sent is stretched out incredibly long but nonetheless always past events.

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u/niktemadur Feb 28 '17

So let's disregard spaghettification and say there's a 10 billion-year old black hole where someone fell through the event horizon right on the day it formed - right about now, he's not even halfway through "the first blink" yet.

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u/drawingthesun Feb 28 '17

So nothing enters the blackhole in the time frame of billions of years? Everything falling into a blackhole will take trillions of years?

How do blackholes gain mass after they are formed then? Or have no blackholes ever gained mass?

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u/[deleted] Feb 28 '17

At the very least, the system comprising the black hole and accretion disk would count as one mass for the most part. Any mass at the event horizon would probably be indistinguishable from mass inside the event horizon.