Support NeoGAF

[Fenderputty]

Well, the time slows down for light as well, and since frequency is the inverse of the period, the frequency of the light emmited near the horizon as measured by the distant observer decreases. This is the gravitational redshift.

Since the frequency is proportional to photon energy, the energy decreases as well. You may imagine the photon loses energy climbing out of the gravitational well of the BH.

Eventually, the light is so stretched and low energy that you can't detect it anymore, so not only you see the person slow down, but his image gets fainter and redder until its below the sensitivity of your detector, and then you don't see the guy anymore.

This makes perfect sense and how I visualized what it would actually look like. So even though it's "stuck" the the observer won't see that image in perpetuity due to the energies being reduced.

I would also assume this changes based on the size of the BH. The larger the diameter the longer the transition to the event horizon takes place. So we would see the object for longer periods if the black hole is a super massive one correct?

 

[All Possible Ways]

This makes perfect sense and how I visualized what it would actually look like. So even though it's "stuck" the the observer won't see that image in perpetuity due to the energies being reduced.

I would also assume this changes based on the size of the BH. The larger the diameter the longer the transition to the event horizon takes place. So we would see the object for longer periods if the black hole is a super massive one correct?

The time dilation factor can be written as (square root of) 1-rs/r, where rs is the BH radius and r is your radial distance. You see that what matters is the ratio rs/r, such that if you are at 2 times the hole's radius, the amount of slowdown is the same, no matter how big the bh is.
A well defined question might be how long it takes for a free-falling object to go from say, three times the bh radius to two times it, along a radial trajectory. I worked it out and was surprised to learn it takes exactly twice as long if the black hole is twice as big, so it is a linear relation!

edit: In hindsight I guess I shouldn't be surprised since the only scale in the problem is the black hole radius, so any distance or time you calculate has to be directly proportional to it. Still, I learned something!

 

[SofNasciment-]

The very center of our galaxy is a black hole? I never knew this...

I miss space science... I miss being interested in stuff like that...

Must play Mass Effect 2, dude!

 

[Fenderputty]

The time dilation factor can be written as (square root of) 1-rs/r, where rs is the BH radius and r is your radial distance. You see that what matters is the ratio rs/r, such that if you are at 2 times the hole's radius, the amount of slowdown is the same, no matter how big the bh is.
A well defined question might be how long it takes for a free-falling object to go from say, three times the bh radius to two times it, along a radial trajectory. I worked it out and was surprised to learn it takes exactly twice as long if the black hole is twice as big, so it is a linear relation!

edit: In hindsight I guess I shouldn't be surprised since the only scale in the problem is the black hole radius, so any distance or time you calculate has to be directly proportional to it. Still, I learned something!

This seems like a more technical way of agreeing with me? Regarding the ratio, my question was more in respect to a finite distance.

An object that's 50k miles away from flying directly into the event horizon of a super massive BH will look different to the observer who's watching an object approach a smaller back hole from 50k miles. The observer sees something different while watching those object fly those 50k miles respectively as they approach the event horizons.

Correct?

 

[Xe4]

The very center of our galaxy is a black hole? I never knew this...

I miss space science... I miss being interested in stuff like that...

Not just any blackhole, a supermassive black hole with weighing more than 4,000,000 times the mass of the sun.

At the center of pretty much every galaxy is a supermassive black hole too, and we're not entirely sure why (although there are some hypotheses).

 

[Insane Metal]

there's a super massive black hole at the center of ALL galaxies.

Not true, most galaxies would be the correct answer.

 

[fin]

Galaxies are like hurricanes in space.

 

[All Possible Ways]

This seems like a more technical way of agreeing with me? Regarding the ratio, my question was more in respect to a finite distance.

An object that's 50k miles away from flying directly into the event horizon of a super massive BH will look different to the observer who's watching an object approach a smaller back hole from 50k miles. The observer sees something different while watching those object fly those 50k miles respectively as they approach the event horizons.

Correct?

Here's the thing, the answer to your question was not at all obvious to me, so I had to reformulate it in a precise way so I could work out the answer, that is all.

Since what enters the formulas is the ratio, if you use a fixed distance, like your 50k miles, the answer is not so simple and the time to cross this distance for different sized BHs will no longer be linearly proportional to the radius of the BH.

For black holes that are very small compared to 50k miles, it takes a long time, merely because the object is far from the BH, since in this case time dilation is negligible. As the mass increases, it take less time to cross the 50k miles, because the BH's gravitational pull becomes stronger. Eventually, the time it takes will begin to increase again, because the time dilation starts to become increasingly important.

 

[Fenderputty]

Here's the thing, the answer to your question was not at all obvious to me, so I had to reformulate it in a precise way so I could work out the answer, that is all.

Since what enters the formulas is the ratio, if you use a fixed distance, like your 50k miles, the answer is not so simple and the time to cross this distance for different sized BHs will no longer be linearly proportional to the radius of the BH.

For black holes that are very small compared to 50k miles, it takes a long time, merely because the object is far from the BH, since in this case time dilation is negligible. As the mass increases, it take less time to cross the 50k miles, because the BH's gravitational pull becomes stronger. Eventually, the time it takes will begin to increase again, because the time dilation starts to become increasingly important.

Ok this makes sense. Thank you for putting up with my questions lol

I was under the assumption that SMBH behave differently because the distances in which time dilation occurs is greater than a small one. Which is kinda where my head was when asking

 

[blu]

Not true, most galaxies would be the correct answer.

Isn't it a matter of time until a spiral galaxy gets its BH centre?

 

[Angry Grimace]

It probably leads to a world filled with warring Greek gods.

 

[Mr. PlayStation]

Make me stay murph!

 

[llien]

does this mean we will all die

You are not alone. There is entire movie about it:
http://www.imdb.com/title/tt2333804/


PS
I personally was more concerned with universe expansion accelerating. Dead alone in cosmos somehow felt more terrifying than "we all will be consumed by a black hole".

 

[CarlisleDavid1979]

Wonder what would happen when our galaxy and andromeda finnaly merge.

 

[danthefan]

Wonder what would happen when our galaxy and andromeda finnaly merge.

Fun fact, by the time that happens the Earth will either be uninhabitable or will have ceased to exist at all.

The SMBHs will merge eventually I think, shit loads of energy get released in the process.

 

[Montresor]

Make me stay murph!

How come murph don't want me man?

 

[Mihos]

Wonder what would happen when our galaxy and andromeda finnaly merge.

Some stars ejected into space, a spike is star formation. Surprisingly, very few if any star collisions. The 2 galaxies will pass right through each other many times before settling into a single elliptical galaxy.

This black hole is suspected to have come from one of the many dwarf galaxies we have already captured and merged with.

 

[CarlisleDavid1979]

Fun fact, by the time that happens the Earth will either be uninhabitable or will have ceased to exist at all.

The SMBHs will merge eventually I think, shit loads of energy get released in the process.

Some stars ejected into space, a spike is star formation. Surprisingly, very few if any star collisions. The 2 galaxies will pass right through each other many times before settling into a single elliptical galaxy.

This black hole is suspected to have come from one of the many dwarf galaxies we have already captured and merged with.

Space, for me is the most fascinating science out there. If only I was born 1000 years from now.

 

[Boss Doggie]

Ideon is fucking up again.

 

[test_account]

Sagitarius ass hole?

Isnt it God's asshole? They already found his eye and hand.

 

[andthebeatgoeson]

Indeed, so that's why a 1.4 trillion km 'across' black hole sounds like someone messed up their units and a couple powers of 10. A black hole that fits in your pocket would have many several times more mass than the earth (and consequently gravity). One with the mass of our sun would only be a couple miles. So a black hole that has a diameter that is about 1/7th of a light year inside our own galaxy sounds impossible. I don't even think our galaxy (or Andromeda and any neighboring satellite galaxies) would exist with such a monster.

Don't discount science reporting messing something up. Or, 'up to 1.4 trillion' conveying inaccuracy. They may not be able to completely measure it.

 

[ManUnkindH]

Not me! I'm living forever. The tooth fairy said so.

 

[andthebeatgoeson]

Space, for me is the most fascinating science out there. If only I was born 1000 years from now.

Don't ignore the science happening on Earth.

I'll just spend my last years in New Florida, apologizing to my kids.

 

[amishpriest99]

Meh, I still think it's Sha Ka Ree in the center of the galaxy.

 

[Jinroh]

What's pretty crazy with black holes is that for an outside observer since time seems to stop the closer you get to the center of a black hole they are in a state of eternal collapse.

It basically means from what I understand that nearly all the external mass the black hole acquired is still stuck near the event horizon, the core of the black hole (which we wrongly define as a singularity) being only the central part of a star that collapsed to a state we can't yet define.

So from our point of view pretty much everything that "fell" into a black hole, including the collapsing star is still mostly intact. Crazy, isn't it?

edit: Also if the quantum bounce theory happened to be correct, a black hole would explode before someone falling in it could reach its center (but that person would be vaporized in the explosion anyway)

 

[Melkezadek]

Space, for me is the most fascinating science out there. If only I was born 1000 years from now.

I bum myself thinking about this all the time. Sucks. If I had one wish.

 

[Dr Zhivago]

Wonder what would happen when our galaxy and andromeda finnaly merge.

On human timescales, nothing. The whole process will take millions of years.
I presume the sky will look cool just before the collision though.

 

[Ferr986]

Well, the time slows down for light as well, and since frequency is the inverse of the period, the frequency of the light emmited near the horizon as measured by the distant observer decreases. This is the gravitational redshift.

Since the frequency is proportional to photon energy, the energy decreases as well. You may imagine the photon loses energy climbing out of the gravitational well of the BH.

Eventually, the light is so stretched and low energy that you can't detect it anymore, so not only you see the person slow down, but his image gets fainter and redder until its below the sensitivity of your detector, and then you don't see the guy anymore.

I was reading this thread and was about to ask this, glad it was cleared. Always wondered about the "seeing the dude stuck in the black hole".

 

[BizzyBum]

Wonder what would happen when our galaxy and andromeda finnaly merge.

It's crazy to me that scientists say earth and life would be fine during the collision. Like, how is that possible?

The night sky as Andromeda is super close would be amazing to witness, though.

 

[FyreWulff]

It's crazy to me that scientists say earth and life would be fine during the collision. Like, how is that possible?

The night sky as Andromeda is super close would be amazing to witness, though.

There's just that much space between everything

 

[MogCakes]

What's really cool to think about is the fact that these tears in spacetime are a perfectly normal part of our universe's workings.

 

[Jinroh]

But they aren't tears, just gravitational wells. It's not any different from a star, it's just proportionally much smaller.

 

[Pejo]

Every so often I think about how absolutely tiny I am in the scale of the universe. It really is humbling and hard to comprehend with how narcissistic humans are by default. I am just kinda pissed that I probably won't be alive to see the advent of:

-Perpetual motion machine that can self power.
-Curing all diseases and extending lifespans

which will lead to the ability for us to actually explore space.

The things that have to be out there...

 

[MogCakes]

But they aren't tears, just gravitational wells. It's not any different from a star, it's just proportionally much smaller.

Gravity is the root of it, but spacetime bending to such a degree that even the concept of different directions inside the event horizon doesn't exist constitutes a 'tear' in the typical fabric. Plus spacetime tear sounds cooler.

 

[Jinroh]

Well falling in one direction is kind of what gravity is all about, if I throw you off a plane that's mostly what would happen if the air was light enough. But I get what you mean.

People fantasize a lot about black holes, but they aren't that extraordinary. We just don't understand what happens to matter in the center of a black hole. Without observing it directly we might never have a definitive answer sadly...

 

[MogCakes]

Isn't the spacetime in the interior of the event horizon wonky? Like even if you attempted to turn and go a different direction, no matter where you went the direction would be towards the singularity.

 

[Kimawolf]

Isn't the spacetime in the interior of the event horizon wonky? Like even if you attempted to turn and go a different direction, no matter where you went the direction would be towards the singularity.

Yes.

You sill always move towards the singularity no matter what direction you go. Really trippy.


Also really huge BH you can fall into the outward singularity and be fine for quite awhile.

 

[IndianaJack]

The central area of the galaxy is swarming with black holes, neutron stars, supergiant stars and Wolf-Rayets. It's a fascinating and scary place. The radiation alone would make life impossible anywhere in the first 5000 light years radius.