Crossing an event horizon

[freyar]

It seems like maybe some people are confusing the time measured by the person falling into the black hole and the time measured by the observers who manage to stay outside. You might find the Penrose diagrams to be helpful. The idea of a Penrose diagram is that light rays make 45-degree lines (so massive objects follow trajectories that are always more vertical than 45 degrees), and the ones we'll look at have the angular directions suppressed, just showing radius from some center and time. As an example, look at the diagram for Minkowski spacetime -- the normal flat spacetime of special relativity with trivial gravity -- it's at the top of the page. You'll notice that the sides of the diamond are "lightlike infinity" (all light rays end up on these lines), "spacelike infinity" at the two left-right points of the diamond (where you are if you are an infinite distance away from the center at a fixed finite time), and "timelike infinity" at the top-bottom points (where you are when you're infinitely far into the future or past but at a finite distance from the "center").

Now look at the second diagram and check out the example for the basic black hole (labeled Static "Grey" Wormhole in the diagram) in the second diagram. The person falling into the black hole passes the event horizon and hits the timelike singularity in a finite amount of time according to their watch. However, if they're sending out light pulses as they fall in, you can trace out those 45-degree lines. You'll see that no one can see the last pulse emitted along the horizon unless they're at timelike infinity -- one of the points at the corner of the timelike singularity adjoining the "our universe" diamond. The Real Black Hole is also relevant; the star is collapsing, and eventually it forms an event horizon -- we observers only actually see the event horizon swallowing the star at an infinite time in the future.

A note on the Electrically Charged And/Or Rotating Wormhole: the wormhole tends to collapse if you put any actual mass through it, so you can't really get through to the other universes.

 

[Umbran]

Matter of fact, we should be able to see it all the time, especially with the older black holes, if only that background radiation generated by the accretion disk, and all the rest of the junk that manages an orbit that won't bring it across the event horizon, wasn't obstructing our view.

Well, that, and the fact that the nearest known/suspected black hole is 1600 light years or so from Earth, and we don't have the technology to make out anything like surface detail at that range, even if nothing were in the way.

 

[GameDaddy]

Well, that, and the fact that the nearest known/suspected black hole is 1600 light years or so from Earth, and we don't have the technology to make out anything like surface detail at that range, even if nothing were in the way.

We have other things more relevant at the moment that requires our attentions... I noticed with interest a report on CNN this morning, about two large rocks that flew by earth that were only spotted three days ago on Sunday... Cutting it kind of close, ey?

Reference: In One Day, (Yesterday now...) Two Asteroids buzz Earth.
In one day, two asteroids buzz the Earth - CNN.com

I went ahead and took a look at the Catalina Sky Survey, Which is now finding more than one rock/Iceball a day that makes a rather close transit bwteen the Moon and Earth.

Better yet, On another blog, I came across this video... All the orbits of all the rocks detected since about 1980 or so.. If you can, view the video at high-res at 1080 px...

These are just the ones that have been spotted with their orbits charted, it's not counting the eccentric orbits and the deep orbits that only get close to us infrequently... Also not on this video, The rogue rocks that are coming in from other star systems...

[ame="http://www.youtube.com/watch?v=S_d-gs0WoUw&feature=player_embedded"]YouTube - Asteroid Discovery From 1980 - 2010[/ame]

We are going to get tagged hard long before anyone has a chance to spot something crossing an event horizon of a black hole...

 

[jonesy]

There's talk of meteor death in the other thread:
http://www.enworld.org/forum/media-lounge-off-topic/287979-how-far-we-colonizing-off-earth.html

We are going to get tagged hard long before anyone has a chance to spot something crossing an event horizon of a black hole...

We get tagged on avarage 50,000 times every year. But it's all small stuff. The Sun and Jupiter act as pretty efficient vacuum cleaners.

 

[Joshua Randall]

Minor thread necromancy. (The body isn't that cold yet.)

Assuming you had a spaceship with superpowerful engines made of superstrong material, could you "hover" outside the event horizon, like in the classic Disney movie The Black Hole?

And would you see/detect anything interesting at the accretion disk? (I know you can't see the hole itself, by definition.)

 

[Umbran]

Assuming you had a spaceship with superpowerful engines made of superstrong material, could you "hover" outside the event horizon, like in the classic Disney movie The Black Hole?

In short - Yes. At least until you ran out of fuel.

For smaller black holes, there's a point where no matter how strong the material of the ship might be, your body wouldn't take the tidal stresses. See the Larry Niven short story "Neutron Star" for a description.

And would you see/detect anything interesting at the accretion disk?

Well, you'd see material undergoing compression heating possibly to the point it gives off X-rays. You'd see dynamics of an accretion disk, which we've never seen up close before.

But really wild and wacky stuff? I can't think of any offhand.

 

[jonesy]

Spam post reported.

Also, this just in:
Astronomy.com - Astronomer leverages supercomputers to study black holes and galaxies

Those gas density maps look really interesting.

 

[freyar]

Massive numerical simulations like that are really becoming an important part of mainstream astrophysics, especially when it comes to understanding the structure and formation of galaxies.

 

[jonesy]

Massive numerical simulations like that are really becoming an important part of mainstream astrophysics, especially when it comes to understanding the structure and formation of galaxies.

Speaking of which:
HubbleSite - Detailed Dark Matter Map Yields Clues to Galaxy Cluster Growth

Jet Propulsion Lab using the Hubble telescope have been making a map of dark matter. Well, more like a map of mass in space. They also think they've figured out gravitational lensing.

The images look really intersting:
HubbleSite - Detailed Dark Matter Map - Images

 

[freyar]

Speaking of which:
HubbleSite - Detailed Dark Matter Map Yields Clues to Galaxy Cluster Growth

Jet Propulsion Lab using the Hubble telescope have been making a map of dark matter. Well, more like a map of mass in space. They also think they've figured out gravitational lensing.

The images look really intersting:
HubbleSite - Detailed Dark Matter Map - Images

The theory of gravitational lensing in general relativity is quite well understood in that, if you tell me where the mass is, I can tell you how it lenses light (well, maybe not me, but you get the point). The so-called inverse problem is trickier: we see how light is lensed and want to use that to figure where the mass is. People have been making maps like this for years now, but this team has found an improved way to solve this inverse problem. In any case, it seems like the results may be interesting for comparison to simulations, as well.