Starship Asterisk*

Orbiting a Black Hole

Explanation: What would it look like to orbit a black hole? Since the strong gravity of the black hole can significantly alter light paths, conditions would indeed look strange. For one thing, the entire sky would be visible, since even stars behind the black hole would have their light bent to the observer's eye. For another, the sky near the black hole would appear significantly distorted, with more and more images of the entire sky visible increasingly near the black hole. Most visually striking, perhaps, is the outermost sky image completely contained inside an easily discernible circle known as the Einstein ring. Orbiting a black hole, as shown in the above scientifically-accurate computer-created illustrative video, will show stars that pass nearly directly behind the black hole as zipping around rapidly near the Einstein ring. Although star images near the Einstein ring may appear to move faster than light, no star is actually moving that quickly. The above video is part of a sequence of videos visually exploring the space near a black hole's event horizon. (Disclosure: Video creator Robert Nemiroff is an editor for APOD.)

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Nice video, RJN, i think. Maybe i shouldn't have watched it so many times.

I don't agree

Good work, thank you! Maybe the video is a little fast.
Shouldn't there be an area where the escaping light is shattered in all directions? And what about the Jet(s)?
(Then, on the other hand, it did not claim to describe all effects.)

Isn't the universe an amazing and mysterious place?!

Is my perception missing a perspective? It seems the hypothetical observer is orbiting the black hole from left to right in the video. Why do the apparent rings of stars circle the center in opposite directions? Are the clockwise rotations moving away from the observer toward the black hole, and the counterclockwise rotations on the opposite side of the black hole moving toward both it and the observer? Thank you.

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jambo wrote:
Is my perception missing a perspective? It seems the hypothetical observer is orbiting the black hole from left to right in the video. Why do the apparent rings of stars circle the center in opposite directions?

• Perhaps you've had too much to drink.

jambo wrote:Is my perception missing a perspective? It seems the hypothetical observer is orbiting the black hole from left to right in the video. Why do the apparent rings of stars circle the center in opposite directions? Are the clockwise rotations moving away from the observer toward the black hole, and the counterclockwise rotations on the opposite side of the black hole moving toward both it and the observer? Thank you.

You are correct in identifying that the observer is moving from left to right (while continually looking in the direction of the black hole). You can tell that it is so from the movement of star images that are far from the black hole. Those images are unaffected by the lensing caused by the black hole's gravity. However, as the star images get closer and closer to the black hole, the lensing causes the the star images to move in that strange fashion. The purpose of the movie is, precisely, to show the strange way in which images are distorted by gravitational lensing.

On a different subject: If you want to be a stickler, the frame of reference of the observer rotates with the observer. It is so because the observer always looks in the direction of the black hole as it orbits around it. As such, the observer's frame of reference is not an inertial one. The commentary says: "... star images near the Einstein ring may appear to move faster than light ...". Strictly speaking, in the non-inertial reference frame of the observer the stars ARE moving faster than light. (This is the same as the Moon moving faster than light in your reference frame when you are on a merry-go-round that completes one revolution in less than eight seconds.) Of course, seriously, the comment is saying that the images appear to move faster than light in the inertial reference frame of the surrounding universe. The presumption is that the stars are background stars that are not actually moving. Only their images move due to the gravitational lensing cause by the black hole.

Uwe wrote:Shouldn't there be an area where the escaping light is shattered in all directions? And what about the Jet(s)?

Jets are not really properties of black holes, and very few have them. Jets are entirely external to black holes, and are caused by the polar ejection of infalling material (which is not present around most black holes).

It would be quite safe to orbit a black hole unless you were extremely close, and tidal forces became significant. But you sure wouldn't want to be too close to a black hole with an accretion disc and jets!

Sunday, the Science channel had a number of programs outlining the effects/behaviors of black holes. Quite the ultimate reference source for scientific information I know but it gives us amateurs a sense we need to learn more. One program compared a black hole to a large waterfall and the point where a human could no longer swim fast enough to escape; the event horizon. Also claiming the water being a good metaphor for space being drawn inward. The program went on to state the quickly downward moving water was similar to the inward flowing of space into a black hole and that it could move faster than light.

Incidentally, it went on to equate the rebounding of energy at the bottom of the falls to the jets seen coming from, I suspect, active galaxies. Although this probably refers to matter being drawn in rather than just empty space, I’d be curious if it may covered in future programs. And hopefully other discussions today.

My main point/question being, “Was the program accurate in claiming space being drawn into a black hole is similar to water into a chasm?” And does its rate of movement create the “time warp” effect of today’s APOD?

The idea that space (not only matter) can be drawn into black holes has been a topic of my own in questions previously posed in “The Bridge” discussions. I don’t know if I can claim a better grasp on that question. The above mentioned program only sparked a revived interest. Thanks, Ron

If you liked this one, Andrew Hamilton has some similar things on his web page
http://casa.colorado.edu/~ajsh/schw.shtml


That name of today's contributor, Nemiroff, sounds familiar somehow....

I love these! But they are very hard to watch. They date from about 1993, and the technology of simulation animation has advanced amazingly since then. The ones from Andrew Hamilton are also nice, but still date from 1998 it seems.

Are there any modern versions by others with higher resolution, more frames and smoother animation, nicer colors so individual stars are easy to track, convenient controls to slow down, move backwards, zoom in, etc?

If not, is the code that produced them available so others can bring them up-to-date?
[Update: oops: the original apod text links to the code, via the "computer generated" hyperlink: http://adsabs.harvard.edu/abs/1999ascl.soft10006N - cool! Note that the code is in fortran and visualized with a ".pro" program, using a language I can't identify.]

How close do you have to be to a small-to-typical black hole before the whole sky is visible near the Einstein Ring? Can anyone point to some pictures of that sort of limiting case?

Ron-Astro Pharmacist wrote:
My main point/question being, “Was the program accurate in claiming space being drawn into a black hole is similar to water into a chasm?” And does its rate of movement create the “time warp” effect of today’s APOD?

Ron

It's not that the comparison is wrong, but rather that it is useful only within some well defined limits. On the "accurate" side, objects in water falling into a chasm will indeed fall into that chasm too, similar to initially stationary objects falling into a black hole. Conversely, the analogy fails when one considers space itself -- it does not seem to me that space itself falls into the black hole. One needs to delineate precisely-defined experiments to make those types of comparisons more clear.

The "time warp" effect is real -- objects that are far from the black hole appear to be running faster to someone near the black hole. For example a distant watch, if seen through a telescope, would appear to have its second hand circling unusually quickly. I hope this is a help!

- RJN

nealmcb wrote:How close do you have to be to a small-to-typical black hole before the whole sky is visible near the Einstein Ring? Can anyone point to some pictures of that sort of limiting case?

Technically, the entire sky is always visible near a black hole, no matter how far you are from it. The limiting factor is actually how well you can see near the black hole -- in particular its surrounding Einstein ring.

- RJN

Ron-Astro Pharmacist wrote:My main point/question being, “Was the program accurate in claiming space being drawn into a black hole is similar to water into a chasm?” And does its rate of movement create the “time warp” effect of today’s APOD?

I remember that show. I think the analogy is a poor one. Space does not fall into a black hole, space is not moving. Spacetime is distorted by any mass, and that effect is no different around a black hole than around a star, a planet, or an atom. Something different may be going on inside the event horizon of a black hole, but the reality is we have no physics at this time that can begin to describe that.

There are relativistic time effects close to the surface of a black hole, but I don't think we are seeing those reflected in this video.

Incidentally, it went on to equate the rebounding of energy at the bottom of the falls to the jets seen coming from, I suspect, active galaxies.

Another poor example, I think. There's nothing fundamentally different about the jets formed around black holes which have accretion discs, and the jets formed by other rotating bodies under similar conditions.

RJN wrote:The "time warp" effect is real -- objects that are far from the black hole appear to be running faster to someone near the black hole. For example a distant watch, if seen through a telescope, would appear to have its second hand circling unusually quickly. I hope this is a help!

I don't really understand this. Is this a purely optical effect, or is it related to the actual relativistic time compression that occurs near the event horizon, or to some sort of pseudo-superluminal travel while orbiting very close to the event horizon? Or something else?

I didn't follow all the links, so maybe this is mentioned somewhere else. What is the orbital radius in the simulation compared with the Schwarzschild radius?

Chris Peterson wrote:

RJN wrote:The "time warp" effect is real -- objects that are far from the black hole appear to be running faster to someone near the black hole. For example a distant watch, if seen through a telescope, would appear to have its second hand circling unusually quickly. I hope this is a help!

is it related to the actual relativistic time compression that occurs near the event horizon

It is the relativistic blueshift. Anything redshifted appears to run slow. Anything blueshifted appears to run fast.

- RJN

Mind bending!

3 dimensional motion projected on a flat screen is a challenge specially if light comes right at you and masnifests itself as a stationary point. Is there any observation that entire galaxies come to an end being swallowed up by increasingly " bigger " black hole objects ?

Chris Peterson wrote:Space does not fall into a black hole, space is not moving.

Just what the heck is "space", really??

Beyond wrote:

Chris Peterson wrote:Space does not fall into a black hole, space is not moving.

Just what the heck is "space", really??

What is "really", really?

Here is the link to a slower paced version of the video I made a few months ago, using Dr.Nemiroff's simuation.

Chris Peterson wrote:

Beyond wrote:

Chris Peterson wrote:Space does not fall into a black hole, space is not moving.

Just what the heck is "space", really??

What is "really", really?

That which you said does not move and does not fall into a black hole, which is understandable. IF it does not move, how could it fall. But what is it that does not move?