The background is Axel Mellinger's All-Sky Milky Way Panorama (by permission).
Dive in!
For an explanation of what happens in the movie, read on below.
Notice that you cannot tell when you pass through the horizon.
The distance in the stereo movie is the “affine distance”, which is the natural generalization of distance along the past lightcone to an emitter in general relativity6.
The stereo movie has been adapted to human binocular vision. The movie does not represent what you would actually see with your two eyes if you visited a real black hole. In reality, the curved spacetime would distort wavefronts of light away from spherical, confusing your binocular perception. The conflicting visual cues might make you feel queasy. But the failure of binocular vision is merely a limitation of beings who have evolved in flat spacetime. Trinocular vision would work fine. The three-eyed ape at right, drawn by my daughter Wildrose, would have no problem leaping from tree to tree in a highly curved spacetime.
At left is a
Hubble Space Telescope image of the center of M87,
the giant elliptical galaxy at the center of the Local Supercluster of galaxies.
M87 contains the largest black hole whose mass has yet been measured,
6 billion times the mass of our Sun9.
Emerging from the galaxy is a powerful
jet
which Hubble has clocked at 6 times the speed of light.
Click on
4D Perspective
to find out why this does not contradict relativity's assertion
that nothing can move faster than light.
It is this simplicity that gives me the audacity to make movies of black holes, and to have some confidence that they portray black holes accurately, provided of course that the theory of General Relativity is correct.
The movies on this page show the simplest of all kinds of black hole, a Schwarzschild black hole, which has mass, but no charge, and no spin. The Schwarzschild geometry describes the geometry of empty space surrounding any spherical mass.
Real black holes are likely to be more complicated than the Schwarzschild geometry: real black holes probably spin, and the ones that astronomers see are not isolated, but are feasting on material from their surroundings.
When a black hole first forms from the collapse of the core of a massive star, it is not at all a no-hair black hole. Rather, the newly collapsed black hole wobbles about, radiating gravitational waves. The gravitational waves carry away energy, settling the black hole towards a state where it can no longer radiate. This is the “no-hair” state.
Color | Zone |
---|---|
Green | Stable circular orbits |
Yellow | Unstable circular orbits |
Orange | No circular orbits |
Red line | Horizon |
Red | Inside the horizon |
The green region is a “safe” zone where circular orbits are stable.
The yellow region is a “risky” zone where circular orbits are unstable. If you are on an unstable circular orbit, then a tiny burst on your maneuvering thrusters will send you into the black hole, or off into outer space.
The orange region is a “danger” zone where there are no circular orbits, stable or unstable. To remain in orbit in this zone, you must keep firing your rockets. The closer to the horizon you get, the harder you must fire your rockets to keep from falling in.
The red line is the horizon, from within which there is no escape.
The clock records your “proper” time, the time that you actually experience in your brain, and that your wristwatch shows. In the movie, the clock slows down not because time is slowing down (à la 1979 movie “Walt Disney's The Black Hole”), but because it is more interesting to run the movie more slowly nearer the singularity, so that you can see more clearly what happens there.
The time is in seconds if the black hole has a mass of 5 millions suns, approximately equal to the mass of the supermassive black hole at the center of our Galaxy. On your trajectory, it takes 16 seconds to fall from the horizon to the singularity.
The orange cross at the center of the image at left (click on it for a larger version) marks the position of the supermassive, 4 million solar mass, black hole at the center of the Milky Way, our Galaxy.
The resulting gravitational lensing is illustrated at right.
The black hole appears to “repel” the image radially,
which in turn stretches the image transversely.
Parts of the image nearer the black hole are repelled more,
so the image appears compressed radially.
Sterero version:
960×480 gif (20MB)
This animation is not realistic! The Earth would be tidally torn apart in about one orbit if it were orbiting this close to a black hole of this mass.
Notice that when the Earth recedes from us, it appears reddish (redshifted) and slowed, and conversely when the Earth approaches us it appears blue (blueshifted) and speeded up.
The background to this animation is the
2-Micron All Sky Survey (2MASS).
You can see the “north” and “south” poles of the black hole simultaneously. That's because the black hole bends light around it, so that in effect you can see around the back of the black hole.
Astronomers argue that, if a black hole is accreting, then the inner edge of the accretion disk probably lies at the innermost stable orbit. At that radius, gas peels off from the accretion disk orbiting the black hole, and falls headlong into the black hole.
But you have chosen a trajectory with not quite enough angular momentum to go into unstable circular orbit,
so you continue on into the black hole.
Although photons can in principle get “stuck” in circular orbit at the photon sphere,
in practice the orbit is unstable,
so photons do not concentrate there,
and you do not see anything special as you pass through the photon sphere.
Instead, the horizon splits into two as you pass through it. Click on Penrose diagrams to understand more about why the horizon splits in two.
Without the grids (animation at right),
you would not see any sign that you crossed the horizon.
Yes, the animation is boring, isn't it.
The same view in stereo.
The misconception arises because if you lower yourself very slowly towards the horizon, firing your rockets like crazy just to stay put, then indeed your view of the outside universe will be concentrated into a small, bright circle above you. Click on the button to see what it looks like if you lower yourself slowly to the horizon. Physically, this happens because you are swimming like crazy through the inrushing flow of space (see Waterfall), and relativistic beaming concentrates and brightens the scene ahead of (above) you. See 4D Perspective for a tutorial on relativistic beaming. But this is a thoroughly unrealistic situation. You'd be daft to waste your rockets hovering just above the horizon of a black hole. If you had all that rocket power, why not do something useful with it, like take a trip across the Universe?
If you nevertheless insist on hovering just above the horizon, and if by mistake you drop just slightly inside the horizon, then you can no longer stay at rest, however hard you fire your rockets: the faster-than-light flow of space into the black hole will pull you in. Whatever you choose to do, the view of the outside Universe will not disappear as you pass through the horizon.
Click on the button at left (with the horizon grid) or right (without the horizon grid) for an animation of the appearance of the outside Universe as you lower yourself slowly to the horizon. The Universe appears brighter and brighter as you approach the horizon, tending to infinite brightness at the horizon. But again, no one with any sense would do this.
As you fall further inside the horizon,
the Schwarzschild bubble enlarges.
The same view in stereo.
The gravity at your feet is stronger than the gravity at your head — as long as you fall in feet first, so that your feet are nearer the black hole than your head. You feel this difference in gravity between your feet and your head as a tidal force, which pulls you apart vertically in a process called “spaghettification”. At the same time as you are pulled apart vertically, you are crushed in the horizontal direction, like a rubber band being pulled. So if you would like to be taller and thinner, then one way to achieve that is to fall into a black hole (and be sure to fall in vertically!). However, like many diets, the improvement to your shape will be only temporary.
Trivium:
it is a general fact
you will be torn apart by a black hole approximately a tenth of a second
before you hit the singularity,
independent of the mass of the black hole.
This is because the free-fall time goes as the inverse square root of the tidal force,
tff = (G M / r3)−1/2.
The same view in stereo.
If you have some transverse motion (some angular momentum) about the black hole, as in the movie, then relativistic beaming concentrates and blueshifts the scene in the direction of your motion.
You never get to see the singularity,
because all light is headed towards the singularity, none away from it.
The same view in stereo.
The same view in stereo.
Geometrical intuition, bolstered by pictures like this one would suggest that the center of the Schwarzschild black hole is a point. That intuition is misleading. If you and a friend fall into a black hole at the same time but at different locations (in latitude and longitude), you do not approach each other as you approach the singularity. Rather, the diverging tidal force channels the parts of your body along the inward radial direction. Far from meeting your friend at the singularity, you cannot even put out your arms to touch her.
“The” singularity is not a point. Rather, it is a 3-dimensional spatial boundary where general relativity commits suicide. New physics, presumably quantum gravity in some form, must replace general relativity at singularities. What that new physics is remains a profound unanswered question.