Light paths and falling objects

A black hole's gravity bends the light that passes near it. BlackHoles.fyi can draw the routes that light takes on its way to you.

You can also drop a small object into the hole, to see how its fall looks from far away.

Each part carries a label saying how real it is: worked out from the physics, following a model another team published, chosen for the picture, or partly worked out and partly chosen.

The paths of light

Partly worked out from the physics

Lines that show the routes light takes past the hole on its way to you.

Each path is found the same way the picture is: by following light back from your eye and bending it as the hole's gravity would. It is then drawn where it really runs in space, as if the hole's gravity did not bend your view of it. Paths stop at the middle of the glowing disc of gas that circles the hole. The picture gives that disc some thickness, so near its rim a path can end a little off what you see.

No paper is listed for this part. Each path comes from the same tracing of light as the picture itself.

The object you can drop in

Partly worked out from the physics

A small object falling towards the hole, so you can see how its fall looks from far away.

Its fall, the time on its own clock and on yours, the delay of its light and its fading are worked out. It is drawn as a dot whose size and colour are chosen, and the fainter images its light makes by circling the hole are left out, so a real one would fade more slowly.