Why are photons sucked into black holes if they are massless "particles"?

Question

Black holes suck in all mass within range of its gravitational pull. However, light is also pulled in to the black hole. Does a photon have a mass so small its negligible like an electron? Why does light get sucked into a black hole?

Answer 1

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They aren't sucked in. They simply follow the 'straight-line' geodesic of the spacetime that's warped by the presence of the mass of the black hole. That's the essence of general relativity.

Answer 2

bragadog has given you the simplest explanation, that the escape velocity (once you've crossed the event horizon) is faster than the speed of light. You should realize that both space and time are severely distorted around a black hole.

However, unlike mass, photons are not "sucked into" a black hole. If the path of a photon (including the distortion of space around the black hole) isn't going to cross the event horizon, the photon will pass by the black hole, and not fall in. However, if the photon's path crosses the event horizon, it can never escape.

If something with mass, however, passes near a black hole, it will be pulled inwards, and will spiral inwards (perhaps after orbiting it a whole bunch of times).

But the behavior is a little different for mass vs. photons; mass is "pulled in", but photons have to "jump in".

Edit: Despite several people who have claimed differently, PHOTONS DO NOT HAVE MASS! They do have momentum (regardless of whether the Higgs Boson exists or not) but their mass is zero.

Answer 3

Take an ice rink, a nice flat surface. Toss a hockey puck across it. How does it travel? I'm betting you know it goes straight.

This is essentially what everything wants to do unless theres an outside force. An astute observer notes that photons have exactly 0 mass -- no mass, not even a tiny bit, not even undetectably small, nothing, zero, exactly zero, not even a tiny "dm" of mass; and that since F=ma, for a photon F must always be 0.

But, black holes warp space and time so much that they alter the meaning of straight. It no longer is straight according to us. It's straight meaning the shortest path from a to b. On a flat plane, this is a line. But in a different topology, say a curved space, this will ALWAYS be a curve. This is how light can be bent around objects. It is the warped space-time that alters the geometric manifold that the Universe obeys within that region. This alters the meaning of a straight line (in essence, photons always take the geodesic -- minimum distance path). But near a black hole, the geodesic can be a path that leads straight into the black hole, regardless of whether or not it can escape.

And an electron's mass is not negligible. If you want to talk negligible masses, go talk about neutrinos.

Source(s):

Somewhat related to gravitational lensing, except here the masses aren't big enough to "suck" in the light, only big enough to severely distort it.

Answer 4

What is fascinating about your question is the range of replies. Our teachers think they understood what they were taught. We think we understand what was passed on to us, so we leap in to try and explain to you.
And non of it is "right". Some are "better" than others but the subject is too hard and too involved to be tackled in the time and space (sic) available here.

It feels so frustrating....that there is so much to unravel and no time to do it in ( and remember - it can't actually be unraveled, just made a little more intelligible ). I'm not going to try but you should know, the photon has to be regarded as having no mass ( in our usual understanding of "mass" ).
I'm going fruit picking. Back to reality.

Source(s):

Old teacher

Answer 5

Photons DO NOT for any purposes have mass. They do however have momentum, imbued by the Higg's boson (though still in debate if it exists). This is what causes them (basically) to feel the effects of a black hole. However, it is a little more complicated, and you need to know a good deal of math to understand it.

Answer 6

The escape velocity from a black hole is higher than the speed of light in vacuum

Answer 7

Actually Photons do have Mass and it is Equal to Planck-Constant*Frequency / Speed of Light^2 ( hv/c^2 ), and this Mass - even Small - is of course affected by the gravitational fields, and in case of the gravitational field of a black hole it has a certain distance as the Even of Horizon, beyod which it can no way escape of the Gravitational Field

Answer 8

light is both wave and has mass.