Aren't there any number of event horizons for a black hole?

No. every frequency of light travels at exactly the same speed. The speed of light is a physical constant of exactly 299,792,458 meters per second. It is a profound benchmark.

(How can the speed of light be measured exactly?

In 1983, the meter was redefined in the International System of Units as the distance traveled by light in 1⁄299,792,458 of a second. As a result, the numerical value of the speed of light in meters per second is now fixed exactly by the definition of the meter.)

.

>Are there more than one event horizon for the various wavelengths in the electromagentic spectrum?

No. All forms of light move at the same speed, so the event horizon for them is the same.

>I know, yes the speed of light has been fairly constant over time, but gravitation is acting on mass not speed, so some photons must have a different mass than others? or no?

They do. But gravity acts simply as an acceleration. It exerts proportionally more force on objects with larger mass, so that the acceleration is the same. This is a really basic principle of newtonian universal gravitation and was demonstrated by Galileo hundreds of years ago.

The reason light objects seem to fall more slowly than heavy objects is that here on Earth, we have air, and air resistance acts more on objects that are larger relative to their mass. So a feather not only falls more slowly than a brick, but also more slowly than a small chunk of brick that weighs the same as the feather. In space, with no air resistance, this is not the case.

when the escape velocity of a gravity well exceeds the speed of light, that stellar object is referred to as a black hole. The entire EM spectrum from deep infrared to ultra high end x-rays/gamma rays/comic rays ALL travel at one single speed... the speed of "light". This speed has NOTHING to do with the visibility of light, its the entire spectrum that travels at this speed.

The mass of a photon isn't an issue because black holes are not "vacuum cleaners" which "suck up" light. They are objects in space with gravity. The earth is a hole, the moon is a hole, the sun is a Big Hole... the way to get out of the hole is to "escape".... fling yourself up with enough speed that you fly out... you cant stop half way up and cling to the side and rest.... its all or nothing.... escape velocity or you fall back in. For a black hole..... escape velocity > c

AT the event horizon, matter is being torn apart by tidal forces and the unequal stresses of gravity. that is why radiation (sometimes) is emitted at the edge of the gravity field. The horizon where these events take place is the event horizon.

No, there is only one event horizon for a black hole. All EM radiation of any wavelength has the same speed.

<MORE>

Light, and all photons of the EM spectrum, have zero rest mass. You can't use Newton's version of gravity when dealing with light, since his model is incomplete... you need to study Einstein's Theory of General Relativity for the effects of gravity on light, which imply gravity is not a mutual force based on the total mass of a syste,, but an actual curvature of space caused by things with mass. It even gets more complicated than that when you study the stress-energy tensor... which suggests that light DOES have gravity of its own. But that is even too complicated for me to fully understand.

A back hole can exist because of the curvature of space and time. Space and time are wrapped back up onto themselves and radiation no matter of what wavelength travels in that framework of space and time. That's why wavelength does not matter when you consider a black hole and what can and can not escape it.

PERFECT book for that is "A Theory of Time and Space" by Steven Hawking

Believe me, you'll learn so much about black holes, and even time travel.