beyond gamma rays?

[The_Radiation_Specialist]

I was just wondering if there is an electromagnetic radiation with a frequency higher than gamma rays. Or if it is possible at all.

[Tensor]

I was just wondering if there is an electromagnetic radiation with a frequency higher than gamma rays. Or if it is possible at all.

Gamma rays are just the name given to the very highest frequency, most energetic part of the EM spectrum. So, basically, as the frequency get higher, they are still called gamma rays. We don't have another name for that part of the spectrum.

[Fortunate]

Thus, two "gamma ray" observatories may actually be observing totally different parts of the electromagnetice spectrum. G.L.A.S.T. will cover about three orders of magnitude, from 20 Mev to 300 Gev, as described here. The article also says that SWIFT covers a lower energy regime.

Other telescopes have observed gammas in the range from 1 Tev to 20 Tev as described here. Each telescope has its own range. I believe that the "current program" is to complement G.L.A.S.T. with new, ground-based gamma ray telescopes covering a multitude of ranges.

[Ken G]

Yes, I'm afraid the terminology is a bit of a mess. Originally, a gamma ray was simply a photon that came from a nucleus, and those tended to be the highest energy reactions known. But cosmic rays are even higher, and there is really no other word except either gamma ray or cosmic ray, and neither are very descriptive.

[The_Radiation_Specialist]

is there a limit to the frequency of gamma rays? What is the highest electromagnetc frequency ever known?

[Fortunate]

is there a limit to the frequency of gamma rays? What is the highest electromagnetc frequency ever known?

There is no limit in terms of definition. Here is a recent (2004) paper discussing the possibility that the most energetic cosmic ray ever detected by the Fly's Eye cosmic ray detector was actually a photon. This cosmic ray had an energy in excess of 3x10²⁰ Ev. The paper concludes that although it seems unlikely that the primary was a photon, that this possibility "cannot be excluded."

[The Bad Astronomer]

As has been pointed out, there is no limit to the frequency of gamma rays. It's an open-ended spectrum. At the other end, radio waves extend to infinite wavelength (0 frequency if you prefer).

While there is no theoretical limit to the energy of a gamma ray, there is a practical one. Beyond a certain energy they can't get very far before interacting with the interstellar medium (gas and dust between stars) and turning into very high energy particles. This happens when they have roughly a trillion times the energy of visible light. We do see some gamma rays with this energy, and it's a big mystery where they come from!

[suntrack2]

gamma rays are originated from which place in the universe, is there any certain path of the gamma rays from where they emits firstly?

sunil

[Relmuis]

I have read somewhere that a gamma photon of sufficient energy may spontaneously decay into an electron and a positron. Which would mean that the vacuum is opaque to very short wavelengths.

Is this correct? (I would doubt it, because a photon flies at light speed, so how could it have a half life for any kind of spontaneous decay?)

[korjik]

spontaneous decay cant occur too often cause that would cut off the gamma over a couple MeV. electron mass is about half a MeV. I believe that there has to be a trigger to get the decay, like what BA was saying above

[Ken G]

You need two photons to conserve energy and momentum, so the decay isn't "spontaneous", it requires a second photon. Though it can be pretty much any photon, it just has to be there. But it doesn't happen too often, the cross section is not large enough.

[Relmuis]

So the classical image of light waves passing through each other without being changed thereby would not be right in this case? And I might provoke the forming of electron-positron pairs by pointing a laser (or even a strong flashlight) near a source of gamma radiation?

[Nereid]

I've not heard of the formation of a particle-antiparticle pair creation being mediated by a photon (I thought you needed something that has a non-zero cross-section with photons, so even neutrinos won't do).

Although the EHE (extremely high energy) regime is beyond what we're likely to be able to explore directly with accelerators etc here on Earth, at least for the next century or three, it's one which entities in our local ~100Mpc apparently don't even break into a sweat to reach, producing tonnes of stuff.

To even begin to understand the physics of this regime, we will almost certainly have to develop at least one major extension to the current Standard Model.

[Ken G]

So the classical image of light waves passing through each other without being changed thereby would not be right in this case? And I might provoke the forming of electron-positron pairs by pointing a laser (or even a strong flashlight) near a source of gamma radiation?

Yes, that's right. The inverse process of electron-positron annihilation is the creation of two photons with a total energy in excess of 1 MeV, so if you start out with that much energy in photons, you can go the opposite way. I don't know how to calculate the cross section, that's quantum electrodynamics.