Reading about Gamma ray bursts and wondering why they don't get shifted

[Onceler]

Some are over three billion light years away and they are still Gamma rays.
I would think that the Doplar effect would have shifted them down into a less energetic wave.
How can this be?

 

[Biftheunderstudy]

They are doppler shifted, GRB's are just that crazy. (You should be careful with Doppler shifting, strictly speaking this is a Cosmic redshift)

Redshifts at that distance are really hard to pin down though and the way the most distant ones are done is through measuring the observed frequency of lyman-alpha absorption from the IGM.

 

[Onceler]

So Gamma rays don't get shifted at all? I would think that something 13 billion light years away would get shifted to a lower frequency regardless of how energetic it is.

 

[wirednuts]

they do lose energy over distance... they are just insane compared to anything else we know. the amount of energy is mind boggling.

 

[Ayah]

a slightly redshifted GRB gamma ray is still a gamma ray. your issue is of magnitude.

 

[Jeff7]

a slightly redshifted GRB gamma ray is still a gamma ray. your issue is of magnitude.

This.

You start out with an absolutely ridiculously powerful high frequency gamma ray burst.

By the time it gets here, it's only marginally less absolutely ridiculously powerful, at a slightly lower frequency. It's still very much in the "gamma ray" band.


I'll build a 50 terawatt infrared laser and fire it at a Twinkie 3 miles away.

Then I'll crank it down by 2% and fire again.

That Twinkie isn't going to care much about that difference.


Then I'll either get hired by the government, or locked away by the government. :sneaky:

 

[SMOGZINN]

So Gamma rays don't get shifted at all? I would think that something 13 billion light years away would get shifted to a lower frequency regardless of how energetic it is.

Gamma rays do get red-shifted. Some of the Gamma Rays that start out definitely get red shifted down to X-ray or lower frequencies. Gamma ray is just what we call any frequency of 10^19Hz or over. By the 'or over' we mean all the way to the Planck length. So, they start out really, really, really energetic and get red shifted down to just really energetic.

 

[silverpig]

a slightly redshifted GRB gamma ray is still a gamma ray. your issue is of magnitude.

This.

For standard visible light, if you have a green photon at 550 nm, and red shift it by a factor of two, your wavelength is now 1100 nm, well into the IR range.

If you have a gamma ray photon at 10^-3 nm, and red shift it by a factor of two, your wavelength is now 5 * 10^-2 nm, which is still a gamma ray.

 

[Net Prowler]

wow this stuff is pretty cool. makes me want to be an astronomer or physicist now....