Extremely high energy particle

[Captain Scarlet]

The second highest-ever energy particle has been detected apparently. The Guardian article below says

 

When ultra-high-energy cosmic rays hit Earth’s atmosphere, they initiate a cascade of secondary particles and electromagnetic radiation in what is known as an extensive air shower.

Some charged particles in the air shower travel faster than the speed of light, producing a type of electromagnetic radiation that can be detected by specialised instruments.

… what is meant by that second paragraph? “Faster than light”? A case of journalistic misunderstanding? @andrew s? @vlaiv?

https://phys.org/news/2023-11-telescope-array-second-highest-energy-cosmic-ray.html
 

https://www.theguardian.com/science/2023/nov/24/amaterasu-extremely-high-energy-particle-detected-falling-to-earth?CMP=Share_iOSApp_Other
 

Magnus

[vlaiv]

13 minutes ago, Captain Scarlet said:

A case of journalistic misunderstanding?

I'd say so.

[iantaylor2uk]

Actually I think the journalist may be correct - cosmic rays can generate Cherenkov radiation - this is where charged particles travel faster than light in the specific medium they are travelling in.

The speed of light in air is very slightly lower than the speed of light in a vacuum so this could potentially happen.   

[vlaiv]

18 minutes ago, iantaylor2uk said:

Actually I think the journalist may be correct - cosmic rays can generate Cherenkov radiation - this is where charged particles travel faster than light in the specific medium they are travelling in.

The speed of light in air is very slightly lower than the speed of light in a vacuum so this could potentially happen.   

I think you are absolutely right.

[andrew s]

@iantaylor2uk has it right. The particles are moving faster than the speed of light in air.

[Zermelo]

This story just popped up in the DM science section too, and was another chance for one of their interns to show their lack of scientific knowledge:

"The cosmic phenomenon carried the energy of 240 quintillion electron volts - that's 240 billion billion (followed by 18 zeros).
For comparison, a typical lightning bolt is about 300 million volts."

So, if you're not sure what type of quantity an electron volt is measuring, just Google for something big, that's measured in Volts instead. You might as well compare it with the size of Wales.

I converted the 240EeV to around 38 Joules of energy - enormous for a single cosmic ray particle, but small beer in the macroscopic world. The average energy of a lightning bolt is apparently around 10⁹ J, which is just a bit larger.

 

Edited November 26, 2023 by Zermelo
formatting

[robin_astro]

The astronomer from across the pond they had on the BBC radio programme ( "inside science" or "science in action", I forget which)  likened it to the energy in a pitched baseball  so 0.15kg at say 100km/hr (a rather slow pitch ? I'm no expert on that particular sport) which would work out at ~ 0.15*28^2 / 2 = ~ 60 Joules.  That's a lot of energy of you happened to be in its way though. How much energy would it dissipate passing through your body I wonder ?

Cheers

Robin

[badhex]

I literally just used the original paper for the oh-my-god particle as a source in the UCLan Cosmology assignment I submitted last week, so I was reading this very article (the phys.org one) as additional information. The thing I found particularly interesting which is not totally clear is that the GZK cutoff is actually more complicated. GZK also suggests a distance which is think is about 160 mil ly. 

As I understand it, when a UHECR proton detected on earth has energy above the GZK cutoff, it actually shouldn't be possible for it to have come from a source outside the GZK horizon. A proton with that much energy travelling through the interstellar medium will collide with a photon from the CMB and create a Delta+ particle, which is unstable and then quickly decays back into either a proton or neutron, plus pion radiation of the appropriate charge. This takes about 20% of the energy of the original proton, and will happen multiple time over the distances involved, slowing it down significantly, thus anything detected on earth with that much energy must have come from within the GZK horizon. 

The big problem is that nothing we know of exists within that horizon which can accelerate particles to those high energies. 

It's obviously more complicated than that and I don't pretend to understand all of the background, but I thought that bit was fascinating. 

Edited January 22 by badhex

[Mr H in Yorkshire]

On 26/11/2023 at 09:17, Zermelo said:

You might as well compare it with the size of Wales.

Bigger than a bread basket but smaller that Yugoslavia. A quote from a surrealist play I heard about 50 years ago.