Cosmic Rays: They Aren’t What We Thought They Were

by Nancy Atkinson on April 19, 2012

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IceCube team poses for a picture in front of deployment tower after the completion of the IceCube Neutrino Detector in December of 2010. Photo by: Chad Carpenter/NSF

The origin of cosmic rays has been one of the most enduring mysteries in physics, and it looks like it’s going to stay that way for a while longer. One of the leading candidates for where cosmic rays come from is gamma ray bursts, and physicists were hoping a huge Antarctic detector called the IceCube Neutrino Observatory would confirm that theory. But observations of over 300 GRB’s turned up no evidence of cosmic rays. In short, cosmic rays aren’t what we thought they were.

But, just like Thomas Edison who said that “every wrong attempt discarded is another step forward,” physicists view this latest finding as progress.

“Although we have not discovered where cosmic rays come from, we have taken a major step towards ruling out one of the leading predictions,” said IceCube principal investigator and University of Wisconsin–Madison physics professor Francis Halzen.

Cosmic rays are electrically charged particles, such as protons, that strike Earth from all directions, with energies up to one hundred million times higher than those created in man-made accelerators. The intense conditions needed to generate such energetic particles have focused physicists’ interest on two potential sources: the massive black holes at the centers of active galaxies and gamma ray bursts (GRBs), flashes of gamma rays associated with extremely energetic explosions that have been observed in distant galaxies.

IceCube is using neutrinos, which are believed to accompany cosmic ray production, to explore these two theories. In a paper published in the April 19 issue of the journal Nature, IceCube scientists describe a search for neutrinos emitted from 300 gamma ray bursts observed, most recently in coincidence with the SWIFT and Fermi satellites, between May 2008 and April 2010. Surprisingly, they found none – a result that contradicts 15 years of predictions and challenges one of the two leading theories for the origin of the highest energy cosmic rays.

Aurora seen behind the IceCube Lab. Photo by: Sven Lidstrom/NSF

The detector searches for high-energy (teraelectronvolt; 1012-electronvolt) neutrinos, and in their paper the team said they found an upper limit on the flux of energetic neutrinos associated with GRBs that is at least a factor of 3.7 below the predictions. This implies that either GRBs are not the only sources of cosmic rays with energies greater than 1018

"The result of this neutrino search is significant because for the first time we have an instrument with sufficient sensitivity to open a new window on cosmic ray production and the interior processes of GRBs," said IceCube spokesperson and University of Maryland physics professor Greg Sullivan. "The unexpected absence of neutrinos from GRBs has forced a re-evaluation of the theory for production of cosmic rays and neutrinos in a GRB fireball and possibly the theory that high energy cosmic rays are generated in fireballs."

IceCube is a particle detector at the South Pole that records the interactions of a nearly massless neutrinos. The instruments observe neutrinos by detecting the faint blue light produced in neutrino interactions in ice. Neutrinos can easily travel through people, walls, or entire planets, like Earth. In order to detect their rare interactions, IceCube is built on an enormous scale. One cubic kilometer of glacial ice, enough to fit the great pyramid of Giza 400 times, is instrumented with 5,160 optical sensors embedded up to 2.5 kilometers deep in the ice.

GRBs, the universe's most powerful explosions, are usually first observed by satellites using X-rays and/or gamma rays. GRBs are seen about once per day, and are so bright that they can be seen from half way across the visible Universe. The explosions usually last only a few seconds, and during this brief time they can outshine everything else in the universe.

Scientists say that improved theoretical understanding and more data from the compete IceCube detector will help scientists better understand the mystery of cosmic ray production. IceCube is currently collecting more data with the finalized, better calibrated, and better understood detector.

IceCube is operated by a collaboration of 250 physicists and engineers from the USA, Germany, Sweden, Belgium, Switzerland, Japan, Canada, New Zealand, Australia and Barbados.

More info on IceCube.

Paper in Nature.

Source: IceCube/University of Wisconsin

About 

Nancy Atkinson is Universe Today's Senior Editor. She also is the host of the NASA Lunar Science Institute podcast and works with Astronomy Cast. Nancy is also a NASA/JPL Solar System Ambassador.

bookmanjohn April 19, 2012 at 2:02 PM

Isn’t that 10^12 electron volts for a teravolt, , n0t 1012?

NancyAtkinson April 19, 2012 at 4:28 PM

Thank you, fixed.

lcrowell April 20, 2012 at 12:31 AM

An electron volt is a unit of energy. One electron volt is 1.6×10^{-19} joules. This does have a relationship to a volt. We consider Ohm’s law that P = VI, or power equals volts times amps. Amps is a unit of current or the time rate of change of charge A = de/dt. So the power or watts is P = Vde/dt. Now power is the time rate of change of energy P = dE/dt and so we can write the change in energy is

dE = Vde,

or V = dE/de. Physically this means that an electron with a unit of electrical charge 1.6×10^{-19}coulombs under one volt of electrical potential gains one electron volt worth of energy.

LC

Lord Haw-Haw. April 20, 2012 at 6:35 PM

A comprehensive explanation LC much obliged, Georg Ohm (1789-1854) left a colorful legacy:

http://www.science20.com/chatter_box/genius_georg_ohm-86122

zetetic elench April 19, 2012 at 2:14 PM

a telescope buried in dark ice.
can they get a vector on the passage or do they just detect an excess number of them going by?
no correlation to GRBs! amazing.

Peristroika April 19, 2012 at 8:58 PM

Nope, no vector. Shame really.

squidgeny April 20, 2012 at 11:57 AM

That’s not true; IceCube is sensitive to Cherenkov radiation, which betrays a neutrino’s direction. A collection of detections with a common direction can be used to infer a point source.

zetetic elench April 20, 2012 at 1:09 PM

ah hah. yes but do they? and in the information used in an attempt to derive a source? it seems the other way round. ie, detect spurious GRB event then look for neutrinos. the way they look for optical afterglows.

krenshala April 20, 2012 at 3:21 PM

Hopefully they document any neutrino detections even if they aren’t just after a GRB (or other “significant” event), and a correlation may be attempted by checking the data later.

zetetic elench April 20, 2012 at 1:09 PM

ah hah. yes but do they? and in the information used in an attempt to derive a source? it seems the other way round. ie, detect spurious GRB event then look for neutrinos. the way they look for optical afterglows.

Peristroika April 19, 2012 at 8:58 PM

Nope, no vector. Shame really.

Jon Souter April 19, 2012 at 2:37 PM

But are they looking for regular correlating neutrinos – or the kind that travel faster than light?
;-)

David Krauss April 19, 2012 at 3:33 PM

ISTR LC mentioned the interstellar/intergalactic medium dispersing EM radiation but not neutrinos. This was in the context of SETI: dispersion breaks down signal integrity over short interstellar distances.

Over intergalactic distances, wouldn’t the neutrinos arrive well ahead of the EM flash? Would the difference be minutes or years?

Peristroika April 19, 2012 at 9:00 PM

Interstellar medium (whatever that might be) might disperse EM radiation but it won’t slow it down. In fact, if neutrinos have a mass, then they should theoretically come AFTER the EM because they can’t actually travel at light speed. Intergalactic medium is negligible to radiation and wouldn’t slow it if it weren’t.

David Krauss April 20, 2012 at 2:32 AM

Dispersion is the result of refractive index varying over frequency. Refractive index is a measure of how much light is slowed down, and higher frequencies go slower.

The neutrons and the photons are both going pretty close to (absolute vacuum) light speed. But over a billion light-years, one part per trillion still comes out to half a day.

SJStar April 19, 2012 at 5:35 PM

Maybe the EU’ers might be right. Incredibly large extragalactic magnetic fields maybe be the cause of the colossal accelerations – either now or sometime in the early universe’s history? Seems like we need a interplanetary probe to see if the comic ray rate changes away from the Earth, perhaps even a place with an atmosphere like on Saturn’s moon Titan, to see if the cosmic showers are the same and behave the same. It would be truly startling if the source was terrestrial, say like fireballs stated in the article! (The only test would be something like Titan’s atmosphere to prove that… Umm.)

Torbjörn Larsson April 19, 2012 at 7:17 PM

Nitpicks:

- They have measured galactic magnetic fields now, they are weak.

Qs: How could the galactic fields withstand the proposed difference in magnetic strength and show incursions at all? What would generate the difference? Why should M fields be pushed into gaps of knowledge, especially considering the point above (weak fields observed)?

- Nothing local can generate that much energy.

FullofWind April 19, 2012 at 9:24 PM

The galactic magnetic field is not representative of the magnetic field everywhere.

It’s like arguing that the Earth’s magnetic field is too small to produce high-energy radiation, yet if the conditions are right, a terrestrial lightning bolt produces an electromagnetic pinch that is so large, that even gamma rays may be produced.

Electric fields accelerate charged particles wherever there are plasmas, and its does much more efficiently than gravity. The Sun produces changing magnetic fields (electric fields) that accelerates the solar wind away from its immense gravitational field, and jets do the same away from black holes. Jets also pinch (knots) that accelerates plasma across galaxies.

Torbjörn Larsson April 20, 2012 at 7:02 PM

“The galactic magnetic field is not representative of the magnetic field everywhere.”

Indeed, that was my point. Since the weak galactic field would have visible excursions but hasn’t, the difference between galactic and intergalactic field can’t be that high.

Of course I wasn’t mentioning really high local fields (say, at magnetars) because it wasn’t relevant for the above point. “Local” was an ambiguous reference to _our_ local environment as described by SJStar (“if the source was terrestrial, “).

Dennis Patterson April 19, 2012 at 6:33 PM

“1.21 Gigawatts!!!!!! 1.21 Gigawatts!!!!!! Great Scott!!!!!! How could I have been so careless!!!!” — Dr. Emmett Brown

Torbjörn Larsson April 19, 2012 at 7:13 PM

New law of physics: neutrinos always come up short.

- When they were suggested, it was because of an energy/impulse deficit.
- When they measured the Sun, neutrinos were missing in flavors due to their oscillation.
- When they measure CR, neutrinos are missing in higher energy.

“A neutrino walks into the bar.

“- Sorry, we don’t serve neutrinos here”, says the bartender.
“- There is always a deficit on your account.””

Steve Black April 19, 2012 at 9:39 PM

How about:
A Neutrino enters a bar. The neutrino says, “How about a Flavorful Oscillation on ice” The bartender does not respond:)
Bazinga!

squidgeny April 20, 2012 at 12:00 PM

A neutrino enters a bar. It exits without affecting anyone.

krenshala April 20, 2012 at 3:15 PM

I think you mean: A neutrino walks into a bar … and right out the other side.

Steve Black April 20, 2012 at 10:09 PM

Neutrino humor sometimes just seems to pass on through the audience. Thanks for the comments:)

Aqua4U April 19, 2012 at 8:33 PM

Sounds suspiciously like the energy required to create these particles might come from nearby antimatter annihilation? Apparently there is an unexplained electromagnetic ‘kick’ in the process?

i.e. Twist that dimension til it pouts!

Aqua4U April 19, 2012 at 9:08 PM

I LIKE the champagne bottles in the snow next to the team… Bubbly anyone? On a side note… I wonder how much it cost to transport that vino to the SP?

Torbjörn Larsson April 20, 2012 at 7:12 PM

The nearby station is claimed to have the best kitchen, not only on the continent, but perhaps on a few others. People get crazy enough without an exceptionally good kitchen when being voluntarily bottled up for many months without sunlight.

The boat cargo rate don’t cost much above the basic cost of getting them there. They probably have a good small & fresh cargo business with the tourist boats that go there anyway.

danangel April 21, 2012 at 3:03 AM

US Navy Operation Deepfreeze was said to have the best food in the Navy, even beating the galleys on Nuclear Subs. Whatever it takes to keep them from going crazy.

Peristroika April 19, 2012 at 9:02 PM

Wow, wouldn’t it be easier to just detect the cosmic rays directly? Then you could fix their vector and pinpoint a direction. Haven’t we got a satellite to do this beyond the interference of the atmosphere?

Al Wilson April 20, 2012 at 2:33 PM

Galactic magnetic fields scramble the directions of cosmic rays, thus impossible to pinpoint their origin directly.

lcrowell April 20, 2012 at 12:16 AM

What this means is GRBs do not involve weak interactions. This rather surprising, for highly energetic events tend to cause lots of interactions.

LC

Ettore Greco April 21, 2012 at 8:21 AM

Contrary to what science still believes, at the time of the Big Bang there were no atoms but only waves carrying energy through the infinite Void. The Universe is that limited invasion of energy in the infinite Void. If we could view the Universe from outside, It would look like an egg-shaped cloud with winds running in perpetual motion inside of It.
The energy is like those winds running at maximum speed and pushing out the borders of the Universe.

The Universe continues to expand because the waves traveling at the border of the Universe have never encountered, nor will ever encounter, any interference from the Void. These waves will forever expand the Space of the Universe they create and leave behind.

Wave-behavior relates to the medium in which the waves travel.
Thus, wave-behavior at the border of the Universe is different than wave-behavior within the Universe.

Inside the Universe, waves change their frequencies by colliding with other energy during their travel. These waves, because of the encountered interference, continue to transform part of their original energy in other forms. Waves travel gradually releasing heat, or amounts of energy, and their original short wavelengths become longer and longer as they carry less and less energy than they did when they first started to travel. These waves lose energy releasing it in form of other waves with wavelengths longer than their own.

For example, the gamma rays, over time, diminish their energy level (and their frequency) to become X rays, from X rays they will become ultraviolet and so on. The original quantum is not lost but distributed into other forms of energy through “spontaneous symmetry breaking”.

Once reached an almost flat longitude (and lower critical energy level) these waves solidify into hydrogen atoms breaking up their energy like the split ends of a broken hair in two opposite elements: proton and electron (after a transition from subatomic particles).
When the hydrogen atoms are reached by the heat (or energy) of other incoming waves they fuse together to create more complex forms of energy.

http://www.wavevolution.org

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