by Jill Sakai, University of Wisconsin
Though still under construction, the IceCube Neutrino Observatory at the South Pole is already delivering scientific results — including an early finding about a phenomenon the telescope was not even designed to study.
- This “skymap,” generated in 2009 from data collected by the IceCube Neutrino Observatory, shows the relative intensity of cosmic rays directed toward the Earth’s Southern Hemisphere. Researchers from UW-Madison and elsewhere identified an unusual pattern of cosmic rays, with an excess (warmer colors) detected in one part of the sky and a deficit (cooler colors) in another.
IceCube captures signals of notoriously elusive but scientifically fascinating subatomic particles called neutrinos. The telescope focuses on high-energy neutrinos that travel through the Earth, providing information about faraway cosmic events such as supernovas and black holes in the part of space visible from the Northern Hemisphere.
However, one of the challenges of detecting these relatively rare particles is that the telescope is constantly bombarded by other particles, including many generated by cosmic rays interacting with the Earth’s atmosphere over the southern half of the sky. For most IceCube neutrino physicists these particles are simply background noise, but University of Wisconsin-Madison researchers Rasha Abbasi and Paolo Desiati, with collaborator Juan Carlos Díaz-Vélez, recognized an opportunity in the cosmic ray data.
“IceCube was not built to look at cosmic rays. Cosmic rays are considered background,” Abbasi says. “However, we have billions of events of background downward cosmic rays that ended up being very exciting.”
Abbasi saw an unusual pattern when she looked at a “skymap” of the relative intensity of cosmic rays directed toward the Earth’s Southern Hemisphere, with an excess of cosmic rays detected in one part of the sky and a deficit in another. A similar lopsidedness, called “anisotropy,” has been seen from the Northern Hemisphere by previous experiments, she says, but its source is still a mystery.
“At the beginning, we didn’t know what to expect. To see this anisotropy extending to the Southern Hemisphere sky is an additional piece of the puzzle around this enigmatic effect — whether it’s due to the magnetic field surrounding us or to the effect of a nearby supernova remnant, we don’t know,” Abbasi says.
The new result publishes Aug. 1 in The Astrophysical Journal Letters, published by the American Astronomical Society.
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“A picture is worth a thousand words” and some may generate a million questions. We have only just begun a journey of a billion years. Before we finish, we will answer a trillion questions and still have not even begun to know who we are or where we came from or why.
From the paper
“It is tempting to try to interpret the cosmic-ray excess as
an artifact of the heliospheric magnetic field. However, the
maximum gyroradius of a 10 TeV cosmic-ray proton in a 1 μG
magnetic field is about 0.01 pc, i.e., much larger than the size of
the heliosphere. As a consequence, the observed anisotropy is
more likely to be connected to features of the local interstellar
magnetic field at distances <1 pc. We are also investigating
L198 ABBASI ET AL. Vol. 718
the possibility that the cosmic-ray excess is associated with
structures in theGalactic magnetic field at larger distance scales,
or with diffusive particle flows from a nearby Galactic source
such as Vela."
In order to clarify the issue, the Ice cube was designed to check for neutrinos.
BUT , and this is what this paper is about, ordinary galactic cosmics, i.e charged particles of various kinds, from protons and antiprotons to ions , to positive and negative muons and electrons.
They have to be charged in order to create the cosmic ray showers that will be detected as background to the desired neutrino signals ( cerenkov light probably), and because of the design of the experiment they are in the Tera electron volt range, TeV.
Lucy Skywalker says:
July 31, 2010 at 6:31 pm
Don´t be surprised if the current “Flintstones Universe” paradigm is wrong: All stars and galaxies are connected to the “grid”, as shown in this beautiful image of Andromeda in the infrared ( a “rosary” of stars connected to a central star):
http://apod.nasa.gov/apod/ap100219.html
A single source of cosmic rays would pepper one hemisphere of the Earth, like a torch shining on a sphere. With this in mind it looks like a very strong single source to the ‘left’ and a weaker single source from the ‘right’.
It would be interesting to see the map for the whole Earth to see if the pattern continues!
Enneagram says:
July 31, 2010 at 2:42 pm
“According to H.Svensmark GCR always mean clouds increase”
There are databases of ultra high energy GCR events dating back to the 1940s; no one has found much of a systematic correlation between these events and any form of increased clouds, precipitation, heating or cooling.
Comic ray energies are measured in some multiple of an electronVolt; lets recall that 1eV=1.6*10^-19 Joule. So a TeV cosmic ray is thus on the order 10^-7 Joule of energy. Detectable? yes. An agent of climate change? Hardly.
Michael Schaefer says:
July 31, 2010 at 4:06 am
Well,to me this picture looks like they have finally found scientific evidence for the Big Bang insofar, as the red – hot – area may show the direction to the center of the Universe i.e. the point, where the Big Bang actually happened – while the blue, cold area looks just the other way, i.e. away from the center of the Universe.
‘fraid not. if you want to see big bang stuff, go look at WMAP. Note that both are milky way oriented coordinates so that the center of our galaxy is in the middle of the chart.
As Anna V mentioned already, it’s got to be high energy cosmic rays. That’s because lower energy cosmic rays have bent paths meaning we have no way to determine the direction of their travel.
As for trying to ‘see’ far with the cosmic rays, the high energy ones that don’t change their direction substantially due to magnetic fields (outside our solar system) also cannot travel that far because of interaction (collisions) with the cosmic microwave background photons. In other words, high energy cosmic rays cannot travel large distances on par with the size of the universe. And, lower energy cosmic rays get twisted around direction wise due to the magnetic fields present in the galaxy and outside the galaxy such that there’s no information left as to where or what direction they come from.
“”” anna v says:
July 30, 2010 at 10:19 pm
Of course to be noted that they are talking of very large energies, TeV., that show this anisotropy. It would be interesting, with regard to Svensmark’s hypothesis, to see whether cloud cover correlates with this anisotropy. “””
Anna, would not one also have to map the Cosmic ray distribution along with the map of moisture distribution in the atmosphere to arrive at a Svensmark type picture of an interraction.
Having cosmic rays where there is no humidy is not a help. Does that sound reasonable to you ?
George E. Smith says:
August 2, 2010 at 5:44 pm
Well, George, If the map given were a map of the earth, as I presumed in my comment, there would be a meaning in it, and yes, humidity would have to play a role. But as is, the map is a sky map, i.e. oriented to constellations ( which is not shown) . I would need to read the paper to comment further instead of guessing.
It is true that very high energy cosmic rays, as these are, are rare and thus cannot affect the climate. They do point a direction though from which energy is being spewed in galactic cosmic rays, and the neutral components of these could arrive with higher frequency from the directions derived. Gamma rays for example and neutral atoms. Due to the rotation of the earth the correlations would be complicated of course, and a latitudinal model 🙂 would be needed. Since they will be neutral no strong correlation with the sun cycles would be expected.
I think Svensmark has demostrated some correlation of galactic cosmic rays and albedo, so this, if the numbers worked out, would be one more contribution messing up the albedo picture.
just a guess
particles are funneled along by magnetic/plasma lines
IceCube spies unexplained pattern of cosmic rays
..Abbasi saw an unusual pattern when she looked at a “skymap” of the relative intensity of cosmic rays directed toward the Earth’s Southern Hemisphere, with an excess of cosmic rays detected in one part of the sky and a deficit in another. A similar lopsidedness, called “anisotropy,” has been seen from the Northern Hemisphere by previous experiments, she says, but its source is still a mystery.
.. The pattern of cosmic rays also reveals more detail about the interstellar magnetic fields produced by moving gases of charged particles near Earth, which are difficult to study and poorly understood.
.. Since nearly all cosmic signals are influenced by the interstellar magnetic fields, a better overall picture of these fields would aid a large range of physics and astronomy studies, she says, adding that their newly reported findings rule out some proposed theories about the source of the Northern Hemisphere anisotropy. http://www.news.wisc.edu/18256
This all sky map reminds me of the Cassini all sky map of the heliosphere and its anisotropy and related interstellar magnetic field interaction.
http://www.nasa.gov/images/content/394390main_Mitchell-Cassini-Press-Conf-Pres-short-Rev-B%202.jpg
http://www.nasa.gov/images/content/394391main_Mitchell-Cassini-Press-Conf-Pres-short-Rev-B%203.jpg