Monster neutrino solves cosmic-ray mystery

Source of the fast and furious? (Image: NASA/CXC/UMass/D. Wang et al)

Source of the fast and furious? (Image: NASA/CXC/UMass/D. Wang et al)

A COSMIC coincidence could be the first clue to the origin of a high-energy neutrino spotted in Antarctica – and may help pinpoint the source of high-energy cosmic rays that bombard Earth’s atmosphere.

Cosmic rays are massive charged particles that barrel through deep space with energies that dwarf those achieved at particle accelerators on Earth. Some may be accelerated to such high speeds by supernovas, but others have mysterious roots.

“The origin of cosmic rays is one of the most intriguing questions in astrophysics,” says Toshihiro Fujii at the University of Chicago. But because they can be deflected by magnetic fields, their sources are difficult to trace. Continue reading Monster neutrino solves cosmic-ray mystery

A Cosmic Muon Observer Experiment for Students

Overview of the CosMO setup in operation with three scintillator boxes (right), the DAQ card (center), and the readout netbook with the graphical user interface (left)

Overview of the CosMO setup in operation with three scintillator boxes (right), the DAQ card (center), and the
readout netbook with the graphical user interface (left)

CosMO – A Cosmic Muon Observer Experiment for Students
R. Franke, M. Holler, B. Kaminsky, T. Karg, H. Prokoph, A. Schönwald, C. Schwerdt, A. Stößl, M. Walter
What are cosmic particles and where do they come from? These are questions which are not only fascinating for scientists in astrophysics.
With the CosMO experiment (Cosmic Muon Observer) students can autonomously study these particles.
They can perform their own hands-on experiments to become familiar with modern scientific working methods and to obtain a direct insight into astroparticle physics.
In this contribution we present the experimental setup and possible measurements.
The detector consists of three scintillator boxes. Events are triggered and read out by a data acquisition board developed for the QuarkNet Project.
With a Python program running on a netbook under Linux, the trigger and data taking conditions can be defined. The program displays the particle rates in real-time and stores the data for offline analysis.
Possible student experiments are the measurement of cosmic particle rates dependent on the zenith angle, the distribution of geometrical size of particle showers, and the lifetime of muons.
Twenty CosMO detectors have been built at DESY.
They are used within the German outreach network Netzwerk Teilchenwelt at 15 astroparticle-research institutes and universities for project work with students.
Read more at http://arxiv.org/pdf/1309.3391v1.pdf

The most powerful particles in the Universe

a cosmic smash

Illustration of an air shower. We recognize the so-called  uores- cence light (UV or bluish), and the generation of light particles named pions (), which rapidly decay into even lighter leptons (e; ; ) and photons ( )

Illustration of an air shower

Wolfgang Bietenholz
This year we are celebrating 101 years since the discovery of cosmic rays.
They are whizzing all around the Universe, and they occur at very different energies, including the highest particle energies that exist. However, theory predicts an abrupt suppression (a “cutoff”) above a specific huge energy.
This is difficult to verify, the measurements are controversial, but it provides a unique opportunity to probe established concepts of physics – like Lorentz Invariance – under extreme conditions.
If the observations will ultimately contradict this “cutoff”, this could require a fundamental pillar of physics to be revised….
Read more: http://arxiv.org/pdf/1305.1346v1.pdf

New insights into what triggers lightning

What initiates a lightning strike? In the image above, multiple cloud-to-ground and cloud-to-cloud lightning strikes are observed during a night-time thunderstorm. (Courtesy: NOAA)

What initiates a lightning strike? In the image above, multiple cloud-to-ground and cloud-to-cloud lightning strikes are observed during a night-time thunderstorm. (Courtesy: NOAA)

Cosmic rays interacting with water droplets within thunderclouds could play an important role in initiating lightning strikes. That is the claim of researchers in Russia, who have studied the radio signals emitted during thousands of lightning strikes. The work could provide new insights into how and why lightning occurs in the first place.
Although most people have witnessed a flash of lightning during a thunderstorm at some point in their lives, scientists still do not completely understand what triggers the discharge in the first place. Lightning has been studied for hundreds of years, yet while many possibilities for observation are available – there are about 40 to 50 lightning strikes per second across the globe – predicting the onset of a strike is difficult…. Read more at http://physicsworld.com/cws/article/news/2013/may/07/new-insights-into-what-triggers-lightning

Huge cosmic-ray observatory set for Siberia

Researchers construct a prototype detector for the planned $46m Hundred Square-km Cosmic Origin Explorer, which will be based in the Tunka Valley in Siberia. (Courtesy: Martin Tluczykont/University of Hamburg)

Construction has begun in the Tunka Valley near Lake Baikal in Siberia, Russia, on the world’s largest cosmic-ray observatory. The first prototypes for the $46m Hundred Square-km Cosmic Origin Explorer (HiSCORE) are now being installed and when complete by the end of the decade the facility will consist of an array of up to 1000 detectors spread over 100 square kilometres. HiSCORE will aim to solve the 100-year-old mystery surrounding the origins of cosmic rays – particles that originate in outer space and are accelerated to energies higher than those achieved in even the largest man-made particle accelerators.
HiSCORE is a collaboration between three institutes in Russia – the Institute for Nuclear Research of the Russian Academy of Sciences in Moscow, Irkutsk State University in Siberia and Lomonosov Moscow State University – as well as DESY, the University of Hamburg and the Karlsruhe Institute of Technology, all in Germany. The unprecedented size of the array will allow scientists to investigate cosmic rays within an energy range of 100 TeV to 1 EeV – a relatively unexplored region.
HiSCORE’s detectors are designed to observe the radiation created when cosmic rays hit the Earth’s upper atmosphere. This causes a shower of secondary particles that travel faster than the speed of light in air, producing Cherenkov radiation in the process that can be picked up by HiSCORE’s photomultiplier tubes. This radiation can be used to determine the source and intensity of cosmic rays as well as to investigate the properties of high-energy astronomical objects that emit gamma rays, such as supernova remnants and blazars. “We are especially interested in galactic objects that accelerate cosmic rays to energies around peta-electron-volts – or pevatrons – that have yet to be discovered,” Martin Tluczykont from the University of Hamburg, who is co-ordinating the project, told Physics World. “They are crucial to a solution of the origin of cosmic rays.'”
With its remote location, Lake Baikal is rapidly becoming a hotbed for cosmic-ray research. It already hosts the Tunka-133 cosmic-ray observatory, which has been in operation since 2009, and is also home to the Baikal Deep Underwater Neutrino Telescope (BDUNT), which is located 1.1 km below the surface of the lake and observes the Cherenkov radiation produced by high-energy neutrinos. The BDUNT is set to be replaced by the Gigaton Volume Detector, which will be one of the world’s largest neutrino telescopes when it is complete later this decade.
Read more: physicsworld.com

Flaring black holes may solve cosmic ray puzzle

WHERE do ultra high-energy cosmic rays come from? These charged particles zoom to Earth from outer space, but why is a mystery. Now a possible source – gamma-ray bursts, which seemed to have been ruled out – have received a new lease of life.

Gamma-ray bursts are usually created by exploding stars, which produce neutrinos. So last April, when the IceCube neutrino detector in Antarctica saw no neutrinos accompanying high-energy cosmic rays, astronomers favoured galaxies with active supermassive black holes at their cores as the source of the rays.

But a more recent study found that only one galaxy was powerful enough to have produced cosmic rays with such high energies. The rest appear to come from galaxies that seem too weak.

This posed a “perplexing problem”, says Glennys Farrar of New York University, one of the study authors. Then they found a clue: gamma-ray burst GRB110328A, which happened in March 2011. Its afterglow persisted for over a week, instead of a few hours like normal ones. The culprit was most likely a star falling into a galaxy’s central black hole. This would make a weak black hole flare up, producing a burst of gamma rays that in turn spits out cosmic rays, suggests Farrar (arxiv.org/abs/1207.3186v1).

The trouble is testing the hypothesis. Gamma rays travel at the speed of light, so would arrive millennia ahead of any cosmic rays. Farrar hopes to strengthen the idea by matching more cosmic ray emissions with weak active galaxies.

Read more: www.newscientist.com

Antiproton Radiation Belt Discovered Around Earth

Physicists have long suspected that antiprotons must become trapped in a belt around Earth. Now they’ve found it

The Earth is constantly bombarded by high energy particles called cosmic rays. These are generated by the Sun and by other sources further afield. (The source of the highest energy cosmic rays is still a mystery).

The particles are generally protons, electrons and helium nuclei and when they collide with nuclei in the Earth’s upper atmosphere they can produce showers of daughter particles. These showers can be so extensive that they can easily be observed from the ground.

Astronomers long ago realised that these collisions must produce antiprotons, just as they do in particle accelerators on Earth. But this raises an interesting question: what happens to the antiprotons after they are created?

The antiprotons lie sandwiched between the inner and outer Van Allen belts (in red) around the Earth

Clearly, many of these antiparticles must be annihilated when they meet particles of ordinary matter. But some astronomers always suspected that the remaining antiprotons must become trapped by the Earth’s magnetic field, forming an antiproton radiation belt.

Now astrophysicists say they’ve finally discovered this long-fabled belt of antiprotons.

In 2006, these guys launched a spacecraft called PAMELA into low Earth orbit, specifically to look for antiprotons in cosmic rays.

But, like most spacecraft in low Earth orbit, PAMELA must pass daily through the South Atlantic Anomaly, a region where the Van Allen Radiation Belts come closest to the Earth’s surface. It’s here that energetic particles tend to become trapped. So if any antiprotons are caught up in the mix, that’s where PAMELA ought to find them.

Now the PAMELA team has analysed the 850 days of data, looking only at the times when the spacecraft was in the South Atlantic Anomaly (about 1.7 per cent of this time).

Lo and behold, these guys found 28 antiprotons. That’s about three orders of magnitude more than you’d expect to find in the solar wind, proving that the particles really are trapped and stored in this belt.

Antiprotons "annihiliate" if they come into contact with normal protons

This constitutes “the most abundant source of antiprotons near the Earth”, say the PAMELA team.

The South Atlantic Anomaly is well known as a thorough nuisance. Because of the high energy particles here, the Hubble Space Telescope must be switched off when it passes through several times a day; and the International Space Station has extra shielding to protect astronauts from its effects.

The discovery of an additional belt of antiprotons won’t have much impact on the danger it represents–the number of antiprotons is tiny compared to the electrons and protons trapped there.

But it’s always interesting to have theoretical predictions confirmed. That’s good science at work.

Ref: arxiv.org/abs/1107.4882: The Discovery Of Geomagnetically Trapped Cosmic Ray Antiprotons

http://www.technologyreview.com/blog/arxiv/27058/
http://www.bbc.co.uk/news/science-environment-14405122

Astronomy Without A Telescope – Oh-My-God Particles

Centaurus A - one of the closest galaxies with an active galactic nucleus - although it is over 10 million light years away. If you are looking for a likely source of ultra-high-energy cosmic rays - you may not need to look further.

Cosmic rays are really sub-atomic particles, being mainly protons (hydrogen nuclei) and occasionally helium or heavier atomic nuclei and very occasionally electrons. Cosmic ray particles are very energetic as a result of them having a substantial velocity and hence a substantial momentum.

The Oh-My-God particle detected over Utah in 1991 was probably a proton traveling at 0.999 (and add another 20 x 9s after that) of the speed of light and it allegedly carried the same kinetic energy as a baseball traveling at 90 kilometers an hour.

Its kinetic energy was estimated at 3 x 1020 electron volts (eV) and it would have had the collision energy of 7.5 x 1014 eV when it hit an atmospheric particle – since it can’t give up all its kinetic energy in the collision. Fast moving debris carries some of it away and there’s some heat loss too. In any case, this is still about 50 times the collision energy we expect the Large Hadron Collider (LHC) will be able to generate at full power. So, this gives you a sound basis to scoff at doomsayers who are still convinced that the LHC will destroy the Earth.

Now, most cosmic ray particles are low energy, up to 1010 eV – and arise locally from solar flares. Another more energetic class, up to 1015 eV, are thought originate from elsewhere in the galaxy. It’s difficult to determine their exact source as the magnetic fields of the galaxy and the solar system alter their trajectories so that they end up having a uniform distribution in the sky – as though they come from everywhere.

But in reality, these galactic cosmic rays probably come from supernovae – quite possibly in a delayed release process as particles bounce back and forth in the persisting magnetic field of a supernova remnant, before being catapulted out into the wider galaxy.

And then there are extragalactic cosmic rays, which are of the Oh-My-God variety, with energy levels exceeding 1015 eV, even rarely exceeding 1020 eV – which are more formally titled ultra-high-energy cosmic rays. These particles travel very close to the speed of light and must have had a heck of kick to attain such speeds.

Left image: The energy spectrum of cosmic rays approaching Earth. Cosmic rays with low energies come in large numbers from solar flares (yellow range). Less common, but higher energy cosmic rays originating from elsewhere in the galaxy are in the blue range. The least common but most energetic extragalactic cosmic rays are in the purple range. Right image: The output of the active galactic nucleus of Centaurus A dominates the sky in radio light - this is its apparent size relative to the full Moon. It is likely that nearly all extragalactic cosmic rays that reach Earth originate from Centaurus A.

However, a perhaps over-exaggerated aura of mystery has traditionally surrounded the origin of extragalactic cosmic rays – as exemplified in the Oh-My-God title.

In reality, there are limits to just how far away an ultra-high-energy particle can originate from – since, if they don’t collide with anything else, they will eventually come up against the Greisen–Zatsepin–Kuzmin (GZK) limit. This represents the likelihood of a fast moving particle eventually colliding with a cosmic microwave background photon, losing momentum energy and velocity in the process. It works out that extragalactic cosmic rays retaining energies of over 1019 eV cannot have originated from a source further than 163 million light years from Earth – a distance known as the GZK horizon.

Recent observations by the Pierre Auger Observatory have found a strong correlation between extragalactic cosmic rays patterns and the distribution of nearby galaxies with active galactic nuclei. Biermann and Souza have now come up with an evidence-based model for the origin of galactic and extragalactic cosmic rays – which has a number of testable predictions.

They propose that extragalactic cosmic rays are spun up in supermassive black hole accretion disks, which are the basis of active galactic nuclei. Furthermore, they estimate that nearly all extragalactic cosmic rays that reach Earth come from Centaurus A. So, no huge mystery – indeed a rich area for further research. Particles from an active supermassive black hole accretion disk in another galaxy are being delivered to our doorstep.

http://www.universetoday.com/86490/astronomy-without-a-telescope-oh-my-god-particles/