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PAMELA measurements published in Science Express 

There is a hidden accelerator in the universe


04.03.2011 -

The PAMELA experiment - an international scientific enterprise coordinated by the National Institute for Nuclear Physics (INFN - Istituto Nazionale di Fisica Nucleare) - has discovered that the protons and helium nuclei in cosmic rays in the Galaxy are not accelerated to high energies in the same way (in the range of hundreds of GeV). This could mean that there are various types of cosmic particle accelerators that act with different mechanisms. In fact, until now, it was believed that this "job" was carried out by the highly turbulent remains of large, exploded stars (supernovae), in exactly the same way for all charged particles. Now, however, the observations made by PAMELA show that protons and helium may be accelerated by different sources.

 

The study that explains this phenomenon will be published online tomorrow in Science Express, an online magazine providing electronic publication of selected papers from the American magazine Science, in advance of full print.

 

The data was collected by PAMELA between 2006 and 2008 and relates to the flow of protons and helium nuclei; in other words almost all the cosmic radiation that we intercept. It has been discovered that the spectrum of the protons and that of the helium nuclei have different paths. This difference could therefore be proof that something is causing them to accelerate in different ways.

 

One theory could be the existence of an unknown acceleration mechanism that acts differently for the various particle species. A more traditional explanation suggests that galactic cosmic rays are accelerated both by novae, enormous nuclear explosions caused by hydrogen accumulation on the surface of a white dwarf, and by a different kind of supernova. Protons are supposedly accelerated by the explosion of smaller supernovae, where the stellar atmosphere is mainly rich in protons, and the helium nuclei in larger stars, where the stellar atmosphere is richer in helium. These different conditions could produce the diverse effects on their energy flows, as observed by PAMELA.

 

"These results," states Piergiorgio Picozza, Principal Investigator for PAMELA, "seriously call into question the paradigm that holds that cosmic rays are accelerated solely by the shock wave from supernova remains, then propagated throughout the Galaxy. They require more complex acceleration processes that will soon be the subject of an in-depth theoretical study. This is an important advance in our understanding of cosmic ray acceleration mechanisms in our Galaxy, one that complements the recent AGILE and FERMI experiments."  

 

PAMELA is an experiment on a Russian satellite that orbits at a height of between 350 and 610 km and is the result of a collaboration between the National Institute for Nuclear Physics, the Russian Space Agency and Russian research institutes, with the participation of the Italian Space Agency (ASI - Agenzia Spaziale Italiana) and contributions from German and Swedish space agencies and universities.

 

PAMELA (Payload for Antimatter Matter Exploration and Light nuclei Astrophysics) is an experiment resulting from a collaboration between the National Institute for Nuclear Physics (INFN - Istituto Nazionale di Fisica Nucleare), the Russian Space Agency and Russian research institutes, with the participation of the Italian Space Agency and contributions from German and Swedish space agencies and universities. The satellite equipment PAMELA was launched in orbit from the Baikonur cosmodrome (Kazakhstan) on 15th June 2006 and since then has been collecting data aboard the Russian satellite Resurs-DK1, that orbits the Earth at a height of between 350 and 610 km.

 

The contribution of the Trieste division of INFN in AREA Science Park

The primary purpose of the PAMELA experiment is to study the different components that make up primary cosmic radiation, with a precision and a range in terms of energy intervals never before achieved. To achieve these objectives, PAMELA uses various advanced, high performance particle detectors, capable of identifying the different particles in cosmic rays by the simultaneous measurement of their charge, their velocity and their energy.

One of the main components of PAMELA has been entirely designed and developed by researchers in INFN's Trieste Division. This is the electromagnetic calorimeter, a sophisticated detector capable of measuring the energy of the particles passing across it and identifying, with extreme precision, the various types, separating protons and nuclei from electrons and positrons. The Trieste Division also coordinates all the data analysis work from the experiment.

 

 

 

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