Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

NYU physicist isolates first source

13.01.2005


Professor Glennys R. Farrar, a physicist at New York University, today announced that, for the first time, a source of ultra-high energy cosmic rays has been isolated and studied, a major breakthrough in the field. Ultra-high energy cosmic rays--which rarely hit the earth--are believed to be the result of extremely powerful cosmic phenomena, such as the creation or accretion of massive black holes. In addition to elucidating the origin of these remarkable particles and the systems that create them, the findings also shed light on the nature of very large scale magnetic fields, which are suspected to permeate space between galaxies. The announcement was made in a report to the American Astronomical Society meeting in San Diego, California.



The result was made possible by applying a new analysis technique to data from two different observational teams using distinct approaches to finding and measuring powerful cosmic rays. The analysis will enable physicists to explore in a sustained and focused fashion how such energetic particles are produced.

The data upon which this work is based were obtained by the Akeno Giant Air Shower Array (AGASA) experimental collaboration in Japan and the National Science Foundation’s High Resolution Fly’s Eye Air Fluorescence Detector (HiRes) collaboration in Utah. The hints of possible clusters of cosmic ray occurrences detected by AGASA and HiRes individually were each too weak to be statistically convincing, and previous analysis methods were unsuitable for studying the combined dataset. In a paper in press (Astrophysical Journal), Farrar and the HiRes collaboration used the "method of maximum likelihood" to analyze the combined AGASA and HiRes datasets, revealing a tightly clustered group of four ultra-high energy events from one segment of the sky. The probability that such a well-correlated cluster of particles arises simply by coincidence is calculated to be a less than one in a hundred. Nevertheless, the authors caution that such coincidences do happen and note that a posteriori probability estimates are hazardous, so stress that more data are needed before firm conclusions can be drawn.


Farrar reported today on two follow-up studies. In one project, Farrar, Andreas Berlind, and David Hogg of NYU studied the environment of the source and the intervening region using data from the Sloan Digital Sky Survey• and information from NASA’s Extragalactic Database. This work clarifies how the observed bundle of particles could have come so far through space without being jostled apart, and it identifies potential sources of the cosmic rays.

In the other project, Farrar extended the Maximum Likelihood analysis to infer the properties of the magnetic fields in space between the source and Earth. This enabled lower energy data to be included in the analysis, uncovering yet another event likely to come from the same source. The group of five events already teaches us a lot about what and where the source may be, according to Farrar.

Until now, the only way astrophysicists could examine the cosmos has been to study light (electromagnetic energy) emitted and absorbed by stars, gas, and dust in a variety of wavelengths from low energy radio waves to optical photons and high energy X-ray and gamma rays. The bundle of ultra-high energy cosmic particles announced today, assuming it is not a statistical fluke, is therefore a breakthrough for cosmic ray astronomy. This is the first time material particles from the distant universe have been identified which have propagated together from their origin in some cataclysmic event without straying apart and losing the memory of their source. Exploring them in greater detail and with more data will give a unique perspective on extreme events such as the creation of black holes.

Cosmic rays of ordinary or high energy are common and well-understood. However the nature and source of the highest energy cosmic rays--with energies above a few times 1019 electron Volts (few tens of Ecta-eV)--has been a mystery. The highest energy particles are extremely rare--just one hits the Earth per square kilometer per century--and only about 100 have ever been observed. Some have almost a trillion times more energy as ever achieved in the highest-energy man-made accelerators, or an energy equivalent to concentrating the kinetic energy of a bowling ball, with thousands of trillions of protons and neutrons into a single proton.

The very existence of such particles presents a quandary to physicists. Few if any astrophysical systems are capable of accelerating particles to such energies. The most likely candidates would be gamma ray bursts or active galactic nuclei also known as blazers and quasars. However, according to the laws of special relativity, the ultrahigh energy cosmic rays (UHECRs) produced by such phenomena should lose energy when they collide with the omnipresent cosmic microwave background radiation left over from the Big Bang.

Therefore, unless the standard laws of physics are violated at these otherwise inaccessible energies, the highest energy UHECRs we see must have originated within about 50-100 million light years of Earth. Yet no plausible source had been identified so nearby in the direction of the highest energy UHECRs previously observed. This leads some theorists to propose that the UHECRs are not produced by astrophysical accelerators, but are the by-products of the decay of invisible but super-heavy relics of the Big Bang waiting to be discovered in the extended halo of the Milky Way, or by some other exotic process. The new discovery should help clarify just what is the source of these ultra-high energy particles.

"Nature has been very, very kind in presenting us with this opportunity to unravel one of the real mysteries of physics," said Farrar. "If, as widely supposed, tumultuous magnetic fields fill most of the cosmos, then charged particles such as these ought to be deflected when traveling to Earth and would not point back to their sources. The discovery of this bundle of cosmic rays seems to tell us that there is at least one direction in which the fields are sufficiently weak that the particles are not dispersed – just as one can sometimes see a patch of blue sky through a break in the clouds."

"By incredible luck, the source of this handful of ultra-high energy particles is in just the right direction to be seen clearly," she said. "Thanks to this, we will be able to simultaneously study the nature of the magnetic fields between galaxies and the nature of the source. The experimental teams and the pioneers before them deserve tremendous praise for developing the techniques needed to do this science."

The High Resolution Fly’s Eye is the only UHECR observatory presently in operation in the northern hemisphere. The Pierre Auger Observatory in Argentina--an international collaboration of several hundred physicists supported in part by the National Science Foundation--is just coming online. It has 10 times greater sensitivity than previous experiments and will report its first results next summer. Given its location in the southern hemisphere, the Auger Observatory cannot see the new source reported here (which is in the vicinity of the Big Dipper), but it will view the center of the Milky Way Galaxy and several nearby superclusters of galaxies. Astrophysicists are waiting eagerly to know whether other identifiable bundles of UHECRs will be seen in those regions.

An intriguing note is that the energy distribution of particles arriving at Earth during a few-year period is completely different if UHECRs are created in a "burst"--as in the collapse of a massive star to a black hole--than if they are accelerated more slowly in a continuous process such as when matter accretes onto a pre-existing supermassive black hole. Farrar points out that when her analysis technique is applied to the lower energy AGASA data that have not yet been released, no new events would be expected for a burst, such as a gamma ray burst, while a number of new events should be discovered if the source is continuous such as an AGN. Interestingly, the information so far is consistent with either a GRB or AGN as possible source.

While the cluster of events studied in this work are not yet statistically compelling, they auger well for the future of cosmic ray astrophysics. Ten times more data, which would become available if the northern hemisphere extension of the Pierre Auger Observatory were constructed, would allow unambiguous confirmation or rejection of the hypothesis these events are from a single source, and would allow detailed study of the nature of the source and the magnetic fields along the particles’ trajectory to Earth.

James Devitt | EurekAlert!
Further information:
http://www.nyu.edu

More articles from Physics and Astronomy:

nachricht NASA's Fermi catches gamma-ray flashes from tropical storms
25.04.2017 | NASA/Goddard Space Flight Center

nachricht DGIST develops 20 times faster biosensor
24.04.2017 | DGIST (Daegu Gyeongbuk Institute of Science and Technology)

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Making lightweight construction suitable for series production

More and more automobile companies are focusing on body parts made of carbon fiber reinforced plastics (CFRP). However, manufacturing and repair costs must be further reduced in order to make CFRP more economical in use. Together with the Volkswagen AG and five other partners in the project HolQueSt 3D, the Laser Zentrum Hannover e.V. (LZH) has developed laser processes for the automatic trimming, drilling and repair of three-dimensional components.

Automated manufacturing processes are the basis for ultimately establishing the series production of CFRP components. In the project HolQueSt 3D, the LZH has...

Im Focus: Wonder material? Novel nanotube structure strengthens thin films for flexible electronics

Reflecting the structure of composites found in nature and the ancient world, researchers at the University of Illinois at Urbana-Champaign have synthesized thin carbon nanotube (CNT) textiles that exhibit both high electrical conductivity and a level of toughness that is about fifty times higher than copper films, currently used in electronics.

"The structural robustness of thin metal films has significant importance for the reliable operation of smart skin and flexible electronics including...

Im Focus: Deep inside Galaxy M87

The nearby, giant radio galaxy M87 hosts a supermassive black hole (BH) and is well-known for its bright jet dominating the spectrum over ten orders of magnitude in frequency. Due to its proximity, jet prominence, and the large black hole mass, M87 is the best laboratory for investigating the formation, acceleration, and collimation of relativistic jets. A research team led by Silke Britzen from the Max Planck Institute for Radio Astronomy in Bonn, Germany, has found strong indication for turbulent processes connecting the accretion disk and the jet of that galaxy providing insights into the longstanding problem of the origin of astrophysical jets.

Supermassive black holes form some of the most enigmatic phenomena in astrophysics. Their enormous energy output is supposed to be generated by the...

Im Focus: A Quantum Low Pass for Photons

Physicists in Garching observe novel quantum effect that limits the number of emitted photons.

The probability to find a certain number of photons inside a laser pulse usually corresponds to a classical distribution of independent events, the so-called...

Im Focus: Microprocessors based on a layer of just three atoms

Microprocessors based on atomically thin materials hold the promise of the evolution of traditional processors as well as new applications in the field of flexible electronics. Now, a TU Wien research team led by Thomas Müller has made a breakthrough in this field as part of an ongoing research project.

Two-dimensional materials, or 2D materials for short, are extremely versatile, although – or often more precisely because – they are made up of just one or a...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Expert meeting “Health Business Connect” will connect international medical technology companies

20.04.2017 | Event News

Wenn der Computer das Gehirn austrickst

18.04.2017 | Event News

7th International Conference on Crystalline Silicon Photovoltaics in Freiburg on April 3-5, 2017

03.04.2017 | Event News

 
Latest News

NASA's Fermi catches gamma-ray flashes from tropical storms

25.04.2017 | Physics and Astronomy

Researchers invent process to make sustainable rubber, plastics

25.04.2017 | Materials Sciences

Transfecting cells gently – the LZH presents a GNOME prototype at the Labvolution 2017

25.04.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>