Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Cosmic accelerators discovered in our galaxy by UCLA physicists, Japanese colleague

18.08.2010
Physicists from UCLA and Japan have discovered evidence of "natural nuclear accelerators" at work in our Milky Way galaxy, based on an analysis of data from the world's largest cosmic ray detector.
The research is published Aug. 20 in the journal Physical Review Letters.

Cosmic rays of the highest energies were believed by physicists to come from remote galaxies containing enormous black holes capable of consuming stars and accelerating protons at energies comparable to that of a bullet shot from a rifle. These protons — referred to individually as "cosmic rays" — travel through space and eventually enter our galaxy.

But earlier this year, physicists using the Pierre Auger Observatory in Argentina, the world's largest cosmic ray observatory, published a surprising discovery: Many of the energetic cosmic rays found in the Milky Way are not actually protons but nuclei — and the higher the energy, the greater the nuclei-to-proton ratio.

"This finding was totally unexpected because the nuclei, more fragile than protons, tend to disintegrate into protons on their long journey through space," said Alexander Kusenko, UCLA professor of physics and astronomy and co-author of the Physical Review Letters research. "Moreover, it is very unlikely that a cosmic accelerator of any kind would accelerate nuclei better than protons at these high energies."

The resolution to the paradox of the nuclei's origin comes from an analysis by Kusenko; Antoine Calvez, a UCLA graduate student of physics who is part of Kusenko's research group; and Shigehiro Nagataki, an associate professor of physics at Japan's Kyoto University. They found that stellar explosions in our own galaxy can accelerate both protons and nuclei. But while the protons promptly leave the galaxy, the heavier and less mobile nuclei become trapped in the turbulent magnetic field and linger longer.

"As a result, the local density of nuclei is increased, and they bombard Earth in greater numbers, as seen by the Pierre Auger Observatory," said Kusenko, who is also a senior scientist at the University of Tokyo's Institute for Physics and Mathematics of the Universe (IPMU).

These ultra–high-energy nuclei have been trapped in the web of galactic magnetic fields for millions of years, and their arrival directions as they enter the Earth's atmosphere have been "completely randomized by numerous twists and turns in the tangled field," he said.

"When the data came out, they were so unexpected that many people started questioning the applicability of known laws of physics at high energy," Kusenko said. "The common lore has been that all ultra–high-energy cosmic rays must come from outside the galaxy. The lack of plausible sources and the arrival-direction anisotropy (the nuclei have different physical properties when measured in different directions) have been used as arguments in favor of extragalactic sources.

"However, since the cosmic rays in question turned out to be nuclei, the galactic field can randomize their arrival directions, taking care of the anisotropy puzzle. As for the plausible sources, the enormous stellar explosions responsible for gamma ray bursts can accelerate nuclei to high energies. When we put these two together, we knew we were on the right track. Then we calculated the spectra and the asymmetries, and both agreed with the data very well."

Kusenko hopes this research will enhance the understanding of "astrophysical archeology."

"We can study the collective effects of gamma ray bursts that have taken place in the past of our own galaxy over millions of years," he said.

Stellar explosions capable of accelerating particles to ultra-high energies have been seen in other galaxies, where they produce gamma-ray bursts. The new analysis provides evidence that such powerful explosions occur in our galaxy as well, at least a few times per million years, Kusenko said.

Kusenko and his colleagues predict that the protons escaping from other galaxies should still be seen at the highest energies and should point back to their sources, providing Pierre Auger Observatory with valuable data.

The Pierre Auger Observatory records cosmic ray showers through an array of 1,600 particle detectors placed about one mile apart in a grid spread across 1,200 square miles, complemented by specially designed telescopes. The observatory is named for the French physicist Pierre Victor Auger, who in the 1920s discovered air showers.

Kusenko's research was federally funded by the U.S. Department of Energy and NASA. Nagataki's research was funded by the Japan Society for the Promotion of Science.

For more information on Kusenko's research, visit www.physics.ucla.edu/~kusenko.

UCLA is California's largest university, with an enrollment of nearly 38,000 undergraduate and graduate students. The UCLA College of Letters and Science and the university's 11 professional schools feature renowned faculty and offer more than 323 degree programs and majors. UCLA is a national and international leader in the breadth and quality of its academic, research, health care, cultural, continuing education and athletic programs. Five alumni and five faculty have been awarded the Nobel Prize.

Stuart Wolpert | EurekAlert!
Further information:
http://www.physics.ucla.edu/~kusenko
http://www.ucla.edu

More articles from Physics and Astronomy:

nachricht Space radiation won't stop NASA's human exploration
18.10.2017 | NASA/Johnson Space Center

nachricht Study shows how water could have flowed on 'cold and icy' ancient Mars
18.10.2017 | Brown University

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: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Osaka university researchers make the slipperiest surfaces adhesive

18.10.2017 | Materials Sciences

Space radiation won't stop NASA's human exploration

18.10.2017 | Physics and Astronomy

Los Alamos researchers and supercomputers help interpret the latest LIGO findings

18.10.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>