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Ultra-High Energy Cosmic Rays Come From Outside The Milky Way

Travelling with a speed of lights, cosmic rays are atomic nuclei. Scientist says that high energy cosmic rays coming from outer space are hitting the earth.

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Cosmic rays
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New York, September 24, 2017: Researchers have found that some ultra-high energy cosmic rays that occasionally hit Earth come from a distant source outside the Milky Way.

Cosmic rays are atomic nuclei that travel through space at speeds close to that of light. Low-energy cosmic rays come from the Sun or from our own galaxy, but the origin of the highest-energy particles has been the subject of debate ever since they were first discovered fifty years ago.

Do they come from our Galaxy or from distant extragalactic objects?

The study published in the journal Science demonstrated that those cosmic rays with energies a million times greater than that of the protons accelerated in the Large Hadron Collider – the world’s largest and most powerful particle accelerator – come from much further away than from our own galaxy.

They were detected from 2004 to 2016 at the largest cosmic ray observatory ever built, the Pierre Auger Observatory in Argentina.

“We are now considerably closer to solving the mystery of where and how these extraordinary particles are created — a question of great interest to astrophysicists,” said Karl-Heinz Kampert from University of Wuppertal in Germany.

“Our observation provides compelling evidence that the sites of acceleration are outside the Milky Way,” Kampert who is spokesperson for the Auger Collaboration, which involves more than 400 scientists from 18 countries, said.

Cosmic rays are the nuclei of elements from hydrogen to iron. The highest-energy cosmic rays, those of interest in this study, only strike about once per square kilometre per year — equivalent to hitting the area of a soccer field about once per century.

Such rare particles are detectable because they create showers of secondary particles — including electrons, photons and muons – as they interact with the nuclei in the atmosphere.

These cosmic ray showers spread out, sweeping through the atmosphere at the speed of light in a disc-like structure, like a dinner plate but several kilometres in diameter.

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At the Auger Observatory, the shower particles are detected through the light they produce in several of 1,600 detectors, spread over 3,000 square kilometres of western Argentina and each containing 12 tons of water.

Tracking these arrivals tells scientists the direction from which the cosmic rays came.

After racking up detections of more than 30,000 cosmic particles, the scientists found one section of the sky was producing significantly more than its share.

The probability of this happening by a random fluctuation is extremely small, the scientists said — a chance of about two in ten million.

“This result unequivocally establishes that ultra-high energy cosmic rays are not just random wanderers of our nearby universe,” Paolo Privitera of University of Chicago who heads the US groups participating in the project, said. (IANS)

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Superstar Eta Carinae’s Cosmic Rays May Reach Earth: Study

Astronomers know that cosmic rays with energies greater than one billion electron volts (eV) come to us from beyond our solar system.

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Superstar Eta Carinae's Cosmic Rays May Reach Earth: Study
Superstar Eta Carinae's Cosmic Rays May Reach Earth: Study. Pixabay

Eta Carinae, the most luminous and massive stellar system within 10,000 light years, is accelerating particles to speeds comparable to that of light — some of which may reach Earth as cosmic rays, suggests a new study.

“We know the blast waves of exploded stars can accelerate cosmic ray particles to speeds comparable to that of light, an incredible energy boost,” said the lead author of the study Kenji Hamaguchi, an astrophysicist at NASA’s Goddard Space Flight Centre in Greenbelt, Maryland.

“Similar processes must occur in other extreme environments. Our analysis indicates Eta Carinae is one of them,” Hamaguchi said.

Astronomers know that cosmic rays with energies greater than one billion electron volts (eV) come to us from beyond our solar system.

But because these particles — electrons, protons and atomic nuclei — all carry an electrical charge, they veer off course whenever they encounter magnetic fields. This scrambles their paths and masks their origins.

For this study, published in the journal Nature Astronomy, the researchers used data from NASA’s NuSTAR space telescope.

Launched in 2012, NuSTAR can focus X-rays of much greater energy than any previous telescope.

Using both newly taken and archival data, the team examined NuSTAR observations acquired between March 2014 and June 2016, along with lower-energy X-ray observations from the European Space Agency’s XMM-Newton satellite over the same period.

“We’ve known for some time that the region around Eta Carinae is the source of energetic emission in high-energy X-rays and gamma rays,” said Fiona Harrison, the principal investigator of NuSTAR.

Carina Nebula
Carina Nebula. Pixabay

“But until NuSTAR was able to pinpoint the radiation, show it comes from the binary and study its properties in detail, the origin was mysterious,” said Harrison, who also serves as a professor of astronomy at California Institute of Technology (Caltech) in Pasadena.

Eta Carinae, located about 7,500 light-years away in the southern constellation of Carina, is famous for a 19th century outburst that briefly made it the second-brightest star in the sky.

This event also ejected a massive hourglass-shaped nebula, but the cause of the eruption remains poorly understood.

The system contains a pair of massive stars whose eccentric orbits bring them unusually close every 5.5 years.

Also read: Brain Damage Caused by Cosmic Rays Can be Prevented With this Drug

The stars contain 90 and 30 times the mass of our Sun and pass 225 million km apart at their closest approach — about the average distance separating Mars and the Sun. (IANS)