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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.

ALSO READ: NASA’s Asteroid-chasing Spacecraft Osiris-Rex Swinging by Earth on Way to Space Rock

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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Milky Way’s neighbouring galaxy is of same size, not bigger

With Andromeda no longer considered the Milky Way's big brother

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UFO religion as a concept is now becoming a part of popular understanding.
Countless galaxies exist in the universe, each hiding secrets that humankind is yet to unearth. Pixabay
  • Astronomers discover that the other galaxy nearest to us is the same size as ours
  • The name of the other galaxy is Andromeda
  • It is heavier than sun but the same size as Milky Way

In what could put a galactic arms race to rest, astronomers have discovered that our nearest big neighbour, the Andromeda galaxy, is roughly the same size as the Milky Way.

It had been thought that Andromeda was two to three times the size of the Milky Way, and that our own galaxy would ultimately be engulfed by our bigger neighbour.

Galaxy nearest to Milky Way is not larger than it. VOA
Galaxy nearest to Milky Way is not larger than it. VOA

But the new study, published in the journal Monthly Notices of the Royal Astronomical Society, evens the score between the two galaxies.

It found the weight of the Andromeda is 800 billion times heavier than the Sun, on par with the Milky Way.

The research suggests scientists previously overestimated the amount of dark matter in the Andromeda galaxy.

Also Read: Planets Beyond Milky Way Galaxy Discovered For First Time

“We had thought there was one biggest galaxy and our own Milky Way was slightly smaller but that scenario has now completely changed,” said Prajwal Kafle from the University of Western Australia.

“By examining the orbits of high speed stars, we discovered that this galaxy has far less dark matter than previously thought, and only a third of that uncovered in previous observations,” he said.

Andromeda  is heavier than sun. VOA
Andromeda is heavier than sun. VOA

The study used a new technique to measure the speed required to escape a galaxy.

“When a rocket is launched into space, it is thrown out with a speed of 11 km per second to overcome the Earth’s gravitational pull,” he said.

“Our home galaxy, the Milky Way, is over a trillion times heavier than our tiny planet Earth so to escape its gravitational pull we have to launch with a speed of 550km/s,” Kafle said.

Andromeda is same size as the Milky way galaxy. Wikimedia Commons
Andromeda is same size as the Milky way galaxy. Wikimedia Commons

“We used this technique to tie down the mass of Andromeda,” he added.

The Milky Way and Andromeda are two giant spiral galaxies in our local Universe, and light takes a cosmologically tiny two million years to get between them.

With Andromeda no longer considered the Milky Way’s big brother, new simulations are needed to find out what will happen when the two galaxies eventually collide, suggests the study.