The Oh My God Particle! Where did it come from?
Welcome to the second article of the series where we explore the unknown in the realms of science and technology. Check out the first article, “The Existence of One Way Functions? Here is a Million Dollar Math Problem!” if you haven’t before!
With that being said, let us make you go ‘Oh my god!’ with this piece today!
Introduction
What is the true nature of this universe? To answer this question humans have come up with myriad stories trying to describe our spectacular existence. We test our stories and learn what to keep and what to throw away. But the more we have learnt, the more complicated and weird our stories have become, some of them so much that it is really hard to know what they’re actually about! One such particle that questions the nature of everything we know is the mysterious Oh My God Particle. It has such a weird and godly nature that scientists couldn’t resist naming it ‘Oh My God’!
What is the nature of this particle? How did we detect them? What were the observations associated with it? We will explore it further here but before that, let’s have a brief overview of what cosmic rays are.
Cosmic Rays
Cosmic rays are nothing but atomic fragments that come down to Earth from far away places in the universe, but where exactly? we don’t know that yet but scientists have speculated that the origin of these particles is related to supernovae or star explosions. Discovered in 1912, they are found to travel very close to the speed of light.
The Oh My God Particle is a type of cosmic ray that has been baffling scientists since it’s discovery.
How was this particle discovered?
It was October 15, 1991. Little did we know that humanity was going to be visited by one of the most baffling entity from outer space yet. A single atomic nucleus traveling at 99.999,999,999,999,999,999,9951% of the speed of light crashed through Earth’s atmosphere and streaked across the Utah sky. The nucleus quickly disintegrated into a shower of subatomic particles and lights. This light was seen by the Fly’s Eye Observatory, a collection of over sized tin cans that were an early experiment by the University of Utah to spot high energy cosmic rays in the universe.
Scientists analyzing Fly’s Eye’s data calculated that the cosmic ray responsible for this particular flash must’ve had a kinetic energy of 300 exa-electron. That’s 48 joules, an amount of energy we associate with macroscopic, not subatomic objects. That single atomic nucleus carried as much kinetic energy as a good sized stone thrown at your head at 50 miles an hour! The particle was dubbed the Oh-My-God particle. Nothing like it had ever been seen before. In fact, cosmic rays of such energy were supposed to be impossible!
Nature of the Oh-My-God Particle
Let’s break down this discovery and try to find the true nature of the particle and to answer the question as to what makes this particle so godly. Most cosmic ray particles are single protons, the nuclei of hydrogen atoms and a fair number of helium nuclei. But about 1% of cosmic rays are heavier nuclei, as heavy as iron.
Gamma rays and even anti-matter particles come in at all energies, from a sickly billion electron volts at the low end to crazy 1020 electron volts or higher, like the Oh-My-God particle. The higher the energy, the rarer they are. At the lowest energies, the cosmos flings one particle every second per square meter of the Earth’s surface. At energies up near that of the OMG particle, they are incredibly rare. Only a handful have been spotted since the first, giving a rare estimate of 1 per square kilometer every couple of centuries.
How can we detect them? Where do they come from?
So where do these things come from? To accelerate a particle to the energies of cosmic rays, you need a particle accelerator. We have built artificial ones on Earth using giant rings and powerful magnetic fields. It turns out that the universe is full of natural particle accelerators. It is believed that most low energy cosmic ray particles come from supernova explosions within our galaxy. When a star explodes, the expanding shock wave carries a strong magnetic field. It can trap particles and accelerate them until they’re energetic enough to escape the shock. The higher the energy of the cosmic ray, though, the more likely it is to have originated from outside our galaxy. The exact sources of these extra-galactic cosmic rays are more mysterious.
They may come from magnetic acceleration in Quasars, or perhaps they’re blasted out in gamma-ray bursts. The Oh-My-God particle shouldn’t exist at all in the first place because the universe is basically opaque to particles with such high energies. Empty space isn’t really empty, it’s full of low-energy microwave photons left over from the heat glow of the very earliest of times. This is the cosmic microwave background radiation.
Cosmic rays with energies over 5×10^19 eV, that is about 8 joules, can’t travel far before smacking into these photons and giving up some of their energy. This is the called the Greisen-Zatsenpin-Kuzmin or GZK limit.
It was thought that no cosmic ray could ever exceed it, but guess what? the OMG particle was a whopping six times more energetic! Only a very small number of these extreme energy cosmic rays have been seen since the OMG particle.
What makes it more perplexing is the fact that they must have come from a nearby source, close enough to our galaxy to not be wiped out by the cosmic microwave background radiation. We are talking close by on cosmic scales, so within 1 to 200 million light years.
But at that distance, sources like quasars and gamma-ray bursts should be very obvious. Yet they seem to come from nowhere in particular. We do see more than the average number coming from the direction of the Ursa Major cluster, but there’s no obvious source there. It’s still a mystery exactly what produces these extreme cosmic rays and how close to the Earth these sources are. Part of the challenge in understanding cosmic rays is that our atmosphere and magnetic field shield the surface of the Earth so well. But we should count that as a blessing.
In the past, astronauts traveling outside Earth’s magnetosphere have indeed reported mysterious flashes of light, which may be due to Cherenkov radiation from cosmic rays passing through their eye’s vitreous humor, or from the particles hitting their optic nerves. Even ISS astronauts are subjected to a significant radiation risk. Along with solar outbursts, cosmic rays are one of the most serious obstacles to manned interplanetary travel.
What Exactly is Cherenkov Radiation?
It is known that no particle or object can exceed the speed of light, which is said to be the maximum possible speed limit of this universe. However, there is a small catch here. We are referring to the speed of light in vacuum.
Light travels at different speeds in different media. For example, light travels only at about 3/4th it’s speed in water. That brings us to the next argument, can a particle exceed the speed of light in a different medium where light travels much slower relatively? Of course it can! and when that happens with a charged particle like that of an electron or a proton, you get what is called the Cherenkov Radiation. This is analogous to sonic boom in case of sound.
Future Work
As we figure out the origins of these particles, cosmic ray astronomy is becoming an increasingly powerful tool for investigating our amazing universe. But even now, these particles are extremely useful. The highest energy cosmic rays, like the Oh-My-God particle, generate collisions far more energetic than our largest particle accelerator, the Large Hadron Collider. Studying cosmic rays may crack open the mysteries of both the largest and the smallest scales of space-time.
(This article was co-authored by Zeeshan Mushtaq and Aditya Vivek Thota of The Research Nest)
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References
- ChoJul, A., GamilloAug, E., ServickAug, K., CohenAug, J., Davis, V., Gamillo, E., . . . E&E News. (2017, December 10). Physicists spot the potential source of ‘Oh-My-God’ particles. Retrieved July 20, 2018, from http://www.sciencemag.org/news/2014/07/physicists-spot-potential-source-oh-my-god-particles
- Wolchover, B., & Quanta Magazine. (n.d.). Ultrahigh-Energy Cosmic Rays Traced to Hotspot. Retrieved July 20, 2018, from https://www.quantamagazine.org/ultrahigh-energy-cosmic-rays-traced-to-hotspot-20150514
- (n.d.). Retrieved July 27, 2018, from http://www.cosmic-ray.org/reading/flyseye.html#SEC10
- Oh-My-God particle. (2018, July 13). Retrieved August 27, 2018, from https://en.wikipedia.org/wiki/Oh-My-God_particle
