Leonard Kelley holds a bachelor's in physics with a minor in mathematics. He loves the academic world and strives to constantly explore it.
Punch the wall.
Yeah, I started this article with that recommendation. Go ahead (gingerly, of course)! When your fist hits the surface, it stops unless you have enough force to penetrate it. Now imagine you punching the wall, and your fist goes right through it without breaking the surface. Weird, right? Well, it would be even weirder if you fired a bullet into a stone wall and it too went through it without actually piercing the surface. Surely this all sounds like science fiction, but tiny nearly massless particles called neutrino’s do just that with everyday matter. In fact, if you had a light-year of solid lead (a very dense or particle-heavy material), a neutrino could go through it unscathed, not touching a single particle. So, if they are so hard to interact with, how can we do any science with them? How do we even know they exist?
First, it is important to establish that neutrinos are easier to detect than it would seem. In fact, neutrinos are one of the most common particles in existence, only outnumbered by photons. Over a million pass through the nail of your pinky every second! Because of their high volume, all it takes is the right set-up, and you can start collecting data. But what can they teach us?
One rig, the IceCube Observatory, located near the South Pole, is going to try to help scientists such as Francis Halzen uncover what causes high-energy neutrinos. It uses over 5000 light sensors several kilometers below the surface to (hopefully) record high energy neutrinos colliding with normal matter, which would then emit light. Such a reading was spotted in 2012 when Bert (@1.07 PeV or 1012electron volts) and Ernie (@1.24PeV) were found when they generated 100,000 photons. Most of the other, normal energy neutrinos range ones come from cosmic rays hitting the atmosphere or from the sun’s fusion process. Because those are the only known local sources of neutrinos, anything that is above the energy output of that range of neutrinos may not be a neutrino from around here, such as Bert and Ernie (Matson, Halzen 60-1). Yeah, it could be from some unknown source in the sky. But don’t count on it being a by-product of a Klingon’s cloaking device.
In all likelihood, it would be from what is creating cosmic rays, which are difficult to trace back to their source because they interact with magnetic fields. This causes their paths to be altered beyond hopes of restoring their original flight path. But neutrinos, no matter what of the three types you look at, are not affected by such fields and thus if you can record the entry vector one makes in the detector all you have to do is follow that line back, and it should reveal what created it. Yet when this was done, no smoking gun was found (Matson).
As time went on, more and more of these high energy neutrinos were detected with many in the 30-1,141 TeV range. A bigger data set means more conclusions can be reached, and after over 30 such neutrino detections (all originating from the southern hemisphere's sky) scientists were able to determine that at minimum 17 did not come from our galactic plane. Thus, they were created in some far-off location outside the galaxy. Some possible candidates for what is then creating them include quasars, colliding galaxies, supernovas, and neutron star collisions (Moskowitz “IceCube,” Kruesi "Scientists").
Some evidence in favor of this was found on December 4, 2012, when Big Bird, a neutrino that was over two quadrillion eV. Using the Fermi Telescope and the IceCube, scientists were able to find that blazar PKS B1424-418 was the source of it and UHECRs, based on a 95% confidence study (NASA).
Further evidence for black hole involvement came from Chandra, Swift, and NuSTAR when they correlated with IceCube on a high energy neutrino. They backtracked the path and saw an outburst from A*, the supermassive black hole residing in our galaxy. Days later, some more neutrino detections were made after more activity from A*. However, the angular range was too large to definitely say it was our black hole (Chandra "X-ray").
That all changed when 170922A was found by IceCube on September 22, 2017. At 24 TeV, it was a big event (over 300 millions times that of its solar counterparts) and after backtracking the path found that blazar TXS 0506+056, located 3.8 billion light-years away, was the source for the neutrino. On top of that the blazar had recent activity that would correlate to a neutrino and after reexamining data scientists found 13 prior neutrinos had come from that direction from 2014 to 2015 (with the result found to be within 3 standard deviations). And this blazar is a bright object (in the top 50 known) showing that its active and likely to be producing much more than we see. Radio waves as well as gamma rays also showed high activity for the blazar, now the first known extragalactic source for neutrinos. It is theorized that newer jet material leaving the blazar collided with older material, generating neutrinos in the high-energy collision resulting from this (Timmer "Supermassive," Hampson, Klesman, Junkes).
And as a brief sidebar, IceCube is looking for Greisen-Zatsepin-Kuznin (GZK) neutrinos. These special particles arise from cosmic rays that interact with photons from the cosmic microwave background. They are very special because they are at the EeV (or 1018 electron volt) range, way higher than the PeV neutrinos seen. But so far, none have been found, but neutrinos from the Big Bang have been recorded by the Planck spacecraft. They were found after scientists from the University of California observed minute temperature changes in the cosmic microwave background that could have only come from neutrino interactions. And the real kicker is that it proves how neutrinos cannot interact with each other, for the Big Bang theory accurately predicted the deviation scientists saw with the neutrinos (Halzan 63, Hal).
Chandra. "X-ray telescopes find black hole may be a neutrino factory." astronomy.com. Kalmbach Publishing Co., 14 Nov. 2014. Web. 15 Aug. 2018.
Hal, Shannon. "The Big Bang's Particle Glow." Scientific American Dec. 2015: 25. Print.
Halzen, Francis. "Neutrinos at the Ends of the Earth." Scientific American Oct. 2015: 60-1, 63. Print.
Hampson, Michelle. "A cosmic particle spewed from a distant galaxy strikes Earth." astronomy.com. Kalmbach Publishing Co., 12 Jul. 2018. Web. 22 Aug. 2018.
Junkes, Norbert. "Neutrino produced in a cosmic collider far away." innovations-report.com. innovations report, 02 Oct. 2019. Web. 28 Feb. 2020.
Klesman, Allison. "Astronomers catch ghost particle from distance galaxy." Astronomy. Nov. 2018. Print. 14.
Kruesi, Liz. "Scientists Detect Extraterrestrial Neutrinos." Astronomy Mar. 2014: 11. Print.
Matson, John. “Ice-Cube Neutrino Observatory Detects Mysterious High-Energy Particles.” HuffingtonPost. Huffington Post, 19 May 2013. Web. 07 Dec. 2014.
Moskowitz, Clara. “IceCube Neutrino Observatory Takes a Hit From Exotic Space Particles.” HuffingtonPost. Huffington Post, 10 Apr. 2014. Web. 07 Dec. 2014.
NASA. "Fermi Helps Link Cosmic Neutrino to Blazar Blast." Astronomy.com. Kalmbach Publishing Co., 28 Apr. 2016. Web. 26 Oct. 2017.
Timmer, John. "Supermassive black hole shot a neutrino straight at Earth." arstechnica.com. Conte Nast., 12 Jul. 2018. Web. 15 Aug. 2018.
- How Can We Test for String Theory?
While it may ultimately prove to be wrong, scientists know of several ways to test for string theory using many conventions of physics.
© 2014 Leonard Kelley
Leonard Kelley (author) on August 30, 2019:
Thank you! I shall endeavor to!
Halemane Muralikrishna from South India on August 29, 2019:
Very nice article, even a biologist like me can understand. Keep enlightening us with more
Leonard Kelley (author) on December 20, 2014:
Neutrinos can be slowed by matter but it has to be VERY dense and even then there are no guarantees. And yes they do have a small amount of mass that contributes to their flavor changes.
Blackspaniel1 on December 20, 2014:
Nice hub. If I recall, neutrinos slow by friction with matter, which set the basis for the time dilation experiment. And they are not completely without mass, just a small mass each, and that would depend on the velocity if it is relativistic.
Leonard Kelley (author) on December 11, 2014:
Thanks, appreciate the response!
Sara Johnson from United States on December 10, 2014:
Wow - this is very good and comprehensive. Excellent intro to particle physics!