cosmos – ThursdayAgain

For the first time the hard-to-detect particles at the bottom of the physics food-chain, neutrinos, have been explicitly seen to actively change flavor. Results presented yesterday by the Tokai to Kamioka (T2K) experiment provide the missing details of how our universe works down in the basement of the cosmos.

Neutrinos are ghost-like, difficult to see, particles that have some strange & unexplained abilities. They come in three classes, known as flavors: electron (νe), muon (νμ) & tau (ντ) neutrinos. The earliest neutrino experiments used naturally occurring sources of the particles, such as the Sun (electron neutrinos) & cosmic rays (muon neutrinos), to understand more about how they interacted with the universe they seem to underpin. Unfortunately the particles seemed to be unaware of the theories they were supposed to prove as far fewer neutrinos were seen than were predicted; neutrinos out in the wild seemed to be disappearing between being created & subsequently detected in the various experiments that looked for them. After almost 30 years of experimentation all was “finally resolved” (& if you believe that you probably also believe that the Wizard lives at the end of the yellow brick road). It was proven that naturally occurring neutrinos were not disappearing, but instead were changing into other types of neutrino which could not be seen, due to “having too low an energy level.”

Generators have now been developed to investigate this bizarre characteristic now known as oscillation. The generators create beams of muon-type neutrinos (because physicists copied cosmic ray particle showers). Experimenters saw the muon-type neutrinos disappearing as expected, because of the disappearance they were assumed to be changing into tau-type neutrinos, which did not have enough energy to produce a tau particle & so be witnessed directly.

For the first time, in Japan, neutrinos have now actively been seen to change from one flavor to another rather than just disappearing. The T2K experiment has seen muon neutrinos change character to become electron neutrinos after a journey of 295km across Japan. The certainty of this measurement is quoted as 7.5 standard deviations from zero or to put in terms of percentage over 99.99999999999% sure that blind chance or outside interference is not responsible.

What a great place this neighborhood is, & what a shame that Google’s street view & the GPS don’t give us all the details. I guess we’ll just have to keep looking around & poking about in the corners (& of course, where does all this leave the poor-old tau neutrinos?)

On second thoughts,..... — On second thoughts,…..

The universe it seems looks like a foggy night at the seaside, with a few lighthouses dotted around at random. At least, that’s the latest picture from NASA’s Fermi space telescope, it shows hundreds of the most violent & explosive objects in the universe, with just a hint of dark matter in the background.

Over the last 3 years, the Fermi Large-Area Telescope has been in orbit, scanning the sky for gamma rays with an energy of 10 – 300 geV (gigaelectronvolts), more powerful than those previously seen by satellites, but still too weak to spot from earthside.

Now NASA has released the first map of the entire sky at these higher energy levels. It shows over 500 individual sources, set against a hazy background of gamma rays.

The majority of the sources are blazars, distant galaxies with violent, massive black holes at their centres. Most of the rest are pulsars, intensely bright & dense neutron stars with powerful magnetic fields, spinning & flashing like interstellar lighthouses.

The background gamma ray haze is more equivocal: it is partly the result of high-energy cosmic rays, remnants of distant & massive explosions, seen as it collides with gas in our own galaxy. But the Fermi team is seeing almost a third more gamma rays at these energies than they would expect.

It has been suggested (as it always is when anything odd turns up in the cosmos) that this could be evidence of dark matter, the stuff thought that make up 85% of the universe. According to some theories, “Dark matter particles are their own antiparticles, colliding & annihilating with each other & producing gamma rays”. (Nope, that didn’t make any sense to me either.)

Fermi is no stranger to the hunt for the dark stuff. In 2012, it detected a spike in gamma rays at 130 geV, only for dark matter to be ruled out as the source 6 months later. Earlier this year, another Fermi signal started to look more like dark matter, as other possible explanations for it were ruled out.

This neighborhood just gets weirder & weirder, the more time you spend here, & so far all we are doing is looking out the window.