CSI Milky Way: Cosmic Ray Shooters Finally Identified

We are under constant attack and we cannot escape our assailant.  No matter where we hide, each of us is riddled with 30 hyper-speed bullets every second.  You can’t run, either.  We’d probably be dead by the time we got to the neighbor’s.  Don’t bother trying to call for help; the perpetrator also targets our communication satellites.  We’ve known of this unprovoked assault for ages, but only recently have we conclusively proved just who’s out to get us.

The electricity and ionization in the atmosphere was the first clue that something was up.  There was something very energetic disrupting our atoms.  Henri Becquerel’s 1896 discovery of radioactivity seemed to make this an open and shut case, as decay of heavy isotopes within the Earth took the blame.  International intrigue cast doubt on the culprit’s identity in 1909, when German physicist Theodor Wulf took an elctrometer to the top of the Eiffel Tower and found the levels of radiation there were actually greater than at the ground surface.  No one on the beat believed him.  The case grew cold.

Victor Hess, though, was unsatisfied.  He wanted to go higher.  in 1912 Hess used a hot air balloon to take three enhanced versions of Wulf’s electometers to a height of 17,000 feet, where they measured an ionization rate four times what you’d expect at sea level.  Wulf had been right.  The barrage was coming from beyond, not from within.  The Sun became the next suspect, but Hess was able to rule it out by performing the same experiment during a near-total solar eclipse, with the moon blocking much of the Sun’s radiation.  The tricky detective work earned him the Nobel prize in 1936, but it ultimately left us with more questions than answers.  What was causing the ionization, and who was behind it?

Robert Millikan had already worked his way up the ranks when he picked up the assignment in the 1920′s.  Coining the term “cosmic rays,” Millikan believed gamma rays were the offender’s ammunition of choice.  But the ballistics didn’t check out.  In 1927 J. Clay dared to question the respected veteran by pointing out that cosmic rays were more intense at higher latitudes, swept there by the Earth’s magnetic field.  They couldn’t be light waves like gamma radiation; they had to be charged particles.  Experiments in the ’30′s, spurred by Bruno Rossi’s insights, showed that cosmic ray intensity was also greater from the west, indicating the particles were positively charged.  The weapon had been found.  High-speed protons.  But what could accelerate the tiny projectiles to such velocities, as high as 95% the speed of light?

cosmic rayImage from (where else?) cosmicray.com

Fingering the perp continued to prove difficult.  The line-up over the decades included magnetic variable stars, nebulae, active galactic nuclei and more, but no single scofflaw could be picked out. Supernovae became the prime suspects, as the expanding envelopes from their explosions could possibly provide the power needed to boost the protons’ speed to deadly levels.  Charged particles get deflected by other matter as they rocket through space, however, making the locations of the shooters hard to pin down.  The forensics were hand-cuffed.  Technology had to advance to uncover the well-hidden tracks.

Beginning in 2008, Stanford University’s Stefan Funk and his team set up a four year stakeout with the Large Array Telescope of NASA’s Fermi Gamma-ray Space Telescope.  They focused their attention on two supernova remnants in the Milky Way.  As it turned out, gamma rays were the key after all. While the trajectories of the proton bullets themselves may be too tricky to track, their gamma ray by-products zip right through, unaltered.  In February of 2013 the group announced that the observed energies matched the predictions.  They had a positive ID.


Pop the corks and call the D.A. After a century of hard-nosed investigation, we’ve got our man.  It was a circuitous route to the truth that in a way brought us back to where we started.  It goes to show that when you start tugging on a tangled thread, you never know where it’ll lead.  Gut instincts and gumshoe hunches only get you so far if you don’t have the observations and technology to back them up, though.  Even seemingly intractable cases can be solved given enough progress of time and technique.

I do hope the judge goes easy on the sentence, though.  Despite their cosmic ray malfeasance, supernovae have a history of community service.  It’s thought that elements heavier than lead can only be produced in stellar explosions, meaning many of our most precious minerals wouldn’t be here without them.  Some even speculate that a supernova may have triggered the collapse of the dust cloud that formed the entire solar system to begin with.  What a crazy, mixed up universe we live in, where a progenitor can turn on its own creation.  I’m getting too old for this shit.

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