Cosmic Life Rays

By John McCormick and Beth Goldie

SCIENCE FICTION OF THE 1930s is rife with death rays of various sorts, but depending on circumstances a real world death ray can also be a life ray. Even the most dangerous cosmic events can be essential to life as we know it.

From the standpoint of life, human life at least, two of the most important space phenomena are truly cosmic in nature—cosmic rays and the supernovae which appear to be the major, if not the only source of the cosmic particle streams which bombard our planet daily.

Supernovae are the source of all heavy elements in the universe and thus in solid planets while cosmic rays have a profound effect on how life does or doesn’t develop.

Too little ionizing radiation and mutation rates can fall so low that life doesn’t evolve fast enough to keep up with changes in the environment or to create life forms which have the ability to spread across the globe. On the other hand, if you get too much radiation, the surface of the Earth will literally be burned away.

But these two cosmic forces, exploding stars and cosmic rays are thought to be very closely related so we wouldn’t have one without the other. If either is actually essential to life, both are, by that link, essential.

Cosmic Rays

Shooting through space with far more energy than particles generated by the 16.8 mile (27Km) CERN Large Hadron Collider/Accelerator (LHC), protons and other particles constantly bombard the Earth and threaten space missions, but only recently has actual evidence demonstrating their origin been found.

Long suspected to originate somehow in association with supernovae events, researchers at Stanford University and SLAC National Accelerator Laboratory (Funk, Ackerman, etc.—for those of the “Laugh In” generation, not Funk and Wagnalls) using the Fermi Large Area Telescope (LAT) have found the first direct evidence that cosmic ray protons are accelerated in supernova remnants (SNRs), characteristic pion decay gamma rays.

Note: If you have lost track of NASA satellites, the FLAT is also known as the Gamma-ray Large Area Space Telescope (GLAST) and includes both the LAT and a gamma ray burst instrument.

Since they are particles rather than actual “rays,” cosmic rays are massively deflected by Earth’s as well as the ubiquitous other magnetic fields in the galaxy, scattering them so much that it is impossible to determine their point of origin, so getting outside the atmosphere and near Earth orbit can be a big assistance in determining that origin.

What researchers look to for real evidence of the origin of cosmic rays are the gamma rays (actual electromagnetic rays in this case) which are generated with very specific characteristics when cosmic rays strike other particles in space.

Cosmic rays and, in particular, their source(s), are supremely important to us because if they originate in all supernovae, then any supernova event in our galaxy could affect life on Earth—drastically!

We will look at the evidence—both pro and con—regarding their origin later in this article, but first some background information may be useful.

Described in 1912 by Victor Hess, cosmic rays were discovered almost contemporaneously with Einstein’s first serious work—the same time when physics left the realm of reality (hence of understanding) for almost 99 percent of everyone outside of scientists and science fiction fans.

Today’s world of information overload where new discoveries come so fast means that even scientists in extremely narrow specialties, let alone laypersons, can barely keep up with just the headlines in their own field.

(BTW—The situation is about to become incredibly worse, or better, if you are a scientist or interested layperson, with the move to publish research, especially mathematics and particle physics, freely on the Internet.)

Nevertheless, it is difficult, verging on impossible, for the average person under the age of 50 even to fully appreciate just how recently our knowledge of the universe has expanded beyond the solar system.

People who care to pay attention know a great deal about the solar system, stars, even galaxies and such esoteric events as the Big Bang—knowledge so common even Bare Naked Ladies sing about it.

But, in sober fact, a century of scientific research has left many of the most basic questions still unanswered; among those basic questions is the actual origin of cosmic rays, which is suspected but as yet unproven.

Discovery

At first cosmic rays were just the term used to explain why early radiation detectors were indicating ionizing radiation in the absence of any known radioactive substance; today we recognize them as both a cause of evolution and a galactic threat.

If you wonder how such basic questions can be unanswered, it is important to recall that just during the lifetime of our oldest citizens science has progressed from radiation detectors consisting of charged metal leaves in a Mason jar (electroscope) to sophisticated electronic detectors.

Early radiation detectors were simply two connected pieces of metal (hence having identical charges) which repelled each other and spread apart—you can build one yourself from items found in most kitchens—a bit of wire, aluminum foil, and a glass jar; there are instructions on YouTube.

The way this works is that radiation ionizes the air near the electroscope causing the instrument to discharge permitting the foil leaves to come closer together— the faster they move, the higher the radiation level.

Cosmic rays were Hess’ explanation for why his instruments discharged more quickly as he rose in a balloon. A Nobel Prize was awarded to him in 1936 from his work making those measurements.

Originally cosmic rays were thought to be electromagnetic in origin, hence the term “ray” that was applied to them.

It is a sad commentary on the state of current science education that although it was shown in the 1930s that the “rays” were bent by the earth’s magnetic field (light and other EM aren’t affected by a magnet), today, 80-plus years later, some textbooks still include cosmic rays as part of the electromagnetic spectrum.

Cosmic rays have long interested high-energy physicists not just because of the mystery surrounding their origin but, before giant particle accelerators, they were the only source of the “bullets” nuclear physicists used to investigate the world of subatomic particles—that is, while astrophysicists concerned themselves with their origin, experimental physicists used cosmic rays as tools.

In fact, some cosmic rays not only rival the gigantic CERN LHC in terms of the energy of the particles, they surpass the power of the largest accelerator human beings have been able to build, with speeds that equate to power in the range of 10,000,000,000,000,000,000,000 electron volts, a billion times more powerful than those produced at CERN.

The cosmic question facing high-energy physicists is just how really massive numbers of particles can even be accelerated to such high energy levels.

An obvious candidate for the source of cosmic rays was the most powerful event in astrophysics, the supernova, but at first this was simply because no other energy source of that magnitude was known—actual evidence for this hypothesis is just now emerging.

Supernovae are incredibly powerful nuclear explosions where a single star destroys itself in a day or two so catastrophically that its energy output rivals that of an entire galaxy—a spectacular event for astronomers, but a disaster for any cosmic neighbors.

(Supernova remnant, a bubble-shaped shroud of gas and dust that is 14 light-years wide and is expanding at 4 million miles per hour, at right, photographed by NASA's Spitzer Space Telescope, Hubble Space Telescope, and the Chandra X-ray Observatory.)

Normal stars, that is, those living their lives and dying a quiet death due to their size, operate on fusion, the energy released when hydrogen atoms are forced together to form helium—the same as a fusion bomb.

In fact, if all stars were main sequence objects similar to our sun, there would be no life on Earth, for that matter, no Earth or any other solid planet, just (perhaps) gas giants such as Jupiter.

Why? Simple; main sequence stars fuse hydrogen (single proton) with one hydrogen (no neutrons), deuterium (one neutron), or three tritium (one proton and two neutrons) into helium (two protons and two neutrons), and stop there, turning the known remnants of the Big Bang from hydrogen into helium, which is fine for cooling superconductors but not something with which to build a solid planet.

Some really massive stars have enough internal pressure to transform a cosmically tiny, but in human scale significant, percentage of their mass into elements as heavy as oxygen. But when a star is massive enough, even the fusion-generated outward force in a star is not enough to keep it from collapsing from gravity because the elements higher than hydrogen involved don’t produce as much energy.

When the star reaches the point at which pressure and temperature are so high that carbon atoms (actually only their nuclei) begin to fuse, “controlled” stellar fusion will always run amuck and the stellar mass will collapse, vastly increasing the temperature and pressure. At that point an explosion of cosmic proportions is inevitable; that is when energies are sufficient to generate really heavy elements—all the rest of the stable elements in the periodic table.

If you want to build a planet and eventually develop carbon-based life, you need novae and supernovae because they are the only source of heavy elements such as calcium and all the apparently vital trace elements.

Is a Supernova Powerful Enough to Generate Cosmic Rays?

One problem with proposing that supernovae are the source of cosmic rays is the relatively slow speed of the matter expelled by a supernova. The speed of that material is only on the order of 7-12 percent of the speed of light.

The most energetic cosmic rays travel at approximately 99.95 percent of the speed of light, incredibly faster and incredibly more energetic.

Still, the supernova is incredibly powerful, the most powerful source of energy known (with the possible exception of a black hole) and some feature of the supernova explosion may provide a launching platform for the incredibly high energy particles making up cosmic rays.

For several decades, research into the source of cosmic rays has mostly focused on discovering a mechanism for their creation. Making protons is simple, you can do it at home by ionizing hydrogen, but accelerating them with a billion times more energy than the CERN supercollider is a bit more difficult.

To determine the origin of cosmic rays we need to both come up with a plausible mechanism for acceleration and a way to locate their source.

Other Evidence for Linking Cosmic Rays to Supernovae

In addition to the energy levels involved in a supernova explosion, another reason scientists look to them as the probable source of cosmic rays is their composition.

Although, as with almost everything else material in the universe (which excludes dark energy and dark matter—the primary constituents), cosmic rays are mostly protons (hydrogen nuclei), they are actually made up of every element and, surprisingly enough in almost the same ratios as these elements are found in the Earth.

Since Earth and other non-gas giant planets and moons are known or believed to be made up of the remnants of supernovae, the fact that cosmic rays show the same relative proportions is a strong indication that they also originate in supernovae. They are likely to be either part of the ejecta or any unfortunate planets which may have existed in super-giant star systems.

Despite the fact that cosmic rays are made up of the same elements as the solar system and in approximately the same proportions (neglecting the sun which contains most of the solar system’s mass and is almost entirely hydrogen and helium), the few differences are significant and are thus another reason cosmic rays are associated with supernovae.

With the exception of electrons that make up only a tiny percentage of cosmic rays—perhaps another clue to their incredible energy (cosmic rays are mainly positive ions)—some elements and isotopes are found in higher concentrations. Those associated with nuclear decay of elements, such as carbon, make up a significant portion of supernovae.

IK Pegasi A—Death Rides a Pale Horse?

Supernovas are as important to life on Earth as the Big Bang but they are also a giant threat because they are so powerful they can penetrate Earth’s magnetic shield. If a nearby star went supernova and generated cosmic rays they could be so intense as to render Earth sterile.

In itself, IK Pegasi A is just a normal star similar to the sun—a minor variable A class main sequence star—and couldn’t become even a nova, let alone a supernova that could threaten nearby inhabited solar systems. But it has a companion, IK Pegasi B, a massive white dwarf expected to eventually suck off and consume enough of A’s stellar mass to go supernova in a million years or so.

While it is true that a supernova is only dangerous to other nearby systems, the term “nearby” is meant in celestial terms, and the Pegasi binary system is only about 145 light years away—an uncomfortably close neighbor when referring to the greatest known explosive force not just in the galaxy but (other than the Big Bang) the greatest in the universe.

Yet Another Annoying Historical Note

Fewer than 100 years ago it was first proposed that stars used nuclear processes to generate energy. In 1920, Arthur Eddington suggested that hydrogen fusion was the actual mechanism.

The carbon-nitrogen-oxygen reaction wasn’t proposed for larger solar masses until 1939.

But the idea that heavy elements were created in super massive stars is credited to a scientist who was also a colossus in science fiction, Fred Hoyle.

Is it any wonder that real investigation of the source of cosmic rays didn’t begin until the 1950s?

Sir Fred was a bit cantankerous. For example, although he coined the term Big Bang on a BBC broadcast, he rejected the theory himself.

Fred Hoyle is the father of heavy element or nova and supernova stellar nucleosynthesis (the actual fusion mechanism), developed and published between the mid-40s and mid-50s .

The Most Recent Origin Evidence

Gamma ray origin has again become a hot topic for discussion recently because of work done with the Fermi LAT, which has been able to detect unique particle spectra in two Super Nova Remnants (SNRs)—identified in stellar catalogs as IC 443 (1.5 kilo-parsecs distant) and W44 (2.9 kpc)—both very close to the solar system in cosmic terms, being about 10,000 light years away. That is, they exploded about the same time as human “history” began.

The results of a gamma ray study were published just this February in the AAAS Journal of XX Science (disclaimer: I am a member of the AAAS) but the initial speculation about the SNR origin was made by Shklovskii in 1953.

This is truly one of the great puzzles of modern high-energy physics, and little wonder because cosmic rays can be anywhere from a million to a billion times more powerful (in electron volts) than can be generated by the gigantic Large Hadron Collider in Geneva.

The more deeply you look into cosmic ray origin theories, the more complex the problem becomes. For example, some researchers divide cosmic rays themselves into two categories—Galactic Cosmic Rays (GCRs) and Extra-Galactic Cosmic Rays.

GCRs are the less energetic, with the dividing line usually set at about 10 to the 18th ev. By way of comparison, the maximum output of the LHC is a relatively (relativistically?) paltry 10 to the 13th ev.

The currently most widely accepted theory is that because intense magnetic fields are required to accelerate protons and other ionized particles to the relativistic speeds seen in gamma rays, there needs to be some way of generating temporary fields of great intensity.

A supernova expels material at a high velocity, which, despite the lack of atmosphere, creates a shockwave similar in kind to that seen in explosions on Earth; it is believed that this shockwave can compress existing magnetic fields sufficiently to accelerate the particles exiting the supernova to cosmic ray velocities.

The specific mechanism for acceleration is known as diffusive shock acceleration (DSA) or first order Fermi acceleration. What Fermi proposed was that particles encountering a shock wave with moving magnetic fields would react by gaining energy as they bounce back and forth between moving magnetic fields. There is a major problem with this theory: just how a particle would enter the shockwave region in the first place? Perhaps this problem is explained if it is an energetic particle being ejected from a supernova.

If high energy protons can be shown to originate in SNRs, that would provide significant evidence that SNRs are indeed the cause of gamma rays—in essence that is just what data from the Fermi LAT has shown.

Because extremely high energy protons actually generate very specific gamma ray signatures when they collide by first creating pi mesons that immediately decay into two gamma rays, each having an energy of 67.5 MeV—one-half the rest mass of the meson times the speed of light squared (E=mc*c).

Being effected by doppler and other variations, the spectrum of gamma rays generated this way would not be precise but would certainly center on that energy and that is just what was found in four years of observations.

Other Theories for Origin

Supernovae are not the only potential source of cosmic rays recently considered by scientists. In 2007, researchers at the Pierre Auger Observatory in Argentina reported a possible alignment between cosmic rays and galactic nuclei, suggesting that black holes may be the particle accelerators that create high energy cosmic rays. By 2010, the same scientists had cast doubt on this evidence; this idea is generally discounted these days because, as reported by the original researchers, the particles detected are now believed to be iron nuclei instead of protons.

The Superbubble Theory of Origin

A variant of the SNR origin concept, the superbubble hypothesis says that unless individual SNRs are extremely efficient cosmic ray generators (required energy estimates range from three percent to 30 percent of the entire energy output of a supernova), then most cosmic rays must originate not even from the massive power of a single supernova but from groups of supernovae.

The vast majority of supernovae are supergiant stars that collapse under their own gravitational field (core collapse); these stars are often found in clusters that can collapse at about the same time, perhaps one being triggered by ejecta, cosmic rays, or shock waves from adjacent stars.

These groups are known as superbubbles and are almost impossible to observe in any detail, but it is believed that some have been observed in the Large Magellanic Cloud galaxy.

(Superbubbles in the Large Magellanic Cloud, right, courtesy of C. Smith, U. of Michigan, NASA Astronomy Picture of the Day.)

Another origin theory is based on the electromagnetic field generated by the spin of spiral galaxies such as the Milky Way. According to Maxwell, all moving charged particles generate magnetic fields, galaxies are no exception and they generate gigantic magnetic fields that are also in motion and could therefore accelerate charged particles such as cosmic rays.

The galactic origin hypothesis attributes the magnetic field to only a sort of background cosmic ray source and doesn’t contradict the supernovae origin hypothesis, so the recent Fermi Array results don’t disprove either the superbubble or galactic spin origin concepts.

Cosmic Ray Observatories

The above-mentioned Auger Observatory is a 3,000-square-kilometer array of detectors in Patagonia.

The Aussie contribution to this field down under is the CANGAROO Array (Collaboration between Australia and Nippon for a Gamma Ray Observatory) somewhere in the Outback.

Even more extreme observatories have been built in an attempt to either discover or prove the source of cosmic rays.

Another notable example is the IceCube, a detector array larger than the Eiffel Tower, buried under a kilometer of ice in the Antarctic (to filter out less energetic particles).

A Few Notes on Detectors

If you were wondering just how such energetic particles are detected, the first step is often to shield the detector from other, less energetic, particles; this is particularly true for one common detector that uses giant water tanks surrounded by photometers.

A common way to detect tera-electron volt (TeV) particles is to make use of the Cherenkov radiation effect first detected by Pavel Alekseyevich Cherenkov, a 1958 Nobel Laureate. Detectors look for the electromagnetic radiation generated in water when a very energetic charged particle passes through the water (or any dielectric medium). This is the source of the eerie glow seen in water bath nuclear reactor cores.

Cherenkov radiation occurs when the particle is moving faster than the speed of light. That sounds impossible, but remember that the speed of light is much slower in any media than it is in a vacuum and it is not particularly difficult to accelerate particles faster than the speed of light in, for example, water.

These events can be very interesting because they occur not simply when something moves faster than light, but faster than the phase velocity of light, which can be as slow as zero.

Another strange characteristic is that Cherenkov radiation is not limited to a single frequency and the power is proportional to the frequency—that is why reactor cores glow blue.

A Cosmic Certainty

Although it has taken a full century to develop any actual scientific proof that cosmic rays originate in supernovae, the competing theories only purport to account for a small part of the observed cosmic rays.

The instruments needed to collect the necessary data are most probably already in place, so a few years from now we should have actual “proof” in a scientific sense.

But, whether we finally have a solution to the origin question or not, the importance and threat posed by both cosmic rays and supernovae are not in question. If a nearby star went supernova it would end all life on Earth, at a minimum, by stripping all the atmosphere from the planet due to the blast wave. There is already a solar wind from old Sol that probably stripped the atmosphere from Mercury. Magnify it by a million times and you have the “wind” from a supernova.

Supernovae and probably cosmic rays are essential to the creation of life and both could end life here. Add in ice ages vs. global warming, the effect of Luna on earth, possible seeding of life by small asteroids (panspermia), or destruction by large asteroid impact, and life appears to be an exercise in probability.

Should we ignore those threats we can eliminate or mitigate simply because a supernova may someday occur? Or, should we play the odds by taking all the precautions we can, fighting pollution, colonizing the moon as a base to deflect asteroids, and so forth.

And, if cosmic rays aren’t a real enough threat for you, remember that a gigantic black hole is eating away at the heart of our galaxy. 

John McCormick has been published more than 17,000 times. He has written for “Post-Newsweek Tech Media,” “BYTE,” “TechRepublic.com(CNET/CBS),” and about 110 other print publications. Beth Goldie edits almost everything he writes. She also wrote one of the very first commercially published hypertext documents.