I have written before here, here, and here – among other places – about the lack of evidence of intelligent life elsewhere in our Galaxy. But recently I watched a potentially game-changing science documentary on Netflix that seems to be critically relevant to the issue of the existence of life, intelligent or otherwise, in our or any other galaxy. The Netflix documentary, which is quite accessible to people with little or no technical knowledge of astronomy or astrophysics, is entitled, somewhat melodramatically, The Real Death Star (hereafter Death Star). I watched Death Star, and began to formulate my own speculations about the possible effects of gamma ray bursts in any galaxy unfortunate enough to suffer one, in particular, the unfortunate consequences for life in general – and intelligent life in particular. In fact, my curiosity was piqued to such an extent by the material along toward the end that I began to do a Bing and Google search based on the five-word phrase “intelligent life gamma ray bursts”. So imagine my astonishment when my Bing and Google searches returned several “hits”: astrophysics papers, peer-reviewed and authored by credentialed professionals in the field, that basically repeated my previous naïve, non-professional speculations. (For example, see here, here, and here.) Gamma-ray bursts (hereafter GRBs) may resolve the Fermi Paradox I referred to in my “Skeptic’s Collection” columns that I linked to in the first sentence.
So what are GRBs? Back in … if I remember … the 60s, the US launched a constellation of satellites of the Vela series that were intended to monitor Soviet compliance with atmospheric nuclear-warhead testing. The detonation of a nuclear warhead produces an explosion that is very bright in the gamma-ray spectrum. So any test of a Soviet nuclear device in the earth’s atmosphere would be detected in real time, and would constitute prima facie evidence that the USSR was violating warhead-testing agreements. But what the Vela constellation detected was not nuclear detonations in the earth’s atmosphere, but nuclear detonations – tremendous gamma-ray fluxes – in deep space. How deep in space? Long story short, the gamma-ray sources, each lasting from a fraction of a second to a few seconds, were not even originating in our Milky Way Galaxy, because the explosions were not concentrated along the plane of our Galaxy. Instead, they were occurring at cosmological distances measured in millions, even billions, of light-years. Furthermore, the gamma-ray sources were pretty evenly distributed over the entire sky. Gradually, the awesome truth dawned on observational astronomers and theoreticians alike: to be as bright in the gamma-ray spectrum as these explosions were, and in order to be observed at such stupendous distances, whatever was causing the GRBs would have to be the most powerful explosions since the Big Bang. Eventually, it turned out that, once observational astronomers could detect the afterglow of a GRB, each GRB was associated with a very distant, cosmologically distant, galaxy. Each GRB was bright enough in gamma rays to be detected quite literally halfway across the observable Universe.
This begs the question of what causes GRBs. If you are interested in the details, I highly recommend you watch that Netflix science documentary, The Real Death Star. Again, long story short: it turns out that the only mechanism that can account for the output of that much gamma-ray energy is the collapse into a black hole of a super-massive star, perhaps a star of several-dozen, perhaps 20, solar masses. Such massive stars can collapse into black holes in a fraction of a second to a few seconds – the observed lifetime of GRBs – and in the process convert the entire star’s mass into energy, according to Einstein’s famous formula of E=mc2. Because of the tremendous pressure of the collapse, the gamma-ray flux takes the form of two beams of energy emitted in opposite directions. Imagine a GRB as a lighthouse that emits gamma rays instead of visible light. So powerful are these two beams of gamma rays that any planet anywhere in the galaxy containing the GRB, and that lies in the path of the beam, will be fatally irradiated, basically sterilized of all life, even if that planet is on the opposite side of the galaxy from the emitting GRB. (In fairness, I should say that not all GRBs are this powerful, but many are.) The radiation flux of GRBs is just that powerful. For any form of life, intelligent or otherwise, in that searing line of fire … well … it is point-game-set-and-match-hang-up-your-jock-strap-and-hit-the-showers. The show is over.
Now, you might think that if a planet were not in the line of fire, the radiation would have little or no effect. Instead of a lighthouse, imagine the GRB as a machine gun. If you stand beside the machine gun instead of directly in front of it, you would not be harmed. But GRBs are centered on black holes, and black holes are not machine guns. There is strong theoretical reason to believe that most black holes – and therefore most GRBs – not only rotate on their axis, but that they also precess. You can observe precession when a child’s top begins to lose momentum and slow down: the axis of rotation begins to wobble. Something like this probably happens with black holes and GRBs: the gamma-ray source begins to wobble. Imagine that the soldier firing the machine gun is drunk and rotates the machine gun erratically as he fires it. In that case, standing beside the machine gun would probably afford no safety. So the GRB would not emit merely a beam of death, but a cone of death: the conical pattern described as the GRB precesses. That would not affect the intensity of the gamma-ray flux, but it would affect the area of the galaxy jeopardized by the GRB. Furthermore, even if the angle of precession close to the black hole were only a fraction of an arc-second, far enough away from the black hole, the diameter of the cone of death would widen out to perhaps thousands of light-years – again, with no change in gamma-ray intensity. Any form of life inside that cone would be exterminated once the gamma-ray wave front reached it, even if the wave front, traveling at the speed of light, took thousands of years to arrive. It is quite conceivable that, depending on where the GRB was located, the cone of death could sterilize the entire galaxy.
Anyway, I think you probably see where I am heading in terms of relating this to Enrico Fermi's famous question vis a vis intelligent life elsewhere in the Universe: Where is everybody? Please understand: I am speculating now. But it may well be the case that numerous life-forms evolved intelligence, both in our Milky Way Galaxy and in other galaxies in the Universe, but that at some point, the galaxy hosting those intelligent beings was subjected to the gamma-ray flux from a GRB. In fact, one of the papers I discovered and cited in the first paragraph estimated that, over the last 500 million years, there is at least a 50-50 chance that our Milky Way Galaxy experienced a gamma-ray event and that this catastrophe may account for one of the five great extinction events in earth's history.
GRBs are rare. The only reason they seem abundant is because the Vela satellites, and subsequent generations of X-ray instruments, survey such an enormous volume of the sky. But as rare as they are, we should remember the following grim principle: It Only Takes One. (Actually, in the interest of not oversimplifying a complex issue, I should say that it is not this easy. How deadly a GRB can be depends on the type of GRB one is talking about -- astronomers have developed several categories of GRBs, some more energetic than others -- and how the GRB's gamma-ray beam is oriented. If the orientation of the cone of death is out of the galactic plane, relatively little damage could be done. If the cone of death is oriented within the galactic plane, it will be quite lethal. Think of my hypothetical drunken machine gunner pointing his machine gun straight up instead of more or less parallel to the plane of the battlefield. Also, to truly sterilize an entire galaxy, it would probably be necessary for the galaxy to suffer a few to several GRBs, appropriately situated, over a few-billion-year time frame -- just as it would be important to situate machine guns properly to provide fire cover for an entire battlefield. But a few billion years is a minuscule time-frame in a cosmos with a history of around 13.8 billion years. There is plenty of time for GRBs to extinguish life in any given unlucky galaxy.)
This is a rather dismal conclusion -- and, again, I am speculating -- given the vision evoked of potentially dozens (hundreds? thousands?) of extraterrestrial, even extragalactic, civilizations evolving and arising to greatness, only to be cut down in their prime by a single star, perhaps on the other side of the host galaxy, collapsing into a black hole and generating enough gamma radiation to sterilize the planet these magnificent beings inhabited. Should we someday achieve star travel, we may well find evidence of such civilizations in the form of ruined cities that were once inhabited multiple millennia, perhaps hundreds or even thousands of millennia, in the distant past. Once in a while, in such a distant future, we might even find and manage to decipher the records of those alien astronomers that recorded the GRB that was in the process of destroying their race and their civilization. For all we know, the Universe may consist of a vast array of cosmic graveyards holding the remains of entire civilizations. Perhaps a real-life USS Enterprise would be tasked, not with "discovering new life and new civilizations," but by writing the obituaries of dead civilizations -- and hoping that someone would be left to write our own, should the Milky Way Galaxy experience its own GRB whose beam was pointed at us.
(All of which begs a rather macabre question: what would humans experience if the earth were in the path of the gamma-ray emissions from a GRB? [The following is taken partly from Death Star and partly from my knowledge of radiation physics.] The answer depends partly on how powerful the GRB was and on its distance from us. For the most powerful GRBs, observations indicate that there is really no such thing as a "safe distance". First, we would see an apparent second sun in our skies: the GRB itself. At almost the same time, the very air around us would fluoresce a bright blue due to ionization. That would last a few to several minutes. Gamma ray ionization would promote the oxidation of nitrogen in the earth's atmosphere. It is also possible to speculate that the oxidation of nitrogen would "eat up" much of the oxygen in the atmosphere, by chemically binding the oxygen to nitrogen, so we might begin to suffocate for lack of free oxygen. [Some of the oxides of nitrogen would probably assume the form of nitrous oxide -- so called "laughing gas" -- which has a powerful sedative effect. So some of us would probably be very relaxed and "buzzed out" while we died. The Universe has a rather dark sense of humor. In addition, the intense gamma-ray flux might catalyze the formation of nitrogen dioxide, a precursor of nitric acid, which would turn the earth's atmosphere a kind of dirty reddish shit-brown. This just keeps getting better, right? ] The ozone layer would almost certainly be stripped away, resulting in the loss of protection from solar radiation, especially in the UV spectrum -- which would, in turn, result in a fearful epidemic of carcinomas, especially skin cancers, due to DNA damage. There would be a similarly catastrophic epidemic of birth defects and outright sterilization of both men and women. Birth rates would plummet. Ditto apocalypse-scale damage to plants and animals and their reproductive capacities. All the above we could expect from a powerful GRB located within a light-year radius of, say, five digits, e.g., 10,000 or 15,000 light-years. Because of the finite speed of light, we would never see it coming, except for a few observational astronomers who might see it briefly before their eyes vaporized. We can only speculate how many intelligent species have had to deal with just such consequences over the billions of years of the Universe.
However ... in all fairness, I should say that several papers have recently been published on the arXiv.org web site arguing that [a] intelligent technological species can, given highly advanced technical means, actually mitigate the effects of GRBs, e.g., see the abstract here, and the paper itself here, or that [b] a "phase transition" model of the development of life in a galaxy can actually benefit from GRBs, e.g., see the abstract here, and the paper itself here. Fear not! The math is only of freshman-calculus caliber.
Perhaps a perverse analogy would be to reminisce about Magic Slates. Are you old enough to remember playing with a Magic Slate? During my childhood and adolescence, I used them up and discarded them in numbers that would probably suffice to fill my car's passenger compartment and trunk. You sketched on the slate or wrote on it. Then, when you finished or got bored with what you had done, you erased your work by the simple expedient of lifting the films away from the slate underneath, eradicating all the pictures and text you had created on the Magic Slate. The existence of GRBs is theologically problematical: perhaps -- who knows for sure? -- God uses galaxies as a magic slate to create living beings, intelligent beings, eventually entire civilizations. Then, having become bored with Her creations, She lifts the film of the Slate by igniting a gamma-ray burst, clearing all life from the galaxy and wiping the Slate clean.
As the late Prof. Martin Reif, a history professor of mine at Wichita State University, was fond of saying when I was an undergraduate sometime in the Pre-Cambrian Sic transit gloria mundi.
Life is unfair.
James R. Cowles
Vela satellite … NASA … Public domain
Gamma ray burst … NASA … Public domain
Gamma ray burst … NASA … Public domain
Colliding galaxies … NASA … Public domain
Globular cluster 47 Tucanae … NASA … Public domain
Enrico Fermi … US Dept of Energy … Public domain