Betelgeuse and biological time: Who’s afraid of a supernova!?
In this essay, J.K. Obatala explains “why” and “how” supernovae explosions occur—and relates them to the origin of life. He writes, against a backdrop of global excitement over the inevitable eruption of the bright star “Betelgeuse”. Although an immediate blow-out is now considered unlikely, astronomers don’t rule it out. The Guardian thus seeks to pre-empt any “spiritual” or “mystical” connotations, such a celestial display might carry—in case nature springs a surprise!
What if a second “Sun,” suddenly ignited in the afternoon sky? Or an intrusive light-source, started vying with the gibbous Moon – flaring out, from where a familiar red star once twinkled? That would be a supernova explosion—a seminal cosmic event—erupting in Orion constellation, where the bright star Betelgeuse is being blasted into oblivion.
Dazzling Orion the Hunter, with its three brilliant—and strikingly slanted—“Belt Stars,” is the most easily recognizable of the International Astronomical Union’s 88 official constellations (star-groups with distinctive patterns). Betelgeuse beams leftward, just above the Belt.
Orion’s iconic “shoulder,” has been getting lots of attention. A “Betelgeuse Workshop” was held in Paris, as far back as 2012. But global excitement reached a fever pitch last December, when astronomers found that the fabled red supergiant was dimming lopsidedly and shrinking.
Betelgeuse has now stopped dimming: And could reclaim its status, as the night sky’s 10th brightest star! Even so, scientists insist that it must blow eventually: Any time, from this minute to the next 100,000 years. When it does, they predict one hell-of-a light show—viewable worldwide, day and night, and lasting for months!
The problem though, is that such a dramatic celestial display, might unsettle many ill-informed Nigerians. In some cases, feelings of fear and dread could, conceivably, morph into a dangerous “End-Time” delusion: An apocalyptic and potentially suicidal mindset.
“How you react,” stresses Dr. Ahmad Shaba, Director, Strategic Space Applications, at the National Space Research and Development Agency (NASRDA), “has a lot to do with your personal history—with what you’ve read, the sermons and lectures you’ve heard and the movies you’ve seen.”
In short, he counsels, coping with the eruption would depend “on whether you’ve learned enough astronomy to avoid a mental meltdown. One should also be able to fend off material and emotional predators. Otherwise, you could lose lots of money—and possibly your life.”
Shaba is adding NASRDA’s voice, to a swelling cautionary chorus, insisting that Betelgeuse’s plight is not “spiritual”. Nor are supernovae, as such, rare. Thousands have been recorded, since 1885. “Today,” Wikipedia reports, “amateur and professional astronomers are finding several hundred every year…”
“What then,” you are bound to ask, “is the big deal about Betelgeuse?” Well, unlike other recent progenitors, it belongs to the Milky Way Galaxy (our Sun’s star group), which averages only two per century—and is, as Dieter Hartmann put it to Sky & Telescope, “long overdue for its next supernova”.
The last naked-eye burst in our galaxy, dates back to 1680. Another, the historic SN 1987A, occurred 33 years ago, in the Large Magellanic Cloud—a satellite galaxy of the Milky Way, 168,000 lightyears out. A Betelgeuse blast would be comparatively close; and, for the first time, astronomers could watch, from start to finish.
Why study stellar explosions? The universe (all the energy, matter, space and time that exists) is a vast, and complex, system of interrelated units—which includes you, me and the planet we inhabit! So, the more we learn about the universe, the better we understand ourselves.
Look around! Everything you see, is made of atoms—most of which, stars bequeathed. As Michigan State University Physicists, Artemis Spyrou and Hendrik Schatz aver, in The Conversation, “Element by element nuclear processes in stars take…hydrogen atoms and build heavier elements.”
Big stars, are munificent chemical donors—since they can fuse elements heavier than helium. They’ve richly endowed Earth, with industrially useful and biogenic substances. The latter, not incidentally, consist of chemical components, for the bio-contrivance that winks and smiles at you in the mirror!
The American Association of Variable Star Observers notes that visible light makes up only 13 per cent of the radiation Betelgeuse emits. Yet it is seeable enough, to have been mythicized as the “shoulder” of Orion in Europe, a “fierce lion” among the Xhosa of South Africa and a “fiery club” in native Australian lore.
This high celestial profile, belies the 700 lightyears that separate us from Betelgeuse —keeping in mind, that just one lightyear (the distance light travels in 12 months, at 300,000 km per second) amounts to roughly 10 trillion km!
The upshot, is that Alpha Orionis (to use its Latin appellation), has awesome bulk properties. More mundanely: Betelgeuse is a bee-ig mammy-tappy! An illustration of the Atacama Large Millimeter Array (ALMA), depicts a behemoth that would—if it replaced the Sun—engulf all the planets, out to Jupiter!
ALMA’s diagram, visualizes jaw-dropping stats: Betelgeuse has 20 times the Sun’s mass (i.e., 20 “solar masses”) and 1,500 times its diameter (the Sun itself, being 1.4 million km wide!). Thanks to this huge radiating surface, its peak brightness is 14,000 solar luminosities!
Betelgeuse originated as a contracting clump of gas, in the Orion Molecular Cloud, which (like countless similar clumps) heated up to 10 million kelvins (K)—and began nuclear fusion. It was born into an age-group of big blue stars—the Orion OB1 Association—with surface temperatures of up to 30,000 K.
But, Wikipedia recounts, Betelgeuse was later ousted from the Association, under pressure from exploding supernovae. It is now a “runaway star,” racing through the interstellar medium (the space between stars), at 30 km per second.
As it careers through the cosmos, a melodrama is unfurling in Betelgeuse’s core. Two physical forces—Heat and Gravity—are locked in a back-and-forth tussle, a “You push me, I push you” scenario. “Heat” heaves stellar mass outward, against “gravity’s” ceaseless tug towards the centre.
“The simple model,” explains an outreach posting of the Australian Telescope National Facility, “…is of a dense gas/fluid in a state of hydrostatic equilibrium. The inward acting force, gravity, is balanced by outward acting forces of gas pressure and the radiation pressure”.
Gravity will, in time, prevail—collapsing Betelgeuse into a stellar corpse, called a neutron star. Yet the alluring reds, yellows, oranges, blues and whites of the dark sky, indicate that heat is, heroically, holding its own, at least in the interim.
Otherwise, we wouldn’t see a firmament of colours. The myriad tints and hues of stars, signify varying intensities of heat being radiated from their surfaces. Stellar colours, send the same quantitative message, as the flames in your cooker: Blue is hottest and red coolest, with gradations in between.
But whereas your cooker sources its fuel externally, Betelgeuse generates its energy internally, through nucleosynthesis. In the hydrogen-fuel phase, four protons (hydrogen nuclei) are fused into a helium nucleus (alpha particle). The reaction transforms 0.7 per cent of the protons’ mass into energy.
Hydrogen consumption, is the longest period in stellar life. The famous Hertzsprung-Russel (H-R) diagram thus depicts this phase, graphically, as the “main sequence” —an oblique reference to the habit stars have, of fusing progressively heavier nuclei, in rapid succession, after a sustained diet of hydrogen.
Big stars burn their fuel faster than small ones. Hence Betelgeuse is in crisis, after just 10 million years—while our Sun (a dwarf star) has five billion years remaining, in a lifespan of 10 billion. Betelgeuse left the main sequence one million years ago, theory holds, and has been a red supergiant for 40,000 years.
Gone are the “O-B” days. Bloated, and radiating at a clement 3,950 K., Betelgeuse is now relegated to spectral class “M”, on a scale that ranks stars, from hot to cool, “O,” “B,” “A,” “F,” “G,” “K” or “M”. (You can use this mnemonic, to remember the scale: “Oh Be A Fine Girl (or Guy) Kiss Me!”)
Yet as early as 1923, the famous Cambridge astronomer, Arthur S. Eddington, apprised readers of Scientific Monthly that radiation from the surface of Betelgeuse, “is just the marginal temperature of the furnace, affording us no idea of the terrific heat within.”
A NASA table (Imagine The Universe), delineates enormous fusion temperatures: It takes 0.8 billion K to forge neon and magnesium from carbon; 1.5 billion K to fuse neon into oxygen and magnesium; 2.0 billion K for Oxygen to yield silicon and sulfur; and 3.3 billion K to meld silicon nuclei into iron.
“Iron,” is the endgame in stellar evolution—beyond which, the fusion of lighter nuclei into heavier ones, stalls. That’s because, in the accepted model, iron nucleons are bound so tightly, that fusing them consumes, rather than releases, energy.
Betelgeuse’s fate, is therein foreshadowed. No fusion, no heat—and no outward push, again. So, “gravity” gets a walkover win: And, in celebration, sends all the progenitor’s mass crashing inward, onto its core, at a quarter of the speed of light!
“As a result,” says NASA, “an explosive shock wave travels out from the core…and accelerates the surrounding layers. In addition, …energy from… neutrinos (nearly massless elementary particles) cause (most) of the star’s mass to be blown off into space…. Astronomers refer to this as a Type II supernova.”
The visual effect, may evoke “End-Time” fears in some. But, in reality, supernovae kickstart biological time! They not only blast heavy atoms (iron, gold, tin, lead, etc.) into space, but also carbon, oxygen, nitrogen, sulfur and phosphorus (biogenic elements): To be recycled, into new planetary systems.
Thus, Priscilla Long’s panegyric, in The American Scholar, aptly strokes supernovae: “From where did we get the iron in our blood, the carbon in our cells, the oxygen in our lungs? From exploding stars, that’s where. We may or may not be starry-eyed, but we are all part star”.
•Obatala is Nigeria’s best-known amateur astronomer—having written a weekly column, in The Guardian, for 16 years (until 2017). He gives public lectures on the subject, and is an External Advisor to the National Space Research and Development Agency (NASRDA).