Supernovae, the explosions that end the lives of certain stars, are amongst the brightest and most dramatic events in the Universe. They release as much energy in a few minutes as the Sun will in a ten billion year lifetime. A nearby supernova is rare, but can be seen with the naked eye, and these suddenly appearing flares of light were amongst the first evidence that the heavens were not immutable. Perhaps unsurprisingly, they’ve attracted their fair degree of attention from the writers of science fiction.

A Threat from our Sun

Amongst the earlier fears to be expressed by science fiction was that our Sun might go supernova, or perhaps experience a less energetic (but still deadly to life on Earth) nova. Perhaps understandably, the terms supernova and nova are often used interchangeably in twentieth century science fiction, even though astronomers distinguished between them as early as 1934. In fact we now know these events arise from very different types of stars. Most supernovae occur when a massive star exhausts its fuel and its core collapses. A subset of supernovae, and the more common novae, arise from a completely different type of event and a different type of star - material falling onto a white dwarf from a binary companion. In a nova a layer of this material ignites and releases a flare of light. In a type Ia supernova the entire white dwarf star collapses under its new weight and explodes. However the origin of these events in binary systems was not well understood until the late 1960s.

The premise that the Sun might explode - whatever the mechanism - drove a number of works in which the world was rendered uninhabitable, and was often mentioned in passing as a driver of extraterrestrial colonisation.

A striking example in which a solar nova features more prominently is The Songs of Distant Earth (Clarke, 1986). Set on the world of Thalassa, this novel contrasts the experiences of early colonists (the descendants of children born of automated gene banks sent to an extrasolar world, centuries before) with those of newly-arrived passengers on the Magellan, a faster-than-light spaceship which carries the last humans escaping Earth’s solar system as the Sun goes nova [4]. The narrative focuses on relationships between individuals, but also explores the differing cultural values which have arisen between the two groups of descendants of Earth humanity, and the emotional trauma of seeing the Sun and Earth destroyed:

He had witnessed scenes that no one could ever forget and which would haunt Mankind until the end of time… With his own eyes, he had seen the volcanoes of Mars erupt for the first time in a billion years; Venus briefly naked as her atmosphere was blasted into space, before she herself was consumed; the gas giants exploding into incandescent fireballs. But these were empty, meaningless spectacles compared with the tragedy of Earth. (Grafton Books paperback edition, 1987, pg 29)

When the novel was written, a genuine fear existed that the Sun was approaching the end of its lifetime. The solar neutrino problem suggested either that the physics of solar fusion was fundamentally misunderstood or that the Sun was in the process of exhausting its fuel - and Clarke discusses this problem and the imminent-nova theory in some detail. In reality, the solution to this problem was eventually found in particle physics rather than astronomy in the form of neutrino oscillations [5], and we now believe our Sun to be a stable star with billions of years ahead of it.

In fact, the prospect of the Sun ending its life in either a supernova or a nova is effectively nil. It is far too small for a core collapse supernova, without the interior structure needed to power a catastrophic explosion. It also lacks the binary partner now known to be responsible for the classical nova and supernova type Ia phenomena. However this does not preclude the possibility of our Sun releasing massive flares or other outbursts later in its evolution. Larry Niven explored this possibility in his short story “Inconstant Moon” (1973) which describes the torrid and hectic atmosphere of a California night whose overly-brilliant Moon hints at catastrophe irradiating the other side of the planet. Recent works by Cixin Liu, such as his novella “The Wandering Earth” (2000), have also focussed on the (valid) astronomical prospect that the Sun will go through a brief but dramatic brightening known as a “helium flash” towards the end of its life. While this would be extremely short-lived in astrophysical terms, it might be enough to irradiate the Earth’s surface. We believe that the Sun is likely about 5 billion years away from undergoing a helium flash, rather than the few centuries suggested by Liu, and that it will become a red giant before this occurs, but (unlike a nova) it will at least experience this evolutionary state!

A Vulnerable Earth 

Even if our own Sun is unlikely to die a dramatic death in the near future, that does not mean Earth is immune to the effects of other, more distant supernovae. A sufficiently close event could boil the oceans and strip the ozone layer, while even more distant stellar detonations could potentially irradiate the planet, causing damage to human DNA and potentially mass extinctions of Earth life.

This danger is explored in a range of science fiction. Earths irradiated by supernovae (or still-more-energetic gamma ray bursts) are amongst the infinite number of alternate realities hypothesised by Terry Pratchett and Stephen Baxter in their Long Earth series of novels. In The Long Cosmos (2016), such an event irradiates a relatively nearby example of an alternate Earth in the probability spectrum (known as West 3,141). In the context of the novel, this emphasises that while such events are unlikely, they occur at random (regardless of what's happening on the Earth's surface) and present a very real threat which our own reality could also experience.

Our own Earth is indeed subject to irradiation by a single catastrophic supernova in The Supernova Era (Liu 2003, English translation 2019). Cixin Liu begins his novel with the premise that a star 25 times more massive than our Sun has been lurking just 8 parsecs (about 25 light years) from Earth, but remained unseen behind a cloud of obscuring dust. After going through a flare which passed largely unnoticed in the eighteenth century, it goes through a core-collapse supernova with devastating effect: everyone over the age of 13 is doomed to die within a year, leaving a world entirely inhabited by children. The book focusses on the fascinating thought experiment of the type of world and international politics that might result.

The interaction between physics and biology is decidedly suspect here: for every irradiated adult to die in a conveniently narrow time window, regardless of their location during the event (i.e. deep mines, ocean depths or open air), genetics or treatment, while leaving children entirely unaffected, goes rather beyond the supposed “ability to repair chromosomes” Liu attributes to everyone below a conveniently-arbitrary age threshold. By contrast, the astronomy is fairly good - the physics here is lovingly described in the opening chapters, with the details of the core collapse and its observable signatures as seen from Earth. When the book was first written in 1989 (there was a substantial delay before first publication), it was perfectly plausible that a massive dust-obscured star could indeed be that close. Unfortunately (or very fortunately indeed, depending on your perspective) a series of infrared all-sky survey projects in the last thirty years, including 2MASS and the surveys of the Spitzer, Herschel and WISE telescopes, have effectively ruled out this possibility. A star that massive would heat its dust envelope, and that dust would glow brightly in the thermal maps of the infrared making such an object impossible to miss.

Another novel, Supernova by Roger McBride Allen and Eric Totani (1991), explores the impact on Earth of a less-commonly-considered lower mass star explosion, when the nearby white dwarf star Sirius B explodes as a type Ia supernova. The novel focuses on a young research astronomer who is working to predict this type of event, and the race against time between him completing his work and the arrival of the supernova blast wave, all amidst the fin de siecle millennialism of the end of the twentieth century. Since the Sirius binary is less than 3 parsecs from the Sun, the impacts are not pleasant. While Allen is the better known novelist, co-author Totani was an academic astrophysicist studying supernovae, lending the novel verisimilitude [3], although in reality it's very unlikely Sirius B is actually this unstable.

Death on Other Worlds?

The search for life on other worlds is a major preoccupation of both science and science fiction. The chances of finding such life is often parameterised by the Drake Equation. However a key term in the equation is L - the lifetime of a civilisation. The reality of supernovae in the Universe means that planets beyond the Solar System may also be vulnerable to extinction level radiation exposure, reducing this lifetime - and often supernovae present the biggest threat.

One interesting example to be found in science fiction is the home star of Superman. The reasons for the destruction of Krypton - which results in the young Kal El/Clark Kent’s escape to Earth - vary between versions of the story. However Krypton’s sun is typically shown as a large red star, and in at least a few of Superman’s many reinventions (e.g. Superman the Movie, Superman Returns) it is explicitly stated or shown to have exploded, destroying Krypton and setting subsequent events in train.

Perhaps the most memorable story to explore both the drama and pathos of a world’s extinction can be found in Arthur C Clarke’s short story “The Star” (1955). In this story an explorer ship comes across a vast monument, marked by radiation and giant structures on a supernova-slagged world. Beneath, they find an archive recording the doomed civilisation that built it - and their loss presents a deep challenge to the faith of the ship’s astrophysicist, a Jesuit priest:

Perhaps if we had not been so far from home and so vulnerable to loneliness, we should not have been so deeply moved. Many of us had seen the ruins of ancient civilizations on other worlds, but they had never affected us so profoundly. This tragedy was unique. It is one thing for a race to fail and die, as nations and cultures have done on Earth. But to be destroyed so completely in the full flower of its achievement, leaving no survivors—how could that be reconciled with the mercy of God?

While the story is short, it evokes a strong sense of both the wonder of discovery and the impact of loss, as well as asking profound questions about the operation of the Universe and the role of deity within it. It also presents readers with a challenging thought experiment - if Earth were threatened in the same way, what aspects of art, culture and science would we choose to preserve?

Star Killers

If the prospect of worlds being destroyed by random chance is a tragedy, then the idea of detonating stars through deliberate action is potentially a horror… but not necessarily so. Unsurprisingly, science fiction provides examples here too, with the visual impact of the explosions appealing particularly to science fiction television and film.

BBC TV series Doctor Who skirted the boundaries between justice and genocide in 1988’s “The Remembrance of the Daleks” when the Doctor deployed an ancient weapon known as the Hand of Omega to destroy the home sun of Skaro - the world of the Daleks. While the Daleks had been warned, had (yet again) invaded Earth, were themselves responsible for enormous atrocities, and do not seem to have been seriously inconvenienced by the loss in the long term, this was still rather an apocalyptic decision [1].

The crew of Stargate SG1 were faced with perhaps a slightly less torturous choice when they chose to detonate the sun of Vorash in the episode “Exodus” (2001). Rather than a long-considered confrontation, this was very much an option of last resort in an attempt to destroy a battle fleet. The world Vorash itself was desertified and populated only by a base which was evacuated. Rather than Doctor Who's un-defined effect of a semi-sentient ancient weapon (to which Clarke’s law applies [2]), the method used to trigger the supernova here is explained in some detail: an open wormhole (in the form of the eponymous stargate) is dropped into the star and connected with a black hole. The resultant mass loss disrupts the balance between radiation pressure and gravity in the star, causing it to undergo a sudden collapse. The plausibility of this is difficult to evaluate - the stargate would likely not have time to reach the star’s core, and so its main effect would be on the stellar envelope. The mass loss would be rapid - far more so than physical processes in the star which attempt to reestablish equilibrium. This would certainly lead to the star becoming unstable, but whether it could trigger a supernova would need rather complex modelling.

To go from the sublime to the ridiculous, a mention should be made here of the innovative use of supernovae by an advertising agency in the novel Red Dwarf – Infinity Welcomes Careful Drivers by Grant Naylor (1989, based on the 1988-1999 BBC television series). Spaceship crews were sent to fire “nebulon missiles” into 128 carefully selected suns at carefully selected moments. The light, reaching Earth at some distant future time would spell out the words “COKE ADDS LIFE!” across the sky:

OK, it wasn’t wonderful, ecologically speaking. OK, it involved the destruction of a hundred and twenty-eight stars, which otherwise would have lasted another twenty-five million years or so. OK, when the stars exploded they would gobble up three or four planets in each of their solar systems. And, OK, the resulting radiation would last long past the lifetime of our own planet.
But it sure as hell would sell a lot of cans of a certain fizzy drink.
(Red Dwarf: Infinity welcomes careful drivers, Grant Naylor, 1989)

The mechanism of these missiles is far from clear, but the imagery is certainly dramatic.

The Fascination of Supernovae

Supernovae are relatively rare events. While we are now able to identify new events every night using powerful telescope surveys, naked-eye events visible to the general public occur decades if not centuries apart. However they clearly exert a powerful hold over the imagination of science fiction writers, so perhaps we should consider why.

There’s certainly an element of catastrophism here. Post-apocalyptic fiction allows characters to be placed in scenarios of stress and uncertainty that can demonstrate either their best or worst traits. They allow for thought experiments regarding the nature of the survivors and how society might develop in response to such a shock - something very clearly demonstrated in Liu’s The Supernova Era. While mid-twentieth century apocalypses were more often nuclear in nature, and modern authors increasingly consider issues such as climate change, some authors might have opted for stellar threats to allow for a less grim and imminent threat and a more escapist reading experience. Another common theme of apocalyptic fiction, the human tendency to creating ever more powerful, more destructive and less controllable weaponry, is manifest in the fiction of star-killers - once real-world doomsday devices became capable of destroying life on Earth, the destruction of stars was seen as a logical future step.

There is also a long-standing fascination in our culture with the idea that - for all our personal experience to the contrary - the Universe is both mutable and a potential threat, on a scale which far exceeds any plausible human intervention. For many authors this kind of existential threat provides a critique and commentary on the impotence and baseless arrogance of humanity. This was a particularly strong trope in the mid-twentieth century when the white heat of modern technology and the pace of scientific innovation suggested that any problem was solvable given enough effort and money. Invoking supernova-like catastrophes allowed authors either to point out the hubris of that assumption, or, in some cases, to demonstrate it through vast efforts such as interstellar colonisation.

Finally astronomical catastrophism such as the stories mentioned here also often plays with scenarios that position scientists themselves as either heroes or villains. Often astronomers and other scientists are featured as characters in these works - either predicting, observing or occasionally even causing the explosions. The difference in training and experience between the astronomer characters and the majority of the audience gives the characters an air of being “other” and therefore an object of fascination (or perhaps renders them alien and repellent as the plot requires). The very unfamiliarity of supernovae and novae to most of the population (particularly when they are so often confused in science fiction), together with their real-world positioning on the cutting edge of modern research, lends speculative fiction an air of authority and mystery for readers with a limited astronomical background, and it is often astronomers who are shown articulating or explaining those mysteries. Given the huge scale of supernova-type explosions, such fictions might also be taken to show the impotence of scientists who can study a problem, maybe even predict it, but not prevent it.

Fiction involving supernovae ranges from the heroic, constructive drive outwards into the Universe to the depressing and destructive apocalyptic fictions which posit the destruction of human culture and perhaps humanity itself. They nonetheless represent a rare engagement of popular culture with the details of stellar astrophysics, and a useful starting point from which to engage in a wider discussion about the fate of stars and our place in the Universe.