Published in 1955, Arthur C. Clarke’s "The Star" is an unusual take on the relationship between science, religion and science fiction. It’s a short story I discuss with students every year in a workshop on catastrophism as part of a graduate habitability module, and it always inspires interest and conversation. I mentioned it briefly when we talked about supernovae, but since we’re approaching the Christmas season, I thought it was an appropriate moment to revisit this story.

First a brief plot summary (with spoilers - go and read the text now if you prefer… or perhaps watch the rather fun (and pretty short) 1985 Twilight Zone adaptation on youtube or other providers): In the narrative of this short story, we meet a Jesuit priest serving as chief astrophysicist for a space exploration mission. Exploring a supernova remnant, the gaseous cloud which remains after a massive star explodes, the crew discover an archive buried under a tracery of radioactive markers on a half-melted lump of rock - the destroyed system’s equivalent of Pluto. This archive preserves images, sounds and cultural artefacts from another long-gone planet - the system’s Earth-analogue. Emotionally drained by these records and the loss associated with them, the unnamed priest calculates the origin-date of the supernova remnant and the light travel time to Earth. He finds his faith challenged by the realisation that this explosion provided the biblical Star of Bethlehem.

Stellar Remnants

There’s so much to unpack in this short story, but let’s focus on the astronomy. As I’ve discussed before, the threat of supernovae (along with other astronomical catastrophes) was a recurring theme in science fiction through most of the second half of the twentieth century. In “The Star”, Clarke seats his narrative firmly in the contemporary and historical knowledge of supernovae - as he observed:

When a star becomes a supernova, it may for a little while outshine all the massed suns of the Galaxy. The Chinese astronomers watched this happen in A.D. 1054, not knowing what it was they saw. Five centuries later, in 1572, a supernova blazed in Cassiopeia so brilliantly that it was visible in the daylight sky. There have been three more in the thousand years that have passed since then.

He also accurately reflects the physics of supernovae as it was known at the time, and most of it, including a detailed description of the supernova remnant, remains valid even now:

We came slowly in through the concentric shells of gas that had been blasted out six thousand years before, yet were expanding still. They were immensely hot, radiating even now with a fierce violet light, but were far too tenuous to do us any damage. When the star had exploded, its outer layers had been driven upward with such speed that they had escaped completely from its gravitational field. Now they formed a hollow shell large enough to engulf a thousand solar systems, and at its centre burned the tiny, fantastic object which the star had now become—a White Dwarf, smaller than earth, yet weighing a million times as much.

 The only flaw in this from a modern astronomical perspective is in the last line. For a star to go supernova it must be somewhat more massive than our own Sun, big enough to have a core of heavy elements. A star of that mass will collapse all the way to a neutron star (supported by neutron star degeneracy pressure) when it goes supernova rather than a white dwarf (which is supported by electron degeneracy). Such a neutron star core would be as small not just as Earth but as a medium-sized town instead.

There’s a possible secondary confusion here. Another kind of spreading cloud of stellar debris with a white dwarf remnant at the centre is a planetary nebula. These do indeed come from lower mass stars at the end of their lives, but require the central star to have been in a binary and are not associated with supernovae. The distinction between these two types of systems was recognised by astronomers in the late 1930s, but the distinctively different origin mechanisms of planetary nebulae and supernova remnants were still uncertain and the detailed astrophysics was less clear to the general public when Clarke was writing than it is now.

 Either way, this technical detail gives the narrator character authority, rooting his theological and ethical dilemma firmly in his scientific background. They also give the story a sense of realism which balances the fictional elements of the journey described. The hint of a date - a thousand years after 1572 and thus in the 26th century - is also subtle and almost a throwaway line in the midst of the scientific information, far less jarring than a direct statement, and less likely to interrupt the necessary suspension of disbelief. As of the current date, incidentally, there has only been one further Galactic supernova detected (SN1604), so Clarke is predicting two more in the centuries between now and his projected future (broadly in line with current expectations).

Life and Death

As well as the physics of supernovae though, Clarke also addresses the consequences of supernovae for habitability and life in the Universe. 

Before its explosion, his stellar remnant had hosted a solar system with an Earth-analogue and a Pluto-analogue. This is, of course, similar to our own Solar System, and was in line with astronomers’ expectations of the time. We now believe that solar systems come in a wide variety of configurations, although it’s hard to comment on how common each is - our observations are still heavily biased towards those quite unlike our own: giant jupiters very close to their host stars are far easier to detect than Sun-like systems, and the latter may also be common but currently unseen.

Clarke’s system is irradiated by a supernova, destroying the inner (Earth-like) planets, and melting the surface of the Pluto-like world. In the event of a supernova occurring, planets at Earth-like distances would indeed be destroyed. In fact, it’s likely that the Pluto-like world would also be destroyed, or ejected from its system rather than remaining bound to the remnant. Certainly if it did manage to remain bound, it would be heated to temperatures of millions of degrees, hot enough to melt the surface. And, while long-half-life isotopes would still create a radiation signature, that might well be drowned out by the radioactivity of isotopes generated during the explosion itself - a drop of fresh water lost in the ocean.

It’s also an unfortunate fact that Clarke’s narrative of a supernova-induced extinction has overlooked an important stage of stellar evolution: while an Earth-like world would certainly be destroyed by a supernova, it would likely be destroyed or rendered uninhabitable hundreds of millions of years earlier, when its sun expanded into the red giant phase. While this may or may not lead to an Earth-like planet being engulfed in the star (simulations of our own Solar System suggest the probabilities are finely balanced), it would certainly move a previously-habitable planet out of the evolved primary sun’s newly-redefined habitable zone. 

Nonetheless, Clarke highlights an important point: stellar lifetime and the occurrence of nearby supernovae or other catastrophes represent an important constraint on the survival of life in the Universe, and hence on our predictions for the prevalence of life at the current time. While Frank Drake, in his famous equation for calculating this, used the chances of technological civilisations destroying themselves, stellar evolution represents a more fundamental limit for any life form unable to escape its host system and environs. Thus it’s more than possible that if other life - or better still intelligent life - has come into existence in the Universe, we may miss one another temporally, like ships passing in the night.

While he was writing, Clarke rooted his narrative in the then-known physics and represented them largely accurately. While we cannot know what he would elect to do if writing today, it’s interesting to speculate that either he’d frame his extinction narrative against the onset of the sun’s red giant phase (as Cixin Liu did in his novella “The Wandering Earth", 2000), or else that he’d envisage a larger, hotter sun, and a world at significantly larger distances from its primary which might experience a brief few millions of years of viable habitability before its sun dies: a flicker of light in the dark.

Ineffable Design

Just to finish, let’s take a brief look at religion. It’s often asserted that religion and science are directly opposed. While many scientists do hold to that opinion, for many others the relationship between the two is more nuanced: science measures and predicts the world around us, it tells us how the world works and the rules it follows, it tells us little or nothing about why those rules exist or how the Universe came to be. For many scientists with faith, that is the role of religion. This is the sentiment embodied in a Biblical quotation which appears above the door of the Cavendish Physics Laboratory in Cambridge: “The works of the Lord are great; sought out of all them that have pleasure therein’”. It is also the position (now) taken by the Vatican, who sponsor a cutting edge research observatory, together with its astrophysicists [1].

Like the character in Clarke’s The Star, many of these Vatican astrophysicists are members of the Society of Jesus - known as Jesuits. This religious order prioritises scholarly studies and has contributed a number of notable scientists, including Georges Lemaitre, who is largely responsible for conceptualising what we now know as the Big Bang. So, in his narrator character, Clarke was accurately capturing a plausible role for someone who was deeply learned in both religion and scientific knowledge, and who had comfortably reconciled them without considering either diminished.

But that’s not the beginning and end of Clarke’s exploration. At the climax of the story, the main character questions why the alien race had to burn to announce the birth of God’s son. At its root this is the same, impossible to answer, question which religion must always face: why do bad things happen to good people? As Clarke clearly indicates in the text, neither this story nor any other can answer that eternal dilemma. Nonetheless it is notable that in this instance, while the priest’s faith is shaken, ultimately he accepts that he cannot know or understand the mind of deity: if we are to accept that there could conceivably be a supreme creator who is not constrained by the scientific laws They established, then we must accept that They are also beyond the comprehension of our limited four-dimensional, intra-universal consciousness.

Arthur C. Clarke’s "The Star" is a complex text, which, despite its short length, explores a surprising range of ideas and emotions. It encapsulates a snapshot of the early confusion over supernovae and their sources, as well as the distress of a humanity whose beliefs are confronted by a wider Universe and who, ultimately, fear to find themselves alone. The 1985 Twilight Zone version of "The Star" adds a coda, giving the end of the story a more optimistic tone. Whether enjoying this, or contemplating Clarke’s original ending, it’s certainly a story that asks questions of its readers, and of the Universe around us.