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Fiction meets real data
In Andy Weir's Project Hail Mary, an alien microorganism called astrophage is consuming the energy output of nearby stars. Dimming them, cooling their planets, and threatening all life in the solar neighbourhood. The infection begins at Tau Ceti and spreads from star to star.
Every star in this story is real, but thankfully the Astrophages are a product of Andy Weir's amazing imagination. However, let's look at how he imagined that the star jumping organism actually spread through our part of the galaxy.
The premise of Project Hail Mary is simple and terrifying: astronomers notice that the Sun's luminosity is dropping. Not by much — a fraction of a percent per year — but the trend is real and accelerating. Something is feeding on it.
That something is astrophage. A microscopic organism that absorbs stellar energy, breeds in the photosphere, and migrates between stars. The infection did not start at the Sun. It started at Tau Ceti, roughly 12 light-years away, and spread outward through a chain of nearby hosts. By the time anyone on Earth noticed, the Sun was already one of many victims.
A note on distances: this site normally uses parsecs — the natural unit when measuring stellar distances by parallax, which is exactly what the Gaia and Hipparcos satellites did, and the unit used throughout our other lessons. Here we use light-years, because that is the unit Andy Weir uses in the novel, and the human scale of the journey matters to the story.
Scroll through the tour below to trace the infestation through real space.
Sol · 0 light-years
We start at home. An astronomer has detected an anomalous spectral feature in solar observations — a signature that has no business being there. It becomes known as the Petrova line. Further study reveals the cause: the Sun is being robbed of energy by an unknown life form, and its luminosity is falling as a result.
The effect is subtle at first. But on a timescale of decades it will trigger catastrophic global cooling and the collapse of agriculture. Earth is on a countdown, and the clock is already running.
Looking toward Tau Ceti · 12 ly
Turn toward Tau Ceti. It is a Sun-like star: spectral type G8, slightly cooler and smaller than the Sun, about 12 light years away. To the naked eye it is unremarkable: magnitude 3.5, visible from the southern hemisphere.
But Tau Ceti is where the astrophage infestation started. It was the first star to dim. By the time human instruments could detect the change, the organism had already begun its migration to neighbouring stars.
Arriving at Tau Ceti
Tau Ceti up close. A quiet, solitary star. No known close stellar companions, a debris disc, and several candidate exoplanets. In the novel's timeline, this is where astrophage first established itself, feeding on the star's energy and reproducing in vast quantities.
From here, migrating astrophage followed the simplest rule: travel toward the nearest bright source of energy. The organism does not choose — it absorbs stellar energy, converts it to mass, and releases it again as a very specific frequency of light, using that thrust to propel itself toward the next host.
First spread · jumps of 5.5 and 10 light-years
The first stars to fall after Tau Ceti were Epsilon Eridani and 40 Eridani. The connecting lines show the migration routes — each one a crossing of the void, powered by stored stellar energy converted back into directed light at a precise, characteristic frequency.
Epsilon Eridani — the shortest hop from Tau Ceti, just 5.5 light-years. A young K-type star with a known debris disc and at least one confirmed exoplanet. Young, active, and rich in energy — exactly what astrophage needs. It sits about 10.5 light-years from the Sun.
40 Eridani — 10 light-years from Tau Ceti, about 16 from the Sun. A triple system: a K-dwarf primary named Keid, a white dwarf companion, and a red dwarf. If you've read the book, you'll know why this system matters more than just as a waypoint on the infection map.
The relay · jumps of 7.8 and 4.7 light-years
From Epsilon Eridani, astrophage crossed 7.8 light-years to reach Sirius — the brightest star in our night sky, twice the mass of the Sun, and pumping out twenty-five times its luminosity. For an energy-feeding organism, it is the most irresistible target in the neighbourhood. Sirius is 8.6 light-years from the Sun.
From Sirius, the next hop was a short one: just 4.7 light-years to WISE 0855−0714, a cold, solitary brown dwarf sitting 7.4 light-years from the Sun. You will not see it in the star field: it is far too faint to appear in either the Gaia catalogue (which this site is built on) or the older Hipparcos survey that supplies our brighter stars. Discovered only in 2014 by NASA's WISE infrared satellite, it is one of the coldest known objects outside the Solar System — around 250 K, colder than a winter night on Earth.
Yet in the novel, this invisible relic is the critical relay. Without it, the chain from Sirius to the Sun cannot close. The astrophage does not care about brightness — it needs proximity. WISE 0855−0714 is perfectly placed.
The last hops · jumps of 4–8 light-years
From WISE 0855−0714, the infection fanned out to four stars at once. The Sun was not special. It was simply nearby.
Sol — a jump of 7.4 light-years from WISE 0855. A G-type dwarf, middle-aged, stable, and utterly ordinary. By the time the dimming was noticed, astrophage had been feeding for years.
Wolf 359 — the closest hop of this final burst, only 4.4 light-years from WISE 0855. One of the faintest stars known, a red dwarf so dim it is invisible to the naked eye despite sitting just 7.9 light-years from the Sun. It became famous as the site of a fictional battle in Star Trek — and now, in another fiction, it falls to astrophage.
Lalande 21185 — 7.0 light-years from WISE 0855, 8.3 from the Sun. Another red dwarf, the brightest red dwarf in the northern sky. Quiet, cool, and ancient — possibly twice the age of the Sun. It has at least one confirmed exoplanet.
Ross 128 — the longest jump in this final fan, 7.6 light-years from WISE 0855, about 11 from the Sun. A red dwarf notable for its confirmed Earth-sized planet orbiting in the temperate zone. Ross 128 b receives about 1.4 times the flux that Earth gets from the Sun. If anything in this story could harbour life, this is where the odds are shortest.
Look at the shape of the web. Each hop follows the nearest viable star. The geometry of our corner of the galaxy — the actual three-dimensional arrangement of these real stars — is what determines the pattern of the infestation.
40 Eridani · 16 light-years · looking home
We end in orbit around 40 Eridani — not just because it sits at the edge of the infection map, but because of what happens here in the novel. To say more would be to spoil one of the best surprises in recent science fiction. Read the book.
From here, the Sun is just another star: unremarkable, anonymous, lost among thousands of brighter points. Sixteen light-years is nothing on a galactic scale — and yet it is enough to make home invisible. The astrophage did not care about our civilisation or our history. It followed the light. And the light led here, and there, and everywhere nearby.
Real geography
Every position in the tour comes from real stellar catalogues — primarily Gaia, supplemented by Hipparcos for the brightest stars. The astrophage has no navigation. It drifts toward the nearest luminous host. The shape of the infestation is the shape of our actual stellar neighbourhood.
The invisible relay
The critical stepping stone between Sirius and the Sun is a brown dwarf that neither Gaia nor Hipparcos can see — it is simply too cold and too faint for optical surveys. Only the WISE infrared satellite found it, in 2014. It is marked here by coordinates alone. The novel's chain of infection depends on an object that barely registers as a star at all.
Scale
The entire infection network fits inside a sphere of about 16 light-years radius. The Milky Way is roughly 100,000 light-years across. This crisis is galactically microscopic — and yet it threatens every planet orbiting every star within reach.
Fiction & science
The stars, their positions, distances, and spectral types are all real. Astrophage is fiction — no known organism feeds on stellar energy. But the spatial logic is genuine: this is how a nearest-neighbour spread would actually move through our corner of the galaxy.
The book
This tour is inspired by Project Hail Mary (2021). The novel follows a lone astronaut sent to Tau Ceti to find a way to stop the astrophage and save the Sun. If you have not read it, the less you know going in, the better.
