On 9 October 2022 a flash arrived from about 2.5 billion light-years away and became one of the brightest gamma-ray bursts ever recorded. Astrophysicist Vladimir Lipunov, who spends his working life catching such flashes, was asked a plain question on the Osnova podcast: what if one went off close to us?
His answer starts with the shape of the thing. A gamma-ray burst does not shine in all directions like a lamp. Its energy leaves in a thin relativistic jet, a narrow stream of matter moving close to the speed of light. Lipunov calls it a laser pointer. The word he reaches for is ukazka, and he stops to note that it is a Russian one. If the pointer is aimed at your eye, he says, "we'd better not be living here."
What does "close" mean? He puts the danger zone at a few thousand parsecs, which is a few tens of thousands of light-years. That is inside our own galaxy. A burst at that distance would be a spectacle for anyone who survived it. It would flare about 50 to 100 times brighter than the full Moon, bright enough to read a newspaper by.
The reading light is the harmless part. Lipunov's worry is what the beam does if it lands on a planet. Most of us have been through an X-ray at some point, he says, a chest scan. Here the body would be hit by photons a thousand times stronger. The ozone layer, the thin shield that screens the ground from harmful radiation, gets blown away. Mutations begin, "and all sorts of rubbish, at a minimum." For the reader the stakes are about as large as they get: the sky above everyone could stop protecting us.
He is calm about the odds. By his count such an event happens about once in 100 million years. He announces the number with a showman's pause, telling his host that now he will exclaim that he knows who died on Earth at that moment. He doesn't claim to know, and he doesn't claim that any past extinction was caused this way. He only says the odds are very low, and that the risk is real.
It blows the ozone layer away, mutations begin, and all sorts of rubbish, at a minimum. There. It's a factor like this, an anti-civilisation factor.
Естественно, сносится озоновый слой, начинаются мутации и всякая фигня, минимум. Это такой фактор, такой антицивилизационный фактор есть.
— Vladimir Lipunov, Osnova, 10:48
Lipunov raises this only in passing. It is a remark answering the host's question, not a theory he builds out. He moves on within a minute, back to how astronomers catch these flashes. The details are left open: how big the dose would be at ground level, what the aim of the jet would have to be, how close is close enough.
Other scientists have been working on part of that. A study in Communications Earth & Environment in June 2024, led by Theodoros Christoudias, modelled a gamma-ray burst from a cosmic explosion at 100 parsecs. That is far closer than the thousands of parsecs Lipunov talks about. Gamma rays are strongly absorbed above about 30 kilometres altitude, and the nitrogen oxides they produce in the air recovered within weeks. The planetary effect came out remarkably small.
The two do not directly contradict each other. The model and the remark are about different distances and different setups, and the study does not test Lipunov's laser-pointer geometry. But they do show how much depends on the details of the aim, the distance and the air.
The same burst of October 2022 also left a mark on our own planet from far away. Satellites and ground instruments picked up a disturbance in the upper ionosphere and a large electric-field kink at about 500 kilometres altitude, as reported in Nature Communications in November 2023 by Mirko Piersanti and colleagues. The burst was billions of light-years off, and it still jostled the top of our atmosphere.
So Lipunov's picture is a strange mix of comfort and unease. Over a human lifetime the chance is next to nothing. Over the age of life on Earth it is something that could have happened more than once. And there is one more twist he leaves hanging: the jet comes in a pair. One beam goes toward us, the other the opposite way, as momentum demands. Nobody has yet found a black hole left flying off like a rocket. Some astronomers, he says, are still waiting.
