The shell of an exploded star can swallow light for up to a hundred days. The core inside it collapses in a few tens of seconds.
That mismatch is the problem with supernovae. Vladimir Lipunov, an astrophysicist who has spent his career on binary stars and on telescopes that hunt for sudden flashes, calls the worst offenders "ugly": you cannot look in and see how a black hole is made. The shell is thrown off, it absorbs, and by the time it clears, the event you wanted to watch is long over.
What would you gain by seeing it? Every black hole astronomers have studied is already old. Some are billions of years old. Those in pairs with a blue star may be only tens of millions. Lipunov finds the other end of the story more interesting: how they are born. A black hole forms in a few tens of seconds, and almost nobody has seen it.
Most collapses go quietly, as plain supernovae. A few tenths of a percent do something else. In those, the core is spinning so fast that the centrifugal force pushes back against gravity. Lipunov's picture is the figure skater who pulls in her arms and spins faster. A core that squeezes itself gets the same boost, and if the spin is large enough, the collapse stalls. The core has to shed its rotation first, through some kind of friction, magnetic or otherwise. A collapse that normally takes a few thousandths of a second now runs about 100,000 times slower. Some bursts last hours.
That slow, spinning birth throws out a narrow jet, a relativistic beam. Here is the turn. The jet starts at the centre and bores outward through the star.
But a supernova is a fur coat, and you can't see anything under it. A gamma-ray burst is a pointer that has come through from the centre, where the core is collapsing.
Но сверхновая звезда – это шуба, под которой ничего не видно. А гамма-сплеск – это такая указка, которая проникла из центра, там, где ядро коллапсирует
— Vladimir Lipunov, Osnova, 15:01
Through that hole you see, all the way down to the black hole itself, what happens in gamma rays. Lipunov adds that the same event shows up in visible light too, but only if a telescope is aimed at the right patch of sky within a few tens of seconds, before the glow fades. Speed is the whole game.
Nature Astronomy in April 2024 reported something that fits the spinning picture. Observations of the burst GRB 221009A with the James Webb Space Telescope picked out the supernova that went with it. The authors concluded the burst came from the collapse of a rapidly rotating massive star.
Lipunov's own group works on the fast part. A paper on arXiv in December 2024, from his group's side of the field, says robotic telescope networks are what catch the early, bright optical afterglows of bursts. He is not shy about the result. His group posts 500 to 700 alerts a year, and in one burst their telegram reached NASA's site first. Of this business he says they took first place in the world, and he dares you to name another business where anyone can say that.
