Somewhere in the cosmos, a billion light years from Earth, a star died in spectacular fashion. For months, its explosion shone with colossal intensity, far surpassing the brightness of an ordinary supernova. But what was truly extraordinary was not just its brilliance: For the first time, astronomers believe they have seen the birth of the engine that powers some of the most luminous stellar explosions in the universe.
That engine is a magnetar, a neutron star that defies many of the laws of physics. Have a diameter of about 20 kilometers, but they concentrate a mass comparable to that of the Sun. That basically means that a teaspoon of this star would weigh about the same as all the cars on the planet combined.
Another characteristic of this type of star has to do with its gravity. The surface of a neutron star has gravity 100,000 to 200 billion times stronger than that of Earth. If it were possible to get close to it, we would end up crushed to a sheet of atoms. As if this were not enough, it rotates thousands of times per second. But where these stars really They challenge the imagination is in their magnetic field. The Earth’s magnetic field is relatively weak: about 0.5 gauss at the surface. A magnetar can reach 10¹⁴ or 10¹⁵ gausswhich means that its magnetism is billions of times more intense than that of the Earth.
Well, it is precisely this object that a team of scientists from the University of Berkeley has seen come into being. The discovery, described in the journal Nature, confirms a hypothesis proposed more than a decade ago by astrophysicist Dan Kasen: Some of the brightest starbursts in the cosmos get their energy from a newborn magnetar hidden at the heart of the explosion. This is the story.
The so-called superluminous supernovae were discovered in the early 2000s. Since then they have been a headache for astronomers. These explosions They can shine ten times brighter than a typical supernova and also remain luminous for much longer than expected. According to classical models, when the iron core of a massive star collapses, the star expels its outer layers and the brightness should decrease relatively quickly.
However, in these cases the glow seemed to be powered by some additional source of energy. The theory proposed by Kasen suggested that, After the star collapses, the core could transform into an extremely magnetized neutron star: a magnetar.
The characteristic of these stars, linked to their speed of rotation, would be one of the mechanisms linked to this extra energy: by rotating so fast, the magnetic field of the magnetar accelerates charged particles that collide with the material ejected by the supernova. That energetic bombardment could act as a hidden engine that keeps the explosion glowing for much longer. The problem was that until now no one had been able to directly observe that engine. The key came with supernova SN 2024afavdiscovered at the end of 2024 and observed by the Las Cumbres global telescope network.
For more than 200 days, astronomers measured its brightness. At first the behavior seemed normal: the luminosity reached its maximum about 50 days after the explosion. But then something unexpected happened. Instead of fading smoothly, as happens in most supernovae, the brightness began to oscillate. Four small ripples appeared in the light curve of the explosion.
Astronomer Joseph Farah, of the University of California, Santa Barbara, He compared the pattern to the sound of a bird: each oscillation was slightly faster than the previous one, producing an effect similar to a trill whose frequency gradually increases. That behavior was the missing clue. The study led by Kasen revealed that part of the material ejected by the explosion would have fallen back towards the newborn magnetar, forming an accretion disk of extremely hot gas.
If that disk is not perfectly aligned with the magnetar’s rotation axis, a phenomenon predicted by Albert Einstein’s theory of general relativity comes into play: the so-called Lense-Thirring effect. This effect indicates that a massive object spinning at high speeds can drag the very fabric of space-time around it. This drag causes the disk of matter to begin to wobble slowly, like a misaligned top.
In this case, that movement would cause the disk to periodically block or reflect part of the magnetar’s light, producing a kind of flashing cosmic beacon. As the material falls toward the magnetar, the disk spins faster and faster and the brightness oscillations become more frequent. This pattern coincides exactly with the “trill” observed by telescopes. From the observations, astronomers were able to estimate some properties of the newborn object. The magnetar would be spinning once every 4.2 milliseconds and its magnetic field would be approximately 300 billion times more intense than that of Earth. These figures fit perfectly with what is expected from a young magnetar.
The interesting thing is that Kasen’s team believes that this phenomenon could be much more common than is thought. New observatories, such as the Vera C. Rubin Observatory, will soon begin mapping the sky with unprecedented sensitivity. That could reveal dozens of these peculiar stellar explosions.