By the time you have finished reading this sentence, five stars in the observable Universe will have exploded violently, as supernovae. By this time tomorrow – and approximately once a day thereafter – an almost inconceivably powerful source of unknown nature will have showered the Universe with an intense blast of high-energy gamma radiation.

As cosmic events go, gamma-ray bursts (GRBs) and supernovae rank among the most spectacular, but nobody has sought to forge a link between the two – until now. Three reports in Nature now attempt the task. A GRB that occurred on 25 April this year (GRB980425) occurred at the same time, and in the same patch of sky, as a supernova called SN1998bw, which occurred in a galaxy about 140 million light years away.

In one report in Nature, Jan van Paradijs of the University of Amsterdam, the Netherlands, and colleagues, show this coincidence was – well, more than just a coincidence. But if the two events are connected, astronomers will have to come to grips with a new type of supernova – and a new type of GRB.

Supernovae happen when a star, more massive than our Sun, exhausts its nuclear fuel. The pressure of radiation, exerted outwards from the centre, is no longer enough to support the star's immense weight. The result is a sudden collapse. The core of the star shrinks to become a supermassive neutron star. At the same time, the outer layers of the star are shed, forming a rapidly expanding sphere.

Nobody knows what causes GRBs, in contrast. Many GRBs emanate from remote parts of the Universe, so it is hard to imagine the power of a source of almost pure gamma-radiation, expending the energy of a supernova in a few seconds, visible from halfway across the Universe.

Some researchers have imagined GRBs being caused by a class of immensely powerful supernova – a 'hypernova' – in which a gigantic star explodes, leaving a core of of 2.9 times the mass of our Sun, or more. Unsupported, a mass as large as this would collapse beyond the neutron-star state, becoming a black hole. The explosion would blast a shell of material into space. If the star had been spinning and had a strong magnetic field, electrons from the ejecta would be accelerated to a large fraction of the speed of light. Crashing into the interstellar medium, these accelerated electrons would produce an intense shock wave that would generate a pulse of gamma radiation.

Could SN1998bw have been some kind of hypernova, physically related to GRB1998bw? Shri R. Kulkarni of Caltech, Pasadena and colleagues think it can. Their reasoning comes from radio-telescope observations of SN1998bw. In the radio sky, SN1998bw was the brightest supernova ever recorded. In most supernovae, radio emission takes a few days to reach a peak, and then slowly subsides. In SN1998bw, in contrast, the radio emission came as one big blast. Kulkarni and colleagues suggest that the radio emission was caused by electrons accelerated to close to lightspeed. These same electrons, slamming into the interstellar medium, could have produced the gamma-ray pulse associated with GRB980425.

In the third report in Nature, Ken'ichi Nomoto of the University of Tokyo, Japan and colleagues explore a 'hypernova' model that would package all these events together in a convincing whole.

Independent of the possible association with the gamma-ray emission, the radio luminosity – with all that implies about electrons accelerated to relativistic velocities – makes SN1998bw a highly unusual supernova. But the association with GRB1998bw presents a problem. A GRB of the observed luminosity emanating from a source just 140 million light years away – just across the pond, in cosmological terms – is a cosmic pipsqueak, with a source just one ten-thousandth the power of bigger, beefier GRBs from further away. So, while we introduce a newer, mightier class of supernova into the cosmic zoo – we may have to admit a weedier, nerdier kind of GRB through the turnstile.