By Paul Rincon
Science reporter, BBC News
The outburst was spotted by the Swift space telescope
Astronomers have been able to capture and record the first moments when a massive star blows itself apart.
After decades of searching, researchers have used the world's top telescopes to observe the remarkable event.
Previously, scientists had only been able to study these "supernovas" several days after the event.
The results, published in the journal Nature, show that within two hours of the blast, a giant fireball scattered radioactive debris across space.
The phenomenon was detected by the Swift space telescope, a collaboration between the US space agency (Nasa), the UK and Italy.
Supernovas are some of the most spectacular events in the Universe, producing the same amount of energy as trillions of nuclear bombs detonating simultaneously.
Typically, they occur when a massive star - more than eight times the mass of the Sun - runs out of fuel and collapses to form a hot relic called a neutron star.
Their extreme brightness allows them to be seen in distant galaxies.
But observers cannot pick up this optical emission until several hours or days after the explosion, so a supernova's first moments are shrouded in mystery.
Death of a star
The event in the constellation of Lynx was captured by pure chance.
Alicia Soderberg, from Princeton University in New Jersey, and her colleagues were using Swift to survey the spiral galaxy NGC2770.
They saw an extremely luminous X-ray outburst in an area of sky that had shown nothing bright just two days earlier.
They attribute the outburst to the breaking out of the supernova shockwave, which ploughs its way through the star's gaseous outer layers - blowing it to smithereens.
"We were in the right place, at the right time, with the right telescope," Dr Soderberg explained.
Dr Kim Page, from the University of Leicester, who led the X-ray analysis, commented: "This observation is by far the best example of what happens when a star dies and a neutron star is born."
Swift's X-ray instrument was largely developed at Leicester by a team led by Professor Alan Wells. He told the BBC that Swift had been designed from the outset to tackle issues such as the early behaviour of supernovas.
The initial observations were followed up by some of the world's major telescopes. They observed the blast for more than 30 days to rule out the possibility this event could be anything other than a supernova.
"We were able to observe the evolution of the explosion right from the start,” said co-author Edo Berger, from the Carnegie Observatories in California.
"This eventually confirmed that the big X-ray blast marked the birth of a supernova."
Astronomers say that supernovas are part of the story of how we came to be, because these tremendous explosions created many of the heavy elements from which planets are made.
The authors say the event will help astronomers fill in gaps about the properties of massive stars, the birth of neutron stars and black holes, and the impact of supernovas on their environments.