It was so bright it could have been seen "with a pair of binoculars" - despite happening TEN BILLION light years from Earth, according to the team. It provides the clearest picture yet of mysterious gamma ray bursts (GRBs) that have fascinated astronomers for decades, ever since they were first discovered in the late 1960s.
They are so spectacular they give off as much energy in seconds as the sun in its entire 10 billion year lifetime! It was so bright it could have been seen "with a pair of binoculars" - despite happening TEN BILLION light years from Earth, according to the team.
It provides the clearest picture yet of mysterious gamma ray bursts (GRBs) that have fascinated astronomers for decades, ever since they were first discovered in the late 1960s. They are so spectacular they give off as much energy in seconds as the sun in its entire 10 billion year lifetime!
A gamma ray burst happens when a massive star dies, collapses into a brand new black hole and explodes as a supernova. It spews out jets of gas across the universe at the speed of light. A planet caught in the line of fire would lose its atmosphere instantly and would be left a burnt cinder.
Robotic telescopes spotted the blast, dubbed GRB 160625B, in June 2016. It is so far away the 13.8 billion year old universe was just 3.8 billion years old at the time. The only bigger cosmic fireworks display scientists know of is the Big Bang. By an incredible one-in-10,000 chance experts at Bath University, along with colleagues at NASA and around the world, detected its light as the star died.
Head of physics Professor Carole Mundell said:
“It was so bright you could have seen it with a pair of binoculars. They usually happen instantly, but this time we got a flash of light lasting a second that acted as a warning. Then there was a delay of about 100 seconds, giving us enough time to position the telescopes. That is quite unusual, and the burst lasted longer than normal, a few minutes which was fortunate. Although very distant, this burst was extremely bright and we were excited when we realized our super-fast robotic telescopes had captured the early time light.”
This allowed them to probe the magnetic fields very close to the black hole itself by measuring the polarisation properties of the light. Her team followed how this changed in time, as the explosion developed. The study, published in the journal Nature, reveals the role of magnetic fields in these immense explosions, as well as what the physical conditions are driving gamma ray bursts.
Lead author Dr Eleonora Troja, of the University of Maryland, said:
“Gamma-ray bursts are catastrophic events, related to the explosion of massive stars 50 times the size of our sun. If you ranked all the explosions in the universe based on their power, GRBs would be right behind the Big Bang. In a matter of seconds, the process can emit as much energy as a star the size of our Sun would in its entire lifetime. We are very interested to learn how this is possible.”
Short-lived GRBs are intense flashes of high energy light detected by space-based telescopes orbiting above the Earth's atmosphere. But they have been hard to explain with standard explosion theories. Magnetic fields were suspected as being key but this was hard to prove since the explosions happen many millions of light years from Earth and are gone in seconds or minutes, never to repeat. Now using new, autonomous robotic telescopes the team were able to measure a special property of the light that probes magnetic fields - its polarization.
Co author Prof Mundell, world-leading expert in the technology, said:
“The origin and nature of magnetic fields is one of largest unsolved problems in modern astrophysics. GRBs are natural laboratories for extreme physics and the technique we use allows us to probe magnetic fields directly.”
The group's data suggest strong magnetic fields form close to the new black hole and drive energy and material outwards in a tightly focussed beam.
Prof Mundell said:
“We have shown previously using slower autonomous robotic telescopes that magnetic fields must be important and help to guide the material outwards at high speed but, until now, we were never fast enough to capture bright visible light at the same time as the high energy gamma rays produced during the explosion itself. There is intense debate about the nature of these high speed flows - how material can be accelerated to such high speeds, what physical mechanism produces the light that we catch with our high-energy satellites, and most of all, what, if anything, is the role and origin of magnetic fields.
Our results are important because they show that magnetic fields are present close to the central black hole, are threaded through the material that is ejected at ultra-high speeds in the explosion and ultimately focus and accelerate the material to large distances from the black hole.”
The study also suggests synchrotron radiation - which results when electrons are accelerated in a curved or spiral pathway - powers the initial, extremely bright phase of the burst, known as the 'prompt' phase. Until now there had been several other possible explanations but these results give a clearer picture of what physical conditions create GRBs.
Dr Troja said:
“Our study provides convincing evidence that the prompt GRB emission is driven by synchrotron radiation. This is an important achievement because, despite decades of investigation, the physical mechanism that drives GRBs had not yet been unambiguously identified.”
NASA's Fermi Gamma-ray Space Telescope first detected the gamma-ray emission from GRB160625B. Shortly afterwards, Russia's ground-based MASTER-IAC telescope in the Canary Islands followed up with optical light observations while the prompt phase was still active.
One light year is almost six trillion miles. A mass extinction on Earth 450 million years ago is believed to have been caused by a gamma ray burst in a nearby part of our galaxy.