- Earth gets blasted by mild gamma ray bursts (GRBs) most days. But sometimes a giant flare GRB arrives at our galaxy, sweeping along energy that dwarfs our sun. The latest burst erupted from a rare, powerful neutron star called a magnetar.
- For the first time, a second explosion of such a magnetar burst was detected, and that data matched to a model developed by UJ researcher Prof Soebur Razzaque and others.
- The extreme explosions from these bursts can disrupt mobile phone reception but can also be messengers from the very early history of the universe, which the MEERKat radio telescope in South Africa can help decipher.
“Our sun is a very ordinary star. When it dies, it will get bigger and become a red giant star. After that it will collapse into a small compact star called a white dwarf.”
“But stars that are a lot more massive than the sun play a different end game,” says Prof Soebur Razzaque. He is Director at the Centre for Astro-Particle Physics (CAPP) at the University of Johannesburg.
Razzaque lead a team predicting gamma ray burst behaviour for research published in Nature Astronomy in January 2021.
“When these massive stars die, they explode into a supernova. What’s left after that is a very small compact star, small enough to fit in a city about 20km across. This star is called a neutron star, so dense that just a spoonful of it would weigh tons on earth,” he says.
It’s these massive stars and what’s left of them that cause the biggest explosions in the universe.
A telling split second
Scientists have known for a while that supernovas spout long GRB’s which last longer than two seconds. In 2017, they found out that two neutron stars spiralling into each other can also give off short GRB’s which last less than two seconds.
But that could not explain any of the other GRBs that researchers could detect in our sky on almost a daily basis.
This changed in a split of a second on 15 April 2020.
On that day, a giant flare GRB swept past Mars. It announced itself to satellites, a spacecraft and the International Space Station orbiting around our planet. NASA’s Fermi LAT telescope and other instruments gathered lots of data about it.
The elusive cosmic visitor lasted just 140 milliseconds, about the blink of an eye, and was named GRB 200415A.
Bursts from another source
All the previously known gamma ray bursts were traced to supernovas or two neutron stars spiralling into each other.
“In the Milky Way there are tens of thousands of neutron stars,” says Razzaque. “Of those, only 30 are currently known to be magnetars.
“Magnetars are up to a thousand times more magnetic than ordinary neutron stars. Most emit X-rays every now and then. But so far, we know of only a handful of magnetars that produced giant flares. The brightest we could detect was in 2004. Then GRB 200415A arrived in 2020.”
A giant flare is so much more powerful than solar flares from our sun, it’s hard to imagine. Large solar flares from our sun disrupt cell phone reception and power grids sometimes.
Second wave nabbed for the first time
In 2005 research, Razzaque predicted a second explosion during a giant flare.
For the current research in Nature Astronomy, he headed a team that developed an updated theoretical mode for the second explosion.
“No two gamma-ray bursts (GRBs) are ever the same, even if they happen in a similar way. We’re still trying to understand how stars end their life and how these very energetic gamma rays are produced,” says Razzaque.
“GRB 200415A was the first time ever that both the first and second explosions of a giant flare were detected,” he says.
Messengers about deep time
If the next giant flare GRB happens closer to our home galaxy the Milky Way, a powerful radio telescope on the ground such as MeerKAT in South Africa, may be able to detect it, he says.
“That would be an excellent opportunity to study the relationship between very high energy gamma-ray emissions and radio wave emissions in the second explosion.”
The better we understand these fleeting explosions, the better we may understand the universe we live in. A star dying soon after the beginning of the universe could be disrupting cell phone reception today.
“We can detect gamma-ray bursts going back to when the universe was a few hundred million years old,” says Razzaque.
“That is at an extremely early stage of the evolution of the universe. The stars that died at that time… we are only detecting their gamma-ray bursts now, because light takes time to travel.”
“This means that gamma-ray bursts can tell us more about how the universe expands and evolves over time.”
