Rare star giant gamma-ray burst GRB 204015A captured close to our home galaxy
The earth is blown up by mild short gamma ray bursts (GRBs) most days. But sometimes a giant flare like GRB 200415A arrives at our galaxy sweeping along energy dwarfing our sun. In fact, the most powerful explosions in the universe are gamma-ray bursts.
Now, researchers have shown that GRB 200415A came from another possible source for short GRBs. It broke out of a very rare, powerful one neutron star called a magnetar.
Previously discovered GRBs came from relatively far away from our home galaxy The Milky Way. But this one was much closer to home, in cosmic terms.
GRB explosions can disrupt cell phone reception on Earth, but they can also be messengers from the very early history of the universe.
“Our sun is a very common star. When it dies, it gets bigger and becomes a red giant star. Then it collapses into a small compact star called a white dwarf.
“But stars that are much more massive than the sun play a different endgame,” says Prof Soebur Razzaque of University of Johannesburg.
Razzaque leads a team that predicts GRB behavior for research published in Natural astronomy January 13, 2021.
“When these massive stars die, they explode in a supernova. What’s left after that is a very small compact star, small enough to fit in a valley approx. 20 km over. This star is called a neutron star. It is so dense that just a spoonful of it would weigh tons on the ground, ”he says.
It is these massive stars and what is left of them that are causing the biggest explosions in the universe.
On April 15, 2020, a huge wave of X-rays and gamma rays, lasting only a fraction of a second, swept over the solar system and triggered detectors on NASA and European spacecraft. The GRB 200415A event was a giant glare from a magnetar, a type of city-size neutron star that boasts the strongest known magnetic fields. Prof Soebur Razzaque from the University of Johannesburg shares what happens during a giant flare-up and how these powerful explosions can tell us more about the history of the universe. Animation credit: NASA’s Goddard Space Flight Center / Chris Smith (USRA / GESTAR). Video credit: Therese van Wyk, University of Johannesburg.
A talking split second
Scientists have long known that supernovae spray long GRBs that explode for longer than two seconds. In 2017, they found that two neutron stars sprouting into each other can also emit a short GRB. The 2017 burst came from safe 130 million light-years away from us.
But that could not explain any of the other GRBs that scientists could discover in our skies almost daily.
This changed in a split second at. 04.42 US Eastern Time on April 15, 2020.
That day a huge flare GRB swept past March. It advertised itself for satellites, a spacecraft and the International Space Station orbiting our planet.
It was the first known giant flare since the 2008 launch of NASA’s Fermi Gamma-ray space telescope. And it lasted only 140 milliseconds, almost a moment’s blink.
But this time, the orbiting telescopes and instruments captured far more data about the giant flare GRB than the previous one, which was discovered 16 years earlier.
Bursts from another source
The elusive cosmic visitor was named GRB 200415A. The Inter Planetary Network (IPN), a consortium of scientists, found out where the giant flare came from. GRB 200415A exploded from a magnetar in the galaxy NGC 253, in the sculptor constellation, they say.
All the previously known GRBs were traced to supernovae or two neutron stars that sprouted into each other.
“In the Milky Way, there are tens of thousands of neutron stars,” says Razzaque. “Of these, only 30 are currently known to be magnetars.
“Magnets are up to a thousand times more magnetic than ordinary neutron stars. Most people emit X-rays every now and then. But so far, we only know a handful of magnetars that produced giant flares. The brightest we could detect was in 2004. Then GRB 200415A arrived in 2020. ”
Galaxy NGC 253 is outside our home, the Milky Way, but it is only 11.4 million light-years from us. It’s relatively close when we talk about the nuclear power of a giant flare GRB.
A giant flare is so much more powerful than the sun’s rays from our sun, it’s hard to imagine. Large sunbeams from our sun sometimes interfere with cell phone reception and power grids.
The giant flare GRB in 2004 also disrupted communications networks.
Second wave nabbed for the first time
“No gamma-ray bursts (GRBs) are ever the same, even if they happen in a similar way. And no two magnets are alike. We are still trying to understand how stars end their lives and how these very energetic gamma rays are produced, Razzaque says.
“It is only within the last 20 years that we have all the instruments to detect these GRB events in many different ways – in gravitational waves, radio waves, visible light, X-rays and gamma rays. ”
“GRB 200415A was the first time ever that both the first and second explosions of a giant flare were detected,” he says.
Understanding the second wave
In 2005 research, Razzaque predicted a first and second explosion during a giant flare.
For current research in Natural astronomy, he led a team including Jonathan Granot from Open University in Israel, Ramandeep Gill from George Washington University and Matthew Baring from Rice University.
They developed an updated theoretical model or prediction of what another explosion in a giant flare GRB would look like. After April 15, 2020, they were able to compare their model with data measured from GRB 200415A.
The data from the Fermi Gamma-ray Burst Monitor (Fermi GBM) tells us about the first explosion. Data from the Fermi Large Area Telescope (Fermi LAT) tell us about the other, ”says Razzaque.
“The second explosion occurred about 20 seconds after the first and has much higher gamma ray energy than the first. It also lasted longer. However, we still need to understand what happens after a few hundred seconds. ”
Messengers of deep time
If the next giant flare GRB happens closer to our home galaxy the Milky Way, a powerful radio telescope on Earth like MeerKAT in South Africa might detect it, he says.
“It would be an excellent opportunity to study the relationship between very high energy gamma ray emissions and radio wave emissions in the second explosion. And it tells us more about what works and does not work in our model. ”
The better we understand these volatile explosions, the better we can understand the universe we live in.
A star that dies shortly after the beginning of the universe could disrupt cell phone reception today.
“Even though gamma-ray bursts explode from a single star, we can detect them very early in the history of the universe. Even going back to when the universe was a few hundred million years old, ”says Razzaque.
“It is at an extremely early stage of the evolution of the universe. The stars that died at that time … we only detect 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.”
Reference: January 13, 2021, Natural astronomy.
DOI: 10.1038 / s41550-020-01287-8