Gamma ray bursts, as shown in this illustration, are the most powerful explosions in the universe. They expend most of their energy in gamma rays, light that is much more energetic than the visible light we can see with our eyes. Credit: NASA, ESA and M. Kornmesser
Rare Star’s Giant Gamma-Ray Burst GRB 204015A captured near our home system
The earth is blown most days by light short gamma ray bursts (GRBs). But sometimes a giant torch like GRB 200415A arrives at our galaxy and wipes out energy that dwarfs our sun. In fact, the most powerful explosions in the universe are gamma-ray bursts.
Now scientists have shown that GRB 200415A came from another possible source for short GRBs. It erupted from a very rare, powerful neutron star called a magnetar.
GRBs that were detected earlier come relatively far from our home system, the Milky Way. But this one was closer to home, in cosmic terms.
GRB explosions can disrupt the reception of the cell phone on earth, but it can also be messengers from the early history of the universe.
Another endgame
“Our sun is an ordinary star. If 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 much more massive than the sun play a different endgame,” says Prof Soebur Razzaque of the University of Johannesburg.
Razzaque leads a team that predicts GRB behavior for research conducted in Natural Astronomy on January 13, 2021.
‘When these massive stars die, they explode into a supernova. What remains after that is a very small, compact star that is small enough to fit in a valley of about 20 km (2 km). This star is called a neutron star. It is so dense that only a spoonful of it would weigh tons on earth, ‘he says.
It is these massive stars and what remains of them cause the biggest explosions in the universe.
On April 15, 2020, a giant wave of X-rays and gamma rays that lasted only a fraction of a second swept across the solar system, sending indicators on NASA and European spacecraft. The GRB 200415A event was a giant torch of a magnetar, a kind of neutron star in the city known for its strongest magnetic fields. Prof Soebur Razzaque of the University of Johannesburg tells what happens during a giant torch, 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 second
Scientists have known for some time that supernovae spray long GRBs, which burst for longer than two seconds. In 2017, they discovered that two neutron stars spiraling into each other could also give a short GRB. The 2017 eruption comes from a safe 130 million light-years from us.
But that could not explain any of the other GRBs that researchers could detect in our air almost daily.
It changed to Eastern Time on April 15, 2020 at 4:42 am US time.
On that day, a giant glow swept past GRB March. It announced itself to satellites, a spacecraft and the International Space Station orbiting our planet.
It was the first known giant torch since the launch of NASA’s Fermi Gamma ray telescope in 2008. And it lasted only 140 milliseconds, in the blink of an eye.
But this time, the orbiting telescopes and instruments captured more information about the giant glow GRB than the previous 16 years before.
Bursts from another source
The elusive cosmic visitor was named GRB 200415A. The Inter Planetary Network (IPN), a consortium of scientists, has determined where the giant flame came from. GRB 200415A explodes from a magnetar in the galaxy NGC 253, in the sculptor constellation, they say.
All the previously known GRBs have been detected after supernovae or two neutron stars spiraling into each other.
“There are tens of thousands of neutron stars in the Milky Way,” says Razzaque. ‘Of these, only 30 are currently known as magnetares.
“Magnets are up to a thousand times more magnetic than ordinary neutron stars. Most emit X-rays every now and then. But so far we only know a handful of magnets that have produced giant torches. The brightest we could detect was in 2004. Then GRB 200415A arrived in 2020. ”
Galaxy NGC 253 is outside our house, the Milky Way, but it is only 11.4 million light-years from us. This is relatively close when we talk about the nuclear braai power of a giant torch GRB.
A giant torch is so much more powerful than solar torches from our sun, it’s hard to imagine. Large solar flares from our sun sometimes disrupt the reception of the cell phone and power supplies.
The huge glow GRB in 2004 also interrupted communication networks.
Second wave hit for the first time
‘No two gamma ray bursts (GRBs) are ever the same, even if they happen in a similar way. And also no two magnets are the same. We are still trying to understand how stars end their lives and how these very energetic gamma rays are produced, says Razzaque.
“We have only had all the instruments in place for the past twenty years to detect these GRB events in different ways – in gravity waves, radio waves, visible light, X-rays and gamma rays. ”
“GRB 200415A was the first time that both the first and second explosions of a giant torch were observed,” he says.
Understand the second wave
In 2005, Razzaque predicted a first and second explosion during a giant torch.
For current research in Natural Astronomy, he led a team including Jonathan Granot of the Open University in Israel, Ramandeep Gill of George Washington University and Matthew Baring of Rice University.
They developed an updated theoretical model, or prediction, of what a second explosion in a giant torch GRB would look like. After 15 April 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 second, ”says Razzaque.
‘The second explosion occurred about 20 seconds after the first explosion and has much higher gamma ray energy than the first. It also took longer. We still need to understand what happens after a few hundred seconds. ‘
Deep time messengers
If the next giant glow GRB gets closer to our Milky Way, the Milky Way, a powerful radio telescope on the ground like MeerKAT in South Africa could possibly detect it, he says.
‘It would be an excellent opportunity to study the link between very high energy gamma ray emissions and radio waves in the second explosion. And that will tell us more about what does and does not work in our model. ”
The better we understand these volatile explosions, the better we can understand the universe in which we live.
A star that dies shortly after the start of the universe could disrupt the reception of the cell phone today.
‘Even though gamma-ray bursts burst from a single star, we can trace it from early in the history of the universe. Even returning to the universe was a few hundred million years old, ‘says Razzaque.
‘This is at a very early stage of the evolution of the universe. The stars that died then … we only now see their gamma-ray bursts, 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