So far, we’ve only had close calls of gamma-ray explosions so large that scientists have suggested that if they occurred within our solar environment (less than 1,000 light-years away), they could potentially trigger mass extinctions on Earth.
Some 440 million years ago, reports Nature, a nearby gamma-ray burst may have wiped out much of life on Earth. Astrophysicist Adrian Melott, of the University of Kansas, and colleagues hypothesize that the fossil record from the end of the Ordovician period fits with how such a cosmic explosion a few thousand light years away could have changed the environment. In that time, more than 100 families of marine invertebrates became extinct; it was the second most devastating mass extinction in our planet’s history.
GRB Rocks Andromeda
In 2014, telescopes around the world pointed to our neighboring Andromeda Galaxy (above) and looked into all wavelengths of light to learn more about a gamma-ray burst reported by NASA’s Swift satellite, believed to be an explosion of the collision of two neutron stars – the dead cores of massive stars, with the mass of our sun crushed to the size of a small city.
Neutron star collision
When these neutron stars merge, the explosion is so powerful that it can be seen from all over the universe. Astronomers suspect that up to a third of all short gamma-ray bursts come from merging neutron stars into globular clusters of old stars, blinding entire galaxies with high-energy radiation and destroying nearby worlds.
The colliding neutron stars exploded in less than a second (while the optical light can persist for several hours before fading) and radiated gamma rays that traveled undisturbed for 2.5 million years until they hit NASA’s Swift satellite, designed to support the 35-year-old — ancient mystery of the origin of gamma-ray bursts, which scientists believe are the birth cries of black holes. Within minutes, telescopes around the world were following it, and an hour later, people around the world were following it on Twitter.
“Usually the universe moves slowly, with huge galaxies whirling around in slow motion as measured by human standards, and then every now and then something pops and it’s a race against time to take it all in and learn,” said Alan Duffy with the Swinburne University Center for Astrophysics.
The giant GRB explosions create shock waves that travel at nearly the speed of light in the surrounding gas which then glows at X-ray, optical and radio wavelengths. Because the shocks move at nearly the speed of light, the Harvard Center for Astrophysics (CfA)must Einstein’s special theory of relativity be used when calculating what an observer would see.
“The GRB appeared as a small ring expanding faster than the speed of light”
“Contrary to common sense,” says the CfA, the relativistic shock due to gravitational microlensing predicted by Einstein’s general theory of relativity will appear to an observer as a small ring expanding faster than the speed of light. The ring will appear small due to its sheer distance from the GRB – equivalent to spotting a wedding ring two million miles away; like seeing an “o” on this page from the moon.”
“Earthbound Telescopes.” reports the CfA, “are limited to a resolution of about one arc second due to turbulence in our atmosphere. Better resolution is achieved in space, but the apparent magnitude of the GRB shock is still more than 100,000 times smaller than the Hubble Space Telescope’s resolution of 0.1 arc second.”
“The night sky, seen in high-energy light, flashes continuously as gigantic explosions, bright enough to be seen from the entire length of the Universe, erupt and travel toward us. It’s a violent world,” Duffy noted.
Much closer to home – An object with a magnetic field a thousand trillion times stronger than that of our sun
Fast forward to 4:42 a.m. US Eastern Time on April 15, 2020, when a giant eruption GRB swept past Mars, announcing itself to satellites, a spacecraft, and the International Space Station orbiting our planet. And it only took 140 milliseconds, about the blink of an eye.
A research team at the University of Johannesburg led by Soebur Razzaque, a coordinator of the Fermi-Large Area Telescope (LAT) Collaboration’s GRB and GW science group, revealed that this giant GRB outburst, 200415A, originated from another possible source. GRBs that was also very close to home from a cosmic point of view. It erupted from a rare, powerful neutron star called a magnetar, a type of young neutron star and the most magnetic objects in the universe, with a gravity a billion times that of Earth and a magnetic field a thousand trillion times stronger than that of our sun.
The Inter Planetary Network (IPN), a consortium of scientists, found that GRB 200415A exploded from a magnetar in galaxy NGC 253 about 11.4 million light-years from Earth toward the constellation Sculptor. All previously known GRBs have been traced to supernovas or two neutron stars merging into each other. NGC 253 is beyond our home, the Milky Way, but is only 11.4 million light-years away. That comes relatively close when we’re talking about the nuclear destructive power of a giant GRB flare.
Milky Way is home to tens of thousands of neutron stars
Previously detected GRBs came from relatively far away from our own galaxy, the Milky Way. But this one came from much closer to home, in cosmic terms. “There are tens of thousands of neutron stars in the Milky Way,” says Razzaque. “Of those, only 30 are currently known as magnetars.
“Even though gamma-ray bursts from a single star explode, we can detect them very early in the history of the universe. Even if we go back to when the universe was a few hundred million years old,” says Razzaque. “That is at an extremely early stage in the evolution of the universe. The stars that died then… we’re just now detecting their gamma-ray bursts, because light takes time to travel. This means that gamma-ray bursts can tell us more about how the universe is expanding and evolving over time.”
Source: High-energy emission from a giant magnetar burst in the Sculptor galaxy. Natural Astronomy (2021). DOI: 10.1038/s41550-020-01287-8
Image credit: Magnetar, Shutterstock license
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Maxwell Moe, astrophysicist, NASA Einstein Fellow, University of Arizona. Max can be found two nights a week investigating the mysteries of the universe at Kitt Peak National Observatory. Max received his PhD in astronomy from Harvard University in 2015.