So far, we have had only close calls from gamma ray explosions so large, scientists have suggested, that if they occurred within our solar neighborhood (less than 1,000 light years) they could potentially trigger mass extinctions on Earth.
Some 440 million years ago, reports Nature, a nearby gamma-ray burst may have extinguished much of life on Earth. Astrophysicist Adrian Melott, of the University of Kansas, and colleagues hypothesize that the fossil record of the end of the Ordovician period fits with how such a cosmic explosion a few thousand light years away could have altered the environment. At that time, more than 100 families of marine invertebrates died out; 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) looking in all wavelengths of light to learn more about a gamma ray burst reported by NASA’s Swift satellite thought to be an explosion from the collision of two neutron stars–the dead cores of massive stars, with the mass of our Sun crushed into the size of a small city.
Neutron Star Collision
When these neutron stars merge, the explosion is so powerful it can be seen from across the Universe. Astronomers suspect that up to one-third of all short gamma ray bursts come from merging neutron stars in globular clusters of old stars, blinding whole galaxies with high-energy radiation and destroying nearby worlds.
The colliding neutron stars exploded in less than a second (while the optical light can last for a matter of hours before fading) shining out in gamma rays which travelled undisturbed for 2.5 million years until hitting NASA’s Swift satellite, designed to solve the 35-year-old mystery of the origin of gamma-ray bursts, which scientists think are the birth cries of black holes. Within minutes, telescopes across the world were tracking it and an hour later people around the world were following it on Twitter.
“Typically the Universe moves slowly, with enormous galaxies swirling around in slow motion as measured by human standards and then just occasionally something will go bang and it’s a race against time to record and learn everything you can,” said Alan Duffy with the Swinburne University Center for Astrophysics.
The titanic GRB explosions create shock waves that travel at close to the speed of light into the surrounding gas which then glows at x-ray, optical, and radio wavelengths. Because the shocks are moving at nearly the speed of light, reported the Harvard Center for Astrophysics (CfA), Einstein’s theory of special relativity must be employed in 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 because of gravitational microlensing predicted by Einstein’s theory of general relativity will appear to an observer as a small ring that is expanding faster than the speed of light. The ring will appear small because of the enormous distance to the GRB –equivalent to spotting a wedding ring two million miles away; like seeing an “o” on this page from the Moon.”
“Earth-bound telescopes.” report the CfA, “are limited to about one arcsecond resolution by turbulence in our atmosphere. Better resolution is achieved in space, but the apparent size of the GRB shock is still more than 100000 times smaller than the Hubble Space Telescope resolution of 0.1 arcsecond.”
“The night sky seen in high-energy light is continuously flashing as titanic explosions, bright enough to be seen from across the length of the Universe, erupt and travel to us. It’s a violent world out there,” observed Duffy.
Much Closer to home –An object with a magnetic field one-thousand-trillion times stronger than our Sun’s
Fast forward to 4:42am U.S. Eastern Time on April 15, 2020 when a giant flare GRB swept past Mars, announcing itself to satellites, a spacecraft, and the International Space Station orbiting around our planet. And it lasted just 140 milliseconds, about the blink of an eye.
A research team at the University of Johannesburg led by Soebur Razzaque, a coordinator of the GRB and GW science group of the Fermi-Large Area Telescope (LAT) Collaboration, revealed that this giant GRB flare, 200415A, came from another possible source for short GRBs that was also very close to home, in cosmic terms. 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 gravity a billion times Earth’s and a magnetic field one-thousand-trillion times stronger than our Sun’s.
The Inter Planetary Network (IPN), a consortium of scientists, figured out that GRB 200415A exploded from a magnetar in galaxy NGC 253 about 11.4 million light years from earth toward the Sculptor constellation. All the previously known GRB’s were traced to supernovas or two neutron stars spiraling into each other. NGC 253 is outside our home, the Milky Way, but it is a mere 11.4 million light years from us. That is relatively close when talking about the nuclear destructive power of a giant GRB flare.
Milky Way Harbors Tens of Thousands of Neutron Stars
Previous detected GRBs came from relatively far away from our home galaxy the Milky Way. But this one was from much closer to home, in cosmic terms. “In the Milky Way there are tens of thousands of neutron stars,” says Razzaque. “Of those, only 30 are currently known to be magnetars.
“Even though gamma-ray bursts explode from a single star, we can detect them from very early in the history of the universe. Even 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.”
Source: High-energy emission from a magnetar giant flare in the Sculptor galaxy. Nature Astronomy (2021). DOI: 10.1038/s41550-020-01287-8
Image credit: NASA