Astronomers discover ancient, very distant gamma-ray burst

NASA’s Neil Gehrels Swift Observatory was peering through eons and eons in September 2021 when it spotted a dramatic explosion, a gamma-ray burst (GRB) that had gone off in the early universe.

The object now known as GRB210905A appears as it did when the universe was still young since its light took 12.8 billion years to reach Earth. Because the intense light of a gamma-ray burst fades quickly, as does its afterglow, astronomers rushed to capture what remained, which appeared as an orange-red dot, with the several instruments at the European Southern Observatory’s Very Large Telescope in Chile, including its X-Shooter spectrograph, as well as robotic telescopes at the La Silla Observatory also in Chile, according to a statement (opens in new tab) from the institution. 

Gamma radiation comes from certain types of particle collisions and from the nuclear decay of radioactive substances (which is one reason nuclear waste is so infamously dangerous). Astronomers think that bursts of these powerful electromagnetic rays flash in the darkness of space at least once a day, and GRBs are some of the most luminous phenomena out there, but they don’t hang around for long. 

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While GRBs are visible, astronomers are careful to measure how much light the burst is emitting at different wavelengths. Like all light sources in space, as wavelengths of light stretch across the void, the GRB’s signal shifts toward the red part of the spectrum. How much the signal changes, called redshift, reflects how far away the source is, with very distant signals often becoming infrared light.

While the human eye cannot see infrared light, an instrument like X-Shooter can, which is how researchers figured out the distance of this object and the length of time its light took to travel to Earth. Such distant objects are usually difficult to observe because they are often faint, but gamma-ray bursts like GRB210905A are tremendously bright and will show up if caught and imaged fast enough.

“Gamma-ray bursts [this distant] are rare events…but they are just a small part of a larger population that future proposed missions promise to uncover,” team lead Andrea Rossi, an astronomer at INAF Bologna in Italy, and his colleagues wrote in a study about the observations published Sept. 21 in the journal Astronomy and Astrophysics.

So where do these mysterious blasts of light come from? The researchers believe that the GRB got its luminous punch from material that was being pulled in by the gargantuan gravity of a black hole. Scientists ruled out the possibility that the signal came from a magnetar — the extremely compact dead core of a massive star with immense magnetic energy — because GRB210905A had too much energy for a magnetar to handle. 

The more that is demystified about gamma-ray bursts, the more could possibly be revealed about what the universe was like when it was young.

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