Astronomers have solved the mystery of where galactic gamma-ray bursts come from
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Image: NASA JPL/CalTech

Bursts of gamma rays that come from active galaxies have long been mysterious to astronomers - they’re one of the brightest electromagnetic phenomena known to occur in the universe, but no one has been able to work out where they originate.

Now an international team of scientists led out of Bonn’s Max Planck Institute for Radio Astronomy believe they’ve found the answer - and it’s located right outside a supermassive black hole.

This type of gamma-rays burst - not to be confused with the one emitted by supernovae - erupt from compact galaxy centres, or nuclei, known as blazars.

As Benjamin Pope, an astronomer from Oxford University in the UK, explains to ScienceAlert: "Blazars are the most compact and brightest sort of quasar - supermassive black holes at the centres of galaxies, 'blazing' with a jet of radiation."

In fact, blazars are among the largest and most energetic objects in the universe. 

"Blazars are known to have bright outbursts in which they give off radiation all the way from radio waves to gamma rays," says Pope. But, until now, scientists weren't sure whether the gamma-ray bursts and the other waves were being emitted from the same place.

By combining data from three of the world’s most advanced single-dish radio observatories, the scientists have now determined that gamma-ray bursts do indeed originate from right near the base of the jet, very close to the supermassive black hole.

"This new work studies the correlation in time between the radio waves and gamma rays, and provides evidence that these are produced from supersonic shocks running down this jet," says Pope.

This is something that scientists had suspected since the 1990s, a press release explains, but it’s the first time they've been able to prove it.

Interestingly, the study found the radio outbursts arrived at their telescopes around six or seven days after the gamma rays

“For the first time we see that the radio delays become smoothly smaller towards higher radio frequencies," Emmanouil Angelakis from the Max Planck Institute for Radio Astronomy says in the press release. “This tells us that the gamma-ray photons are coming from the innermost radio emitting jet regions.”

There’s still a lot left to figure out about these galactic gamma-ray busts, but this is an exciting first step.