Gamma-ray bursts are extremely energetic explosions caused by some of the cosmos’ most remarkable objects: black holes, neutron stars, and the violent deaths of stars. Now, astronomers have found evidence of gamma-ray bursts emerging from the collisions of stars.
The evidence was found using observations made by the Gemini South telescope in Chile (which is operated by the National Science Foundation’s NOIRLab), the Nordic Optical Telescope, and the Hubble Space Telescope.
The telescopes were following up on a gamma-ray burst spotted by NASA’s Swift Observatory in 2019; affectionately named GRB 191019A, the long gamma-ray burst lasted for a little over a minute, and using Gemini South a team of astronomers made longer term observations of it.
They managed to determine the burst’s origin — about 100 light-years out from the core of an ancient galaxy — and based on that observation, determine the source of the burst. The team’s research was published last week in Nature Astronomy.
“Our follow-up observation told us that rather than being a massive star collapsing, the burst was most likely caused by the merger of two compact objects,” said Andrew Levan, an astronomer at Radboud University and the study’s lead author, in a NOIRLab release. “By pinpointing its location to the centre of a previously identified ancient galaxy, we had the first tantalising evidence of a new pathway for stars to meet their demise.”
Because the galaxy is so ancient — it’s at a z-shift of .248, or nearly 3.26 billion light-years away — most stars massive enough to die in gamma-ray-producing supernovae in the region are long dead. The researchers sifted through the data for a supernova that would have accompanied the blast, but their search turned up zilch.
But the galaxy’s core is filled with smaller stars and dense remnants of the massive stars. Thus, the researchers’ suggestion: two of these stellar objects collided near the galactic centre, and the crash was violent enough to produce its own gamma-ray burst.
According to the NOIRLab release, though regions near the galactic centre are crowded with objects like those that caused the recently observed burst, the gas and dust spread throughout the galaxy (and others like it) may shroud such events from view. It’s an issue that may be helped by cutting-edge observatories like the Webb Space Telescope, whose infrared instruments can cut through gas and dust in the cosmos to see more intimate phenomena, like regions of stellar birth.
Like Webb, gamma-ray bursts are themselves having a moment. Last year, astronomers detected the brightest burst yet seen (known as the Brightest of All Time, or the BOAT), and follow-up observations of the rocking blast have shed light on the jets the bursts produce.
The research team hopes to match a gamma-ray burst like GRB 191019A with gravitational waves, which would be found using a detector like LIGO. Meanwhile, the Rubin Observatory’s LSST camera — the largest digital camera ever built — will soon take sweeping images of the cosmos and produce near-real-time alerts when fleeting phenomena, like gamma-ray bursts, occur.
Moving quickly to take data on such momentary events will help astronomers improve their compendia of gamma-ray bursts, supernovae, and other momentarily brilliant cosmic events.
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