Colliding dead stars create one of the largest explosions ever seen

When two dead stars were thrown from their host galaxy, it was one of the largest interstellar collisions ever seen.

After it was first discovered in March 2023, follow-up observations have now revealed that the event was a kilonova, which led to the creation of some of the rarest elements in the universe.

The burst, now known as GRB 230307A, was first observed as a wave of gamma rays by the Fermi Gamma-ray Burst Monitor.

It was the second most powerful burst ever recorded, approximately 1,000 times brighter than most gamma-ray bursts, and lasted a minute rather than the usual two seconds.

The world’s premier telescopes raced to track the event, which found it appeared 120,000 light-years away from the nearest galaxy, suggesting the stars responsible were thrown from their original home.

The super-bright outburst GRB 230307A appears to be a rare collision of two neutron stars, each ejected from their home galaxy. Credit: NASA/ESA/CSA/STScI Andrew Lewan (IMAPP/Warw)

Kilonova explained

The burst GRB 230307A followed the telltale signature of a kilonova.

A kilonova occurs when a neutron star — a stellar remnant, the mass of the Sun packed into a space the size of a city — collides with another neutron star or black hole.

„They expand and cool quickly, and the peak of their light moves quickly from the optical to the infrared,” said Danny Steeks of the University of Warwick, who participated in the study.

Observations by the James Webb Space Telescope yielded evidence of tellurium, an element even rarer than platinum.

While elements lighter than iron are forged within the hearts of living stars, heavier elements such as tellurium can only be produced in the extreme stages of such stellar explosions.

„This is an important next step in our understanding of the role that binary neutron star mergers play in filling out the molecular periodic table,” says Steegs.

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„It’s been 150 years since we first wrote the periodic table,” said Andrew Lewan of Radbot University in the Netherlands, who led the study.

„Thanks to KiloNova and new technology, we’re finally filling in the last blanks about where everything was made.”

Observing the eruption from Mars

Artist's impression of the Mars Odyssey orbiter that discovered GRB 230307A.  Credit: NASA/JPL-Caltech
Artist’s impression of the Mars Odyssey orbiter that discovered GRB 230307A. Credit: NASA/JPL-Caltech

The initial detection of GRB 230307A came from instruments observing the entire sky, but tracking the burst’s precise position meant combining observations from multiple telescopes.

In this case, crucial help came from an unlikely source.

Mars Odyssey, which reached the Red Planet in 2001, is a gamma-ray detector designed to search for carbon-like elements in the Martian atmosphere.

It also happens to pick up bright bursts of gamma rays from further afield – and this is what GRB 230307A was discovered to be.

That is, much of what we know about the most violent events in the universe depends on an aging Martian spacecraft—a beautiful example of interplanetary cooperation.

www.warwick.ac.uk

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