In 2023, astronomers using NASA’s Chandra X-ray Observatory and the Hubble Space Telescope observed an unusual array of short gamma-ray bursts that appear to have originated from the collision of two neutron stars. Follow-up observations allowed the team to pinpoint the approximate location of the signal’s source: a distant galaxy several billion light years away. And as far as they could tell, the galaxy seemed small for something that hosted such a powerful signal. An analysis of the discovery was recently published in The Astrophysical Journal Letters.
“Where we detected a neutron star collision is game-changing,” Simon DiChiara, an astrophysicist at Penn State University and lead author of the study, said in a NASA statement. “This could be the key to unlocking not one, but two important questions in astrophysics.”
peering into space
One of these two questions refers to gamma-ray bursts that clearly do not emanate from the core of a galaxy – where star formation is most active – or, indeed, not from any galaxy at all. The signal, called GRB 230906A, implies that these rogue gamma-ray bursts literally outshine their hosts, such that ground-based observatories are not able to sense even smaller, fainter galactic hosts.
Accordingly, when studying gamma-ray bursts, “an accurate X-ray position is critical to identifying a candidate gamma-ray burst host galaxy that would otherwise be missed or incorrectly assigned,” the team notes in the paper. The researchers also considered the possibility that the galaxy was simply In fact Far away, not necessarily small, but that was the “least likely explanation,” he said in the statement.
The team’s investigation also identified a stream of gas emanating from the host galaxy – about six times longer than the full width of the galaxy. This “tidal tail” probably formed through the gravitational tug-of-war between galaxies over hundreds of millions of years.
“The gamma-ray burst occurred directly within one of these tidal streams, suggesting that it occurred inside a small dwarf galaxy composed of material stripped from its host during a galaxy collision,” DiChiara and study co-author Eleonora Troja, an astronomer at the University of Rome in Italy, wrote in a column on the findings for The Conversation.
creation from destruction
The second question is how heavy elements emerge in stars located far from the center of galaxies. Chain fusion reactions within the most massive stars produce heavy elements such as iron. When these massive stars explode supernova and leave behind a core with a mass about three times smaller than that of the Sun, a neutron star is born.
According to the US Department of Energy, these extremely dense stars are considered one of the major sources of heavy elements like gold and uranium in the universe. The researchers explained that events like GRB230906A – the explosion of these densely packed elements – could essentially scatter the heavier elements to the outskirts of the galaxy, where a future star could capture the elements for itself.
“We got a rare glimpse of how destruction can be a catalyst for creation,” Jane Charlton, the study’s senior author and Penn State astrophysicist, said in a university statement. “The heavy elements in our bodies, for example iron, come from about 10,000 stars that were in our galaxy and died. It took billions of years, but that iron remained on Earth, and as our bodies formed and evolved, they used that material.”
And the similarities could easily continue into our galaxy’s distant future, he said.
“There is a neighboring galaxy to our own galaxy, the Andromeda Galaxy, and four or five billion years from now, it will merge into the Milky Way,” he thought. “The same thing could happen, and tidal tails would form, which would pick up heavier elements and enrich the universe.”
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