Astronomers Observe Neutron Star Crash in Unexpected Environment

Using NASA’s Chandra X-ray Observatory and other telescopes, astronomers traced a short-lived gamma-ray burst event called GRB 230906A to a faint dwarf galaxy embedded in a vast flow of intergalactic gas. This discovery suggests that some neutron star mergers – violent collisions that forge heavy elements like gold and platinum – can occur far from the bright centers of galaxies, potentially explaining why some bursts appear to have no host galaxy.

GRB 230906A occurred in a tiny galaxy in a stream of gas about 4.7 billion light-years from Earth. Image credit: NASA / CXC / Penn State Univ / S. Dichiara / ESA / STScI / ERC BHianca 2026 / Fortuna and Dichiara, CC BY-NC-SA 4.0 / SAO / P. Edmonds.

Neutron stars are the cores left after a star much heavier than the Sun runs out of fuel, collapses in on itself, and then explodes.

They are small but slightly more massive than the Sun, making them surprisingly dense.

Astronomers consider them to be one of the most extreme objects in the Universe.

In recent years, they have collected data on the merger of two neutron stars within medium- and large-sized galaxies.

This latest discovery, however, shows that a neutron star collision could take place inside a tiny galaxy.

“Finding a neutron star collision where we did is a game-changer,” said Dr. Simone Dichiara, an astronomer at Penn State University.

“This could be the key to solving not one, but two important questions in astrophysics.”

The first puzzle that this unprecedented location for a neutron star collision can explain is the fact that gamma-ray bursts, which can be produced by the collapse of two neutron stars, sometimes do not appear at the heart of a galaxy, or a galaxy at all.

The other question this result could answer is how elements like gold and platinum were found in stars located at large distances from the centers of galaxies.

This neutron star collision is unexpectedly located in a tiny galaxy, about 4.7 billion light years away, embedded in a flow of gas that extends some 600,000 light years.

This flow was likely created when a group of galaxies collided hundreds of millions of years ago, removing gas and dust from the galaxies and leaving them in intergalactic space.

“We found a collision within a collision,” said Dr. Eleonora Troja, an astronomer at the University of Rome.

“The collision of galaxies triggered a wave of star formation that, over hundreds of millions of years, led to the birth and eventual collision of these neutron stars.”

To discover event GRB 230906A, which occurred on September 6, 2023, astronomers needed several NASA telescopes, including the Chandra X-ray Observatory, the Fermi Gamma-ray Space Telescope, the Neil Gehrels Swift Observatory and the Hubble Space Telescope.

Fermi discovered colliding neutron stars by capturing the distinctive signal of a gamma-ray burst burst, or GRB.

Having used the interplanetary network to determine a preliminary location of the Fermi Source, astronomers then needed the sharp vision of Chandra, Swift, and Hubble to pinpoint the object’s location more precisely.

NASA missions are part of a growing global network that monitors these changes to solve the mysteries of how the Universe works.

“The precise localization of Chandra’s X-rays made this study possible,” said Dr. Brendan O’Connor, a postdoctoral researcher at Carnegie Mellon University.

“Without this, we would not have been able to link the explosion to a specific source.”

“And once Chandra told us exactly where to look, Hubble’s extraordinary sensitivity revealed the tiny, extremely faint galaxy at that position.”

“We were only able to make this discovery after putting all the pieces together.”

This discovery could explain why some GRBs do not appear to have host galaxies.

This result implies that some host galaxies are too small and faint to be visible in most optical images from ground-based observatories.

GRB 230906A’s unusual location may also help explain how astronomers have spotted elements like gold and platinum in stars at relatively large distances from galaxies.

These stars are generally expected to be older and to have formed from gas that had less time to become enriched in heavy elements during supernova explosions.

Through a chain of nuclear reactions, a collision between two neutron stars can produce heavy elements like gold and platinum, which astronomers witnessed in a well-documented collision observed in 2017.

Events like GRB 230906A could generate elements like these and propagate them to the outskirts of galaxies, eventually appearing in future generations of stars.

Another explanation for the explosion is that it is in a much more distant galaxy, behind the group of galaxies.

“We consider this to be a less likely explanation than the idea of ​​a small galaxy,” the researchers said.

The discovery is reported in an article published in the Letters from astrophysical journals.

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S.Dichiara and others. 2026. A merger within a merger: Chandra identifies short GRB 230906A in a particular environment. ApJL 999, L42; doi: 10.3847/2041-8213/ae2a2f