Scientists capture the first-ever millimeter light observation of an explosive neutron star merger

The ALMA telescope array is sensitive enough to detect the faint afterglows of these cataclysmic events.
Chris Young
Neutron star merger
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  • Scientists detected the first-ever millimeter light observation of a short-duration gamma-ray burst (GRB).
  • They used the Atacama Large Millimeter/submillimeter Array (ALMA) to detect the event.
  • James Webb will soon help to shed new light on the same region of space.

Scientists used the Atacama Large Millimeter/submillimeter Array (ALMA), operated in part by the U.S. National Science Foundation’s National Radio Astronomy Observatory (NRAO), to record the first-ever millimeter-wavelength light from the fiery merger of a neutron star with another star.

The team confirmed the flash of light in their observation to be one of the most energetic short-duration gamma-ray bursts in the history of astronomical observations, a press statement reveals.

Their research, outlined in a paper in an upcoming edition of The Astrophysical Journal Letters, also highlights how the explosion left behind one of the most luminous afterglows on record.

Short-duration GRBs emit more energy than the Sun over its entire lifetime

Gamma-ray bursts (GRBs) are thought to be the brightest and most energetic explosions in the observable universe. They are so powerful that they can emit more energy in mere seconds than our Sun is capable of emitting in its entire lifetime.

GRB 211106A is part of a GRB sub-class called a short-duration gamma-ray burst. This type of explosion is believed to be responsible for the creation of the heaviest elements in the universe, including platinum and gold. They result from the collision and merger of binary star systems containing a neutron star.

“These mergers occur because of gravitational wave radiation that removes energy from the orbit of the binary stars, causing the stars to spiral in toward each other,” said Tanmoy Laskar, who is set to start work as an Assistant Professor of Physics and Astronomy at the University of Utah. “The resulting explosion is accompanied by jets moving at close to the speed of light. When one of these jets is pointed at Earth, we observe a short pulse of gamma-ray radiation or a short-duration GRB.”

Short-duration GRBs usually only last a few tenths of a second, but scientists are able to detect them thanks to the afterglow they leave behind. This is caused by the interaction of the jets with the surrounding gas. Even with the afterglow, they are still hard to detect and less than ten short-duration GRBs have been detected at radio wavelengths. The new observation is the first-ever short-duration GRB to be detected in millimeter wavelengths.

ALMA: Detecting what was once undetectable

The new observation target, GRB 211106A, is roughly 20 billion light-years from Earth. When it was first observed by NASA's X-ray Neil Gehrels Swift Observatory, the host galaxy was undetectable. Using ALMA's incredibly sensitive instruments, however, the researchers were able to shed new light on the violent merger. "ALMA’s unparalleled sensitivity allowed us to pinpoint the location of the GRB [...] with more precision, and it turned out to be in another faint galaxy, which is further away [than previously thought]," said Laskar. "That, in turn, means that this short-duration gamma-ray burst is even more powerful than we first thought, making it one of the most luminous and energetic on record."

Before ALMA, millimeter telescopes weren't sensitive enough to detect the incredibly faint afterglows of short-duration GRBs. The telescope array was also recently used to detect the (at the time) most distant spiral galaxy ever observed and also shed new light on early galaxy formation.

The researchers say this new observation motivates them to look for more faint traces of violent collisions using the telescope array located in the Atacama Desert of northern Chile. As Laskar points out, James Webb will also help to understand short-duration GRBs better. "With JWST," he said, "We can now take a spectrum of the host galaxy and easily know the distance, and in the future, we could also use JWST to capture infrared afterglows and study their chemical composition."

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