Scientists have recorded millimeter-wavelength light from a fiery explosion caused by the merger of a neutron star with another star. The team also confirmed this flash of light to be one of the most energetic short-duration gamma-ray bursts ever observed, leaving behind one of the most luminous afterglows on record.
From: National Radio Astronomy Observatory
August 3, 2022 -- Scientists
using the Atacama Large Millimeter/submillimeter Array (ALMA) -- an
international observatory co-operated by the US National Science Foundation's
National Radio Astronomy Observatory (NRAO) -- have for the first time recorded
millimeter-wavelength light from a fiery explosion caused by the merger of a
neutron star with another star. The team also confirmed this flash of light to
be one of the most energetic short-duration gamma-ray bursts ever observed,
leaving behind one of the most luminous afterglows on record. The results of
the research will be published in an upcoming edition of The
Astrophysical Journal Letters.
Gamma-ray bursts (GRBs)
are the brightest and most energetic explosions in the Universe, capable of
emitting more energy in a matter of seconds than our Sun will emit during its
entire lifetime. GRB 211106A belongs to a GRB sub-class known as short-duration
gamma-ray bursts. These explosions -- which scientists believe are responsible
for the creation of the heaviest elements in the Universe, such as platinum and
gold -- result from the catastrophic 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 will soon commence
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."
A short-duration GRB
usually lasts only a few tenths of a second. Scientists then look for an
afterglow, an emission of light caused by the interaction of the jets with
surrounding gas. Even still, they're difficult to detect; only half-a-dozen
short-duration GRBs have been detected at radio wavelengths, and until now none
had been detected in millimeter wavelengths. Laskar, who led the research while
an Excellence Fellow at Radboud University in The Netherlands, said that the
difficulty is the immense distance to GRBs, and the technological capabilities
of telescopes. "Short-duration GRB afterglows are very luminous and
energetic. But these explosions take place in distant galaxies which means the
light from them can be quite faint for our telescopes on Earth. Before ALMA,
millimeter telescopes were not sensitive enough to detect these
afterglows."
At roughly 20 billion
light-years from Earth, GRB 211106A is no exception. The light from this
short-duration gamma-ray burst was so faint that while early X-ray observations
with NASA's Neil Gehrels Swift Observatory saw the explosion, the host galaxy
was undetectable at that wavelength, and scientists weren't able to determine
exactly where the explosion was coming from. "Afterglow light is essential
for figuring out which galaxy a burst comes from and for learning more about
the burst itself. Initially, when only the X-ray counterpart had been
discovered, astronomers thought that this burst might be coming from a nearby
galaxy," said Laskar, adding that a significant amount of dust in the area
also obscured the object from detection in optical observations with the Hubble
Space Telescope.
Each wavelength added a
new dimension to scientists' understanding of the GRB, and millimeter, in
particular, was critical to uncovering the truth about the burst. "The
Hubble observations revealed an unchanging field of galaxies. ALMA's
unparalleled sensitivity allowed us to pinpoint the location of the GRB in that
field with more precision, and it turned out to be in another faint galaxy,
which is further away. 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," said Laskar.
Wen-fai Fong, an
Assistant Professor of Physics and Astronomy at Northwestern University added,
"This short gamma-ray burst was the first time we tried to observe such an
event with ALMA. Afterglows for short bursts are very difficult to come by, so
it was spectacular to catch this event shining so bright. After many years of
observing these bursts, this surprising discovery opens up a new area of study,
as it motivates us to observe many more of these with ALMA, and other telescope
arrays, in the future."
Joe Pesce, National
Science Foundation Program Officer for NRAO/ALMA said, "These observations
are fantastic on many levels. They provide more information to help us
understand the enigmatic gamma-ray bursts (and neutron-star astrophysics in
general), and they demonstrate how important and complementary multi-wavelength
observations with space- and ground-based telescopes are in understanding
astrophysical phenomena."
And there's plenty of
work still to be done across multiple wavelengths, both with new GRBs and with
GRB 211106A, which could uncover additional surprises about these bursts.
"The study of short-duration GRBs requires the rapid coordination of
telescopes around the world and in space, operating at all wavelengths,"
said Edo Berger, Professor of Astronomy at Harvard University. "In the
case of GRB 211106A, we used some of the most powerful telescopes available --
ALMA, the National Science Foundation's Karl G. Jansky Very Large Array (VLA),
NASA's Chandra X-ray Observatory, and the Hubble Space Telescope. With the
now-operational James Webb Space Telescope (JWST), and future 20-40 meter
optical and radio telescopes such as the next generation VLA (ngVLA) we will be
able to produce a complete picture of these cataclysmic events and study them
at unprecedented distances."
Laskar added,
"With JWST, 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. With ngVLA, we will be able to
study the geometric structure of the afterglows and the star-forming fuel found
in their host environments in unprecedented detail. I am excited about these
upcoming discoveries in our field."
https://www.sciencedaily.com/releases/2022/08/220803093908.htm
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