This artist's impression shows a kilonova produced by two colliding
neutron stars. While studying the aftermath of a long gamma-ray burst
(GRB), two independent teams of astronomers using a host of telescopes
in space and on Earth, including the Gemini North telescope on Hawai‘i
and the Gemini South telescope in Chile, have uncovered the unexpected
hallmarks of a kilonova, the colossal explosion triggered by colliding
neutron stars. Credit: NOIRLab/NSF/AURA/J. da Silva/Spaceengine. download Large JPEG
This Gemini North image, superimposed on an image taken with the Hubble Space Telescope, shows the telltale near-infrared afterglow of a kilonova produced by a long GRB (GRB 211211A). This discovery challenges the prevailing theory that long GRBs exclusively come from supernovae, the end-of-life explosions of massive stars. Credit: International Gemini Observatory/NOIRLab/NSF/AURA/M. Zamani; NASA/ESA. download Large JPEG
This Gemini North image, superimposed on an image taken with the
Hubble Space Telescope, shows the telltale near-infrared afterglow of a
kilonova produced by a long GRB (GRB 211211A). This discovery challenges
the prevailing theory that long GRBs exclusively come from supernovae,
the end-of-life explosions of massive stars. Credit: International Gemini Observatory/NOIRLab/NSF/AURA/M. Zamani; NASA/ESA. download Large JPEG
Cosmoview Episode 58: Kilonova Discovery Challenges our Understanding of
Gamma-Ray Bursts. While studying the aftermath of a long gamma-ray
burst (GRB), two independent teams of astronomers using a host of
telescopes in space and on Earth, including the Gemini North telescope
on Hawai‘i and the Gemini South telescope in Chile, have uncovered the
unexpected hallmarks of a kilonova, the colossal explosion triggered by
colliding neutron stars. This discovery challenges the prevailing theory
that long GRBs exclusively come from supernovae, the end-of-life
explosions of massive stars. Credit: Images and Videos: International
Gemini Observatory/NOIRLab/NSF/AURA, Fermilab, M. Zamani, NASA/ESA, J.
da Silva/Spaceengine, CI Lab, N. Bartmann Music: Written and performed
by STAN DART Video
Kilonova Discovery Challenges our Understanding of Gamma-Ray Bursts.
Interview with Eleonora Troja, astronomer at the University of Rome Tor Vergata. Video
Kilonova Discovery Challenges our Understanding of Gamma-Ray Bursts.
Interview with Jillian Rastinejad, PhD student at Northwestern
University. Video
Interview with Eleonora Troja, astronomer at the University of Rome Tor Vergata. Video
International Gemini Observatory probes aftermath of gamma-ray burst and uncovers surprising evidence of colliding neutron stars
While studying the aftermath of a long gamma-ray burst (GRB),
two independent teams of astronomers using a host of telescopes in
space and on Earth, including the Gemini North telescope on Hawai‘i and
the Gemini South telescope in Chile, have uncovered the unexpected
hallmarks of a kilonova, the colossal explosion triggered by colliding
neutron stars. This discovery challenges the prevailing theory that long
GRBs exclusively come from supernovae, the end-of-life explosions of
massive stars.
Gamma-ray bursts
(GRBs) — the most energetic explosions in the Universe — come in two
varieties, long and short. Long GRBs, which last a couple of seconds to
one minute, form when a star at least 10 times the mass of our Sun
explodes as a supernova. Short GRBs, which last less than two seconds, occur when two compact objects, like two neutron stars or a neutron star and a black hole, collide to form a kilonova
While observing the aftermath of a long GRB detected in 2021, two
independent teams of astronomers found the surprising signs of a
neutron-star merger rather than the expected signal of a supernova. This
surprising result marks the first time that a kilonova has been
associated with a long GRB and challenges our understanding of these
phenomenally powerful explosions.
The first team to announce this discovery was led by Jillian
Rastinejad, a PhD student at Northwestern University. Rastinejad and her
colleagues made this startling discovery with the help of Gemini North, part of the International Gemini Observatory, which is operated by NSF’s NOIRLab.
The Gemini North observations revealed a telltale near-infrared
afterglow at the precise location of the GRB, providing the first
compelling evidence of a kilonova associated with this event [1].
Rastinejad’s team promptly reported their Gemini detection in a Gamma-ray Coordinates Network (GCN) Circular.
Astronomers around the world were first alerted to this burst, named
GRB 211211A, when a powerful flash of gamma rays was picked up by NASA's
Neil Gehrels Swift Observatory and Fermi Gamma-ray Space Telescope. Initial observations revealed that the GRB was uncommonly nearby, a mere one billion light-years from Earth.
Most GRBs originate in the distant, early Universe. Typically, these
objects are so ancient and far flung that their light would have had to
travel for more than six billion years to reach Earth. Light from the
most-distant GRB ever recorded traveled for nearly 13 billion years
before being detected here on Earth [2]. The relative proximity of this
newly discovered GRB enabled astronomers to make remarkably detailed
follow-up studies with a variety of ground- and space-based telescopes.
“Astronomers usually investigate short GRBs when hunting for kilonovae,” said Rastinejad. “We
were drawn to this longer-duration burst because it was so close that
we could study it in detail. Its gamma rays also resembled those of a
previous, mysterious supernova-less long GRB.”
A unique observational signature of kilonovae is their brightness at
near-infrared wavelengths compared to their brightness in visible light.
This difference in brightness is due to the heavy elements ejected by
the kilonova, which effectively block visible light but allow the
longer-wavelength infrared light to pass unimpeded. Observing in the
near-infrared, however, is technically challenging and only a handful of
telescopes on Earth, like the twin Gemini telescopes, are sensitive
enough to detect this kilonova at these wavelengths.
“Thanks to its sensitivity and our rapid-response, Gemini was the
first to detect this kilonova in the near-infrared, convincing us that
we were observing a neutron-star merger,” said Rastinejad. “Gemini’s
nimble capabilities and variety of instruments let us tailor each
night’s observing plan based on the previous night’s results, allowing
us to make the most of every minute that our target was observable.”
Another team, led by Eleonora Troja, an astronomer at the University
of Rome Tor Vergata, independently studied the afterglow using a
different and a different series of observations, including the Gemini South telescope in Chile, [3] and independently concluded that the long GRB came from a kilonova.
”We were able to observe this event only because it was so close to us,” said Troja. “It
is very rare that we observe such powerful explosions in our cosmic
backyard, and every time we do we learn about the most extreme objects
in the Universe.”
The fact that two different teams of scientists working with
independent datasets both arrived at the same conclusion about the
kilonova nature of this GRB provides confidence in this interpretation.
“The kilonova interpretation was so far off from everything we
knew about long GRBs that we could not believe our own eyes and spent
months testing all the other possibilities,” said Troja. “It is only after ruling out everything else that we realized our decade-long paradigm had to be revised.”
As well as contributing to our understanding of kilonovae and GRBs,
this discovery provides astronomers with a new way to study the
formation of gold and other heavy elements in the Universe. The extreme
physical conditions in kilonovae produce heavy elements such as gold,
platinum, and thorium. Astronomers can now identify the sites that are
creating heavy elements by searching for the signature of a kilonova
following a long-duration gamma-ray burst.
“This discovery is a clear reminder that the Universe is never fully figured out,” said Rastinejad. “Astronomers
often take it for granted that the origins of GRBs can be identified by
how long the GRBs are, but this discovery shows us there’s still much
more to understand about these amazing events.”
“NSF congratulates the science teams for this new and exciting discovery, opening a new window onto cosmic evolution,” said National Science Foundation Director Sethuraman Panchanathan. “The
International Gemini Observatory continues to deliver powerful and
nimble resources open to the whole scientific community through
innovation and partnership.”
The International Gemini Observatory is operated by a partnership of six countries, including the United States through the National Science Foundation, Canada through the National Research Council of Canada, Chile through the Agencia Nacional de Investigación y Desarrollo, Brazil through the Ministério da Ciência, Tecnologia e Inovações, Argentina through the Ministerio de Ciencia, Tecnología e Innovación, and Korea through the Korea Astronomy and Space Science Institute.
These Participants and the University of Hawaii, which has regular
access to Gemini, each maintain a National Gemini Office to support
their local users.
Note
[1] Rastinejad and her colleagues made initial follow-up observations of the burst using the Nordic Optical Telescope. Following the critical Gemini North observations, they continued their observations of the fading kilonova with the Karl G. Jansky Very Large Array, the Calar Alto Observatory, and the MMT Observatory, and obtained later observations with the Large Binocular Telescope, the W. M. Keck Observatory, the Gran Telescopio Canarias, and the NASA/ESA Hubble Space Telescope.
[2] Light that has traveled nearly 13 billion years to reach Earth
would have a redshift (z) of about 7. Due to the accelerating expansion
of the Universe, that would roughly equate to a distance of 24.5 billion
light-years today. When talking about large redshifts, those greater
than 1, and cosmically distant objects, it is more accurate to state how
many billions of years the light has traveled rather than a distance in
light-years.
[3] Troja and her colleagues initially observed the afterglow of this event with the Devasthal Optical Telescope, the Multicolor Imaging Telescopes for Survey and Monstrous Explosions, and the Calar Alto Observatory. They obtained observations of the host galaxy with the NASA/ESA Hubble Space Telescope.
Links
- Research paper 1 (will appear after embargo time)
- Research paper 2 (will appear after embargo time)
- Images of the Gemini North telescope
- Videos of the Gemini North telescope
- Images of the Gemini South telescope
- Videos of the Gemini South telescope
Contacts:
Jillian Rastinejad
Northwestern University
Email:jillianrastinejad2024@u.northwestern.edu
Eleonora Troja
Astronomer
University of Rome Tor Vergata
Email:eleonora.troja@uniroma2.it
Charles Blue
Public Information Officer
NSF’s NOIRLab
Tel: +1 202 236 6324
Email:charles.blue@noirlab.edu
Source: Gemini Observatory
