· For the first time, the JWST has observed the rare merger of two dense neutron stars (known as a kilonova) – in a spiral galaxy a billion light years away

· These neutron stars were kicked out of their host galaxy and travelled the equivalent of the Milky Way galaxy’s diameter before merging several hundred million years later

· Kilonovae are so energetic they eject material and create some of the heaviest elements in the periodic table – in this case, tellurium and elements essential to life

For the first time, the James Webb Space Telescope (JWST) has observed the merger of two stars known as a kilonova.

Kilonovae are explosions produced by a dense and compact star (called a neutron star) merging with either a black hole or with another neutron star. Such mergers are energetic enough to throw out material, creating new atomic nuclei (the centres of atoms) – in a process known as nucleosynthesis. The material that forms are some of the heaviest elements in nature, such as gold, platinum and uranium. Astrophysicists can observe these mergers using the JWST.

Now, published today in Nature, scientists including those at The University of Warwick have observed evidence of tellurium, one of the rarest elements on Earth, and infer the presence of several other elements, like iodine, that are essential to life, as a result of a kilonova.

Why are kilonovae hard to investigate?

While neutron star mergers have long been theorised as being the ideal “pressure cookers” to create elements substantially heavier than iron, astronomers have previously encountered a few obstacles in obtaining hard evidence.

Kilonovae are extremely rare, making it difficult to observe these events. Short gamma-ray bursts (GRBs), traditionally thought to be those that last less than two seconds, can be byproducts of these infrequent merger episodes. (In contrast, long gamma-ray bursts may last several minutes and are usually associated with the explosive death of a massive star.)

NASA discovery: GRB 230307A  

The case of the recently observed GRB 230307A is particularly remarkable. First detected by NASA’s Fermi Gamma-ray Space Telescope in March, it is the second brightest GRB observed in over 50 years of observations, about 1,000 times brighter than a typical gamma-ray burst that the Fermi telescope usually observes. It also lasted for around a minute, placing it firmly in the category of long duration gamma-ray bursts, although the observations show a very different origin.

After the first detection, an intensive series of observations from the ground and from space, including with the University of Warwick and University of Sheffield’s ULTRACAM instrument at the European Southern Observatory, swung into action to pinpoint the source on the sky and track how its brightness changed. Observations using gamma-ray, X-ray, optical, infrared and radio observation technologies showed that the visible light the source emitted was faint, evolved quickly, and transitioned from blue to red, and then eventually infrared —the hallmarks of a kilonova.

“Kilonovae form when heavy elements, such as gold and uranium form in the aftermath of the merger of two stars the mass of the Sun, but the size of a city. They rapidly expand and cool with the peak of their light quickly moving from the optical to the infrared” said Professor Danny Steeghs, Department of Physics, University of Warwick, who was involved in the research.

Identifying the kilonova’s location with JWST

While almost impossible to study from the ground, these were the perfect conditions for Webb’s NIRCam (Near-Infrared Camera) and NIRSpec (Near-Infrared Spectrograph) instruments to observe this tumultuous environment. One feature is clear in these observations, some of the light is emitted by tellurium, an element rarer than platinum on Earth.

The highly sensitive infrared capabilities of Webb helped scientists identify the home address of the two neutron stars that created the kilonova: a spiral galaxy about a billion light-years away. These neutron stars were kicked out of their host galaxy and travelled approximately the equivalent of the Milky Way galaxy’s diameter (120,000 light years away) before merging several hundred million years later.

With Webb’s ability to peer deeper into space than ever before and work in tandem with other space telescopes, scientists expect to find even more kilonovae in the future giving more clues as to where life might be possible.

Professor Danny Steeghs, Department of Physics, University of Warwick, said: “This is an important next step in our understanding of the role binary neutron star mergers play in terms of populating the periodic table of elements. It complements the breakthrough achieved a few years ago thanks to gravitational wave detections, exploiting the step change that JWST now represents.

“For us at Warwick it was particularly meaningful to see the ULTRACAM instrument playing a key role. This is a high-speed instrument developed and built by the Universities of Sheffield and Warwick. Our late founding professor of the Astrophysics group, Tom Marsh, played a key role in the development of ULTRACAM and its successor instruments. ULTRACAM observations first detected the visible light component associated with this remarkable burst which then allowed the follow-up with other facilities."

Lead author Professor Andrew Levan, of Radboud University in the Netherlands, and Honorary Professor at the University of Warwick, said: “It is 150 years since we first wrote down the periodic table, and, thanks to kilonovae and new technology, we are finally filling in the last blanks about where everything was made.”

Read the paper here https://www.nature.com/articles/s41586-023-06759-1.

Notes to Editors

The James Webb Space Telescope is the world’s premier space science observatory. Webb is solving mysteries in our solar system, looking beyond to distant worlds around other stars, and probing the mysterious structures and origins of our universe and our place in it. Webb is an international program led by NASA with its partners, ESA (European Space Agency) and the Canadian Space Agency.

Images

Caption: A team of scientists has used NASA’s James Webb Space Telescope to observe an exceptionally bright gamma-ray burst, GRB 230307A, and its associated kilonova. Kilonovas—an explosion produced by a neutron star merging with either a black hole or with another neutron star—are extremely rare, making it difficult to observe these events. The highly sensitive infrared capabilities of Webb helped scientists identify the home address of the two neutron stars that created the kilonova.

This image from Webb’s NIRCam (Near-Infrared Camera) instrument highlights GRB 230307A’s kilonova and its former home galaxy among their local environment of other galaxies and foreground stars. The neutron stars were kicked out of their home galaxy and traveled the distance of about 120,000 light-years, approximately the diameter of the Milky Way galaxy, before finally merging several hundred million years later.

Credits: NASA, ESA, CSA, STScI, Andrew Levan (Radboud University, University of Warwick)

Caption: This graphic presentation compares the spectral data of GRB 230307A’s kilonova as observed by the James Webb Space Telescope and a kilonova model. Both show a distinct peak in the region of the spectrum associated with tellurium, with the area shaded in red. The detection of tellurium, which is rarer than platinum on Earth, marks Webb’s first direct look at an individual heavy element from a kilonova.

Though astronomers have theorized neutron star mergers to be the ideal environment to create chemical elements, including some that are essential to life, these explosive events—known as kilonovas—are rare and rapid. Webb’s NIRSpec (Near-Infrared Spectrograph) acquired a spectrum of GRB 230307A’s kilonova, helping scientists secure evidence of the synthesis of heavy elements from neutron star mergers.

With Webb’s extraordinary ability to look further into space than ever before, astronomers expect to find even more kilonovas and acquire further evidence of heavy element creation.

Credits: NASA, ESA, CSA, Joseph Olmsted (STScI)

University of Warwick press office contact:

Annie Slinn

Communications Officer | Press & Media Relations | University of Warwick

Email: annie.slinn@warwick.ac.uk

07876876934

25 October 2023