Heavy element from stellar fusion detected by JWST

About 150 years ago, the Russian chemist Dmitri Mendeleev created what is known as the periodic table of the elements. He included the lighter ones, like hydrogen, as well as the heavier ones, like iron and more. Now, thanks to the James Webb Space Telescope, we have the opportunity to find out where the heavy elements are forged: they are created by phenomena such as the violent explosions that occur in the cosmos when stars die.

In fact, the Webb observed the second-brightest gamma-ray burst ever observed, GRB 230307A. It was probably caused by the merger of neutron stars, an event known as a kilonova. Using the high sensitivity of this telescope's instruments, scientists captured the first mid-infrared spectrum from inside a kilonova.

The importance of the discovery

For the first time, this discovery allowed the direct identification of a single heavy element produced by such an event. The chemical compound identified is tellurium, but scientists suspect that other heavy elements, such as iodine, may also be present in the material ejected by this kilonova.

Thanks to the James Webb, we now know more about kilonovae.

It should be noted that kilonova events that act as authentic forges for the creation of elements heavier than iron are extremely rare. One of the methods used to detect them is the observation of short gamma-ray bursts (GRBs), which are by-products of such stellar mergers. Long gamma-ray bursts, on the other hand, tend to last several minutes and are usually associated with the explosive death of a star of considerable mass.

The case of GRB 230307A

The case of GRB 230307A is particularly intriguing. First identified in March by NASA's Fermi Gamma-ray Space Telescope, this event is the second brightest gamma-ray burst observed in more than 50 years of monitoring, according to Astrospace.

What makes this discovery even more extraordinary is that GRB 230307A not only was about 1,000 times brighter than a typical gamma-ray burst, but also maintained its intensity for an exceptionally long time, lasting up to 200 seconds. This extended duration, as opposed to typical short gamma-ray bursts, classifies the event as a long gamma-ray burst.

It is interesting to note that despite the unusually long duration of GRB 230307A, the search for its source was made possible by the collaboration of numerous telescopes both on Earth and in space. Observations at various wavelengths, including gamma rays, X-rays, optical, infrared, and radio, revealed that the optical/infrared counterpart associated with this event was characterized by rather low brightness. In addition, this counterpart evolved rapidly over time and showed a strong tendency to become increasingly red, attributes typical of a kilonova.

Tellurium

The powerful instruments available, such as NIRCam and the James Webb Space Telescope's NIRSpec spectrograph, proved ideal for studying the stellar merger event from which GRB 230307A appeared to have originated, especially in the infrared. The instruments captured the emission spectrum of the kilonova, revealing very broad spectral lines, indicating that the material was being ejected at high speed. They also revealed a remarkable aspect: the presence of light emitted by tellurium, an element much rarer on Earth than platinum.

The extraordinary capabilities of the two instruments also allowed scientists to identify with great precision the galaxy of origin of the two neutron stars that merged into the kilonova before being ejected from their home environment. This galaxy was found to be a spiral galaxy, located about 120,000 light-years from the point where the merger took place.