kilonovae: Neutron star collisions produce tellurium
The James Webb Space Telescope (JWST) and other space telescopes were the first to detect tellurium in the afterglow of a long gamma-ray burst.
© NASA, ESA, CSA, STScI, Andrew Levan (IMAPP, Warw) / (webbbtelescope.org/contents/media/images/2023/134/01HAWEGXDBGD2SCH7FAPJ7P62Y?news=true) (excerpts)
Small but powerful: The faint red dot in the circle is the kilonova aurora.
On March 7, 2023, NASA’s Fermi gamma-ray telescope detected an explosion, the second brightest explosion seen to date. GRB 230307A lasted for 200 seconds, making it part of the category of long gamma-ray bursts. A short time later, the afterglow of this eruption was examined using space-based and ground-based telescopes. These observations had to be made quickly because twilight faded quickly.
The gamma-ray burst was most likely the result of a collision between two neutron stars, resulting in a so-called kilonova. During such events, the two neutron stars merge together, ejecting some of their matter into the surrounding space. In these ejected masses, where extreme pressures and temperatures prevail, chemical elements whose atomic masses are much higher than those of iron are also formed. Their formation requires energy, which is generated by kilonovas.
GRB 230307A was studied in the range of gamma rays, high-energy X-rays, visible light, infrared and radio waves. As measurements showed, the infrared glow was weak and faded quickly. The spectrum becomes redder and redder, shifting toward lower-energy radiation. The gas cloud created by the kilonova expanded rapidly and cooled significantly.
When the James Webb Space Telescope was pointed at the kilonova cloud, it could no longer be observed from Earth. The NIRCam and NIRSpec instruments recorded detailed spectra of the infrared source at the scene. There are broad lines in the spectrum showing that the gas is spreading at high speed. One of the lines can be recognized. It comes from tellurium (Te), an element that is very rare on Earth.
In addition, data from the James Webb Space Telescope has made it possible to identify the origin of the neutron binary star: the spiral galaxy in the center of the image. The double star originally consisted of two massive main sequence stars, with the more massive star evolving more quickly into a red giant and exploding as a supernova. The former star’s core collapsed into a neutron star. Later, a slightly lower mass star suffered the same fate.
Due to the impetus of supernova explosions, the binary star system was ejected from the World Island and moved through intergalactic space at high speed. It has traveled about 120,000 light-years, which is roughly the diameter of the Milky Way system. By emitting gravitational waves, the two neutron stars moved closer and closer together, until after billions of years, they combined with each other into a kilonova, producing another short-lived fireworks display.
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