2023-10-26 16:46:37
Just after the Second World War and its stimulating role for the development of nuclear physics, seminal work showed how the stars were the furnaces distilling elements heavier than the hydrogen, helium and lithium of the Big Bang with all their isotopes. But this work had difficulty explaining the quantities of elements heavier than iron, except by involving kilonovae. James-Webb has just consolidated the theory of the synthesis of these elements.
Hubert Reeves comes alas to leave us. He used to say that we were stardust because the astrophysicistnuclear astrophysicist that he was knew well that the alchemy at the origin of the elements of life, producing the nuclei of carboncarbon, oxygenoxygen and nitrogennitrogen was taking place relating to the life and death of starsstars. He had in fact begun his doctoral studies at the time when the American astrophysicist of British origin Margaret Burbidge, her husband Geoffrey Burbidge and along with cosmologist Fred Hoyle and Nobel Prize winner in physicsphysics William Fowler were the authors of an important article published in 1957 which exposed nothing less than the recipe followed by the UniverseUniverse to make the chemical elementschemical elements in stars. L’article has been famous ever since for nuclear astrophysicists under the name B2FH according to the initials of its authors.
Hubert Reeves himself had contributed to solving certain enigmas concerning the origin of the light elements that the B2FH article left unsolved. There was another, that of the detailed origin of elements heavier than iron, such as gold and platinum, the production of which during supernova explosions did not account for the observed abundances.
We have since had ideas.
It was enough to involve intense bombardments of neutron fluxes on iron nuclei which, by capturing them and via betabeta radioactive decay reactions giving protonsprotons, made it possible to obtain elements as heavy as uraniumuranium and various isotopesisotopes also beyond those of iron. We are talking about the addition of neutrons by a rapid process (r process in English), but this process can be slow (s processs like slow).
How to produce this neutron flux? With collisions of neutron starsneutron stars of course, which was to give rise to what we call kilonovae, therefore not as powerful as supernovae. Kilonovae also emit gravitational wavesgravitational waves and normally appear in the form of short gamma-ray bursts, these incredibly powerful flashes of gamma photonsphotons.
The saga of the detection of GW170817. To obtain a fairly accurate French translation, click on the white rectangle at the bottom right. English subtitles should then appear. Then click on the nut to the right of the rectangle, then on “Subtitles” and finally on “Automatically translate”. Choose “French”. © Science vs Cinema
Kilonovae, gamma and gravitational sources
In fact, on August 17, 2017, a gamma-ray bursts (GRB in English), called SGRB170817A, was indeed detected and located on the celestial dome in association with the source of gravitational waves detected by LigoLigo and Virgo: GW170817. The gravitational signal and others in the electromagnetic band confirmed that it was a collision of neutron stars accompanied by the kilonova phenomenon. In this case, it is estimated that around 100 times the mass of the Earth in gold nuclei would have been synthesized by the prodigious flux of neutrons released.
The James-Webb Space TelescopeJames-Webb Space Telescope (JWST) allows us to go a step further in our quest for the origin of heavy elements, as has just been shown in an article published in Nature and a freely accessible version of which can be found on arXiv.
The discovery was made by turning the JWST’s near-infrared gaze toward the gamma-ray burst GRB 230307A identified by NASA’s Fermi and Neil Gehrels SwiftSwift orbiting gamma-ray telescopes. It is the second brightest gamma-ray burst observed in more than 50 years, about 1,000 times brighter than a typical gamma-ray burst observed by Fermi.
A nomadic intergalactic binary system?
James-Webb found associated with it the spectral trace of the element telluretellurium which is the chemical element with atomic numberatomic number 52, symbol Te in Mendeleev’s table. Iron is the chemical element with atomic number 26, symbol Fe and clearly lighter than tellurium. The spectral signature of Te is, as with that of other elements, a sort of barcode with absorption lines on a light spectrum or conversely emission lines. This code is observed in laboratories on Earth, which makes it possible to extrapolate the presence of elements without having to travel light years to do the chemical analysis on site.
Thus, GRB 230307A was produced by a collision of neutron stars and thus we find new direct evidence of the production of elements heavier than iron with a kilonova. We already had similar indications with strontium.
As a bonus, the James-Webb helped establish that the binary system of neutron stars before the collision must have come from a galaxy from which it was ejected during the formation of the neutron stars themselves. Supernovasupernova explosions of neutron star progenitor stars can be asymmetric, which can lead to the equivalent of a rocket propulsion effect.
The binary system would then have traveled approximately the equivalent of the diameter of the Milky Way before merging several hundred million years later.
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