Astronomers with ALMA and NOEMA have carried out the first definitive detection of a radioactive molecule in interstellar space. The radioactive part of the molecule is an aluminum isotope. The observations show that the isotope was scattered into space after the collision of two stars leaving behind what is known as the CK vulpeculae. This is the first time that this element has been directly observed from a known source. Earlier identifications of this isotope stem from the detection of gamma rays, but their exact origin was unknown.
The team led by Tomasz Kaminski (Harvard-Smithsonian Center for Astrophysics, Cambridge, USA) used the Atacama Large Millimeter / Submillimeter Array (ALMA) and the NOrthern Extended Millimeter Array (NOEMA) to detect a source of the radioactive isotope aluminum 26th The source, known as CK Vulpeculae, was first seen in 1
"This first observation of this isotope in a star-like object is also important in the broader context of galactic chemical evolution," notes Kaminski. "This is the first time that an active producer of the aluminum-26 radioactive nuclide has been directly identified."
Kaminski and his team found the unique spectral signature of molecules of aluminum-26 and fluorine (26AlF) in the rubble surrounding CK Vulpeculae, which is about 2000 light-years from Earth. As these molecules spin and rotate through space, they emit a characteristic fingerprint of millimeter-wavelength light, a process known as rotational transition. Astronomers consider this a "gold standard" for the detection of molecules.
The observation of this particular isotope provides new insights into the fusion process that generated CK vulpeculae. It also shows that the deep, dense inner layers of a star, in which heavy elements and radioactive isotopes are forged, can be whirled up by star collisions and thrown into space.
"We are seeing the entrails of a star torn apart three centuries ago by a collision," noted Kaminski.
The astronomers also found that the two stars growing together had a relatively low mass, one of them a red giant star with a mass between 0.8 and 2.5 times our Sun.
Because aluminum is radioactive, it decays to become more stable, and in this process one of the protons in the nucleus breaks down into a neutron. During this process, the excited nucleus emits a very high energy photon, which we observe as a gamma ray.
Earlier evidence of gamma-ray emission has shown that there are about two solar masses of aluminum-26 in the Milky Way, but the process that generated the radioactive atoms was unknown. Because of the way gamma rays are detected, their exact origins were also largely unknown. With these new measurements, astronomers have for the first time detected an unstable radioisotope in a molecule outside our solar system. At the same time, however, the team has come to the conclusion that the production of aluminum-26 by similar objects such as CK-Vulpeculae are unlikely to be the main source of aluminum-26 in the Milky Way.
The mass of aluminum-26 in CK Vulpeculae is about a quarter of the mass of Pluto, and given that these events are so rare, they are very unlikely to be the only producers of the isotope in the Milky Way. This opens the door to further investigation of these radioactive molecules.
European Southern Observatory
Stellar Chemistry, the Universe and Everything in It
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