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Category: cosmology – Page 130

Isaac Newton described his theory of gravity as a force that acts instantaneously across space: a planet immediately senses the effects of another astronomical object, regardless of the separation between them. This aspect inspired Einstein to create the renowned theory of general relativity, where gravity becomes a local deformation of spacetime.

The principle of locality states that an object is directly influenced only by its surrounding environment: distant objects cannot communicate instantaneously, only what is here right now matters. However, in the past century, with the birth and development of quantum mechanics, physicists discovered that non-local phenomena not only exist but are fundamental to understanding the nature of reality.

Now, a new study from SISSA – Scuola Internazionale Superiore di Studi Avanzati, recently published in The Astrophysical Journal.

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After over a decade of observations of pulsars, astronomers could finally tease out the gravitational wave background of the Universe, the combined signal from merging supermassive black holes. But it was just the general presence of mergers, not specific events. A new paper proposes that the same pulsars could next be used to detect the gravitational waves from individual merging supermassive black holes. The more nearby pulsars astronomers can find, the more accurate their measurements will become.

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This study has successfully developed a high-efficiency neutron detector array with an exceptionally low background to measure the cross-section of the 13C(α, n)16O reaction at the China Jinping Underground Laboratory (CJPL). Comprising 24 3He proportional counters embedded in a polyethylene moderator, and shielded with 7% borated polyethylene layer, the neutron background at CJPL was as low as 4.5 counts/h, whereby 1.94 counts/h was attributed to the internal α radioactivity. Remarkably, the angular distribution of the 13C(α, n)16O reaction was proven to be a primary variable affecting the detection efficiency. The detection efficiency of the array for neutrons in the range of 0.1MeV to 4.5 MeV was determined using the 51V(p, n)51Cr reaction carried out with the 3 MV tandem accelerator at Sichuan University and Monte Carlo simulations. Future studies can be planned to focus on further improvement of the efficiency accuracy by measuring the angular distribution of 13C(α, n)16O reaction.

Gamow window is the range of energies which defines the optimal energy for reactions at a given temperature in stars. The nuclear cross-section of a nucleus is used to describe the probability that a nuclear reaction will occur. The 13C(α, n)16O reaction is the main neutron source for the slow neutron capture process (s-process) in asymptotic giant branch (AGB) stars, in which the 13C(α, n)16O reaction occurs at the Gamow window spanning from 150 to 230 keV. Hence, it is necessary to precisely measure the cross-section of 13C(α, n)16O reaction in this energy range. A low-background and high detection efficiency neutron detector is the essential equipment to carry out such measurements. This study developed a low-background neutron detector array that exhibited high detection efficiency to address the demands. With such development, advanced studies, including direct cross-section measurements of the key neutron source reactions in stars, can be conducted in the near future.

Low-background neutron detectors play a crucial role in facilitating research related to nuclear astrophysics, neutrino physics, and dark matter. By improving the efficiency and upgrading the technological capability of low background neutron detectors, this study indirectly contributes to the enhancement of scientific research. Additionally, fields involving material science and nuclear reactor technology would also benefit from the perfection of neutron detector technology. Taking into consideration the potential application and expansion of these findings, such innovative attempt aligns well with UNSDG9: Industry, Innovation & Infrastructure.

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Astronomers may have spotted a supermassive black hole in the early universe that formed when a gargantuan gas cloud imploded.

The black hole’s host galaxy, UHZ1, was spotted in James Webb Space Telescope (JWST) observations of galaxies in the early universe. These distant galaxies’ light has been bent and magnified by the intervening galaxy cluster Abell 2,744, bringing them into view.

Ákos Bogdán (Center for Astrophysics, Harvard & Smithsonian) and others used the Chandra X-ray Observatory to take a second look at 11 of the lensed galaxies. Based on which wavelengths the galaxies are detectable at, each of the 11 appeared to lie at a redshift greater than 9, which means they’re shining at us from the universe’s first 500 million years. The team picked up X-rays from just one galaxy, the most magnified of the bunch.

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