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تسجيل مستخدم جديد2020 Nobel Prize for Physics: Black holes and the Milky Ways darkest secret
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Joseph Samuel
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This article was written at the invitation of Current Science to explain the history and Science behind this years Nobel prize in Physics. The article is aimed at a general audience and provides a popular account and perspective on the subject of black holes.
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The 2016 Physics Nobel Prize honors a variety of discoveries related to topological phases and phase transitions. Here we sketch two exciting facets: the groundbreaking works by John Kosterlitz and David Thouless on phase transitions of infinite orde
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Stellar evolution theory predicts a gap in the black hole birth function caused by the pair instability. Presupernova stars that have a core mass below some limiting value, Mlo, after all pulsational activity is finished, collapse to black holes, whe
reas more massive ones, up to some limiting value, Mhi, explode, promptly and completely, as pair-instability supernovae. Previous work has suggested Mlo is approximately 50 solar masses and Mhi is approximately 130 solar masses. These calculations have been challenged by recent LIGO observations that show many black holes merging with individual masses, Mlo is least some 65 solar masses. Here we explore four factors affecting the theoretical estimates for the boundaries of this mass gap: nuclear reaction rates, evolution in detached binaries, rotation, and hyper-Eddington accretion after black hole birth. Current uncertainties in reaction rates by themselves allow Mlo to rise to 64 solar masses and Mhi as large as 161 solar masses. Rapid rotation could further increase Mlo to about 70 solar masses, depending on the treatment of magnetic torques. Evolution in detached binaries and super-Eddington accretion can, with great uncertainty, increase Mlo still further. Dimensionless Kerr parameters close to unity are allowed for the more massive black holes produced in close binaries, though they are generally smaller.
We show that accreting black hole systems could be sources for keV light dark matter flux through several different mechanisms. We discuss two types of systems: coronal thermal plasmas around supermassive black holes in active galactic nuclei (AGNs),
and accretion disks of stellar-mass X-ray black hole binaries (BHBs). We explore how these black hole systems may produce keV light dark matter fluxes and find that in order to account for the XENON1T excess, the dark fluxes from the observed AGNs and BHBs sources have to exceed the Eddington limit. We also extend the black hole mass region to primordial black holes (PBHs) and discuss the possibility of contributing to keV light dark flux via superradiance or Hawking radiation of PBHs. Besides, black holes can be good accelerators to accrete and boost heavy dark matter particles. If considering collisions or dark electromagnetism, those particles could then escape and reach the benchmark speed of 0.1c at the XENON1T detector.
Edwin Powel Hubble is regarded as one of the most important astronomers of 20th century. In despite of his great contributions to the field of astronomy, he never received the Nobel Prize because astronomy was not considered as the field of the Nobel
Prize in Physics at that era. There is an anecdote about the relation between Hubble and the Nobel Prize. According to this anecdote, the Nobel Committee decided to award the Nobel Prize in Physics in 1953 to Hubble as the first Nobel laureate as an astronomer (Christianson 1995). However, Hubble was died just before its announcement, and the Nobel prize is not awarded posthumously. Documents of the Nobel selection committee are open after 50 years, thus this anecdote can be verified. I confirmed that the Nobel selection committee endorsed Frederik Zernike as the Nobel laureate in Physics in 1953 on September 15th, 1953, which is 13 days before the Hubbles death in September 28th, 1953. I also confirmed that Hubble and Henry Norris Russell were nominated but they are not endorsed because the Committee concluded their astronomical works were not appropriate for the Nobel Prize in Physics.
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