Emission lines due to ionizing radiation from a compact object in the remnant of Supernova 1987A

The nearby Supernova 1987A was accompanied by a burst of neutrino emission, which indicates that a compact object (a neutron star or black hole) was formed in the explosion. There has been no direct observation of this compact object. In this work, we observe the supernova remnant with JWST spectroscopy, finding narrow infrared emission lines of argon and sulfur. The line emission is spatially unresolved and blueshifted in velocity relative to the supernova rest frame. We interpret the lines as gas illuminated by a source of ionizing photons located close to the center of the expanding ejecta. Photoionization models show that the line ratios are consistent with ionization by a cooling neutron star or a pulsar wind nebula. The velocity shift could be evidence for a neutron star natal kick.

Strong Supernova 1987A Constraints on Bosons Decaying to Neutrinos

Majoron-like bosons would emerge from a supernova (SN) core by neutrino coalescence of the form νν→ϕ and ν[over ¯]ν[over ¯]→ϕ with 100-MeV-range energies. Subsequent decays to (anti)neutrinos of all flavors provide a flux component with energies much larger than the usual flux from the "neutrino sphere." The absence of 100-MeV-range events in the Kamiokande-II and Irvine-Michigan-Brookhaven signal of SN 1987A implies that less than 1% of the total energy was thus emitted and provides the strongest constraint on the Majoron-neutrino coupling of g≲10^{-9}  MeV/m_{ϕ} for 100  eV≲m_{ϕ}≲100  MeV. It is straightforward to extend our new argument to other hypothetical feebly interacting particles.

The origin of the elements: a century of progress

This review assesses the current state of knowledge of how the elements were produced in the Big Bang, in stellar lives and deaths, and by interactions in interstellar gas. We begin with statements of fact and discuss the evidence that convinced astronomers that the Sun is fusing hydrogen, that low-mass stars produce heavy elements through neutron capture, that massive stars can explode as supernovae and that supernovae of all types produce new elements. Nucleosynthesis in the Big Bang, through cosmic ray spallation, and in exploding white dwarfs is only ranked below the above facts in certainty because the evidence, while overwhelming, is so far circumstantial. Next, we highlight the flaws in our current understanding of the predictions for lithium production in the Big Bang and/or its destruction in stars and for the production of the elements with atomic number [Formula: see text]. While the theory that neutron star mergers produce elements through neutron-capture has powerful circumstantial evidence, we are unconvinced that they produce all of the elements past nickel. Also in dispute is the exact mechanism or mechanisms that cause the white dwarfs to explode. It is difficult to determine the origin of rare isotopes because signatures of their production are weak. We are uncertain about the production sites of some lithium and nitrogen isotopes and proton-rich heavy nuclei. Finally, Betelgeuse is probably not the next star to become a supernovae in the Milky Way, in part because Betelgeuse may collapse directly to a black hole instead. The accumulated evidence in this review shows that we understand the major production sites for the elements, but islands of uncertainty in the periodic table exist. Resolving these uncertainties requires in particular understanding explosive events with compact objects and understanding the nature of the first stars and is therefore primed for new discoveries in the next decades. This article is part of the theme issue 'Mendeleev and the periodic table'.

Muons in Supernovae: Implications for the Axion-Muon Coupling

The high temperature and electron degeneracy attained during a supernova allow for the formation of a large muon abundance within the core of the resulting protoneutron star. If new pseudoscalar degrees of freedom have large couplings to the muon, they can be produced by this muon abundance and contribute to the cooling of the star. By generating the largest collection of supernova simulations with muons to date, we show that observations of the cooling rate of SN 1987A place strong constraints on the coupling of axionlike particles to muons, limiting the coupling to g_{aμ}<10^{-8.1}  GeV^{-1}.