Multi-messenger astronomy began when a massive star underwent core collapse in a neighboring dwarf galaxy, whose light and neutrinos reached Earth in 1987. Supernova 1987A was observed optically but was also observed through roughly two dozen neutrinos. Modern instruments have the ability to measure electromagnetic signatures in more wavelengths and detect many more neutrinos from a nearby core-collapse supernova, providing insight into an astrophysical phenomena that is not yet fully understood. In this dissertation, we discuss predictions for future core-collapse supernova signals and the nuclear and particle interactions that produce them. We focus on several different aspects related to both typical and rare supernovae.
The diffuse supernova neutrino background (DSNB) - the isotropic background of ~10 MeV neutrinos from all past supernovae - is one such signal that does not rely on a local event for neutrino detection. We update several aspects of theoretical DSNB modeling by (i) using simulation data to better understand neutrino emission spectra as a function of time, (ii) collating recent star formation rate measurements to infer the rate of core collapse in the cosmos, and (iii) performing a signal vs. background analysis of state-of-the-art neutrino experiments. We find that the DSNB is likely to be detected in the next two decades, but large uncertainty on the average neutrino emission spectra combined with unclear treatment of background events prevents a precise timeline.
We also discuss the signatures from rare supernovae driven by magnetorotational engines called protomagnetars. We find that outflows from these central engines can produce pions through inelastic np interactions, resulting in ~0.1 - 10 GeV neutrinos that are detectable for galactic supernovae. We also find that these outflows can synthesize heavier nuclei than traditional supernovae through the `weak r-process.' We compare the nucleosynthesis in supernova outflows to that in compact object mergers and find that mergers are more conducive for creating the heaviest nuclei. We also predict the detection rates of another kind of transient called kilonovae that are powered by the decay of unstable nuclei. Finally, these protomagnetar systems may be able to accelerate nuclei in relativistic jets. If these jets are beamed toward us, the gamma ray lines from the decays of unstable nuclei can be boosted to high energies and are detectable from extragalactic distances. / Doctor of Philosophy / Supernovae are one of the most well studied astronomical phenomena because of how broadly they connect to different fields of physics. This kind of event can be bright enough to be seen visually and has been observed and documented for centuries. Its name derives from nova stella - Latin for `new star' - but supernovae occur as the final stages of a star's life. Core-collapse supernovae are an important subclass that occur for stars several times more massive than our own sun. There is a long history of core-collapse supernova observation - from the naked eye to modern optical telescopes - but only one has ever been observed using a particle other than light. SN1987A was a nearby core-collapse supernova that occurred in 1987 and emitted a large burst of rarely interacting particles known as neutrinos along with its usual optical emission. Only two dozen neutrinos were detected during this event, but nearby core-collapse supernovae are rare and astronomers have been eager for another one. With today's modern neutrino detectors, a nearby core-collapse supernova would yield thousands of neutrino events which would help astronomers learn about the internal physics occurring during the collapse, which an optical signal cannot do.
In this dissertation, we study the ways in which light and neutrinos can teach us more about core-collapse supernovae. We cover another way to observe supernova neutrinos without waiting for one nearby to occur by predicting the signal from the `diffuse supernova neutrino background.' This is a background of supernova neutrinos that constantly surrounds us, but interacts extremely infrequently, so kiloton-mass detectors are needed to detect this background. Measuring this will also shed light on how stars evolve over a galaxy's history.
There are additional subclasses of core-collapse supernovae that give rise to the usual optical and neutrino signal but may also populate the universe with heavy elements, produce higher energy light, and emit higher energy neutrinos. This class is even rarer but are systematically more energetic and are powered internally by objects called `protomagnetars.' We study models of these rare, energetic supernovae and make predictions for each of these signals - heavy elements, high energy light, and high energy neutrinos - to help answer outstanding questions in astrophysics and make predictions for events not yet seen.
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/118751 |
| Date | 03 May 2024 |
| Creators | Ekanger, Nicholas Joseph |
| Contributors | Physics, Horiuchi, Shunsaku, Simonetti, John H., Arav, Nahum, Shoemaker, Ian |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Language | English |
| Detected Language | English |
| Type | Dissertation |
| Format | ETD, application/pdf, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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