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Discovering the physical trigger of the Universe's Most Powerful Supernovae with Gravitational Waves 2024.09.10 334 |
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Discovering the physical trigger of the Universe's Most Powerful Supernovae with Gravitational Waves
It is widely believed that gravitational waves can provide significant insight to the mysterious inner-workings of core-collapse supernovae (CC-SNe). New theoretical research shows that the most energetic CC-SNe may be seen as far as the Virgo cluster and beyond. This new perspective was recently presented at the international conference COSPAR 2024 and will be published in the Astrophysical Journal Letters. Although CC-SNe are quite heterogeneous, this new perspective concerns type Ic supernovae, whose progenitors explode after losing their hydrogen and helium envelopes. These CC-SNe are known because a subclass of them, characterized by large expansion velocities, called SNe-Ic “broad lines” (SNe-Ic BL) is associated with long-duration gamma-ray bursts (GRBs). Importantly, events of this type are likely characterized, at the end of the core collapse, by the formation of rapidly rotating black holes. The energy “reservoir” in this case is represented by their angular momentum, which far exceeds that of the neutron stars that power relatively more frequent core-collapse events. This new perspective is based on a physical trigger with two key ingredients: a rotating black hole and a surrounding compact torus created by high-density matter. This torus can act as a catalyst and facilitate the conversion of part of the spin energy into gravitational radiation. Over time, the torus expands, as the black hole slowly loses rotation speed, and this process produces a characteristic descending chirp in gravitational waves. This process of black hole loss of rotation speed was observed in GW170817B, associated with the kilonova AT2017gfo that followed the double neutron star merger GW170817. Very similar emission is expected from energetic CC-SNe, scaled by mass. It is crucial to note that GW170817B was observed at the extragalactic distance of 40 Mpc, about 1000 times the diameter of the Milky Way. “Considering the current observations and our results, we estimate that, under optimal conditions, we could detect up to about 1 event per year. More conservatively and perhaps more realistically, assuming less favorable conditions and taking into account the limited activity cycles of the detectors, we estimate a detection rate of a few events per decade. This is still significantly higher than the two events per century expected in the Milky Way,” said Maurice van Putten, Professor of Physics and Astronomy at Sejong University and INAF-OAS, who is leading this research together with post-doctoral researcher Dr. Maryam A. Abchouyeh and Massimo Della Valle, Director of Research at INAF-Naples. This result, based on careful calculations, comes from three simple considerations: i) compared to GW170817 (2017), the current generation of detectors is more sensitive; ii) black holes produced in SN-Ic BLs are expected to be relatively more massive, thus iii) allowing a higher energy output at lower frequencies, closer to the “sweet spot” of the LVK detector sensitivity (about 100-250 Hz). For O4, the combination of these three factors pushes the horizon distance of observability of SN-Ic BL producing black holes up to at least tens of Mpc, improving the statistical prospect of a detection by about two orders of magnitude compared to O2.
Image. Horizon distances of initially rapidly spinning black holes by mass-scaling of GW170817B/GRB170817A (blue dot) and detector improvement in O4 over O2. Highlighted is the expected mass range of black holes produced in energetic CC-SNe (magenta). Multi-Messenger Observations of CC-SNe Gravitational waves may have the ability to reveal the central engine and therefore the nature of the remnant of the stellar explosion: neutron stars (NS) or black holes (BH). Distinguishing between these two scenarios based only on electromagnetic observations appears notoriously difficult. Even for very close objects like SN1987A in the Large Magellanic Cloud (LMC), we had to wait about 37 years, with the recent James Webb Space Telescope (JWST) observations to provide convincing evidence for the existence of a NS as a “remnant” of the SN 1987A explosion. A detection of a descending chirp of gravitational waves would unequivocally identify the loss of rotation velocity of a compact object. An energy output exceeding the limited budget of a rapidly rotating neutron star would reveal a BH, indicating a relatively high-mass progenitor. Alternatively, a non-detection would provide indirect evidence for a NS, indicating a progenitor mass likely less than 20 solar masses, as in SN 1987A. The potential GW detection of CC-SNe deep into the Local Universe has finally stimulated the development of new algorithms to detect signals that have so far been missed and to achieve a deep integration with traditional electromagnetic astronomy. "Our study indicates that some supernovae may, in fact, be brighter in their gravitational wave emission than previously believed. This puts gravitational wave astronomy at the forefront even in fields such as CC-SNe, traditionally a “hunting ground” for “electromagnetic” astronomers. “With the entry into operation of future next-generation detectors, such as the Einstein Telescope (ET) in the EU and the Cosmic Explorer (CE) in the UniJ StaJ, the LISA space mission and the THESEUS gamma-ray burst satellite mission, the potential represented by these prospects is immense,” concludes Della Valle. Reference van Putten, M.H.P.M., Abchouyeh, M.A., & Della Valle, M., 2024, ApJL, https://doi.org/DOI: 10.3847/2041-8213/ad710f |
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