Author: Ore Gottlieb

Center for Computational Astrophysics, Flatiron Institute, New York, NY 10010, United States

While the LIGO-Virgo-KAGRA effort has successfully pinpointed hundreds of gravitational wave (GW) signals, all of them were generated in mergers of compact objects. Looking ahead to the next generation of GW interferometers set to begin operations in the 2030s, an intriguing avenue of exploration opens up. The pressing question is what non-inspiral GW sources are waiting to be detected, broadening the scope of possibilities and unraveling the physics of high energy phenomena? Recently, Gottlieb et al. (2023) highlighted the potential of hot and turbulent cocoons within dying massive stars as one of the most promising non-inspiral GW sources in the next generation GW detectors. Cocoons form when jets that are launched during the collapse of the star interact with the stellar envelope, leading to the majority of the jets’ energy being transferred into the inflation of a heated cocoon. The unique combination of the cocoon's large energy reservoir and its asymmetrical shape enveloping the jet generates a vigorous GW signal.

The new paper by Soker (2023) delves into the prospects of detecting GWs emanating from cocoons formed by jittering jets that power core-collapse supernovae (CCSNe). When the jets are jittering, they directly interact with a larger fraction of the stellar envelope, giving rise to a more energetic, but also more homogenous and spherical cocoon. The paper presents an order-of-magnitude analytic estimate suggesting that the GW signal peaks at low frequencies of ~5-30 Hz, within the frequency ranges detectable by current and next-generation detectors. The magnitude of the signal hints at the possibility of detection by next-generation detectors, if CCSNe are indeed powered by jittering jets. The GW signal magnitude is found to be comparable to that anticipated from a proto-neutron star in CCSNe (Mezzacappa et al. 2023), implying potential detection only within our own Galaxy (Srivastava et al. 2019). Nevertheless, the signal holds promise for providing insights into the mechanism underlying CCSNe, offering a means to distinguish between various explosion mechanism theories.

At the moment, this novel non-inspiral GW prediction remains a preliminary estimate, necessitating validation through a rigorous, self-consistent numerical calculation. Follow-up work is imperative to confirm this result, derive the GW spectrum and spectrogram, and calculate the signal-to-noise ratio of such signals for detection rate estimates. If validated, these stochastic burst signals will likely require unmodeled search pipelines in the GW data. This again underscores the importance of conducting more detailed calculations to enhance both the detection prospects and the information gleaned from potential detections. Finally, we need to remember that the timeline for detecting GWs from a supernova in our Galaxy may span decades unless serendipity intervenes.

References:   

O. Gottlieb, H. Nagakura, A. Tchekhovskoy, P. Natarajan, E. Ramirez-Ruiz, S. Banagiri, J. Jacquemin-Ide, N. Kaaz, V. Kalogera, ‘Jet-Inflated Cocoons in Dying Stars: New LIGO-Detectable Gravitational Wave Sources', ApJL, 951, 30 (2023)