🔭 astrophysics

Core-Collapse Supernova detections from Einstein Telescope within the Milky Way

This study utilizes the GWFish simulation framework to demonstrate that the Einstein Telescope, particularly when networked with detectors like Cosmic Explorer, will be capable of detecting gravitational waves from core-collapse supernovae across the entire Milky Way and into nearby satellite galaxies, with detection horizons extending up to approximately 170 kpc depending on progenitor mass and configuration.

Original authors: I. F. Giudice, A. L. De Santis, M. T. Botticella, M. Branchesi, G. Pastorelli, L. Girardi, L. Izzo, E. Cappellaro, M. Della Valle

Published 2026-08-10

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CC BY 4.0

Original authors: I. F. Giudice, A. L. De Santis, M. T. Botticella, M. Branchesi, G. Pastorelli, L. Girardi, L. Izzo, E. Cappellaro, M. Della Valle

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine the universe as a giant, chaotic orchestra. For centuries, we've only been able to listen to the music by looking at the sheet music—the light that stars and explosions send out. This is "electromagnetic astronomy," and it's how we've learned about supernovas, the spectacular deaths of massive stars. But there's a problem: sometimes, the orchestra is hidden behind a thick, dusty curtain. In our own galaxy, the Milky Way, clouds of cosmic dust can block all the light, making a massive explosion completely invisible to our telescopes. It's like trying to watch a fireworks display through a brick wall.

To hear what's happening behind that wall, scientists need a different kind of sense. They need to feel the vibrations. When a massive star collapses, it doesn't just flash; it shakes the very fabric of space and time, sending out ripples called gravitational waves. Think of these waves like the ripples you see when you drop a stone into a pond, but the pond is space itself. These ripples carry information about the violent crash happening deep inside the star, information that light can't escape. The big question for astronomers is: if a star explodes right here in our neighborhood, hidden by dust, will we be able to "hear" it? And if we can, how far away can we be and still catch the sound?

This paper is a forecast for the future, specifically looking at a super-powerful new listening device called the Einstein Telescope (ET). The authors used computer simulations to see if this new telescope, alone or teamed up with another future detector called the Cosmic Explorer, could catch the gravitational waves from a supernova happening anywhere in our galaxy, or even in our nearby satellite galaxies, the Magellanic Clouds. They didn't just guess; they built a virtual Milky Way full of potential exploding stars and tested how well the new detectors would hear them, even when those stars are buried deep in dusty regions where optical telescopes would be blind.

The study found that the Einstein Telescope is going to be an incredible listener. If a massive star (about 15 times the mass of our Sun) explodes anywhere within our galaxy, the ET will almost certainly hear it. The telescope's "hearing range" is estimated to be between about 20 and more than 100 kiloparsecs (a kiloparsec is about 3,260 light-years), depending on the specific details of the explosion. Since the Milky Way is roughly 30 kiloparsecs across, this means the ET could detect a supernova happening anywhere in our galaxy, no matter how dusty the neighborhood is. If the ET works together with the Cosmic Explorer, their combined "ears" could stretch even further, reaching out to about 170 kiloparsecs, which would allow them to hear explosions in the Large and Small Magellanic Clouds, our galactic neighbors.

The researchers also discovered a crucial advantage of listening to gravitational waves: dust doesn't block them. They simulated the amount of dust in our galaxy and found that about 55% of all supernovas in the Milky Way would be too hidden for our current optical telescopes to see. However, the gravitational waves from these hidden explosions would still reach the Einstein Telescope clearly. This means that while we might miss half of the "visual fireworks," we won't miss the "sound" of the crash.

The paper also compared two different designs for the Einstein Telescope: a triangular shape with three arms and a "dual-L" shape with two arms. They found that the dual-L design is slightly better at hearing these signals on its own, offering about a 15-20% improvement in range compared to the triangle. However, once the telescope is teamed up with the Cosmic Explorer, the difference between the two designs becomes much smaller, only about 5-10%, because the partner detector helps fill in the gaps.

In the end, the authors suggest that with a rate of about 1.9 supernovas every 100 years in our galaxy, and the Einstein Telescope's ability to hear almost all of them, there is a roughly 32% chance we will catch at least one of these events during the telescope's first 20 years of operation. This would be a historic moment, giving us a complete, unobscured view of a star's death for the first time, revealing the physics of the explosion that light alone could never show us. It's a promise that even when the universe tries to hide its most violent secrets behind a curtain of dust, we will finally have the ears to hear them.

=== DRAFT ===
Technical Summary: Core-Collapse Supernova detections from Einstein Telescope within the Milky Way

Problem Statement
Core-collapse supernovae (CCSNe) are critical drivers of galaxy evolution and promising sources of gravitational waves (GWs) that probe the physics of stellar collapse. However, detecting these signals remains challenging due to their relatively weak amplitude and the limited sensitivity of current ground-based interferometers. Furthermore, optical observations of Galactic CCSNe are heavily biased by interstellar dust extinction, particularly in the Galactic plane, potentially obscuring a significant fraction of events. The advent of third-generation detectors, specifically the Einstein Telescope (ET), offers the potential to overcome these sensitivity limits. This study assesses the capability of the ET, both alone and in synergy with the Cosmic Explorer (CE), to detect GWs from CCSNe within the Milky Way (MW) and nearby satellite galaxies (Large and Small Magellanic Clouds), while quantifying the impact of dust extinction on multimessenger observability.

Methodology
The authors employed the GWFish simulation framework, customized to integrate:

Waveform Catalogs: State-of-the-art 3D radiation-hydrodynamics simulations from Fornax (Radice et al. 2019; Vartanyan et al. 2023). These catalogs cover progenitor masses from 9 to 25 $M_\odot$ and include both prompt bounce signals and longer-duration proto-neutron star (PNS) oscillations (f- and g-modes) driven by hydrodynamic instabilities (SASI, convection).
Source Population: A realistic all-sky distribution of massive stars generated using the TRILEGAL stellar population synthesis code. This simulation incorporates updated Galactic disk star formation histories (Mazzi et al. 2024) and assumes a Kroupa Initial Mass Function (IMF).
Detector Configurations: The study evaluated four network configurations:
- ET in a triangular ( $\Delta$ ) configuration (three 10 km interferometers).
- ET in a dual-L (2L) configuration (two 15 km interferometers).
- Combinations of the above with the US-based Cosmic Explorer (CE40, 40 km arms).
Detection Metrics: Signal-to-Noise Ratio (SNR) was calculated using a Fisher matrix approach adapted for stochastic waveforms, incorporating high-frequency detector transfer function corrections (breaking the long-wavelength approximation). A detection threshold of SNR $\ge$ 10 was adopted.
Extinction Analysis: To assess optical visibility, the authors mapped the simulated progenitor population against the Planck thermal dust optical depth map, applying Cardelli extinction laws to estimate the fraction of events obscured in optical surveys (limiting magnitude $m_{lim} = 22$ ).

Key Contributions

Framework Integration: The study extends GWFish to handle time-domain CCSN waveforms and realistic Galactic progenitor distributions, enabling self-consistent forecasts of detection horizons and rates.
Rate Estimation: By linking the TRILEGAL star formation rate to the CCSN rate via the IMF, the authors derive a Galactic CCSN rate of 1.9 per 100 years, consistent with multi-proxy estimates in the literature.
Configuration Comparison: A direct comparison of the ET $\Delta$ and 2L designs is provided, quantifying their relative performance for CCSN detection both in isolation and within a global network.
Extinction Quantification: The paper provides a quantitative estimate of the "hidden" fraction of Galactic CCSNe, demonstrating the necessity of GW/neutrino triggers for a complete census of Galactic core-collapse events.

Results

Detection Horizons:
- For a representative 15 $M_\odot$ progenitor, the ET (2L configuration) achieves a detection horizon of $\sim$ 106 kpc (median value, with 90% of detections falling between the 5th and 95th percentiles).
- Horizons generally range from $\sim$ 20 to >100 kpc with 90% confidence, depending on progenitor mass and waveform morphology.
- In a network with CE40, the reach extends to $\sim$ 170 kpc in favorable cases, covering the entire MW disk and providing partial to significant coverage of the Magellanic Clouds (up to >70% for the SMC with CE).
Coverage: The ET alone ensures essentially complete coverage of the Milky Way's stellar disk (radius $\sim$ 15–20 kpc) but offers only partial coverage of the Magellanic Clouds.
Configuration Performance: The 2L configuration provides a 15–20% improvement in detection horizon over the $\Delta$ configuration when operating alone. In a network with CE, this advantage diminishes to 5–10%, as the CE component compensates for the differences.
Optical Visibility: Due to dust extinction, approximately 50% of potential Galactic CCSNe would be too heavily obscured to be detected by optical surveys (limiting magnitude 22). The optical visibility fraction is estimated at $45 \pm 3\%$ , a value largely independent of the intrinsic luminosity of the supernova, confirming that dust is the dominant limiting factor.
Event Rates: Based on the derived rate of 1.9 per 100 years and a detection efficiency near unity for Galactic events, the authors estimate a $\sim$ 32% probability of detecting at least one Galactic CCSN during a 20-year operational lifetime of the ET.

Significance
The paper concludes that the Einstein Telescope will represent a transformative step for multimessenger astronomy regarding Galactic CCSNe. Its primary significance lies in its ability to provide high-probability detection of the next Galactic core-collapse event regardless of dust extinction. While optical surveys will likely miss the majority of events occurring in the inner Galactic disk, the combination of GW and neutrino observations (via networks like SNEWS) will enable the identification of these "hidden" events. This capability allows for targeted follow-up by infrared and high-energy observatories, ensuring a complete census of stellar deaths and providing unprecedented access to the physics of the collapse mechanism, the nuclear equation of state, and the chemical enrichment history of the Galaxy. The authors note that while current results are based on non-rotating progenitor models, the framework is established to incorporate more complex physics (rotation, magnetic fields, massive progenitors) as waveform catalogs expand.

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