🔭 astrophysics

The pair-instability origin of supernova 2023vbw

This paper presents detailed observations and modeling of the hydrogen-rich supernova 2023vbw, which exploded in a low-metallicity dwarf galaxy, providing strong evidence that it was a pair-instability supernova resulting from the complete disruption of a massive progenitor star with an ejecta mass of 170–350 M $_\odot$ .

Original authors: Daichi Hiramatsu, Edo Berger, Daichi Tsuna, Sebastian Gomez, Harsh Kumar, Peter K. Blanchard, Walter W. Golay, Anya E. Nugent, Takashi J. Moriya, D. Andrew Howell, Alexei V. Filippenko, Thomas G. Brin

Published 2026-05-19

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Daichi Hiramatsu, Edo Berger, Daichi Tsuna, Sebastian Gomez, Harsh Kumar, Peter K. Blanchard, Walter W. Golay, Anya E. Nugent, Takashi J. Moriya, D. Andrew Howell, Alexei V. Filippenko, Thomas G. Brink, WeiKang Zheng, Yi Yang, Moira Andrews, K. Azalee Bostroem, Joseph Farah, Curtis McCully, Megan Newsome, Estefania Padilla Gonzalez, Giacomo Terreran

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 a star as a giant, cosmic pressure cooker. Usually, when these pressure cookers run out of fuel, they collapse under their own weight and explode in a relatively standard way, like a firecracker going off. But scientists have long predicted that if a star is massive enough (roughly 140 to 260 times the mass of our Sun) and made of the right "ingredients" (low metal content), something much wilder happens.

Inside these super-heavy stars, the core gets so hot that energy turns directly into matter—specifically, pairs of electrons and positrons. It's like the pressure cooker suddenly turning its own heat into heavy weights. This causes the internal pressure to drop instantly, the star collapses, and then, instead of just fizzling out, it triggers a runaway nuclear explosion so powerful it completely obliterates the star, leaving no black hole behind. This is called a Pair-Instability Supernova (PISN).

For decades, astronomers have been looking for the "smoking gun" of this specific type of explosion. They found some suspects, but they were missing key evidence. That's where SN 2023vbw comes in.

The Discovery: A Cosmic "Ghost" in the Making

On October 12, 2023, a telescope called the Zwicky Transient Facility spotted a new, bright dot in the sky. It was located in a small, dim galaxy far away (about 1.3 billion light-years). At first, it looked like a standard stellar explosion, but as scientists watched it evolve, they realized this was no ordinary firework.

Think of a normal supernova like a campfire: it flares up, burns steadily for a while, and then slowly dies out. SN 2023vbw was different. It was like a slow-burning, super-charged furnace that took months to reach its peak brightness, shone with the intensity of a billion suns, and then lingered for a very long time.

The Evidence: Why This Was the "Perfect" PISN

The team, led by Daichi Hiramatsu, treated this event like a cosmic detective story, gathering clues from light and sound (spectra) to figure out what happened.

1. The Size of the Explosion (The "Ejecta")
When a star explodes, it throws debris outward. By measuring how fast this debris was moving and how much light it gave off, the scientists calculated the mass of the star.

The Analogy: Imagine trying to guess the size of a car by watching how far its pieces fly after a crash.
The Result: The debris weighed between 170 and 350 times the mass of our Sun. This is far too heavy for a normal star to explode. It fits perfectly into the "Goldilocks zone" for a Pair-Instability Supernova, where the star is heavy enough to trigger the electron-positron reaction but not so heavy that it collapses into a black hole immediately.

2. The Fuel (The "Nickel")
Supernovas shine because they create radioactive elements, mostly Nickel-56, which acts like a glowing battery.

The Analogy: A normal supernova has a AA battery; this one had a nuclear reactor core.
The Result: The explosion created between 1.2 and 1.6 Suns' worth of radioactive Nickel. This massive amount of fuel explains why the explosion was so bright and lasted so long.

3. The Shape of the Explosion (The "Disc")
As the light faded, the spectra (the "colors" of the light) showed something strange. The light wasn't coming from a perfect sphere; it was interacting with a ring of gas surrounding the star.

The Analogy: Imagine a firework exploding inside a hula hoop. The firework hits the hoop, creating a secondary, complex pattern of light and sound.
The Result: The star had likely shed a dense, disc-like ring of gas just before it died. This suggests the star might have been part of a binary system (a pair of stars) that merged together, spinning fast and flinging out material like a figure skater spinning with arms out, before finally exploding.

The Verdict

The paper concludes that SN 2023vbw is the first time we have seen a supernova that matches every single prediction for a Pair-Instability Supernova:

It happened in a low-metallicity environment (the right "recipe").
It had a massive progenitor star (the right "size").
It produced a huge amount of radioactive nickel (the right "fuel").
It had the right energy output (the right "explosion").

The scientists compared it to other famous explosions, like SN 1987A, but noted that SN 2023vbw was much more energetic and massive. They ruled out other theories, such as the star being powered by a spinning neutron star (a magnetar), because the star was simply too heavy for a neutron star to survive.

What's Next?

The paper suggests that with upcoming powerful telescopes like the Rubin Observatory and the Roman Space Telescope, we will likely find dozens or even hundreds of these events. Finding more of them will help us understand how the most massive stars in the universe live, die, and spread the heavy elements that make up planets and life itself.

In short, SN 2023vbw is the "Rosetta Stone" of stellar deaths, finally confirming a theory that has been sitting on the shelf for 50 years.

Problem
Theoretical models predict that stars with initial masses of $\sim140-260 M_\odot$ and carbon-oxygen core masses of $\sim50-130 M_\odot$ at low metallicity will undergo copious electron-positron pair production in their cores. This leads to a runaway thermonuclear explosion that completely obliterates the star, known as a pair-instability supernova (PISN). While some previous supernovae have been interpreted as PISN candidates, they have lacked the full range of predicted properties, particularly regarding total radiated energy, ejecta mass, and explosion energy. There remains a need for a confirmed PISN event that matches the theoretical regime in terms of luminosity, duration, and progenitor characteristics to constrain the deaths of the most massive stars in the Universe.

Methodology
The authors present detailed multi-wavelength observations and modeling of the hydrogen-rich supernova SN 2023vbw, discovered by the Zwicky Transient Facility (ZTF) on October 12.5, 2023.

Observations: The study utilizes photometry from ZTF, ATLAS, and the Las Cumbres Observatory (LCO) network across optical bands ( $g, r, i, z$ ), as well as near-infrared data. Spectroscopic follow-up was conducted using the MMT (Binospec), Lick (Kast), Keck I (LRIS), and Gemini North (GNIRS) telescopes, spanning from 134 to 545 days after first light.
Host Characterization: The host galaxy's spectral energy distribution (SED) and emission lines were analyzed to determine metallicity, stellar mass, and star formation rate.
Modeling: The authors employed a semi-analytical light-curve model that tracks hydrogen recombination in the ejecta and energy deposition by radioactive $^{56}\text{Ni}$ . They constrained parameters such as ejecta mass ( $M_{\text{ej}}$ ), kinetic energy ( $E_{\text{ej}}$ ), progenitor radius ( $R_0$ ), and $^{56}\text{Ni}$ mass ( $M_{\text{Ni}}$ ) by fitting the bolometric light curve and spectral evolution. They also modeled the early and late-phase excesses as interactions between the supernova ejecta and a circumstellar medium (CSM).
Comparisons: The derived parameters were compared against numerical PISN models (from BSG, YSG, and RSG progenitors) and standard iron core-collapse supernova (CCSN) models, including those powered by magnetars or fallback accretion.

Key Results

Light Curve and Energetics: SN 2023vbw exhibits a luminous ( $1.6 \times 10^{43}$ erg s $^{-1}$ ) and long-duration (190 days) main peak, followed by a rapid decline and an extended tail. The total radiated energy is $\sim3 \times 10^{50}$ erg, exceeding canonical core-collapse supernovae by more than an order of magnitude.
Progenitor and Explosion Properties: Semi-analytical modeling yields a blue supergiant (BSG)-like progenitor with an ejecta mass of $170-350 M_\odot$ , a radioactive nickel mass of $1.2-1.6 M_\odot$ , and an explosion energy of $(6-13) \times 10^{52}$ erg. These values significantly exceed those of ordinary iron CCSNe (e.g., SN 1987A) and even extreme events like OGLE14-073.
Metallicity: The event occurred in a low-metallicity environment ( $\sim0.1 Z_\odot$ ), consistent with PISN predictions. Spectral analysis indicates weak Fe II absorption, suggesting a metallicity lower than $0.1 Z_\odot$ for the progenitor.
CSM Interaction: The light curve shows an extended cooling phase and a tail-phase excess relative to $^{56}\text{Co}$ decay, both fit by a power-law component ( $t^{-3/8}$ ). Spectra reveal multicomponent line profiles with redshifted emission, indicating interaction with an aspherical, disc-like CSM. The inferred mass-loss rate is $\sim0.05 M_\odot$ yr $^{-1}$ .
Alternative Scenarios: The authors rule out alternative mechanisms such as magnetar spin-down or fallback accretion onto a black hole. These scenarios would require implausible progenitor masses, explosion energies ( $E_{\text{ej}} \approx 10^{53}$ erg), or sustained accretion rates inconsistent with the observed spectral evolution and stellar evolution theory.

Significance
The authors claim that the observed properties of SN 2023vbw—specifically the high ejecta mass, explosion energy, total radiated energy, and low metallicity—are well-matched to the regime of pair-instability supernova predictions. The event provides the first detailed confirmation of a PISN with a hydrogen-rich envelope, likely originating from a massive BSG progenitor formed via a binary merger channel. The discovery of such events, expected to increase with upcoming surveys like the Vera C. Rubin Observatory and the Nancy Grace Roman Space Telescope, will shed light on the formation, evolution, and death of the most massive stars, as well as their implications for the black hole mass gap and early chemical evolution.

The Discovery: A Cosmic "Ghost" in the Making

The Evidence: Why This Was the "Perfect" PISN

The Verdict

What's Next?

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