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A Faint Progenitor System for the Faint Supernova 2024vjm

By analyzing deep pre-explosion images from the Euclid mission, this paper identifies the progenitor of the exceptionally faint Type Iax supernova SN 2024vjm as a system fainter than previously known candidates—potentially involving a subdwarf helium star—while noting that its slow fading rate contradicts the standard Phillips relation used for cosmological distance measurements.

Original authors: Erez A. Zimmerman, Avishay Gal-Yam, Paul J. Groot, Eran O. Ofek, Jan van Roestel, Andrea Pastorello, Stefano Valenti, Aravind P. Ravi, Ping Chen, Steve Schulze, Nadejda Blagorodnova, Maxime Wavasseur

Published 2026-02-12

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CC BY 4.0

Original authors: Erez A. Zimmerman, Avishay Gal-Yam, Paul J. Groot, Eran O. Ofek, Jan van Roestel, Andrea Pastorello, Stefano Valenti, Aravind P. Ravi, Ping Chen, Steve Schulze, Nadejda Blagorodnova, Maxime Wavasseur, Marco A. Gomez-Munoz, Hugo Tranin, Simon de Wet, Giorgos Leloudas, Paul M. Vreeswijk, Lindsey A. Kwok, Michaela Schwab, Saurabh W. Jha, Kate Maguire, David J. Sand, Eric Stringer, Thomas Kupfer, Tamar Faran, Joseph P. Anderson, Jennifer Andrews, Moira Andrews, Avshalom Badash, Steven Bloemen, K. Azalee Bostroem, Ting-Wan Chen, Massimo Della Valle, Georgios Dimitriadis, Yize Dong, Joseph R. Farah, James H. Gillanders, Benjamin Godson, Mariusz Gromadzki, Daichi Hiramatsu, Emily Hoang, D. Andrew Howell, Daryl Janzen, Hanindyo Kuncarayakti, Jiaxuan Li, Joseph D. Lyman, Keiichi Maeda, Mark R. Magee, Curtis McCully, Darshana Mehta, Andrew Milligan, Shane Moran, Yuan Qi Ni, David O'Neill, Jeniveve Pearson, Danielle L. A. Pieterse, Giuliano Pignata, Andrea Reguitti, Daniel E. Reichart, Nicolas Meza Retamal, Rita P. Santos, Simone Scaringi, Manisha Shrestha, Shubham Srivastav, Fiorenzo Stoppa, Bhagya Subrayan, Giorgio Valerin, Xiaofeng Wang, Kathryn Wynn, Ofer Yaron, Weicheng Zang

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

The Mystery of the "Faint and Slow" Cosmic Firework

Imagine you are at a massive fireworks display. Most of the fireworks are huge, bright, and explode with a deafening BOOM, lighting up the entire sky for a few seconds before fading away quickly. In astronomy, these are like "normal" Type Ia Supernovae—massive explosions of dying stars that are so predictable we use them as cosmic rulers to measure the universe.

But every once in a while, you see a tiny, dim spark. It’s not a massive explosion; it’s more like a small, sputtering firecracker. For a long time, astronomers have been puzzled by these "faint" explosions (called Type Iax supernovae). We knew they were different, but we couldn't quite figure out what kind of "firecracker" was causing them.

Recently, a new, incredibly dim firework appeared: SN 2024vjm. This paper describes the investigation into this tiny cosmic spark.

1. The Detective Work: Finding the "Missing" Star

Before a firework goes off, there is a device that holds the gunpowder. In space, that "device" is a star. Usually, when a star explodes, the light is so bright it hides whatever was there before.

However, because this explosion was so incredibly faint, astronomers were able to use a high-tech "time machine"—the Euclid space telescope—to look at a picture of that exact spot taken before the explosion happened.

The Analogy: It’s like looking at a photo of a dark stage before a play starts. If a massive spotlight had exploded, you would have seen a giant lamp in the photo. But in this photo, the stage was almost pitch black. This tells us the "firecracker" wasn't a massive, glowing star; it was something much smaller and dimmer, likely a tiny, compact star called a White Dwarf paired with a very small, quiet companion.

2. The Weird Behavior: The "Slow-Motion" Fade

This is where things get truly strange. Most fireworks follow a rule: the bigger and brighter they are, the faster they fade. This is known as the "Phillips Relation." It’s like a bright candle that burns intensely and then vanishes, while a tiny matchstick flickers for a bit.

SN 2024vjm broke all the rules.

Even though it was one of the faintest explosions ever seen, it didn't vanish quickly. Instead, it lingered. It was a "faint-yet-slow" event.

The Analogy: Imagine a tiny sparkler. Usually, a sparkler burns out in seconds. But this specific sparkler was so weak that it couldn't actually "push" its own smoke away. Because the explosion was so low-energy, the "smoke" (the debris from the star) stayed thick and heavy, trapped right around the explosion site. This thick cloud of smoke acted like a heavy blanket, trapping the heat and light inside and forcing it to leak out very, very slowly.

3. The Leftovers: A Ghost in the Machine

When a massive star explodes, it usually gets completely obliterated—turned into dust and scattered across the galaxy. But because SN 2024vjm was such a "weak" explosion, the scientists believe it didn't destroy everything.

The Analogy: Think of a grenade versus a firecracker. A grenade shatters everything in the room. A firecracker might just pop and leave the pieces of the casing sitting on the floor. The researchers suggest that this explosion likely left behind a "bound remnant"—a small, charred piece of the original star that survived the blast, sitting quietly in the dark.

Why does this matter?

This paper is important because it proves that the "family" of supernovae is much more diverse than we thought. It shows that there is a whole category of "tiny, slow-burning" cosmic events that don't follow the standard rules of the universe. By studying these "misfit" explosions, astronomers are learning more about how stars live, die, and leave behind the building blocks of the cosmos.

Technical Summary: A Faint Progenitor System for the Faint Supernova 2024vjm

1. Problem and Context

Type Ia Supernovae (SNe Ia) are critical cosmological distance indicators due to their uniform thermonuclear origin (White Dwarf explosions). However, the Type Iax subclass presents a significant challenge to this uniformity. SNe Iax are less energetic and highly diverse. While some bright SNe Iax (like SN 2012Z) have identified luminous blue star progenitors (likely helium giant companions), current models fail to explain the properties of the faintest SNe Iax. There is an ongoing debate as to whether these extremely faint events originate from specific White Dwarf (WD) binary systems or from massive progenitor stars.

2. Methodology

The researchers conducted a multi-wavelength follow-up campaign of SN 2024vjm, discovered by the BlackGEM Local Transient Survey. The study employed several advanced techniques:

Deep Archival Imaging: Utilizing high-resolution pre-explosion images from the Euclid space mission to search for a progenitor star at the exact explosion site.
Astrometry: Achieving sub-pixel precision (within 10 milliarcseconds) by averaging multiple ground-based BlackGEM images to pinpoint the explosion site within the Euclid VIS-band image.
Stellar Evolution Modeling: Comparing brightness limits against BPASS (Binary Population and Spectral Synthesis) stellar evolution tracks to rule out various progenitor channels.
Bolometric Light Curve Analysis: Using the Katz integral method to analyze the energy deposition from radioactive $^{56}\text{Ni}$ decay and determine the $\gamma$ -ray escape time ( $t_0$ ).
Spectroscopic Evolution: Analyzing optical and Near-Infrared (NIR) spectra (including JWST data) to measure expansion velocities and chemical abundances (LME, IME, and IGE).

3. Key Contributions

Progenitor Constraints: For the first time, the study demonstrates that not all SNe Iax progenitors are luminous. It provides strict upper limits on the progenitor's brightness, ruling out massive hydrogen-rich stars, massive helium stars, and most Wolf-Rayet stars.
Identification of a New Evolutionary Trend: The paper identifies that the faintest SNe Iax follow a physical correlation opposite to the famous Phillips relation. While normal SNe Ia fade faster when they are fainter, SN 2024vjm (and the faintest Iax subclass) fades more slowly as they become fainter.
Ejecta Dynamics: The study links the slow photometric decline to exceptionally low expansion velocities, which keeps the ejecta optically thick to $\gamma$ -rays for a longer duration.

4. Results

Extreme Faintness: SN 2024vjm reached a peak B-band absolute magnitude of $M_B \approx -12.7$ , making it potentially the faintest supernova observed to date.
Low Nickel Yield: The explosion synthesized only $\approx 3.6 \times 10^{-3} M_\odot$ of $^{56}\text{Ni}$ , two orders of magnitude less than a standard SN Ia.
Progenitor Candidate: The Euclid data suggests the progenitor was likely a low-mass binary system, such as a hot subdwarf (sdB)-WD binary or a low-mass main-sequence companion, rather than a massive star.
Ejecta Mass and Velocity: The ejecta mass is estimated at $M_{ej} \approx 0.1 M_\odot$ . Expansion velocities were remarkably low, dropping from $\sim 3000 \text{ km s}^{-1}$ to $< 1000 \text{ km s}^{-1}$ shortly after peak.
$\gamma$ -ray Trapping: The $\gamma$ -ray escape time was measured at $70\text{--}80$ days, significantly longer than the $30\text{--}45$ days typical of regular SNe Ia.
Bound Remnant: The findings support the existence of a gravitationally bound remnant left behind by the weak deflagration explosion.

5. Significance

This research fundamentally shifts the understanding of the Type Iax subclass. By proving that the faintest Iax events originate from faint progenitor systems and follow a unique "faint-yet-slow" evolution, the paper provides a new physical framework for low-energy thermonuclear explosions. It highlights the necessity of deep, wide-field space surveys (like Euclid, LSST, and the Roman Space Telescope) to probe the extreme ends of the supernova population and refine our models of stellar death and binary evolution.