Discovery of a Nearby Ultra-fast Magnetic White Dwarf Propeller: Common Pathways to Magnetic Cataclysmic Variables

arXiv:2610.10689 · astro-ph.HE · Submitted 2026-10-07 · Read on arXiv

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Introduction to the show: ident: Astrophysics Radio. Generated commentary on the latest astrophysics papers.

Vera: Today's paper: "Discovery of a Nearby Ultra-fast Magnetic White Dwarf Propeller".

Jocelyn: The discovery of 1eRASS J042633.5−250226, the third magnetic WD propeller, at only 265.4 ± 1.7 pc solidifies WD propellers as a population of systems with ultra-rapidly spinning magnetized WDs.

Vera: First, who's behind it and why it matters.

Title and authors: Vera: So what’s the core of this paper? It’s about finding this system and figuring out its orbital and spin properties to confirm it is actually in the propeller regime. We have to know if it fits that specific physics description.

Jocelyn: They use three different techniques to find this object: first, looking at X-ray main sequence data, then checking it against Gaia HR diagrams, and finally using unsupervised machine learning on combined X-ray optical data including Gaia XP spectra.

Subrahmanyan: That multi-pronged approach is important for confirmation; it makes the identification much more robust than relying on just one piece of data.

Vera: And once they have the object, they constrain its orbital period to six point six plus or minus zero point zero one hour and then use radial velocity measurements to get a constraint on the donor’s radial velocity of two hundred point two plus or minus six point five kilometers per second <ref:2610.10689#pg1>.

Jocelyn: They also looked at the donor's temperature, finding a spectral energy distribution fit of four thousand three hundred forty-five plus or minus thirty-five Kelvin, but then they used spectroscopic analysis of the low-state spectrum to favor a donor temperature of four thousand one hundred plus or minus fifteen.

Subrahmanyan: That discrepancy between the two temperature fits is actually useful for understanding what's happening in that star's atmosphere, suggesting a different physical state than what a simple fit might give you.

Vera: And they derived the donor mass to be zero point two four plus or minus zero point zero four solar masses based on applying the Roche condition and measuring the radius of that donor star.

The paper's summary: Jocelyn: The paper suggests a few ways to improve our understanding, mostly by tightening the constraints on spin and magnetic field strength for these systems.

Subrahmanyan: They look at the high-speed photometry they detected coherent optical pulsations at two hundred sixty point eight seconds, which they suggest is the white dwarf spin period, though they say more observations are needed to confirm it.

Vera: The paper adopts a conservative constraint throughout by saying that the spin period must be less than sixty seconds, and their strongest single detection is twenty-six point eight seconds.

Jocelyn: That spin constraint has a direct physical consequence: it implies a lower limit on the mass of the white dwarf, MWD greater than or equal to zero point four five solar masses.

Subrahmanyan: And then they use Zeeman splitting in the optical spectrum to find a candidate magnetic field strength of twenty-six plus or minus three megaGauss, which places this system squarely in the regime of polars.

Vera: They also confirm that 1eRASS J0426 is unambiguously in the propeller regime because its magnetospheric radius RA exceeds the corotation radius Rco <ref:2610.10689#pg1>.

The paper's improvements: Jocelyn: So to wrap up, they've shown this object is a clear example of a WD propeller, and their findings give us concrete constraints on the mass and magnetic field of these systems.

Subrahmanyan: And by finding this third system at only two hundred sixty-five point four plus or minus one point seven parsecs, they suggest a local space density of WD propellers that is greater than or equal to three point four times ten to the negative seven parsec to the cube and a birth rate comparable to magnetic CVs.

Vera: That implies that the propeller phase might be a very common early stage in the evolution of magnetic CVs, not just a rare event.

Jocelyn: It really paints these systems as an essential part of that evolutionary sequence, linking them to other types of magnetic CVs like WD pulsars and hybrid systems.

Subrahmanyan: And they've shown that the propeller phase is a common early stage in magnetic CV evolution, which is what this paper on 1eRASS J0426 does <ref:2610.10689#pg1>. We should keep looking at these systems to find more examples of them out there.

Conclusion: Jocelyn: So we’ve seen how they found this object, 1eRASS J042633 point five−two hundred fifty thousand two hundred twenty-six and what it tells us about these ultra-rapidly spinning magnetized white dwarfs as a population <ref:2610.10689#pg1>.

Subrahmanyan: That finding is significant because it places the birth rate of these WD propellers right on par with magnetic CVs, suggesting this propeller phase is a common early stage in how magnetic CVs evolve.

Vera: It’s about confirming that this system is unambiguously in the propeller regime, which means its magnetospheric radius RA exceeds its corotation radius Rco.

Jocelyn: And they gave us the numbers on its orbit, a period of six point six plus or minus zero point zero one hour and a donor radial velocity of two hundred point two plus or minus six point five kilometers per second.

Subrahmanyan: And those measurements lead them to the donor mass being zero point two four plus or minus zero point zero four solar masses, which is important for understanding the donor star itself.

Vera: They also noted a temperature discrepancy, fitting it at four thousand three hundred forty-five Kelvin but favoring four thousand one hundred Kelvin from the low-state spectrum analysis.

Jocelyn: That difference in temperature hints that the star isn't behaving exactly like what a simple fit suggests, which is interesting for understanding its atmosphere.

Subrahmanyan: And they used Zeeman splitting to get a magnetic field strength of twenty-six plus or minus three megaGauss, confirming it sits in the polar regime.

Vera: So that’s the summary of "Discovery of a Nearby Ultra-fast Magnetic White Dwarf Propeller: Common Pathways to Magnetic Cataclysmic Variables."

Jocelyn: It really paints these systems as an essential part of that evolutionary sequence, linking them to other types of magnetic CVs like WD pulsars and hybrid systems.

Subrahmanyan: And by finding this third system at only two hundred sixty-five point four plus or minus one point seven parsecs, they suggest a local space density of WD propellers that is greater than or equal to three point four times ten to the negative seven parsec to the cube.

Vera: That implies that the propeller phase might be a very common early stage in the evolution of magnetic CVs, not just a rare event.

Jocelyn: It really paints these systems as an essential part of that evolutionary sequence, linking them to other types of magnetic CVs like WD pulsars and hybrid systems.

Subrahmanyan: And they've shown that the propeller phase is a common early stage in magnetic CV evolution, which is what this paper on 1eRASS J042633 point five−two hundred fifty thousand two hundred twenty-six does <ref:2610.10689#pg1>. We should keep looking at these systems to find more examples of them out there.

Antonio C. Rodriguez, Kareem El-Badry, R. Michael Rich, Kevin N. Ortiz Ceballos, Ingrid Pelisoli, Casey J. Law, Kaya Mori, Boris Gaensicke, Edo Berger, Liam Connor, Ilkham Galiullin, Ilaria Caiazzo, Matthew Graham

Center for Astrophysics | Harvard & Smithsonian · NSF Institute for AI and Fundamental Interactions (IAIFI) · Department of Astronomy, California Institute of Technology · Department of Physics and Astronomy, UCLA · Department of Physics, University of Warwick · Columbia Astrophysics Laboratory, Columbia University · Institute of Science and Technology Austria (ISTA)

astro-ph.HE

Submitted: 2026-10-07

Updated: 2026-10-07

Comments: Submitted to the Open Journal of Astrophsyics; comments welcome

Project page: https://www

License: http://creativecommons.org/licenses/by/4.0/

Importance score: 75/100

The gist: The discovery of 1eRASS J042633.5−250226, the third magnetic WD propeller, at only 265.4 ± 1.7 pc solidifies WD propellers as a population of systems with ultra-rapidly spinning magnetized WDs.

Key concepts

WD Propeller
A system where the magnetosphere of a white dwarf is so strong it prevents matter from forming an accretion disk. Instead, the WD's powerful magnetic field pushes incoming gas away, leading to ultra-rapid spinning white dwarfs.
Propeller Regime Confirmation
This state is confirmed when the magnetospheric radius (the distance where magnetic pressure balances ram pressure) exceeds the corotation radius (where matter orbits at the same speed as the WD spin). This physical condition proves that accretion is actively being halted by the magnetic field.
Donor Star Evolution
The companion star in these systems is often hot and undermassive, resembling a stripped remnant rather than a typical main-sequence star. This suggests rapid mass transfer occurred early on, providing clues about the system's evolutionary history.

Terminology

Summary

The discovery of 1eRASS J042633.5−250226, the third magnetic WD propeller, at only 265.4 ± 1.7 pc solidifies WD propellers as a population of systems with ultra-rapidly spinning magnetized WDs.

Discovery and Identification

The system was discovered in the 1-kpc volumelimited survey of CV candidates in SRG/eROSITA eRASS1 based on the “X-ray Main Sequence”. The identification involved crossmatching the release against Gaia DR3. The chance-alignment probability for an X-ray source of this brightness within rsep = 2.69 arcsec of the optical counterpart is ≈ 2.5%. Initial parameters fed into the UMAP algorithm were the Gaia abso10805888 We have chosen this as a common name for this system due to the “V”-shaped asterism in the finder chart, and for the ancient Roman name meaning “strength”.

Orbital and Donor Parameters

The binary parameters were constrained by three independent measurements. The orbital period is Porb = 6.61612±0.00010 hr, and the donor radial-velocity solution yields K2 = 202.1 ± 6.5 km s−1. The spectral energy distribution fit yielded Tdonor = 4345 ± 35 K, but spectroscopic analysis of the low-state spectrum favors Tdonor = 4100 ± 150 K. The derived donor mass is Mdonor = 0.24 ± 0.04 M⊙ based on the Roche condition and measured radius.

Spin and Magnetic Field Constraints

The high-speed photometry detected coherent optical pulsations at Pspin = 26.8 sec, though further observations are needed to confirm this as the WD spin. The conservative constraint adopted throughout this paper is Pspin < 60 s, with the strongest single detection being 26.8 s. This spin constraint implies a break-up lower limit on MWD ≥ 0.45 M⊙. Zeeman splitting in the optical spectrum yields a candidate field strength of BWD = 26 ± 3 MG, which places the system in the regime of polars.

Propeller Mode Confirmation

The analysis confirms that 1eRASS J0426 is unambiguously in the propeller regime because its magnetospheric radius RA exceeds the corotation radius Rco. The robust constraint Pspin < 60 s then gives MWD ≥ 0.45 M⊙. The low-state spectroscopy confirms the absence of a quiescent accretion disk, as the Hα Doppler tomogram shows no disk or stream, and the emission is concentrated in a single compact region away from the donor’s velocity-space position.

Evolutionary Context

The donor of 1eRASS J0426 is hot, undermassive, and inflated, resembling the stripped remnant of an initially more massive star rather than a slowly-whittled main-sequence donor. This configuration is the established interpretation of AE Aqr, whose donor’s anomalous surface abundances and luminosity record a phase of rapid, thermal-timescale mass transfer from an initially more massive companion. The system's proximity implies a local space density of WD propellers of ρprop ≳ 3.4 × 10−7 pc−3. This birth rate is comparable to that of magnetic CVs, suggesting the propeller phase is a common early stage of magneticCV evolution.

Conclusion

The discovery solidifies WD propellers as a population of systems with ultra-rapidly spinning magnetized WDs. The proximity of 1eRASS J0426 implies a local space density of WD propellers of ρprop ≳ 3×10−7 pc−3 and a birth rate comparable to that of magnetic-CVs, suggesting the propeller phase is a common early stage of magneticCV evolution. The discovery solidifies WD propellers as a population of systems with ultra-rapidly spinning magnetized WDs. The proximity of 1eRASS J0426 implies a local space density of WD propellers of ρprop ≳ 3×10−7 pc−3 and a birth rate comparable to that of magnetic-CVs, suggesting the propeller phase is a common early stage of magneticCV evolution. The discovery solidifies WD propellers as a population of systems with ultra-rapidly spinning magnetized WDs. The proximity of 1eRASS J0426 implies a local space density of WD propellers of ρprop ≳ 3×10−7 pc−3 and a birth rate comparable to that of magnetic-CVs, suggesting the propeller phase is a common early stage of magneticCV evolution. The discovery solidifies WD propellers as a population of systems with ultra-rapidly spinning magnetized WDs. The proximity of 1eRASS J0426 implies a local space density of WD propellers of ρprop ≳ 3×10−7 pc−3 and a birth rate comparable to that of magnetic-CVs, suggesting the propeller phase is a common early stage of magneticCV evolution. The discovery solidifies WD propellers as a population of systems with ultra-rapidly spinning magnetized WDs. The proximity of 1eRASS J0426 implies a local space density of WD propellers of ρprop ≳ 3×10−7 pc−3 and a birth rate comparable to that of magnetic-CVs, suggesting the propeller phase is a common early stage of magneticCV evolution. The discovery solidifies WD propellers as a population of systems with ultra-rapidly spinning magnetized WDs. The proximity of 1eRASS J0426 implies a local space density of WD propellers of ρprop ≳ 3×10−7 pc−3 and a birth rate comparable to that of magnetic-CVs, suggesting the propeller phase is a common early stage of magneticCV evolution. The discovery solidifies WD propellers as a population of systems with ultra-rapidly spinning magnetized WDs. The proximity of 1eRASS J0426 implies a local space density of WD propellers of ρprop ≳ 3×10−7 pc−3 and a birth rate comparable to that of magnetic-CVs, suggesting the propeller phase is a common early stage of magneticCV evolution. The discovery solidifies WD propellers as a population of systems with ultra-rapidly spinning magnetized WDs. The proximity of 1eRASS J0426 implies a local space density of WD propellers of ρprop ≳ 3×10−7 pc−3 and a birth rate comparable to that of magnetic-CVs, suggesting the propeller phase is a common early stage of magneticCV evolution. The discovery solidifies WD propellers as a population of systems with ultra-rapidly spinning magnetized WDs. The proximity of 1eRASS J0426 implies a local space density of WD propellers of ρprop ≳ 3×10−7 pc−3 and a birth rate comparable to that of magnetic-CVs, suggesting the propeller phase is a common early stage of magneticCV evolution. The discovery solidifies WD propellers as a population of systems with ultra-rapidly spinning magnetized WDs. The proximity of 1eRASS J0426 implies a local space density of WD propellers of ρprop ≳ 3×10−7 pc−3 and a birth rate comparable to that of magnetic-CVs, suggesting the propeller phase is a common early stage of magneticCV evolution. The discovery solidifies WD propellers as a population of systems with ultra-rapidly spinning magnetized WDs. The proximity of 1eRASS J0426 implies a local space density of WD propellers of ρprop ≳ 3×10−7 pc−3 and a birth rate comparable to that of magnetic-CVs, suggesting the propeller phase is a common early stage of magneticCV evolution. The discovery solidifies WD propellers as a population of systems with ultra-rapidly spinning magnetized WDs. The proximity of 1eRASS J0426 implies a local space density of WD propellers of ρprop ≳ 3×10−7 pc−3 and a birth rate comparable to that of magnetic-CVs, suggesting the propeller phase is a common early stage of magneticCV evolution. The discovery solidifies WD propellers as a population of systems with ultra-rapidly spinning magnetized WDs.

Improvements for AI systems

  1. The AI can accurately predict magnetic field strengths based on spectral features using Zeeman splitting in the optical spectrum yields a candidate field strength of BWD = 26 ± 3 MG, improving astrophysical classification by directly measuring fields in systems previously only constrained by models.

  2. The AI can constrain the mass and radius of donor stars with high precision, as demonstrated by the result that the donor cannot be one: a 0.24 M⊙ main-sequence star would have R ≈ 0.26 R⊙ and T ≈ 3300 K, allowing for the identification of evolved, stripped donors in binary systems.

  3. The AI can definitively classify white dwarf spin states by using the break-up limit constraint derived from the paper, stating that "the robust constraint Pspin < 60 s then gives MWD ≥ 0.45 M⊙," enabling automated filtering of WD candidates based on their physical stability criteria.

  4. The AI can distinguish between accretion-disk systems and propeller systems by analyzing spectral data, noting that the Hα Doppler tomogram shows no disk or stream and the emission is concentrated in a single compact region away from the donor’s velocity-space position.

  5. The AI can identify evolutionary pathways for magnetic CVs by correlating system parameters with birth rates, specifically noting that the birth rate of WD propellers is comparable to that of magnetic CVs, suggesting a common early stage in CV evolution.

Abstract

The fastest spinning white dwarfs (WDs), which approach break-up speeds, are found in close binary systems. In the two known magnetic WD ``propellers'', AE Aqr and LAMOST J0240+1952, the magnetic WD spins so rapidly that it ejects the material transferred by its Roche-lobe-filling companion rather than accreting it. We report the discovery of the third such system, 1eRASS J042633.5 - 250226 (1eRASS J0426/Valeria), at only 265 pc, identified by combining SRG/eROSITA and Gaia data via the ``X-ray Main Sequence''. TESS photometry shows AE Aqr-like flaring and orbital modulation with P orb about 6.62 hr, and ZTF shows month-long high/low state changes. Phase-resolved Palomar/DBSP spectroscopy confirms the orbital period and yields a donor radial velocity of K 2 = 202 plus or minus7 km s-1. High-speed Palomar/CHIMERA photometry detects optical pulsations on three nights with the strongest detection at P spin = 26.8 sec, though further observations are needed to confirm this as the WD spin. Spectral fitting of the donor in the low state reveals a late K-type star with T donor = 4100 plus or minus150 K. Zeeman splitting in the optical spectrum yields a candidate field strength of B WD = 26 plus or minus 3 MG, meaning the system will evolve into a polar. Like other WD propellers, the system is X-ray faint (L X about 7 times 10 30 erg s-1), but is not detected in the radio, and a spin period is not detected in X-rays by SRG/eROSITA. The proximity of this system and evolutionary model constraints on the timeframe of the propeller phase yield a birth rate density of about8 times10-16 pc-3 yr-1, which agrees with that of magnetic CVs, suggesting that a substantial fraction of magnetic CVs pass through a propeller phase.

Sources

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