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Black widow evolution: magnetic braking by an ablated wind
High Energy Astrophysical Phenomena · Submitted 13 Jan 2020
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim We propose instead that the evaporative wind couples to the companion's magnetic field, removes angular momentum from the binary, and maintains stable Roche-lobe overflow.
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The abstract, sentence by sentence
Black widows are close binary systems in which a millisecond pulsar is orbited by a companion a few per cent the mass of the sun. It has been suggested that the pulsar's rotationally powered $\gamma$-ray luminosity gradually evaporates the companion, eventually leaving behind an isolated millisecond pulsar. The evaporation efficiency is determined by the temperature $T_{\rm ch}\propto F^{2/3}$ to which the outflow is heated by the flux $F$ on a dynamical time-scale. Evaporation is most efficient for companions that fill their Roche lobes. In this case, the outflow is dominated by a cap around the L1 point with an angle $\theta_g\sim (T_{\rm ch}/T_g)^{1/2}$, and the evaporation time is $t_{\rm evap}=0.46(T_{\rm ch}/T_g)^{-2}\textrm{ Gyr}$, where $T_g>T_{\rm ch}$ is the companion's virial temperature. We apply our model to the observed black widow population, which has increased substantially over the last decade, considering each system's orbital period, companion mass, and pulsar spin-down power. While the original (Fruchter et al. 1988) black widow evaporates its companion on a few Gyr time-scale, direct evaporation on its own is too weak to explain the overall population. We propose instead that the evaporative wind couples to the companion's magnetic field, removes angular momentum from the binary, and maintains stable Roche-lobe overflow. While a stronger wind carries more mass, it also reduces the Alfv\'en radius, making this indirect magnetic braking mechanism less dependent on the flux $t_{\rm mag}\propto t_{\rm evap}^{1/3}$. This reduces the scatter in evolution times of observed systems, thus better explaining the combined black widow and isolated millisecond pulsar populations.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Black widows are close binary systems in which a millisecond pulsar is orbited by a companion a few per cent the mass of the sun. | background 1.00 | 0.06 | 0.02 | asserted 1.00 |
| s1 | It has been suggested that the pulsar's rotationally powered $\gamma$-ray luminosity gradually evaporates the companion, eventually leaving behind an isolated millisecond pulsar. | background 1.00 | 0.03 | 0.04 | hedged possibility 0.95 |
| s2 | The evaporation efficiency is determined by the temperature $T_{\rm ch}\propto F^{2/3}$ to which the outflow is heated by the flux $F$ on a dynamical time-scale. | method 0.59 | 0.24 | 0.03 | asserted 1.00 |
| s3 | Evaporation is most efficient for companions that fill their Roche lobes. | result 0.63 | 0.29 | 0.03 | asserted 1.00 |
| s4 | In this case, the outflow is dominated by a cap around the L1 point with an angle $\theta_g\sim (T_{\rm ch}/T_g)^{1/2}$, and the evaporation time is $t_{\rm evap}=0.46(T_{\rm ch}/T_g)^{-2}\textrm{ Gyr}$, where $T_g>T_{\rm ch}$ is the companion's virial temperature. | method 0.55 | 0.61 | 0.04 | asserted 1.00 |
| s5 | We apply our model to the observed black widow population, which has increased substantially over the last decade, considering each system's orbital period, companion mass, and pulsar spin-down power. | method 0.57 | 0.90 | 0.04 | asserted 0.95 |
| s6 | While the original (Fruchter et al. 1988) black widow evaporates its companion on a few Gyr time-scale, direct evaporation on its own is too weak to explain the overall population. | gap 0.70 | 0.24 | 0.06 | asserted 0.94 |
| s7 | We propose instead that the evaporative wind couples to the companion's magnetic field, removes angular momentum from the binary, and maintains stable Roche-lobe overflow. | contribution 0.94 | 0.49 | 0.79 | speculative 0.53 |
| s8 | While a stronger wind carries more mass, it also reduces the Alfv\'en radius, making this indirect magnetic braking mechanism less dependent on the flux $t_{\rm mag}\propto t_{\rm evap}^{1/3}$. | result 0.55 | 0.72 | 0.13 | asserted 0.99 |
| s9 | This reduces the scatter in evolution times of observed systems, thus better explaining the combined black widow and isolated millisecond pulsar populations. | interpretation 0.93 | 0.69 | 0.30 | asserted 0.92 |
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The paper
Original abstract
Black widows are close binary systems in which a millisecond pulsar is orbited by a companion a few per cent the mass of the sun. It has been suggested that the pulsar's rotationally powered $\gamma$-ray luminosity gradually evaporates the companion, eventually leaving behind an isolated millisecond pulsar. The evaporation efficiency is determined by the temperature $T_{\rm ch}\propto F^{2/3}$ to which the outflow is heated by the flux $F$ on a dynamical time-scale. Evaporation is most efficient for companions that fill their Roche lobes. In this case, the outflow is dominated by a cap around the L1 point with an angle $\theta_g\sim (T_{\rm ch}/T_g)^{1/2}$, and the evaporation time is $t_{\rm evap}=0.46(T_{\rm ch}/T_g)^{-2}\textrm{ Gyr}$, where $T_g>T_{\rm ch}$ is the companion's virial temperature. We apply our model to the observed black widow population, which has increased substantially over the last decade, considering each system's orbital period, companion mass, and pulsar spin-down power. While the original (Fruchter et al. 1988) black widow evaporates its companion on a few Gyr time-scale, direct evaporation on its own is too weak to explain the overall population. We propose instead that the evaporative wind couples to the companion's magnetic field, removes angular momentum from the binary, and maintains stable Roche-lobe overflow. While a stronger wind carries more mass, it also reduces the Alfv\'en radius, making this indirect magnetic braking mechanism less dependent on the flux $t_{\rm mag}\propto t_{\rm evap}^{1/3}$. This reduces the scatter in evolution times of observed systems, thus better explaining the combined black widow and isolated millisecond pulsar populations.
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References
How the literature uses it
7 arXiv papers cite this in 10 sentences
Papers citing it · 6 sentences without a confident label
Contests it 1 paper
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However, the standard channel fails to account for the observed isolated MSP population within the Hubble time (e.g., [ref] ).
Ultra-compact X-ray Binaries: A Review · Black widows with extremely low masses · contest 0.71
Cites it as background 3 papers
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There is currently no consensus about the evolutionary connection between redbacks and black widows; while some argue that redbacks evolve into black widows, others find that they share a common origin after which they diverge (see, e.g., [ref] ; [ref] ; [ref] ; or the discussion in [ref] ).
Reconciling the Systemic Kicks of Observed Millisecond Pulsars, Spider Pulsars, and Low-mass X-ray Binaries · Introduction · 0.95
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For further theoretical and multiwavelength observational studies of MSPs in spider systems, see e.g. [ref] .
Sub-Millisecond Pulsars: Missing or Impossible? · Sub-MSPs from spiders? · 1.00
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We note recent work by [ref] in which they model outflows from black widow companions considering thermal and dynamical processes in the wind.
Study of spider pulsar binary eclipses and discovery of an eclipse mechanism transition · Mass loss · 0.98
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