---
title: Supernova SN 1181 & Pa 30 Remnant
url: https://www.emergentmind.com/topics/supernova-sn-1181
type: topic
---

# Supernova SN 1181 & Pa 30 Remnant

Supernova SN 1181 is a historically recorded Galactic transient observed in AD 1181, now conclusively identified as a sub-luminous Type Iax supernova event resulting from a double-degenerate merger of white dwarfs. Its remnant, Pa 30 (centering on the O-rich Wolf–Rayet star IRAS 00500+6713 / J005311, also “Parker’s star”), uniquely enables direct study of both the surviving stellar remnant and the ejecta, providing a benchmark for white dwarf merger physics and supernova diversity.

## 1. Historical Observations and Identification

Multiple independent records detail the guest star of AD 1181, including Chinese, Japanese, and, newly, Arabic sources [2509.04127]. These describe a stationary transient in Cassiopeia (al-Kaff al-Khaḍīb), visible for ca. 185 days, peaking at a visual magnitude between 0 and −1.4 ([2301.04807], [2509.04127]). This excludes novae or comets, indicating a supernova event. The new Arabic poem from Cairo, contemporaneous to 1181, identifies the star in Cassiopeia, brighter than α Cas (2.25 mag), closely matching East Asian positional and brightness constraints [2509.04127].

Table 1: SN 1181 Historical Data

| Culture  | Dates (AD 1181) | Sky Region      | Max Brightness         |
|----------|-----------------|-----------------|-----------------------|
| Chinese  | Aug–Feb         | Chuanshe/Cassiopeia | 0.0 > V > −1.4         |
| Japanese | Aug–Feb         | Chuanshe/Cassiopeia | Comparable to Saturn  |
| Arabic   | Dec–May         | al-Kaff al-Khaḍīb (Cassiopeia) | > 2.25 mag (α Cas) |

These records, combined with modern astrometry (Gaia DR3 d ≈ 2.3–2.5 kpc) and extinction (E(B–V) ≈ 0.84), yield a peak absolute magnitude −14.5 > M_V,peak > −16.0 [2301.04807], confirming it as a sub-luminous supernova.

## 2. Remnant Association: Pa 30 and “Parker’s Star”

The identification of Pa 30 as the SN 1181 remnant was established by multi-wavelength investigations [2105.12384]. The SNR is centered on an exceptionally hot hydrogen- and helium-deficient star, exhibiting O-dominated Wolf–Rayet–like spectra. Earlier candidates (e.g., 3C58) are now excluded due to age (>3000 yr) and location inconsistencies [2105.12384], [2509.04127].

Key parameters:

- Central star: IRAS 00500+6713/J005311, T_eff ≈ 200,000–260,000 K, rapid wind v_terminal ≈ 15,000–16,000 km/s [2208.03946], [2301.04809], [2410.10940]
- Nebula diameter: θ ≈ 170″, d ≈ 2.3 kpc, physical size ≈ 1.9 pc
- Remnant age: t_k ≈ d/(2 v_exp) ≈ 990^{+280}_{−220} years [2105.12384]
- Ejecta velocity: v_exp ≈ 1100 km/s, consistent with expansion over ∼840–1150 yr [2301.04807], [2410.10940]

The nebular and stellar spectral and kinematic properties, coupled with position, confirm Pa 30’s association with SN 1181.

## 3. Physical Properties: Structure, Composition, and Kinematics

Pa 30’s nebula displays a unique filamentary, radially symmetric structure, with dozens of filaments converging on its hot central star [2301.04809], [2410.10940]. Electron density diagnostics via [S II] λ6716/λ6731 yield n_e ≈ 100–700 cm⁻³ [2301.04809]. No Hα emission is detected (I[6716/Hα] > 5), with faint [Ar III] λ7136, indicating H-poor, S, Ar-rich composition. Infrared imaging (WISE, Spitzer) reveals a thick shell and a sharp inner edge corresponding to a dust-rich cavity, with dust mass ≈ 8 × 10⁻³ M_☉ at T ≈ 60 K [2208.03946], [2410.10940].

Integral field spectroscopy (KCWI) enables 3D mapping of ejecta velocities and positions ([S II] doublet). The ejecta expansion is nearly ballistic (v = k · r / τ, k ≈ 0.97), with minimal deceleration since explosion [2410.10940]. A pronounced flux asymmetry is observed: redshifted filaments are ∼40% brighter than blueshifted, suggesting explosion asymmetry or uneven ejecta distribution.

Table 2: Pa 30 Remnant Physical Parameters

| Quantity              | Value (approximate)       |
|-----------------------|--------------------------|
| Age                   | 990^{+280}_{−220} yr     |
| Ejecta velocity       | ≈ 1100 km/s              |
| Wind speed (central star) | ≈ 16,000 km/s         |
| Ejecta mass           | 0.15 ± 0.05 M_☉          |
| Dust mass (cold shell)| ≈ 8e-3 M_☉               |
| Electron density      | 100–700 cm⁻³             |

## 4. Double-Degenerate Merger and Type Iax Supernova Mechanism

The spectral and morphological evidence favors a double-degenerate (CO+ONe WD) merger for SN 1181, leading to a subluminous Type Iax explosion [2105.12384], [2208.03946], [2304.14669]. The merger triggers a weak thermonuclear explosion: only part of the system is unbound, ejecting ∼0.1–0.5 M_☉ at ∼1100 km/s, while the remnant star survives as an O-rich-helium-poor compact object. The peculiar abundances—H and He deficiency, O/C dominance, Ne/O < 0.15—exclude standard core-collapse and favor CO-rich merger products [2208.03946].

Late-time evolution is modulated by delayed wind onset (∼810–828 yr post-explosion, after A.D. 1990), interpreted as resulting from Kelvin–Helmholtz contraction and carbon-burning in the ONe core [2304.14669]. The inner X-ray nebula thus forms as the fast wind collides with fallback ejecta, and the outer nebula at the expanding SNR–ISM interface.

Key formula for kinematic age:

$
t_k = \frac{\text{Diameter}}{2 v_{\exp}} = \frac{d \cdot \theta}{2 v_{\exp}},
$
with $\theta$ in radians and $d$ from Gaia astrometry.

## 5. Multiwavelength Observations: X-ray, Infrared, Radio

X-ray imaging (XMM–Newton, Chandra) resolves two nebular components [2304.14669]:

- Inner nebula: wind termination shock, enriched in carbon-burning ashes, angular radius ∼0.77–1.6″, T_shock ≈ 4 MK, metal-rich, low H.
- Outer nebula: shocked SN ejecta and ISM, angular extent ≈ 131″, composition closer to solar.

Infrared SEDs (WISE, AKARI, IRAS) fit cold dust at T ≈ 60 K [2208.03946]; the shell marks a shock boundary correlating with optical filament inner edges.

Radio emission models predict synchrotron fluxes: outer SNR shock (0.1–10 mJy at 0.01–1 GHz), inner termination shock (0.01–0.1 mJy at 1–10 GHz) [2401.12487]. Archival searches (VLASS, NVSS, CGPS) yield non-detections; higher-sensitivity, high-frequency, high-resolution observations are strongly encouraged to resolve the termination shock and assess wind–ejecta interaction dynamics.

## 6. Implications and Broader Significance

The SN 1181/Pa 30 association establishes the first unambiguous identification of a Type Iax supernova in the Galaxy [2105.12384], [2301.04807]. Observational access to both the stellar remnant and young ejecta provides a laboratory for testing merger dynamics, thermonuclear explosion mechanisms, wind evolution, and SNR chemistry. Empirical constraints (t_k, M_ej, v_exp, chemical stratification) support models of failed detonations/sub-Chandrasekhar mass explosions with persistent post-SN winds.

Historically, the multi-cultural records (Chinese, Japanese, Arabic) enable precise cross-dating and localization, validating the merger scenario and challenging earlier associations (3C58) [2509.04127]. Improved dating—down to months—advances reconstructive modeling for remnant ages and progenitor properties.

Future observational priorities include high-resolution integral field mapping (optical, infrared, radio), detailed dust characterization, long-term photometric monitoring of the remnant star, and expansion tracking to further constrain the explosion asymmetry and wind–ejecta interactions.

## 7. Comparative Perspective and Theoretical Importance

Pa 30 represents a benchmark for Type Iax SN remnants with surviving stars. Comparative analysis with extragalactic Type Iax events affirms subluminous, low-energy explosions, small ejecta mass, and unique post-SN dust formation [2208.03946]. Absence of He and H in the ejecta and wind corroborates the double-degenerate merger channel as a key pathway for these supernovae [2304.14669].

The observed nebular and wind structure demands refined models of white dwarf mergers and failed SN explosions, integrating effects of delayed, chemically enriched winds, wind–shell interactions, and asymmetric ejecta [2410.10940]. The presence of a ballistic, asymmetric ejecta distribution and central cavity are of particular interest for simulation and hydrodynamic modeling.

Pa 30/SN 1181 thus provides an unprecedented opportunity to empirically anchor the Galactic occurrence, physics, and post-explosion evolution of double-degenerate Type Iax supernovae.

Source: https://www.emergentmind.com/topics/supernova-sn-1181