The first accurate parallax distance to a black hole (0910.5253v1)

Abstract: Using astrometric VLBI observations, we have determined the parallax of the black hole X-ray binary V404 Cyg to be 0.418 +/- 0.024 milliarcseconds, corresponding to a distance of 2.39 +/- 0.14 kpc, significantly lower than the previously accepted value. This model-independent estimate is the most accurate distance to a Galactic stellar-mass black hole measured to date. With this new distance, we confirm that the source was not super-Eddington during its 1989 outburst. The fitted distance and proper motion imply that the black hole in this system likely formed in a supernova, with the peculiar velocity being consistent with a recoil (Blaauw) kick. The size of the quiescent jets inferred to exist in this system is less than 1.4 AU at 22 GHz. Astrometric observations of a larger sample of such systems would provide useful insights into the formation and properties of accreting stellar-mass black holes.

Analysis of the Accurate Parallax Distance Measurement to V404 Cygni

This paper, authored by Miller-Jones et al., presents a precise determination of the parallax distance to the black hole X-ray binary V404 Cygni. Utilizing astrometric Very Long Baseline Interferometry (VLBI) observations, the team established the parallax to be $0.418 \pm 0.024$ milliarcseconds (mas), corresponding to a distance of $2.39 \pm 0.14$ kiloparsecs (kpc). This result significantly revises the previously accepted distance, marking a substantial advancement in the field of Galactic stellar-mass black hole measurements.

Methodology and Findings

To achieve this precision, the researchers conducted observations with the High Sensitivity Array (HSA) over a year, capturing data at key epochs to optimize the measurement of parallactic displacement. By employing a model-independent trigonometric parallax method—a novel application for such black hole systems due to the required level of precision—they provided a distance measurement unaffected by the systematic uncertainties that typically plague other estimation methods.

The refined distance led to several important insights:

1. Luminosity Evaluation: The new distance estimate implies that V404 Cygni’s peak luminosity during the 1989 outburst was $0.5L_{\text{Edd}}$, confirming that the system was not super-Eddington contrary to previous assumptions using less accurate distances.
2. Kinematic Implications: With accurate proper motion data, the researchers determined the peculiar velocity of V404 Cygni to be $39.9 \pm 5.5$ km/s, suggesting formation via a supernova with potential Blaauw (recoil) kicks. This velocity is consistent with expectations for such systems, not requiring asymmetrical supernova kicks.
3. Jet Characteristics: Upper limits on the size of quiescent jets in the system were reported to be $<1.4$ astronomical units (AU) at 22 GHz. These constraints, in combination with unresolved observed radio emission, suggest the presence of steady, partially self-absorbed synchrotron-emitting jets.

Implications and Future Directions

The precise parallax measurement of V404 Cygni establishes a new standard for distance assessments in Galactic X-ray binaries, addressing long-standing inaccuracies due to uncertain extinction values and their impact on distance calculations. The implications are profound:

• Accretion Physics: With a clearer understanding of luminosities, this work aids in refining models of accretion processes and the associated physics in black holes.
• Black Hole Formation Theories: Peculiar velocity measurements contribute to discussions on black hole formation, potentially differing between direct collapse and supernova-related scenarios.
• Black Hole Event Horizons: A collection of such precise distances could further affirm the evidence pointing to the existence of black hole event horizons, as contrasted with neutron star luminosities.

As VLBI capabilities advance, further applications across additional X-ray binaries become feasible, promising enhanced insights into the characteristics and formation mechanisms of black holes. This paper thus serves as a crucial milestone and a reference point for ongoing and future astrophysical research into black holes and their unique environments.