GW190521: A Binary Black Hole Merger with a Total Mass of $150 ~ M_{\odot}$ (2009.01075v1)

Abstract: On May 21, 2019 at 03:02:29 UTC Advanced LIGO and Advanced Virgo observed a short duration gravitational-wave signal, GW190521, with a three-detector network signal-to-noise ratio of 14.7, and an estimated false-alarm rate of 1 in 4900 yr using a search sensitive to generic transients. If GW190521 is from a quasicircular binary inspiral, then the detected signal is consistent with the merger of two black holes with masses of $85^{+21}_{-14} M_{\odot}$ and $66^{+17}_{-18} M_{\odot}$ (90 % credible intervals). We infer that the primary black hole mass lies within the gap produced by (pulsational) pair-instability supernova processes, and has only a 0.32 % probability of being below $65 M_{\odot}$. We calculate the mass of the remnant to be $142^{+28}_{-16} M_{\odot}$, which can be considered an intermediate mass black hole (IMBH). The luminosity distance of the source is $5.3^{+2.4}_{-2.6}$ Gpc, corresponding to a redshift of $0.82^{+0.28}_{-0.34}$. The inferred rate of mergers similar to GW190521 is $0.13^{+0.30}_{-0.11}\,\mathrm{Gpc}^{-3}\,\mathrm{yr}^{-1}$.

• The paper demonstrates detection of GW190521 with a network SNR of 14.7 and an exceptionally low false-alarm rate.
• It infers individual black hole masses of approximately 85 M⊙ and 66 M⊙, challenging conventional stellar evolution models.
• The study reveals the merger produced a 142 M⊙ intermediate-mass black hole, prompting revisions to astrophysical formation theories.

Overview of "GW190521: A Binary Black Hole Merger with a Total Mass of 150 M⊙"

The paper "GW190521: A Binary Black Hole Merger with a Total Mass of 150 M⊙" presents a detailed paper of the gravitational-wave event GW190521, detected by the LIGO and Virgo scientific collaborations. This event is characterized by the merger of two black holes, resulting in a total mass significantly higher than previously observed binary black hole (BBH) mergers. The paper provides a comprehensive analysis of the detection, including the astrophysical parameters inferred from the data and the implications concerning the formation of intermediate-mass black holes (IMBHs).

Detection and Significance

The gravitational-wave signal GW190521 was observed on May 21, 2019, by the Advanced LIGO and Advanced Virgo detectors. With a short duration and a network signal-to-noise ratio (SNR) of 14.7, the event was identified with an exceptionally low estimated false-alarm rate of 1 in 4900 years. This establishes the high confidence in the detection of a significant gravitational wave transient. Offline analyses further corroborated this detection, utilizing improved calibration and updated data-quality protocols.

Astrophysical Inference

The analysis concludes that if GW190521 originated from a quasicircular binary inspiral, the merging black holes had individual masses of approximately 85 $M_⊙$ and 66 $M_⊙$ and a total mass of about 150 $M_⊙$. Notably, the primary component's mass falls within the pair-instability supernova (PISN) mass gap, a range where theory predicts that black holes should not form from stellar processes. This highlights the event's importance in the paper of stellar evolution and black hole formation, suggesting alternate mechanisms, possibly through hierarchical mergers or stellar mergers, might be at play.

Formation of an Intermediate-Mass Black Hole

The remnant of the merger is an intermediate-mass black hole with an estimated mass of 142 $M_⊙$ and dimensionless spin parameter of 0.72. This makes it one of the first direct observations of an IMBH, bridging the gap between stellar-mass black holes and supermassive black holes. The result is significant as it supports IMBH existence, long-speculated by indirect evidence but rarely confirmed through direct observation.

Implications and Future Prospects

The findings challenge existing theoretical models of black hole formation and indicate possible new astrophysical phenomena. The presence of a black hole mass residing in the PISN gap suggests a need for revised theoretical models incorporating more intricate processes, such as multiple merger events in dense environments like stellar clusters or active galactic nuclei.

Speculative Future Developments

As gravitational wave detectors enhance their sensitivity, particularly in low-frequency domains, it is anticipated that more massive and potentially more complex systems such as GW190521 will be observed. Future ground-based detectors and space missions like LISA promise additional insights into the earliest inspiral phases of such mergers, potentially unraveling further mysteries of massive black hole formation.

In summary, GW190521 represents a pertinent addition to the gravitational-wave catalog, underscoring the need for sophisticated models to comprehend high-mass black hole mergers and the seeds of intermediate-mass black holes in the universe. This paper offers researchers critical data and insights that will likely pivot future black hole research and gravitational wave astrophysics.