The Universality of Black Hole Harmonics: Probing Cosmic Phenomena

A conceptual visualization of two imminent black hole mergers.

Black holes, enigmatic and unavoidable, stand as some of the most captivating phenomena in the cosmos. Researchers at the Heidelberg Institute for Theoretical Studies (HITS) in Germany have postulated that the sound emitted during the coalescence of two black holes predominantly falls within two specific frequency ranges.

The discovery of gravitational waves in 2015, which had been theoretically predicted by Albert Einstein a hundred years prior, laid the groundwork for the 2017 Nobel Prize in Physics and ushered in the era of gravitational-wave astronomy. When two stellar-mass black holes merge, they emit gravitational waves that escalate in frequency—a sound pattern termed as the “chirp.” By scrutinizing the variations in this frequency pattern, researchers can deduce a calculated value known as the “chirp mass,” representing the total mass of the merging black holes.

Traditionally, it was thought that the mass of merging black holes could span a wide range. However, models developed by the HITS team suggest that certain black holes have standardized masses that lead to these universal chirp frequencies.

Numerical simulations reveal distortions in the spacetime surrounding a conjoining binary black hole system. Credit: Deborah Ferguson, Karan Jani, Deirdre Shoemaker, Pablo Laguna, Georgia Tech, MAYA Collaboration.

Fabian Schneider, who spearheaded the study at HITS, notes, “The concept of universal chirp masses is illuminating, not just for understanding the genesis of black holes, but also for deciphering which stars culminate in supernovae explosions.” Moreover, it offers profound insights into hitherto uncertain areas of nuclear and stellar physics and introduces a novel method for scientists to quantify the Universe’s accelerating expansion.

“Implications for the Ultimate Destinies of Stars”

Stellar-mass black holes, with masses ranging from roughly 3 to 100 times that of our Sun, serve as the final evolutionary stages for massive stars that avoid supernova explosions and instead collapse into black holes. These black holes are typically born in binary star systems and undergo multiple episodes of mass transfer between their constituent stars. Specifically, both black holes originate from stars that have lost their outer layers.

Philipp Podsiadlowski of Oxford University, the study’s second author and currently Klaus Tschira Guest Professor at HITS, states, “The process of envelope removal has significant ramifications for the stars’ ultimate destinies. It not only facilitates their transformation into supernovae but also leads to the emergence of black holes with standardized masses, as our simulations now predict.”

Data distribution concerning the chirp masses of all observed binary black hole mergers reveals specific trends. There is a discernible gap in chirp masses between 10 and 12 solar masses, with identifiable peaks around 8, 14, 27, and 45 solar masses. These observations align well with the universal chirps posited by the HITS researchers.

Eva Laplace, the third author of the study, remarks, “Any anomalies in the mass distribution of black holes and their chirps can furnish invaluable insights into their formation mechanisms.”

Extragalactic Exceptions: Black Holes of Substantial Magnitude

From the initial discovery of black hole mergers, it was apparent that certain black holes possess masses far greater than those found in our Milky Way Galaxy. These discrepancies are attributed to their originating from stars with different chemical compositions than those in our galaxy. The HITS research indicates that such stars, when they lose their envelopes in binary systems, produce black holes of either less than 9 or more than 16 solar masses, with few exceptions in between.

The manifestation of universal black hole masses around 9 and 16 solar masses naturally leads to universal chirp masses. Fabian Schneider comments, “While updating my lecture materials on gravitational-wave astronomy, I noted that initial observations from gravitational-wave telescopes hinted at the absence and surplus of chirp masses precisely where our models had predicted. However, due to the limited number of observed mergers, it remains to be seen whether these trends are statistically significant or mere anomalies.”

Regardless of the findings from forthcoming gravitational-wave observations, the outcomes promise to be riveting and will advance our comprehension of the origins of these celestial symphonies in a universe full of diverse cosmic voices.

Reference: “Bimodal Black Hole Mass Distribution and Chirp Masses of Binary Black Hole Mergers” by Fabian R. N. Schneider, Philipp Podsiadlowski, and Eva Laplace, published on 15 June 2023 in The Astrophysical Journal Letters.
DOI: 10.3847/2041-8213/acd77a

The research was financially supported by the H2020 European Research Council.

Frequently Asked Questions (FAQs) about Black Hole Merger Frequencies

More about Black Hole Merger Frequencies

• Gravitational Waves: A New Era in Astronomy
• Heidelberg Institute for Theoretical Studies (HITS)
• The 2017 Nobel Prize in Physics
• Astrophysical Journal Letters: Bimodal Black Hole Mass Distribution and Chirp Masses
• H2020 European Research Council Funding
• Universal Chirp Masses: Understanding Stellar Physics
• Gravitational-Wave Observatories and Their Findings