In a groundbreaking discovery challenging existing theories, scientists have identified evidence of vibrations produced by a black hole resulting from the largest black-hole merger ever detected. This exceptional merger seemed to generate a black hole approximately 150 times the mass of the Sun, defying established theories. The recent findings, published in Physical Review Letters, offer a stringent test for Albert Einstein’s general theory of relativity, which makes precise predictions about gravitational waves and black holes.
The research, led by theoretical physicist Steven Giddings at the University of California, Santa Barbara, signifies a significant advancement in gravitational-wave astronomy. The study scrutinized the gravitational waves produced by the massive black-hole merger, providing insights into the final moments when the resulting black hole transitioned into a spherical shape. Physicist Badri Krishnan, one of the study’s authors, expressed his surprise at witnessing such a measurement in his lifetime, highlighting the magnitude of the achievement.
Since the advent of gravitational-wave astronomy in 2015, the Laser Interferometer Gravitational-Wave Observatory (LIGO) has routinely detected merging black holes. However, the GW190521 event, discovered on May 21, 2019, stood out due to its unique characteristics. The low merging frequency of this event allowed LIGO to capture its last two orbits.
The research team, independent of the LIGO–Virgo collaboration, sought to explore whether the gravitational waves from GW190521 could convey information from the pre-merger phase and the immediate post-merger moments. As two black holes merge, the resulting black hole initially assumes a lopsided shape before rapidly stabilizing into a symmetrical, lowest-energy form within milliseconds.
Similar to a ringing bell emitting specific frequencies determined by its shape, the stabilizing black hole undergoes a ‘ringdown,’ radiating gravitational waves with frequencies dependent on its mass and spin. By analyzing the ringdown frequencies, researchers can estimate the properties of the black hole, offering an alternative approach to the traditional method of measuring spiraling frequencies.
The reanalysis of data from the GW190521 event revealed two distinct ringdown frequencies, indicating a resulting black hole with a mass of approximately 250 solar masses. This challenges the initial analysis by the LIGO–Virgo team, suggesting a much heavier black hole than previously thought and opening new avenues for understanding black-hole mergers and gravitational-wave phenomena.
