Gravitational waves from the most powerful black hole collision have for the first time isolated a component of the signal formed in the immediate vicinity of the event horizon, allowing physicists to measure how the newly formed black hole twists space-time around itself.
Record-breaking collision
The gravitational-wave event GW250114 was detected last year by the LIGO observatory in the United States. It was recognized as the most powerful black-hole collision ever observed. The two black holes orbited each other in a spiral pattern until they merged in a catastrophic collision, resulting in the formation of a single, more massive black hole.
It was precisely due to the extraordinary intensity of this event that the research team was able to isolate a previously undetectable component in the signal. The results of their work were published in the peer-reviewed journal Nature.
Signal originating from the vicinity of the event horizon
A direct wave constitutes gravitational radiation emanating from the vicinity immediately adjacent to the event horizon. Albert Einstein’s general theory of relativity anticipated the existence of this component; however, it has yet to be detected. The primary obstacle was that the direct wave was obscured by significantly stronger signals generated by the merger process itself.
To isolate this component, Neil Lu of the Australian National University and his colleagues devised new analytical techniques for filtering gravitational-wave data. This facilitated the extraction of the subtle signal from among the predominant elements of the total radiation.
Space vortex
The direct wave carries information about the black hole’s rotation and the space-time capture effect predicted by Einstein’s general theory of relativity. Within the ergosphere encircling the event horizon, no object can remain stationary and is compelled to move along with the distorted spacetime.
Thanks to the gravitational wave, scientists were able to measure the rotation rate of the newly formed black hole and the strength of gravity near its event horizon. Gravitational waves remain the only means of obtaining information from this region, since not even light can escape from there.
Test for Einstein
The detection of a straight wave offers a novel approach to testing the general theory of relativity. This opens up a new way to study the region near the event horizon and creates additional opportunities to test the fundamental laws of gravity under extreme conditions. If Albert Einstein’s theory holds true, the parameters of the straight wave, the rotation speed of the horizon, and the surface gravity should concur with each other with high precision. Any deviation may suggest the necessity to refine or augment existing physical models.
Black holes represent one of the phenomena in which the discrepancy between the two most successful physical theories may become evident. General relativity delineates gravity and spacetime on macroscopic scales, whereas quantum mechanics elucidates matter and energy at the smallest scales. At the fundamental level, these theories have not yet been fully reconciled.
In proximity to the event horizon, gravitational forces become so intense that differences between them may become quantifiable. Gravitational waves resulting from black hole collisions are considered the most promising source of data for identifying these differences.
Provided by: phys.org
