Turning Point in Astrophysics: LIGO Proves That Black Holes Are Born as a 'Second Generation'

For many years, the formation of black holes was accepted in the astronomy community as an almost certain law of nature; when a massive star reached the end of its life, it experienced a supernova explosion and left behind a black hole. However, a recent study conducted by researchers at the Massachusetts Institute of Technology (MIT) and published in the prestigious science journal Physical Review Letters proves that the universe has a much more complex nature than we thought. Scientists closely examined the data of 155 black hole pairs recorded by the LIGO gravitational wave detectors in the USA, the Virgo in Italy, and the KAGRA in Japan. The findings reveal that black holes are not only the remnants of dying stars; they can also be born as a result of violent collisions between other black holes.

One of the most striking results of the study is the determination that approximately 14 percent of the detected merging black hole pairs, meaning one out of every seven, consist of these 'second generation' black holes. Scientists call this process 'hierarchical merger', where small black holes collide to form larger ones and this continues in a chain reaction. In other words, in some regions of the universe, first-generation black holes formed from dying stars come together to create new black holes with much larger and massive structures. This situation reveals that gravitational phenomena in the universe cannot be explained by a single method and that our cosmic evolution is an extremely dynamic process.

So how do researchers know that these black holes were born from another collision rather than a dying star? The secret lies in the signals of the gravitational waves reaching Earth, which are created by these giant celestial bodies as they spiral around each other. When two black holes merge, if their rotation axes are not perfectly aligned with their orbital planes, a special oscillating motion called 'orbital precession' emerges, which resembles the wobbling of an unbalanced spinning top. Because second-generation black holes inherit enormous rotational energy from their initial collisions and their masses are generally asymmetrical relative to each other, this oscillation leaves a very clear trace in the gravitational waves.

When MIT researchers examined environments where massive star clusters are dense, they also explained what kind of laboratory these cosmic collisions offer. In places where stars are located so close to each other, the black holes remaining from dying stars easily find each other thanks to gravity and eventually merge in a gravitational dance. According to Kaelen Plunkett, an MIT doctoral student who is the lead author of the study, this new and larger black hole that emerges can easily attract another black hole in the dense stellar environment. This process creates a cycle in these dense clusters, where many black holes reside, that can theoretically repeat forever.

This groundbreaking discovery is also of critical importance in terms of its potential to solve the mystery known as the 'Mass Gap' or 'Dead Zone', which has remained unanswered in astrophysics for a long time. According to traditional stellar evolution models, a supernova explosion is not expected to leave a black hole within a certain mass range; this situation was theoretically seen as a limitation. However, the proof that black holes can merge to create larger black holes shows that these mass gaps can actually be overcome through the collisions of second-generation black holes. These new findings open a new page in our understanding of the nature of the universe's most mysterious and powerful objects, guiding future space observations.