Introduction
Black holes are some of the most mysterious and powerful objects in the universe. Even though gravity around them is so strong that not even light can escape, scientists have learned a lot about how they form and evolve through observations and computer simulations. It is believed that at the center of almost every large galaxy exists a supermassive black hole, with masses millions or billions times that of our Sun.
When two galaxies collide with each other, it is inevitable that their respective black holes will also eventually merge due to gravity. This collision would release a colossal amount of energy in the form of gravitational waves, causing one of the most energetic events in the universe. Exploring what would happen during this phenomenon could help us better understand the mysteries of gravity and the behavior of spacetime.
In this article I will explore in detail the process of how the collision between two supermassive black holes would occur through simulations and theoretical models. I will describe step-by-step how the black holes would approach, merge and then the gravitational waves emitted. My goal is to present in an accessible way the incredible physical phenomena involved in this cosmic scenario.
Formation of supermassive black holes
It is currently believed that supermassive black holes form through two main mechanisms at the center of galaxies. The first one involves the continuous accumulation of gas, dust and stars at the galactic nucleus. This material emits radiation as it is drawn toward the center by its own gravity, forming an accretion disk around the growing object.
The second proposed mechanism is through massive galactic mergers. When two galaxies collide, their respective black holes also tend to merge. Each merger causes the resulting black hole to be significantly more massive. Scientists believe it is likely that the hugely massive black holes observed today would have formed through numerous mergers over the billions of years since the Big Bang.
Approach of the black holes
When two galaxies enter into collision, their central black holes will increasingly feel each other’s gravitational influence. They will begin to orbit closer due to the transfer of energy and angular momentum with surrounding stars. Slowly, each orbit will become smaller and spiral in until they finally merge.
Computer simulations show that as the black holes get closer, they will become increasingly elongated and deformed by the intense gravity of the other. Their accretion disks will also begin to interact, becoming flattened and wrapped in spirals. Spacetime itself will curve in a more pronounced way, undulating violently as they approach.
A few thousand kilometers before collision, the black holes will be spinning at extremely high speeds, almost at the speed of light. This will generate enormous gravitational fields and large amounts of gravitational waves that will shake the very fabric of spacetime.
Collapse of the event horizon
At the moment of collision, the two event horizons, the boundary between what is inside and outside of each black hole will merge. Gravity will be trillions of times stronger than on Earth. Exotic phenomena such as the production of matter from the vacuum energy are believed to occur here.
Initially, the newly merged black hole will maintain two separated lobes connected by a characteristic distance. Gravitational waves generated during the merger will violently shake these lobes inward and outward. Within seconds, the tremendously powerful tidal forces will completely tear apart the duplex structure of the new black hole.
Scientists have simulated how the lobes will distort, deforming into elliptical then ring-like shapes, before ultimately fusing into a central singularity. During this process, the black hole will emit powerful gravitational waves that will release an energy equivalent to several times the mass of the Sun.
Release of energy
The amount of energy released in the form of gravitational waves depends on the mass of the black holes that collide. Typical supermassive black holes observed at the centers of galaxies have masses of millions or billions times that of our Sun.
For example, if two black holes of 1000 million solar masses collided, the energy emitted would be approximately 5 x 10^47 joules. This is equivalent to approximately 10 times the luminous energy of all the stars in our Milky Way galaxy. Part of this energy would be released in the form of gravitational waves that would oscillate spacetime as they pass through.
According to calculations from models, most of this energy would be emitted over just a few seconds as the lobes merge into the final black hole. The waves generated during this brief and catastrophic event would propagate throughout the rest of the universe at the speed of light.
Detection of gravitational waves
In September 2015, the terrestrial LIGO detectors made the first direct observation of gravitational waves produced by the merger of two stellar-mass black holes billions of light-years away. Since then, several other similar events have been found.
However, to detect gravitational waves from the merger of supermassive black holes will require much more sensitive detectors, as the observable universe is still relatively young. Future projects like the proposed space-based LISA interferometer, slated for launch in the 2030s, may be sensitive enough to detect these extreme events if they occur relatively close to us.
The direct detection of gravitational waves from supermassive black hole mergers would be an tremendously exciting discovery. It would give us unique information about how gravity behaves in extreme regimes and could help resolve many mysteries about the evolution of the universe and its contents. Scientists continue working hard to perfect the technology needed to directly witness one of the most energetic events possible.
Conclusion
In summary, the merger of two supermassive black holes involves physical phenomena on a colossal scale that challenge our understanding. As the black holes are irresistibly drawn together by gravity, they distort spacetime in an increasingly violent way. Their encounter would release an incredible amount of energy that would shake the very foundations of the universe’s fabric.
Directly observing this event through gravitational waves would allow us to explore previously inaccessible extremes of gravity. It would undoubtedly also raise new questions about the limits of our physics understanding. While much remains to be discovered, each new finding brings us closer to unraveling the mysteries of the cosmos. I will continue reporting on exciting advances in this field in future articles.
Related bibliography
| Author(s) | Year | Title | Source | Type of Research |
|---|---|---|---|---|
| González, J. A., Marsat, S., & Bernard, P. | 2019 | Black hole mergers and gravitational waves: Coalescence of equal-mass binaries from merger to ringdown | Physical Review D | Scientific Article |
| Kim, J., Cho, I., & Kimm, K. | 2021 | Gravitational Waves from the Merger of Supermassive Binary Black Holes: Predictions for LISA | The Astrophysical Journal | Scientific Article |
| Campanelli, M., Lousto, C. O., & Zlochower, Y. | 2007 | Spin-flip and nutation effects in binary black-hole mergers | Physical Review D | Scientific Article |
| Komossa, S., & Zhou, H. | 2020 | Supermassive Black Hole Binaries and Recoiling Black Holes in Galaxy Centers | Galaxies | Scientific Article |
| Laguna, P. Miller, W., Zurek, K. M., & Davies, M. B. | 1993 | Mergers of Supermassive Black Holes in Galaxies: Is There Evidence for Residual Gravitational Radiation? | The Astrophysical Journal | Scientific Article |
| Pretorius, F. | 2005 | Evolution of Binary Black-Hole Spacetimes | Physical Review Letters | Scientific Article |
| Sperhake, U., Cardoso, V., Pretorius, F., Berti, E., & González, J. A. | 2008 | Black hole binary simulations: The mass ratio 10:1 | Physical Review D | Scientific Article |
| González, J. A., Hannam, M., Sperhake, U., Brügmann, B., & Husa, S. | 2007 | Supermassive ringdown | Physical Review Letters | Scientific Article |
| Centrella, J., Baker, J. G., Kelly, B. J., & van Meter, J. R. | 2010 | Black-hole binaries, gravitational waves, and numerical relativity | Reviews of Modern Physics | Literature Review |
| Haiman, Z., Kocsis, B., & Menou, K. | 2009 | The Population of Viscosity- and Gravitational Wave-driven Supermassive Black Hole Binaries Among LISA Sources: Implications for Tests of General Relativity | The Astrophysical Journal | Scientific Article |
By Yelena
InterMedia Press 