2023-09-02 11:30:17
When two black holes merge, intense gravitational waves are generated, sometimes “kicking” the merged black hole. The faster the black holes move, the more likely they are to collide with each other, which might be the origin of heavy black holes in the universe. James Healy and Carlos O. Lousto of the Rochester Institute of Technology have clarified by simulation that when two black holes collide, the black holes following merging will move at the fastest speed of regarding 29,000 km/s. That’s 5.7 times faster than previous simulations and roughly one-tenth the speed of light. 【▲ Figure 1: Imaginary image of two black holes revolving around each other (Credit: SXS)】 ■ “Speed limit violation” caused by the approach of celestial bodies When multiple celestial bodies approach extremely close , kinetic energy is exchanged by being attracted to each other by gravity. Gravitational interactions can dramatically increase the speed of motion of celestial bodies. A star that has gained extreme speed in such a process is called a “hypervelocity star (HVS)”. The fastest HVS known so far is S5-HVS1, moving at regarding 1755 km/s relative to the center of the Milky Way galaxy. It is estimated that the Sun orbits the center of the Milky Way at regarding 240km/s, which is 7.3 times faster (*1) . It is presumed that S5-HVS1 is moving so fast that it is defying gravity and escaping the Milky Way. It is presumed that such super-velocity stars were formed as a result of extremely close proximity to the supermassive black hole Sagittarius A* (Aster) at the center of the Milky Way. *1…S5-HVS1 is the fastest HVS, but “S4716” is known to be even faster at 8000km/s. However, unlike HVS, S4716 is trapped by the gravity of the black hole at the center of the Milky Way, and revolves with a period of 4.02 years. Its orbit is elliptical, far from a perfect circle, and its orbital speed is estimated to reach 8000 km/s when it comes closest to the black hole. So what happens when black holes get close to each other? In the case of black holes, it is known that not only close encounters but also collisions generate enormous velocities. When black holes approach each other, gravitational waves of enormous energy are emitted, but since the generation of gravitational waves may be biased, the coalesced black holes born following the collision are caused by gravitational waves concentrated at a specific angle. You may be “kicked”. An example of such a black hole is the supermassive black hole in the active galaxy CID-42. It is estimated that there are In this way, collisions between black holes can produce extremely high motion velocities, and the critical velocity was previously estimated to be 5000 km/s. This is approximately 1/60th the speed of light. ■The fastest black hole moves at 10% of the speed of light Mr. Healy and Mr. Lousto of Rochester Institute of Technology performed numerical calculations on the limit velocity produced by the merger of black holes. In order to accurately calculate the intense changes in gravitational waves caused by black holes approaching each other, a supercomputer with high computational intensity is required. In addition, since it is necessary to assume collisions from various angles in order to know the critical speed, the amount of calculation increases as the number of patterns increases. 【▲ Figure 2: It is presumed that the motion speed of the black holes resulting from their merger changes depending on the angle at which the two black holes approach. In this research, calculations were performed assuming a total of 1381 patterns (Credit: James Healy and Carlos O. Lousto)】 【▲ Figure 3: Calculation results of black hole velocities following collision. A collision at the most ideal angle was calculated to produce a maximum velocity of 28562 km/s (although the figure differs from the text, the description in the text takes precedence) (Credit: James Healy and Carlos O. Lousto) ]Healy and Lousto performed calculations assuming 1381 possible collision patterns between black holes. This greatly exceeds the 42 calculated in the study that estimated the upper limit of 5000 km/s. They found that the greatest velocities occurred when colliding at a grazing angle, reaching a maximum of 28,562 (±342) km/s. This is 5.7 times the value indicated by previous numerical calculations and corresponds to regarding one-tenth the speed of light. At this speed, it takes only 1.4 seconds to go around the earth and 13.5 seconds to travel from the earth to the moon. Of course, this maximum speed is only achieved under extremely limited conditions, and most black holes do not move this fast. However, it is important to think regarding the evolution of black holes that a black hole with a fast speed on average is generated.It is presumed that black holes mainly form as a result of the collapse of the core at the center of heavy stars, but there are countless black holes in the universe that are more massive than this method. It is presumed that this occurs when light black holes collide and merge with each other, but the faster the black holes move, the more frequently they collide. is very important for understanding the properties and growth of black holes.SourceJames Healy & Carlos O. Lousto.“Ultimate Black Hole Recoil: What is the Maximum High-Energy Collision Kick?”.(Physical Review Letters) (arXiv) Carlos O. Lousto & Yosef Zlochower. “Hangup Kicks: Still Larger Recoils by Partial Spin-Orbit Alignment of Black-Hole Binaries”. (Physical Review Letters)Laura Blecha, et al. “Constraints on the nature of CID-42: recoil kick or supermassive black hole pair?”. (Monthly Notices of the Royal Astronomical Society) Sergey E Koposov, et al. of the Royal Astronomical Society) Florian Peissker, et al. “Observation of S4716—a Star with a 4 yr Orbit around Sgr A*”.
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