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 could be the origin of heavy black holes in the universe.
James Healy and Carlos O. Lousto of the Rochester Institute of Technology found that if two black holes collided,The black hole after coalescence moves at the fastest speed of about 29,000 km / sThis was made clear by simulation. This is 5.7 times faster than the speed shown in previous simulations.About 1/10th the speed of lightEquivalent to
【▲ Fig. 1: Imaginary image of two black holes revolving around each other (Credit: SXS)】
■ “Speed limit violation” caused by approaching celestial bodies
When multiple celestial bodies approach extremely close, kinetic energy is exchanged by mutual attraction 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 about 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 about 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 after the collision are caused by gravitational waves concentrated at a specific angle. You may be “kicked”.
An example of such a black hole is an active galaxy “CID-42There is a supermassive black hole that is said to exist in “, and as a result of the collision of two black holes,It is flying out at a speed of about 2000km/sIt is estimated that 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.
■ It turns out that 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 critical velocity produced by the coalescence 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 study, calculations were performed assuming a total of 1381 patterns (Credit: James Healy and Carlos O. Lousto)]
【▲ Figure 3: Calculation result of the velocity after the collision of the black hole. 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) ]
Mr. Healy and Mr. LoustoCalculations are performed assuming 1381 collision patterns between black holesDid. This greatly exceeds the 42 calculated in the study that estimated the upper limit of 5000 km/s. As a result, the greatest velocity occurs when colliding at a grazing angle,Up to 28,562 (±342) km/swas found to reachthis is5.7 times the value indicated by previous numerical calculationsandAbout 1/10th the speed of lightEquivalent to 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 about the evolution of black holes that a black hole with a fast speed on average is generated. It is presumed that black holes are primarily the 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 heavy black holes are formed by collisions and mergers of light black holes, but the faster the black holes move, the more frequently they collide. Knowing what happens when black holes approach each other is very important for understanding the properties and growth of black holes.
Source
James 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. “Discovery of a nearby 1700 km s−1 star ejected from the Milky Way by Sgr A*”. (Monthly Notices of the Royal Astronomical Society)Florian Peissker, et al. “Observation of S4716—a Star with a 4 yr Orbit around Sgr A*”. (The Astrophysical Journal)
Text: Riri Ayae
