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Simulation of the movement of stars around the black hole at the center of the Milky Way Galaxy. On the left is the star’s orbit. This orbit has been calculated for 10,000 years. It seems that the stars do not deviate from their orbits. The right panel is a zoom near the center of the crowd. This shows that stars have large variations along their orbits. The yellow orbit, for example, fluctuates over those ten thousand years over a range of forty times the distance of the Earth to the Sun. Credit: Simon Portiges Zwart et al
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Simulation of the movement of stars around the black hole at the center of the Milky Way Galaxy. On the left is the star’s orbit. This orbit has been calculated for 10,000 years. It seems that the stars do not deviate from their orbits. The right panel is a zoom near the center of the crowd. This shows that stars have large variations along their orbits. The yellow orbit, for example, fluctuates over those ten thousand years over a range of forty times the distance of the Earth to the Sun. Credit: Simon Portiges Zwart et al
The orbits of 27 stars orbiting near the black hole at the center of our Milky Way galaxy are so chaotic that researchers cannot confidently predict where they will be in about 462 years. These results were obtained from simulations carried out by three astronomers in the Netherlands and England. The researchers published their findings in two papers in the journal Dr Dan’s International Journal of Modern Physics in Monthly Notices of the Royal Astronomical Society.
Simulating 27 stars and their interactions with each other and with black holes is easier said than done. For centuries, for example, it has been impossible to predict the movements of more than two interacting stars, planets, rocks, or other objects. Only in 2018, researchers from Leiden developed a computer program in which rounding errors no longer play a role in calculations. And they can do it Calculate the movements of three imaginary stars. Now the researchers have expanded their program to include 27 stars that, by astronomical standards, are moving closer to the black hole at the center of the Milky Way.
Simulations of 27 massive stars and black holes produced surprises. Although the stars remain in their orbits around the black hole, interactions between the stars show that their orbits are chaotic. That is, small perturbations caused by fundamental interactions change the star’s orbit. These changes grow exponentially and, in the long term, make the star’s orbit unpredictable.
The black hole sent a shock
“After 462 years, we cannot predict the orbit with certainty. It’s very short,” says astronomer Simon Portijes Zwart (Leiden University, Netherlands). He compared it to our solar system, which can no longer be predicted with certainty after 12 million years.
“So, the environment around a black hole is 30,000 times more chaotic than the environment around us, and we didn’t expect that at all. Of course, the solar system is about 20,000 times smaller, its mass is millions of times less, and it weighs only 20,000 times as much. eight.” “A relatively light hull compared to the big 27 hulls, but if you asked me before, that wouldn’t be a problem.”
According to researchers, chaos arises all the time in more or less the same way. There are always two or three stars close to each other. This causes mutual push and pull between stars. This in turn leads to slightly different star orbits. The black holes orbited by the stars are then pushed away, which is felt by all the stars in turn. In this way, a simple interaction between two stars affects all 27 stars in the central cluster.
Enlarge the orbit
“We ran simulations for 10,000 years,” said Tjaarda Boekholt, a former graduate student at Portegies Zwart in 2015 and now at Oxford University, UK. “From a bird’s eye view, the stars’ orbits appear to remain unchanged over time.” ). “Only when you start zooming in on parts of the orbit do the chaotic differences become visible. This difference can reach a value of forty astronomical units, that is, forty times the distance between the Earth and the Sun.”
Researchers like to compare the chaos in a black hole to cycling through a city. You know approximately how long it will take, but it’s impossible to estimate exactly how long. If the bridge is open, or if someone jumps in front of your bike, you might arrive a few minutes later.
“And this is also how it works for stars surrounding black holes,” said Portiges-Zwart. “You realize that unexpected events often occur, causing exponential changes, which we can now measure. But the implication is that the center of the Milky Way with its black hole and 27 stars orbiting it can no longer be predicted with certainty after 462 years. . “We can no longer reliably predict the positions and velocities of these stars.”
For Portiges Zwart and his colleagues, the year 462 was not very important. “462 years is of course a very short period, but our point is that as astronomers, we have to look differently than before at what happens near black holes,” said Portijes-Zwart. “And we have to find new words for it. For example, I started listing definitions with Tjaarda Bockholt, simply because there were no terms that accurately described the new type of disruptive behavior we were observing.”
Disjointed chaos
The researchers coined the phenomenon of “intermittent chaos.” The term is inspired by evolutionary biology where the opposite occurs: what is called punctuated equilibrium. It’s about evolution in species where there is often a long-term balance that is only occasionally disrupted by traumatic events.
“Before this research, you didn’t know whether the chaos in a simulation was physical in origin, or whether it came from rounding errors and other problems in the calculations,” said co-author Douglas Heggie, a retired mathematician and still active. scientist. Astronomer at the University of Edinburgh (UK) and pioneer in the field of N-body problems.
“We have tested the simulations and basic calculations in several ways,” says Heggie, “Our results hold up. We can now provide real data on the chaotic behavior of multi-star systems. This is amazing. ”
further information:
Tjarda CN Boekholt et al, Chaos and uncertainty in self-retracting multi-body systems, International Journal of Modern Physics Dr (2023). doi: 10.1142/S0218271823420038. on arXiv: doi: 10.48550/arxiv.2308.14803
Simon F. Portiges Zwart et al., Intermittent Chaos and the Unpredictable Evolution of the Central Orbitals of S-Star Galaxies, Monthly Notices of the Royal Astronomical Society (2023). doi: 10.1093/manras/stad2654. on arXiv: doi: 10.48550/arxiv.2308.14817
Magazine information:
arXiv
Monthly Notices of the Royal Astronomical Society
2023-09-13 11:39:45
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