His theories on motion, velocity, and universal gravitation were effectively synthesised by the work of SirIsaacNewton. Newton offered a means for calculating the force of gravity. The Solar System is only one small point of light that circles the center of the universe. Other stars passing close to the Solar System can cause a shakeup that can cause objects to leave their orbits.
The long-term evolution of planetary systems can be influenced by thesestellar flybys. The Solar System's long-term stability has been studied for hundreds of years. Residents of the Solar System may rest easy according to a study. They found out that a star won't affect our Solar System for another 100 billion years. The possibilities are quite frightening beyond that.
Garett Brown is a graduate student in the Department of Physical and Environmental Sciences at the University of Toronto atScarbrough. The associate professor of astrophysics and Brown's mentor was also present. The paper describing their findings was published in the journal. The study of stellar flybys could show a lot about the history of planetary systems.
Brown told Universe Today that this is true of stars like the Solar System.
“The full extent that stellar flybys play in the evolution of planetary systems is still an active area of research. For planetary systems that form in a star cluster, the consensus is that stellar flybys play an important role while the planetary system remains within the star cluster. This is typically the first 100 million years of planetary evolution. After the star cluster dissipates the occurrence rate of stellar flybys dramatically decreases, reducing their role in the evolution of planetary systems.”
The most widely accepted theory for the formation of the Solar System is that the Sun formed from a massive cloud of dust and gas. A disk of dust and gas surrounds the Sun and forms a system of planets. The Sun may have formed due to a close flyby by another star. Brown said stellar flybys are likely to have played a part in planet formation.
When there is a disk of dust and gas around a star, stellar flybys are expected to be responsible for disk truncation. Stars are thought to be responsible for destabilizing the outer planets.
Our Sun formed around 4.5 billion years ago as a part of a star cluster, according to a widely accepted theory. The Solar System could have been altered by being part of a cluster if these theories were true. The role played by stellar flybys depends on how strong the passing star is. They found out that a stellar flyby can cause planets to crash into each other.
Astronomers have had an issue with the Theory of Universal Gravitation for a long time. The N-body problem describes how difficult it is to predict the individual motions of a group of objects interacting with each other. Astronomers are forced to make numerical approximations due to the impossibility of solving this. There are two major issues with these calculations.
“One, the motion of the planets are chaotic, meaning small differences in the initial conditions of the system will result in dramatically different outcomes (even differences as small as one part in a trillion). And two, the timescales involved are dramatically different. We can get a sense for the statistical outcome of a chaotic system using an ensemble of numerical solutions. For the long-term stability of the Solar System this can give us a ratio of simulations that end up destabilizing compared to the number of simulations that remain stable to the end of the integration time.”
“However, solving the timescales issue is much more difficult. Sophisticated numerical methods have been developed over the past 50 years which make this more tractable, but we essentially need to simulate the motion of the planets one day at a time for billions of years. This requires an incredible amount of computational resources. We typically want to know if the Solar System will remain stable for the remaining lifetime of the Sun (about 5 billion years). Even with modern computers (as fast as they are) it can easily take 3-4 weeks to run just one 5 billion year simulation of the Solar System.”
Researchers have to conduct thousands of simulations to get reasonable statistics. Running simulations on a single computer for up to 70 years or more is one of the ways to do this. It makes statistical analysis very difficult and expensive. The Digital Research Alliance of Canada network includes the University of Toronto'sSciNet center.
Two main methods were used to calculate the potential changes caused by steller flybys.
“The first was an analytical approximation developed in 1975 by Douglas Heggie and refined over the years with his collaborators. It’s an approximation that assumes the relative velocity between the two stars is small compared to the orbital velocity of the planets. This analytical estimate allows us to very quickly compute order of magnitude estimates for how a stellar flyby will change the semi-major axis of a planet.”
They used numerical integrations using a multi-purpose N-body code called REBOUND. They were able to measure the system's state before and after a stellar flyby. The results indicated that stellar encounters of this type were not likely to happen for a long time. Brown said that.
In order to have any impact on the long-term stability of the Solar System, critical changes to the orbit of Neptune need to be on the order of 0.03AU or 4.5 billion meters. The chances of instability over the lifetime of the Solar System could go up by 10 times. The region the Solar System is currently in has been estimated to have a critical stellar flyby once every 100 billion years.
“[W]e estimated that we would need to wait about 100 billion years before a stellar flyby past the Solar System would simply increase the odds of dismantling its current architecture by 10 times (and that’s still not a guarantee of destruction).”
It's understandable that the idea of stellar flybys would cause some concern. Large objects are ejected from the outer reaches of a system due to flybys and astronomer theorize that planetary shakeups may be a common feature of a system's evolution. The biggest moon of Neptune is thought to have formed in the Kuiper Belt and was thrown towards the inner Solar System, where it was captured by Neptune and destroyed.
The comets we have are caused by interactions with other star systems. The idea of comets being sent our way by a close flyby sounds apocalyptic. Douglas Adams said, "Don't panic!" The Solar System doesn't influence stellar flybys because they pass light years away.
This is similar to Near Earth Asteroids and the chance that one will collide with Earth someday. The impact event that killed off the dinosaurs is something we know about. NEAs make close passes with Earth every now and then. Two NEAs considered to be potentially hazardous would not threaten Earth for a long time.
What’s more, recent observations by missions like the ESA’s Gaia Observatory have provided the most accurate data on the proper motions and velocities of stars in the Milky Way Galaxy. As Brown noted, this included data on impending flybys and how close they will pass to our system:
“Two notable stars are HD 7977, which may have passed within 3,000 AU (0.0457 light-years) of the Sun some 2.5 million years ago, and Gliese 710 (or HIP 89825), which is expected to pass within about 10,000 AU (0.1696 light-years) of the Sun in about 1.3 million years from now. Doing some rough calculations, both of these stars will have no appreciable effect to the evolution of the Solar System.”
What’s more, a lot will happen between now and then and it’s highly unlikely humanity will be around to witness such an event. Assuming we have not driven ourselves to extinction or left Earth to explore other reaches of the galaxy, planet Earth will cease being habitable long before that. “Considering the Sun will expand and engulf the Earth in about 5 billion years, physically distancing from other stars is not an issue we need to worry about,” said Brown.
ArXiv is further reading.
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