Scientists think they know when an evil star will destroy the Solar System
In 1687Sir Isaac Newton published his magnum opus, Philosophi Naturalis Principia Mathematicawhich effectively synthesized his theories of motion, velocity, and universal gravitation.
In the latter case, Newton offered a way to calculate the gravitational force and predict the orbits of the planets. Since then, astronomers have discovered that the Solar System is just a tiny point of light orbiting the center of the Milky Way Galaxy. Occasionally, other stars will pass near the Solar System, which can cause dramatic oscillations that can kick objects out of their orbits.
These “traverses of the stars” are common and play an important role in the long-term evolution of planetary systems. As a result, the long-term stability of the Solar System has been the subject of scientific investigation for centuries. According to a new study by a team of Canadian astrophysicists, the inhabitants of the Solar System may be calm. After conducting a series of simulations, they determined that a star would not pass by and disturb our Solar System for another 100 billion years. Beyond that, the possibilities are a bit scary!
The research was led by Garett Brown, a computational physics graduate student from the Department of Physical and Environmental Sciences (PES) at the University of Toronto at Scarborough. He joins Hanno Rein, an astrophysics professor (and Brown’s mentor) also from PES at UT Scarborough. A paper describing their findings was recently published in Royal Astronomical Journal Monthly Notice. As they point out in their paper, the study of interstellar flight can reveal a lot about the history and evolution of planetary systems.
As Brown explained to Universe Today via email, this is especially true for stars like the Solar System during its early history:
“The extent to which interstellar flight plays into the evolution of planetary systems is still an active area of research. For planetary systems that form in star clusters, the consensus is that interstellar flight plays an important role while planetary systems remain within star clusters. This is usually the first 100 million years of the planet’s evolution. After star clusters disappeared, the rate of interstellar flybys decreased dramatically, reducing their role in the evolution of planetary systems.”
The most widely accepted theory for the formation of the Solar System is known as the Nebula Hypothesis, which states that the Sun formed from a large cloud of dust and gas (known as a nebula) that underwent gravitational collapse at its center.
The remaining dust and gas then form a disk around the Sun, which gradually builds up to form a planetary system. In one version of the hypothesis, the Sun formed due to a disturbance in the nebula, possibly from a close flyby by another star (or a supernova). But as Brown explains, interstellar flight may also play a role in planet formation.
“During planetary development, when there is a disk of dust and gas around the star, the passing star is expected to be responsible for cutting the disk, which would prevent the formation of planets on wider and more distant orbits,” he said. “For planets that have formed in extensive orbits, interstellar flight is thought to be responsible for eliminating or disrupting the outermost planets.”
Another widely accepted theory is that our Sun formed roughly 4.5 billion years ago as part of a long abandoned star cluster. With these theories in mind, Brown and Rein investigated how being part of a cluster (and therefore subject to stellar flybys) could change the Solar System after the planets formed and were part of an established system. They found that the role that cross-stellar flight plays depends on how strongly a passing star can interfere with the system. They further determined that interstellar flybys could dynamically destabilize the system, causing planets to collide or be ejected.
This presents a significant challenge because of a problem that has plagued astronomers since Newton proposed his Theory of Universal Gravity. In short, it all boils down to the N-body problem, which describes the difficulty of predicting the individual motions of a group of celestial bodies that interact with each other gravitationally. Solving this precisely remains a mathematical impossibility, so astronomers are forced to make numerical estimates. But as Brown says, there are still two major problems with this calculation:
“One, the motions of the planets are chaotic, meaning that a small difference in the initial state of the system will produce very different results (even a difference as small as one part in a trillion). And two, the time spans involved are very different. We can feel the statistical results of a chaotic system using an ensemble of numerical solutions. For the long-term stability of the Solar System, this can give us the ratio of simulations ending up unstable compared to the number of simulations remaining stable until the end of the integration time.”
“However, solving the time span problem is much more difficult. Sophisticated numerical methods have been developed over the last 50 years, which make this easier to control, but we basically need to simulate the motion of the planets one day at a time over billions of years. This requires an incredible amount of computing resources. We usually want to know if the Solar System will remain stable for the remainder of the Sun’s lifetime (about 5 billion years). Even with modern computers (as fast as they are), it could easily take 3-4 weeks to run just one 5 billion year Solar System simulation.”
Even to start getting statistics that make sense, Brown adds, the researchers would need to run thousands of different simulations. There are two ways to do this: running simulations on a single computer for up to 70 years or more or using thousands of different computers simultaneously for a month. This not only makes statistical analysis very complicated but also very expensive. For their analysis, Brown, and Rein used the Niagara supercomputer at the University of Toronto’s SciNet center, which is part of the Digital Research Alliance of Canada network.
As Brown explains, he and Rein used two main methods to calculate the potential for interference caused by steller flybys.
“The first is an analytical approach developed in 1975 by Douglas Heggie and refined over the years with his collaborators. This is an estimate that assumes the relative speed between two small stars compared to the orbital velocities of the planets. These analytical estimates allow us to calculate very quickly the order of magnitude estimates for how flying across a star would change a planet’s semi-major axis.”
Their second method uses numerical integration using REBOUND, an open-source, multi-purpose N-body code for collision dynamics developed by Hanno Rein and his collaborators. Between these two methods, Brown and Rein were able to simulate a flying star passing by numerically and then measure the state of the system before and after it. Ultimately, their results suggest that a solar system disturbance would require a very close fly and this kind of stellar encounter is unlikely for very long. very long. Chocolate Words:
“We found that a critical change in Neptune’s orbit must be on the order of 0.03 AU or 4.5 billion meters to have an impact on the long-term stability of the Solar System. This critical change could increase the probability of instability during the lifetime of the Solar System by up to tenfold. In addition, we estimate that such a critical flying star could occur once every 100 billion years in the current region of the Solar System.
“[W]e estimating that we need to wait about 100 billion years before stars fly past the Solar System would only increase the probability of demolition of the current architecture by ten times (and that’s still no guarantee of destruction).”
Given the Solar System’s turbulent history, it’s understandable that the idea of flying through stars (and the resulting distraction) would cause some anxiety. However, astronomers theorize that “planetary shaking” may be a common feature of system evolution and that large objects are regularly ejected from the outer reaches of the system due to flybys. A good example is Neptune’s largest moon, Triton, which is thought to have formed in the Kuiper Belt and thrown into the inner Solar System, where Neptune captured it (which led to the destruction of Neptune’s original satellite).
In addition, gravitational interactions with other star systems are the reason why we have long-period comets, in which objects kicked out of the Oort Cloud periodically pass through the inner Solar System. The idea that a close fly could send multiple comets toward us (or larger objects like planetoids) sounds like a doomsday scenario! But as Douglas Adams said, “Don’t Panic!” Not only do stellar flybys occur regularly, they typically pass light years across and do not affect the Solar System.
In many ways, it is similar to Near Earth Asteroids (NEA) and it is likely that one will collide with Earth one day. Although we know that devastating impacts have occurred in the past (such as the Chicxulub Impact Event that killed the dinosaurs about 65 million years ago), the NEA makes regular close trajectories that pose no threat. Additionally, a recent analysis of two NEAs deemed “potentially hazardous” (2022 AE1 and Apophis) found that neither would threaten Earth for long.
Moreover, recent observations by missions such as ESA Gaia Observatory has provided the most accurate data on the precise motion and velocity of stars in the Milky Way Galaxy. As Brown notes, this includes data on upcoming flybys and how close they will be to passing to our system:
“Two well-known stars are HD 7977, which may have passed within 3,000 AU (0.0457 light-years) from the Sun about 2.5 million years ago, and Gliese 710 (or HIP 89825), which is expected to pass within approx. 10,000 AU (0.1696 AU). light years) from the Sun in about 1.3 million years from now. Doing some rough calculations, these two stars will have no meaningful effect on the evolution of the Solar System.”
What’s more, a lot will happen between now and then, and it’s highly unlikely that humanity will be around to witness such an event. Assuming we don’t push ourselves toward extinction or leave Earth to explore other galactic ranges, planet Earth will cease to be habitable long before then. “Given that the Sun will expand and swallow Earth in about 5 billion years, physical distance from other stars is not an issue for us to worry about,” Brown said.
This article was originally published on Universe Today by Matt Williams. Read the original article here.
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