The Solar System With Three Suns The Sun

The Solar System With Three Suns The Sun, which has been shining down on the Earth for the past 4.6 billion years, is what makes all life on our planet possible.

The Earth’s position around the Sun is also highly fortuitous; any closer to the Sun, and the seas boil away, becoming far too hot for life to exist. Too far away, and our world becomes a barren, frozen wasteland.

Our planet and star have created conditions that are perfectly suited for life—as we know it. But imagine life somewhere out there, on a world completely alien to us.

Imagine life on a world with not one, but three Suns. You are watching Matter. In this article, you’ll learn about the planet that astronomers think is hiding inside a solar system with three stars. 1,330 light-years away, just off the shoulder of Orion, lies the star system GW Orionis.

The system is a part of a young stellar nursery—a relatively dense region of space where new stars are being created. Our own Sun is around middle-aged—already more than 4 and a half billion years old. But the GW Orionis system is hardly a newborn—possibly less than a million years old.

The system is so young that it probably hasn’t even evolved into stellar adulthood yet. The stars of GW Orionis are classified as “T-Tauri Stars,” an unstable and violent phase before the core becomes hot and dense enough for ongoing thermonuclear fusion.

When this happens, the stars will enter the “main sequence”—the stable phase where a star will spend the vast majority of its life. Aside from its age, the young GW Orionis is fascinating to astronomers because it is a trinary star system—a system with three stars.

The first two components of the system—stars A and B—are separated by a distance of around 116 million miles, which is only 1.25 astronomical units—or “AU.” One AU is defined as the distance between the Earth and the Sun. Both stars are also somewhat larger than our Sun, Star A being 2.75 times as massive, and star B, 1.65 times.

Because the two stars share a similar mass, they actually circle each other in a binary orbit. Their orbits are centered around their common center of mass, which lies about one-third of the way between star A and B.

They complete one shared revolution once every 241 days. The third star in GW Orionis—star C—orbits much further away from the inner binary, at a distance of 854 million miles—just shy of the distance between the Sun and the planet Saturn. Star C is the smallest of the system, at only 88% of the Sun’s mass.

It takes 11 years and 7 months for star C to complete one orbit around the A–B binary. This configuration of orbits—a close, binary pair with a third, more distant companion—classifies the GW Orionis star system as a “hierarchical triple.” Such systems are probably relatively rare in the cosmos, since multiple massive bodies in the same system often leads to unstable and chaotic interactions.

But this distant trio of stars gets even more peculiar: the entire system is surrounded by a wide, flat disk of gas and dust, known as a “protoplanetary disk.” This sort of disk would have once surrounded our own Sun, but the material was eventually cleared away as gravity caused it to collapse down to form the planets, moons, asteroids, and comets that make up our solar system.

Because GW Orionis is still very young, it hasn’t had a chance to shed this protoplanetary disk—it is still in the middle of the process of planetary formation.

Astronomers have seen plenty of protoplanetary disks surrounding other stars in the galaxy, but none of them are quite like this one. First, astronomers would expect the dusty disk to be aligned with the plane of the stars’ orbits—but it isn’t.

Instead, the circumstellar disk appears highly inclined with respect to the central trinary, perhaps by as much as 45 degrees. On top of that, GW Orionis’ disk isn’t much like a solid disk at all, but instead divided up into three concentric rings, one inside the other like a set of cosmic nesting dolls. The outermost dust ring extends for nearly 340 AU—or more than 30 billion miles—making it the largest known ring of protoplanetary dust.

The gaseous part of the disk stretches out even further, to 1300 AU, which is more than 30 times the size of the orbit of Pluto.

The three massive rings are all out of alignment with each other as well as with the central stars, so that each ring is inclined ten to twenty degrees away from the one next to it. And between the central and the middle dust rings, there is also an odd gap, nearly devoid of dust and gas.

This gap occurs at a distance of about 100 AU from its triplet suns, cutting so deep that the inner and outer rings are able to rotate independently of each other. Astronomers have a lot of questions about what is happening inside the GW Orionis system, and there aren’t a lot of answers so far.

The first theory was that, as the three stars spun around each other in their complex orbits, gravitational torques between them worked to tear the surrounding protoplanetary disk apart. Dr. Stefan Kraus and his team at the University of Exeter have been using computer models and simulations to see if this explanation, the so-called “disk-tearing effect,” is even possible.

The answer is… sort of. Alison Young, another member of Dr. Kraus’ team, says “There have been a number of theoretical studies on disk-tearing effects, but this is the first direct evidence of effect occurring in a planet-forming disk.

This demonstrates that it is possible for such disks to be warped and broken and raises the possibility that planets could form on highly inclined orbits around multiple star systems.” However, as exciting as this answer is, it isn’t entirely complete.

While the simulations do show that it is possible for a triple-star system to throw a protoplanetary disk out of alignment, it still isn’t enough to explain the unique, three-banded structure of GW Orionis, or why there is a distinct gap in the ring of dust. Dr. Nienke van der Marel and her colleagues conducted a study using the Atacama Large Millimeter Array to try to get a better look inside GW Orionis.

She and fellow researchers offer an alternative theory to explain the strange nature of the system: A Jupiter-sized planet, or possibly even several planets, are responsible for clearing out the gap in the system’s ring of dust, and for tweaking the disk out of alignment.

Dr. van der Marel said that “our simulations show that the gravitational pull from the triple stars alone cannot explain the observed large misalignment. We think that the presence of a planet between these rings is needed to explain why the disk was torn apart.” The clouds of dust and gas that surround the trinary star system obscure much of what may be happening within, and so it will be difficult to locate their proposed planet.

But that won’t stop astronomers from trying. More studies are already being planned for GW Orionis in the future, to try to get a glimpse of this hypothetical new world. If it’s true that there is a planet, or planets, in orbit around GW Orionis, it would be the very first circumtriple planet—a planet orbiting around three Suns—ever discovered.

Such a rare, unique system could become a holy grail for astronomers, offering valuable new insights into how planetary systems grow and evolve, and revealing unanswered truths about our infinite cosmos. Thank you for watching Matter!

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