These stars are smaller and less massive than the sun, they burn through their smaller complements of hydrogen fuel more slowly, and they shine much longer than stars like the sun. Very large stars, such as the blue giants, tend not to support planetary systems. These stars' high mass drives accelerated fusion reactions in their cores and exhausts their entire complement of hydrogen on a scale of tens of millions of years as compared to billions of years for stars like the sun, which might not allow time for planetary systems to form.
Truly, those stars are enormous. We have also seen stars that are just one tenth the size of our sun. Our Sun is a little unusual because it doesn't have any friends. It's just one Sun surrounded by planets, asteroids, comets, and dwarf planets. But solar systems can have more than one sun. In fact, that's often the case.
More than half of all stars are in multiple star systems. That means the solar system has two or more suns in it. You would weigh twice as much there as you do on Earth! Another planet, called Keplerb, turns out to orbit two stars. A sunset there would provide a view of two setting stars! An illustration that shows what it might look like to stand on the surface of Keplerb.
The planets are relatively close together, too. It has also made a list of more than 3, additional potential exoplanets that astronomers need to study more carefully to be sure that they are indeed planets. While Kepler primarily searched within one particular patch of the sky, TESS is observing the entire sky to locate thousands of planets orbiting the nearest and brightest stars. The James Webb Space Telescope, set to launch in , will also observe many of the exoplanets we have discovered and help scientists reveal details about these distant worlds.
The answers are seldom straightforward, as the case of HD Ab shows. The planet is huge, at least four times the size of Jupiter. It's unclear if there would be enough gas to form such a giant world out at 80 AU from the main star in the system. Also, radiation from the binary pair would have blown much of this material into space, making the accretion process even more difficult, researchers have said.
Another possibility is that the planet formed independently in the large molecular cloud that birthed the three stars, rather than from the disk of leftover material surrounding the main star. The final theory is that the planet formed very close to its parent star, along with a companion planet or two.
Over time, the planets' orbits would have tugged at each other, and eventually such interactions booted HD Ab out to its current location. As for the other planet or planets in this last scenario — if they were close enough to the parent star, they could still be hiding there in its glare, Kratter said.
And the orbits in this system may still be evolving, given that it is so young about 16 million years old; our own solar system, for comparison, is about 4. Planets may also be pushed around by gravitational tugs from the stars in their system, said Beatty, the second author of the paper announcing KELT-4Ab. Most systems with close-orbiting "hot Jupiter" planets have two or three stars in them, he noted; hot Jupiters may therefore form farther out in the system, and then get dragged inward by these stars' gravity.
Depending on where a star is located in the Milky Way, it may be able to hang onto multiple other stars gravitationally over quite large distances.
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