Some "hot Jupiters" in distant stars are much larger than theory predicts. Scientists attributed this to the influence of their aging stars.
Of the more than 3,000 exoplanets known to us today, the hottest Jupiters remain the largest group. With a mass often exceeding the mass of Jupiter, they are much closer to it to their stars, closer than our Mercury. This makes them not only big, but really hot. With this mass, size, and proximity to stars, it's no surprise that "hot Jupiters" are easier to observe than other exoplanets. But scientists still can't explain how these gas giants get so big.
The new version is put forward by an article published in The Astronomical Journal. Princeton astrophysicist Joel Hartman and colleagues worked with the HATNet automated telescope network, observing a pair of particularly large and incandescent "hot Jupiters." HAT-P-65b and HAT-P-66b are located 2700 and 3000 light years from us, respectively. Moreover, the orbit of both planets is ten times less than the orbit of Mercury, so they make a complete revolution around their stars in just 2, 6 and 3 of our days.
However, the sizes of both exoplanets were unexpectedly large. With a mass of HAT-P-65b about half that of Jupiter, it is 1.9 times larger than it, and weighing about 0.8 times the mass of Jupiter, the giant HAT-P-66b has dimensions that are 1.6 times larger than those of Jupiter. According to Hartman, this is much more than what current models of planetary formation predict, which give a maximum of 1.5 Jupiter. However, scientists paid attention not to the planets themselves, but to their parent stars.
Both of them are not too different from the Sun, having approximately the same dimensions and masses of about 1, 2–1, 3 solar. Both are quite old and have gone through about 80 percent of the evolution in the main sequence. At this stage, the stars intensify radiation - this process should gain strength as they approach death. The amplification of radiation further heats up nearby gas giants and causes them to "swell" to a size much larger than one would expect.
Scientists are noticing that their work could make a difference far beyond the "hot Jupiters" topic. It points to the enormous influence that the evolution and state of a star have on the state and evolution of its planets. And if we want to better understand the planets, it is imperative to act with an eye to the stars.