(ORDO NEWS) — When astronomers first started studying exoplanets, they were surprised to find an entirely new class of objects.
These are the so-called hot Jupiters – planets the size of Jupiter, which are closer to their star than Mercury is to the Sun.
Hot Jupiters are relatively rare. They can be found only in 1% of stars with planets. But in star clusters, this percentage is much higher. There they meet several times more often.
A team of astronomers has come up with an analysis that they believe could explain why there are more hot Jupiters in star clusters. The answer is that the stars in the cluster are more densely packed.
They are so close that they simply have to interact with their neighbors in some way. In some cases, they may even capture one of the neighbors.
Thus, even though stars originally formed as single objects, they can become binary systems. Astronomers have found that if this capture happens early enough in the planet’s formation, it could lead to the formation of a hot Jupiter.
If a planet the size of Jupiter forms around a star, and that star grabs a neighbor, the neighbor’s gravitational influence can begin to stretch the planet’s orbit.
As the planet’s orbit stretches out, it becomes more and more elliptical. The farthest point of the orbit becomes more and more distant from the star, while the closest point gets closer.
Eventually, if the planet gets too close to the star, it can be captured into an entirely new orbit, and the ordinary giant planet becomes a hot Jupiter.
Astronomers have found that this happens to about 2% of the stars in the cluster. However, creating a hot Jupiter requires a special set of circumstances, as the orbit must get closer, but not too close.
Astronomers have found that about 4% of the time, gravitational glitches send a planet straight into a star, destroying it.
In general, astronomers have found that if about 10% of stars form giant planets, then in about a billion years there will be enough interactions in a star cluster to cause a migration that turns the giant planet into a hot Jupiter.
Because these interactions rarely occur outside of star clusters, this could go a long way to explain why hot Jupiters are more common in clusters.
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