The stars are seen from Earth. There are a lot of stars in the universe. The image is courtesy of Abdul Azis.
The first planet outside the solar system was discovered in 1992. Since then, telescopes have spotted thousands of these so-called exoplanets, which are planets that are outside the solar system. It's enough to make you wonder if every star has at least one planet.
Jonathan Lunine is the chair of the Department of Astronomy at Cornell University. That is not as far as we know.
Lunine told Live Science that it's always a question of whether you can detect something. One doesn't know. There are plenty of stars where there have been searches for planets, and none have been found to date.
Why are the shapes of the galaxies different?
Lunine said that scientists estimate that there are as many planets as stars in the universe. Some stars, like the sun, as well as TRAPPIST-1, a red dwarf star about 40 light-years away, are home to more than half a dozen planets.
What makes a star host so many planets? The way the star formed is what scientists think it is. Young stars are surrounded by a ring of dust particles. These particles can form larger and larger clumps, which can eventually form planets. Some young stars are not so lucky.
If you have a star formed from a clump of cloud that has a rapid rotation and is contracting instead of spinning out to form a disk, it can break into two or even more pieces and form a multiple-star system. It's possible that the system of two stars or three stars never ends up with a planet if a disk hasn't formed.
The conditions have to be right for a planet to form in a star system.
There are planets in some star systems. Do those systems end up with the material breaking into two clumps and then a disk forming around one of those clumps, or maybe both of those clumps? Is there something that was captured?
Lunine said that a young star's dust-filled clump might spin so slowly that it collapses into a star without ever forming a disk. It's possible for a star to form planets only if another star throws them out of the solar system, or at least send them too far out to be seen. The planet HD 106906 b is 18 times farther from its star than it is from the sun, and it may have been affected by that.
Lunine warned that our knowledge of how many stars host planets is dependent on what we can detect. The transit method uses dips in a star's brightness as a sign that a planet is passing in front of it.
"We can always look at a particular star and say, 'Well, a planet wasn't detected around it, but you know, maybe there's a planet that's kind of small and really circling far from the star and therefore is kind of of.' That is a possibility. There are stars that don't have planets around them.
Live Science published the original article.
