Rogue planets

Welcome back to JJNN

Today's second article is also from the online edition of the Yomiuri Newspaper.

When most people think of solar systems they probably think of one sun (or maybe a binary star) with planets rotating around it. If that image is expanded, most people think of a galaxy as something that contains many solar systems. In other words as something that contains many suns with many many planets rotating around them.

For the longest time that was the basic idea, but that idea was upset by a paper written by Professor Ito Yoshitaka from Nagoya University and assistant professor Sumi Takahiro from Osaka University. The paper, which was published in Nature, detailed that there are probably hundreds of billions of rogue planets in flying around the universe.

What's a rogue planet? Well basically it's a planet that is not gravitationally bound to (thus not revolving around) any star. It's really a cool idea if you think about it. A planet hurdling though space not effected by any star unless it's path happens to get close to a star's gravity well. With a number like "hundreds of billions" and an area the size of the universe as well as an amount of time from when planets started forming to the present time; it could be quite possible that a rouge planet could wander into a star's gravity well and be captured. In other words, it could be possible for an "alien planet" to become part of a solar system. You can see an artist's reprensentation of what a rouge planet might look like below.

Possible repersentation of a rogue planet

This leads us to two questions: How do planets become rouge planets and how can we detect those planets? Rouge planets are created when planets that are rotating around a planet are effected by the gravity of other planets or other objects around the sun and actually get ejected from their orbit. The rogue planets are actually detected because of an effect called gravitational lensing. Basically, an object that has a large mass bends space-time around it to the point in which it actually bends the path of light around it like a huge lens. When one of the rogue planets moves in front of a star (when viewed by the Earth) the amount of light from that star actually increases until the plant moves away from the star.

It is now time for the word of the day. Today's word is 惑星(わくせい). It is pronounced wakusei and it means planet. I am wondering if a percent of the "dark matter" (matter which we can't account for in the universe) is not made up of these rogue planets.