New Study - There is a Planet Orbiting Every Star in our Galaxy
Jason Gibson - January 11, 2012
It was previously thought that most stars in our galaxy didn't have any planets, and those stars that did harbor planets were the exception rather than the rule. New data shows that the reverse is true. The new research results show that most stars in our galaxy do in fact have planets.
This implies that there are billions of planets in our galaxy which is vastly more planets than previous estimates.
A Multitude of Planets -This artist conception reflects the conclusion of this new research. Statistically, most stars in the Milky Way Galaxy in fact have one or more planets orbiting around. Previously, it was thought that planets were relatively rare in the cosmos. Image - ESO.
In 1992, the first planet was discovered orbiting around another star. The rate of planet detection has increased greatly since that first discovery and its hard to believe that prior to 1992 there was no proof at all that other planets existed outside of our solar system.
We've gotten pretty good at detecting extrasolar planets, but we don't have any direct pictures of any of them. They are simply too small, too far away, and they are bathed in the bright light of their parent stars. It would be like trying to take a picture of a gnat buzzing around a light bulb - from hundreds of miles away.
There are three ways that we use to detect planets around other stars:
1) Transit Method - Imagine a star far away that has planets orbiting around it. If things are aligned perfectly, then some of these planets around some stars will pass "in front" of the face of the star as viewed from Earth. Using very sensitive detectors, we can measure the light output of stars and we can see the light decrease each time the planet passes in front of the star.
2) Wobble Method - We usually think that the Sun is absolutely stationary and the planets orbit around. In reality, any star that has a planet orbiting it will wobble very slightly as the planet moves around. Using sensitive detectors we can detect the motion of the star and can calculate the size of the planet that must be orbiting it.
3) Gravitational Microlensing - This one will seem a bit like science fiction. It turns out that stars sitting in space actually bend space and time in the vicinity of the star. This has the effect of bending the path of any light that travel near the star. Imagine that you have a star that you're interested in. Ideally you'd pick a star to study that has other stars and galaxies behind it so that you can see how the light is bent. This is called gravitational lensing because the image of the stars and galaxies that lie behind the star of interest look distorted due to the light bending. They look like they are under a "lens". If the star of interest has planets around it, it bends the light more and we can detect this and calculate the size of the planet.
Gravitational Microlensing - In this image you can see that the light from the galaxies are bent as it travels to Earth. This is caused by the star in the center of the image, which is closer to Earth, bending the light of the other objects which are farther away. Notice that some of the galaxies look bent because of spacetime distortion due to the foreground star in the center. Image - Space Telescope Science Institute
Over a period of six years, astronomers studied millions of stars using an array of southern hemisphere telescopes. They used the gravitational microlensing method to detect the planets and used statistics to show that, on average, every single star in our galaxy has at least one planet orbiting it.
Think about that. Prior to 1992, we had no proof that any planets existed outside of our own solar system. Now, we have hundreds of planets cataloged in detail, with more discovered every year and we have this vast study that shows that planets are much, much more common that we previously thought.
Does this mean that life is out there, somewhere? Nobody knows for sure, but the odds just increased.