The first exoplanets in another galaxy.
Of course, if our own galaxy has exoplanets orbiting stars, then other galaxies will also have exoplanets. However, other galaxies are too far away to detect exoplanets with any of the means we currently have. Now, researchers at the University of Oklahoma claim to have spotted exoplanets in another galaxy using a technique called gravitational microlensing. However, these planets have quite strange behavior.
In our galaxy, we search for exoplanets by observing the stars on which they move. We can detect small fluctuations in the star when planets move around them, but this only works for large planets. The transit method monitors the stars for small dips in brightness from the planets passing in front of them. This can detect smaller planets, but not all solar systems are oriented in such a way that the planets pass in front of the star from our point of view. Gravitational microlensing is a completely different approach predicted by general relativity. Just as a glass lens can magnify an object, the bending of space under gravity can amplify distant sources of energy.
The lenses come from an active galaxy with a black hole (known as a quasar) about 3.8 billion light-years away. The strong gravity from the quasar bends glows towards the Milky Way, causing invisible objects to be visible. The team used the Chandra X-ray Observatory to scan the galaxy (called RXJ1131-1231, at the center of the above image), finding signals that could be planets.
Astrophysicist Xinyu Dai says the technique can detect objects the size of Earth’s Moon or as large as Jupiter. According to the researchers, gravitational microlensing is the only known method that hopes to detect planets at such a great distance, even in science fiction scenarios.
The team’s X-ray observations paint a picture of the galaxy, unlike our own. They estimate that there are 2,000 planets for each star, and that many planets are not tied to individual stars. Instead, they drift through space or jump from one star to another. Could there be trillions of “rogue” planets in this galaxy? That would be wild, to say the least.
The scientific community is still skeptical about the interpretation of this data, but everyone agrees that it is very interesting. Some alternative explanations for the data include clusters of brown dwarf stars or dust clouds. Other experts will pour out data, trying to either confirm or refute these claims. In any case, there is something that can be seen in RXJ1131-1231.