It stands to reason that if there are exoplanets orbiting stars in our own galaxy, then there would also be exoplanets in other galaxies. However, other galaxies are too far away to detect exoplanets by any of the means we currently have. Now researchers from the University of Oklahoma claim to have spotted exoplanets in another galaxy using a technique called gravitational microlensing. These planets seem to have rather odd behavior, though.
In our galaxy, we look for exoplanets by observing the stars they orbit. We can detect small wobbles in the star as planets move around them, but this only works for larger planets. The transit method monitors stars for small dips in luminance from planets passing in front of them. This can detect smaller planets, but not all solar systems are oriented in such a way that planets pass in front of the star from our perspective. Gravitational microlensing is a completely different approach, predicted by general relativity. Just like a glass lens can magnify an object, the bending of space by gravity can amplify distant energy sources.
The lensing comes from an active galaxy with a black hole (known as a quasar) about 3.8 billion light years away. The intense gravity from the quasar bends light toward the Milky Way, bringing previously unseen objects into view. The team used the Chandra X-ray Observatory to scan the galaxy (called RXJ1131-1231, in the center of the above image), finding signals that could be planets.
Astrophysicist Xinyu Dai says the technique can detect objects as small as Earth’s moon or as large as Jupiter. Gravitational microlensing is the only technique known that has any hope of detecting planets at such a great distance, even in “science fiction” scenarios, according to the researchers.
The data from the team’s x-ray observations paints a picture of a galaxy very unlike ours. They estimate there are 2,000 planets for every star, and that many of the planets don’t remain bound to individual stars. Instead, they drift through space or hop 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 of the interpretation of this data, but everyone agrees it’s very interesting. Some alternative explanations of the data include clusters of brown dwarf stars or dust clouds. Other experts will be pouring over the data in an attempt to either validate or refute these claims. Either way, there’s clearly something to see in RXJ1131-1231.
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