All astronomers could see in the past were stars, galaxies, and nebulae. With improved technology, we’ve now directly imaged exoplanets from other solar systems many light-years away. We haven’t seen many though, and there is much to be learned from observing them.
Astronomers have seen so many stars that we’ve witnessed every part of their lives, from their birth in nebulae to their deaths as white dwarfs or neutron stars. The life of a planet, however, is more of a mystery despite the fact that we’re standing on one. Planets are proposed to form from discs of dust accumulating around a young star but this is something that occurred in our solar system billions of years ago. When we look out at our nearest neighbours, all we’ll ever see are boring middle-aged planets.
Now that astronomers have started spotting exoplanets out there in the cosmos, we’re starting to see the different stages that a planet can go through. The idea that planets form from discs of dust around stars has seemed very likely as multiple young stars have been found with discs of dust around them. In 2014, astronomers captured an incredible image that showed gaps where dust was missing, presumably being taken up by the newly formed planets that are forming.
This amazing image shows dust orbiting a very young star called HL Tau, which is 450 light-years from Earth. The dark circles in the dust are gaps so that must be where new planets are forming. In 2014, this was the sharpest ever image using the Atacama Large Millimeter/submillimeter Array (ALMA). As amazing as this image is, ALMA could only really see detail towards the outer edges of the disk. Nearer the centre, the dust appears as a smooth blob because it’s too thick to let through the short radio waves that ALMA detects. To get a better look, astronomers tried the excellently named Karl G. Jansky Very Large Array (VLA) because it detects longer radio wavelengths. The following image shows the ALMA image on the left and the VLA image on the right.
This region of the disc looked like a solid lump of dust before but the item marked “CLUMP” stands out as a round object among the orbiting cloud of dust. This is possibly the first ever image of an exoplanet during the early stages of planet formation, accumulating more and more of the dust as it orbits the star. To get a feel for the object orbiting and growing as it circles its star, check out this amazing picture combining both the ALMA and VLA images together:
In this image it really does look like the dust is accumulating into a sphere or “clump”. What I’d like to see in the future is more images using VLA data to see if we can find a distinctive clump again but at another point in orbit. It’s amazing how much detail we now have when investigating such distant objects.
Main image © ESO/L. Calçada