A very hungry planet in a protoplanetary disc

Today's post is on planets in protoplanetary discs, specifically one observed by the Very Large Telescope in Chile. The image below is the first clear detection of a baby planet in a disc featuring multiple rings, a phenomenon in protoplanetary discs which I wrote about in a previous blog post here.

Stars are formed from molecular clouds in the interstellar medium, the material that fills space with a density of approximately 1 molecule per cubic metre, almost but not quite a vacuum. The way I visualise this extreme low density of gas is imagining a dishwasher, with nothing but a singular molecule in it. Air on Earth, if it filled a dishwasher, would have about a billion billion billion molecules in it (or 10^27 for the more mathematically keen readers). Once molecular clouds reach a critical size and density, they begin to collapse in under the weight of their own gravity, become increasingly hot and dense, and ignite fusion, where two hydrogen molecules fuse together to create heavier molecules such as helium, while releasing some energy in the form of light and heat, forming the central core of a star. Gas swirls around young stars as they grow, eventually flattening out to form 'protoplanetary discs', the birthplaces of planets, and it is from this swirling mass of dust and gas that planets form around their host stars. It is thought that planets may trace out rings in the dusty protoplanetary discs as they orbit their host star, sweeping up debris and dust as they go around.

Protoplanetary disc with rings, featuring the planet WISPIT 2b around its host star. Credit: ESO/R. F. van Capelleveen et al.

The rings in protoplanetary discs such as the one shown above are thought to indicate the presence of hungry planets in the disc, gobbling up material as they sweep around their host stars, growing as they do so. The planet in this image is around 5x Jupiter's mass, and its host star is similar to a young version of our own host star, the Sun. Rather neatly, this observational discovery has added credence to the idea that ring gaps in protoplanetary discs can be created by newly formed planets, which had previously been predicted theoretically and has now been observed by telescopes. This baby planet is so young it is still embedded within its disc. Hydrogen gas has been detected falling on to the planet, meaning it is still accreting matter from its disc surroundings.

This discovery was made possible through an international collaboration of astronomers, a common theme in research nowadays! The observations were taken by the planet hunting SPHERE instrument on the Very Large Telescope (VLT), an extraordinary feat of engineering not only featured in a James Bond film but also responsible for some stunning photos of galaxies, stellar nebulae and planets, which I wrote about in a previous post here. The SPHERE instrument blocks out light from the host star using a device known as a coronagraoh, allowing astronomers to get a clearer look at dim planets which would otherwise be completely outshone by their bright host stars. Since the VLT is a ground based telescope, atmospheric turbulence has to be accounted for when taking detailed observations. This is done using a technique called adaptive optics, which essentially bends the mirrors in the telescope in real time to mitigate the effect of wobbly atmospheric turbulence distorting images of the sky. While that is an incredible challenge of engineering and instrumentation, the final crisp images that this creates are a marvel in themselves.

Certainly very pretty, such research can reveal insights into what our own Solar System may have looked like in its infancy, by observing young planetary systems just beginning in their lives.

It is my intention to write about a new interesting science topic most weekends, and currently in the pipeline are articles about stargazing in the Shropshire countryside, and a walk down memory lane with some elegant maths puzzles. This curious physicist may also be venturing abroad again soon, for another adventure...