It's pretty amazing that the star AS 209 is so close.
It is more massive than the Sun and younger than 1 million years old. It is part of a region of dust and gas where stars are being born.
The ALMA shows that it has a circumstellar disk, a flattened disk of gas of dust. It is common around young stars, but this one stands out because it is broken up into a series of rings, separated by gaps in the material.
One of the outer gaps is caused by a gas giant planet forming there with about the same mass as Jupiter. One of the inner gaps may be due to an orbital resonance, where material travels around the star twice for every single time the planet is in motion. The material at that distance from the star is pulled away by the planet's gravity in the same way that pumping your legs can make you go higher on a playground swing. This is one of the reasons the rings have gaps.
Is there an actual planet there? There are new observations that support its existence. The astronomer who did the work found a bright spot where the planet should be, as well as a large mass in the circumstellar gas at the same spot.
Carbon monoxide gas is common in cold disks. The bright spot is in the middle of an outer ring gap about 30 billion kilometers away from the star. The amount of gas is less than a tenth of Jupiter's mass. They believe this can only be explained by a disk of gas around the planet. It is expected that as material falls onto the planet from the circumstellar disk it will form a disk around the planet.
Gas was seen in a circumplanetary disk for the first time. The light from the dust was used to detect the previous two. There was no light coming from the disk. The upper limit for the amount of dust is 0.027 times Earth's mass. It is not clear why that is a small portion of the gas seen.
There is more proof of the planet. Light can be seen at multiple wavelength thanks to the gas in its disk and ALMA. As the gas in the rings moves around the star, it causes a shift in its light. If a planet is there, you would expect the gas to move at different speeds. The gas in the rings will be accelerated by its gravity.
They found a planetary mass of 1.3 times that of Jupiter, which is in line with previous estimates of what a planet in that gap might have. This is a planet with Jupiter's mass forming in only about a million years, and I wrote about it in 2019. It took 100 billion tons of matter to fall onto the planet for a million years. That is roughly the same amount of time it would take for a dinosaur-killer-sized asteroid to hit.
The birth of a planetary is not easy.
It's also pretty. There are many examples of young stars with disks around them, including many with rings that may be formed because of planets. We can figure out how planets are born if we find more of them. Our own is included. Earth was formed over four billion years ago. We can better understand how we came to be when we watch AS 209.
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