We now know more than 5,000 exoplanets, worlds orbiting other stars. The vast majority of them have been detected by the transit method, when the planet causes a mini-eclipse and blocks a little light from its host star. This is an indirect method; we do not see the planet itself, but only the impact it has on the light of its star.
To date, less than 60 exoplanets have been directly mapped; that is, seen in real images of their stars. This method works best in infrared light with young stars – newly formed planets glow in the IR due to their own heat, while stars don’t usually emit as much infrared radiation, making the planets easier to spot. It also works best for planets that are quite far from their star – 50-300 times farther than Earth from the Sun – so they don’t get lost in glare.
It can work for even young planets. So young, they are still being formed.
AV Venigi – a young star, which is 2-4 million years old, and is about 560 light years from Earth. It is more massive, hotter and brighter than the Sun, and this is what we call a the star of the previous main sequencenot yet completely merging hydrogen and helium in its core, but very close.
It is surrounded by the dust and gas from which it was formed. ALMA sees a ring of dust at a millimeter wavelength that is about 18 billion kilometers from the star, and a flat gas disk much closer to it. The gas disk has spiral sleeves, which, according to theoretical models, could mean a planet or brown. a dwarf – an object intermediate in mass between a planet and a star – there, its gravity disrupts the gas in the disk. The dust ring also breaks off abruptly at the inner edge; another indicator of a decently massive body orbiting a star, its gravity shrinking the inner ring.
With that in mind, a team of astronomers used the huge Subaru telescope in Hawaii and the Hubble Space Telescope to search for any possible planets that are still forming, called protoplanets orbiting AV-Variga.
And seems to have found.
The bright spot is visible at a short distance from the star, about 90 times the distance of the Earth-Sun, or about 14 billion kilometers – a little more than twice as far as Pluto from the Sun. It is outside the main gas disk but inside the dust ring.
AB Aur is moving slowly in our sky relative to more distant objects, and if this spot was a background star or galaxy, then 15 years later it would be in a completely different position in the images. He was spotted in infrared observations made by Hubble in 2007, and is still in almost the same position relative to the star in new observations. This is also seen in images taken with the Subaru telescope, so it is not related to any telescope or processing artifact. It’s real, and moving along with the star.
Not only that, over time the image moves slightly between images around the star corresponding to it rotates around the star at this distance counterclockwise. This would be true for both the protoplanet and for some large gas cluster, so it’s interesting, but not definitive.
But better: its position is consistent with theoretical predictions of where the massive protoplanet should be located to explain the spiraling features in the gas disk, which is interesting.
It is also clearly not a point source, not a simple point in the images. Its size means it has no more than 2 billion kilometers in diameter, which is huge. However, if a planet that is still forming is at such a distance from its star and has a mass about 4 times the mass of Jupiter, it is surrounded by a disk of material that will be about the same size. So, again, this corresponds to a massive protoplanet.
If it were just a lump of dust orbiting a star, the light we see from it would be highly polarized; that is, the waves of light will be strongly aligned. This no seen, indicating that light comes from the object itself, not just from the reflected light. In other words, it glows. It is also seen as light emitted by excited hydrogen, which is expected for a planet surrounded by gas that enters it.
The colors of the spot also match because it is a massive but still very hot planet. Using theoretical models, astronomers best matched the young planet, which is about 9 times the mass of Jupiter, 2.75 times its diameter – quite large, but this is because it is still forming and not yet settled – and with a temperature of about 2000 ° C. Very hot, but again it is expected. This corresponds to a rate of increase – as fast as matter falls on it – about a millionth of the mass of Jupiter each year. Maybe not so much, but Jupiter is a beast. This growth rate is equal to 5,000 trillion tons a day.
That’s 66 billion tons per second. Per other. It’s like a 4-kilometer-wide asteroid – about half the diameter of a dinosaur killer – affecting the protoplanet every second of every day of every year for hundreds of thousands of years. No wonder it glows hot.
Having said all that, this is not convincing proof that this is indeed a growing protoplanet, but it is very convincing proof.
This makes me very happy. As I wrote earlier, the day I worked on Hubble’s observations of this star in 1999. This potential protoplanet was too close to the star to be seen in our data, but new observations were made in a different way that allowed the planet to stand out from the world of the star. Impressive.
And it’s so close to us! We see stars forming all over the Milky Way all the time, and this is another piece of the galactic puzzle that shows that planets are forming with them. The universe is filled with planets, worlds that cannot be counted, and we are just beginning to look for them.
A hint from the race to Tayn Curry, the lead author of this study, for having warned me about his work.