PDS 70, the star that showed us the first confirmed direct image of a planet born last year, had an extra trick in its protoplanetary disk. In retrospect, astronomers have found a second planet – and photographed both.
This gives him the additional honor of being just the second multi-planet system, which was clearly photographed directly.
(The first was HR 8799 with its four exoplanets, one of which has water in the atmosphere, and another is a stormy hell world.)
The two planets orbiting the PDS 70 are the PDS 70b ( which was found by astronomers last year) and the PDS 70c. The new image shows that they hollow out a massive cavity in the protoplanetary disk of gas and dust that surrounds the young star, an orange dwarf only 370 light-years away.
It's a great technical achievement and an incredible thing to see.
We know that there are many exoplanets. Thousands of people have been spotted, mostly by the search for the very low level of dimming that occurs when a planet passes in front of a star, or after the very small shake caused by the planet's gravity hauler.
We also know that when stars re-form, they are orbited by a swirling disk of dust, stones, and gas. It is believed that planetary accretion occurs when particles in the disk collide and stick together, gradually increase in gravity, collect and remove material from the orbit, and eventually form a planet.
Astronomers have taken some pretty amazing pictures of these protoplanetary disks in the past, with clear references to this web cleaning.
Direct photography of a planet, however, is much more difficult. This is because exoplanets are usually very far away and therefore too weak to be seen by our optical telescopes, especially when the reflected light is outshined by the brightness of the star. And sometimes what looks like direct evidence is not what it seems.
So, while we can make a well-founded guess as to whether there are baby planets on these slices, we actually saw very few, meaning that well, it could not be.
"With devices like ALMA, Hubble, or large ground-based optical telescopes with adaptive optics, we see discs with rings and columns everywhere." The question was, are there any planets there? " said astronomer Julien Girard of the Space Telescope Science Institute.
"In this case, the answer is yes."
The images obtained have enabled a whole range of information on the scientists Derive planets.
PDS 70b is about 4 to 17 times the size of Jupiter, as we learned last year, orbiting the star at a distance of about 20.6 miles (3.22 billion kilometers), just a little further than Uranus the sun is circling. A single orbit takes about 120 years.
The planet was discovered using the planetary orbiter SPHERE on ESO's Very Large Telescope with starlight-blocking coronagraph and polarizing filters that block certain wavelengths and focus the telescope on light that can be reflected off a planet starlight.
PDS 70c is slightly smaller, about 1 to 10 times larger than Jupiter. It is also farther out – about 34.5 Au (5.31 billion kilometers or 3.3 billion miles), and its orbital period is almost exactly twice that of PDS 70b. For every two orbits of 70b, 70c will rotate only once.
PDS 70c was discovered with another instrument, the VLT's MUSE spectrograph, and features a new mode that allows the telescope to pick up a hydrogen signal – a gas signature accretion that may be seen on a forming gas giant planet.
This mode was originally not intended for exoplanet hunting, but for the study of galaxies and star clusters. The discovery, however, suggests a possible new way to identify emerging exoplanets within protoplanetary disks.
"We were very surprised when we found the second planet," said astronomer Sebastiaan Haffert from Leiden Observatory.
A surprise that we can all enjoy.
The research was published in Nature Astronomy .