Astronomers see adorable baby planets forming around a young star

370 light years from us, a solar system makes small planets. The star at the center of it all is young, only aged about 6 million years old. And his babies are two huge planets, probably gaseous giants, who feed on gaseous matter from the circumsolar disc of the star.

The host star of this system is called PDS 70. The PDS 70 is a little smaller and less massive than our Sun and continues to accrete the material itself. This young star is a star of T Tauri, which basically means that they are very young and start in life. Because of its youth, the planets are still forming in orbit. And to see that nascent planets continue to form is something that astronomers are just beginning to do well.

"This is the first unambiguous detection of a two-planet system digging up disk space."

Julien Girard, Institute of Space Telescope Sciences.

What makes the images of these young planets still interesting is that they are evidence to support our long-standing theory of planet formation in young solar systems. This theory is called the Nebular Hypothesis and has existed for decades, but without any evidence to confirm it.

The Nebular Hypothesis

Stars form from massive clouds composed mainly of hydrogen, called molecular clouds. Molecular clouds are unstable gravitationally and the gas tends to agglutinate. Eventually, one of these groups starts to snowball and gets bigger and bigger. In doing so, the cloud flattens like a pancake and begins to spin, and when the central mass becomes dense enough, it ignites to form a fusion and a star is born. Many stars are in binary systems when two stars form from the molecular cloud.

But the star in the center is not the only bouquet. Other smaller lumps form in the rotating gas and can turn into planets. Some gaseous planets, like Jupiter and Saturn in our own solar system, can become very large. (Astronomers sometimes call Jupiter and Saturn "failed stars" because they were about to become stars but could not quite get there.)

If you could freeze the process there, you would see a young star in the center of a flat and rotating gas cloud. But in essence you would see ring-shaped holes, where the planets are busy sweeping materials and becoming planets. This process is called accretion. And it is no longer a molecular cloud, but a "protoplanetary disk", because it has the shape of a disk and proto-planets are formed there.

And that's exactly what astronomers see.

See the real planets

What is good with these new images is that we can not only see the gaps and rings that signal the presence of a planet, but also see the planets themselves. And this is only the second time we are certain to see a two planet system making holes in the disc. (A four-planet system called HR 8799 was imaged in 2008.)

"We were very surprised when we found the second planet."

Sebastiaan Haffert, lead author, Leiden Observatory.

"This is the first unambiguous detection of a two-planet system creating a disc slot," said Julien Girard of the Baltimore Institute of Space Telescope Science, Maryland.

In this new study, published in the June 3 issue of Nature Astronomy, the team of astronomers used the MUSE spectrograph on the very large telescope (VLT) of the European Southern Observatory.

Seeing inside a protoplanetary disk is a difficult task. Not only is the star really bright, it dominates the image, but all the gas and dust on the disc can block light from the planets in formation. The MUSE instrument has the power to lock the light emitted by hydrogen into the cloud, indicating that hydrogen accumulates in planets in formation.

"We were very surprised when we found the second planet," said Sebastiaan Haffert of Leiden Observatory, lead author of the newspaper.

"With equipment like ALMA, Hubble, or large ground-based optical telescopes with adaptive optics, we see disks with rings and empty spaces. The open question was: are there any planets out there? In this case, the answer is yes, "explained Girard.

The team spotted a planet called PDS 70c. (Another planet in the same system, called PDS 70b, was first sighted about a year ago.)

The new planet, PDS 70c, is near the outer edge of the disk and about 3.3 billion kilometers from the star. It is about the same distance as Neptune of the Sun. Astronomers have only preliminary estimates of the mass of the planet, but they estimate that the PDS 70c is between 1 and 10 times more massive than Jupiter.

The previously discovered planet, PDS 70b, is about 2 billion kilometers from the star, about the same as Uranus in our solar system. Its mass is between 4 and 17 times that of Jupiter.

Now we are waiting. For the James Webb telescope

Getting images of these young exoplanets is a kind of happy accident for the MUSE spectrograph. The instrument was originally developed to study galaxies and star clusters. But it turns out that it's good to spot exoplanets being formed. And this accident helped to shift the hypothesis of a nebula hypothesis to an accepted theory.

"This new mode of observation has been developed to study galaxies and star clusters at higher spatial resolution. But this new mode is also suitable for exoplanet imaging, which was not the original scientific engine of the MUSE instrument, "said Haffert.

In the future, the James Webb Space Telescope (JWST) will advance the study of young planets forming in these discs. Once the endless waiting for the advanced space telescope is complete, its power should allow astronomers to focus on very specific wavelengths of light emitted by hydrogen scavenging.

This means that scientists will be able to measure the temperature of the gaseous hydrogen in the disc, as well as its density. Knowing these two elements will really help us understand how gaseous giant planets are formed.

But for the moment, at least we have images of the planets and, when astronomers are watching the galaxy and see these young star systems, as well as the holes in the discs, they can be assured that there are actually has planets.