For the first time, astronomers have discovered that men form in the rubbish disk around a large exoplanet. Astronomers have long suspected that this is how larger planets like Jupiter in our own solar system – get their moons. It happens just about a very young star called PDS 70, about 370 light years away in the constellation Centaurus.
The accepted theory of how planets form is called the nebular hypothesis. Everything begins with the formation of a star in a huge gas cloud called a giant molecular cloud (GMC). When the star is formed, the cloud is formed into a rotating flat disk of gas and dust called a protoplanetic disk or other disk. Matera begins to collect lumps in this disc, and these lumps become planets.
If a planet that forms in the disc grows more than about 10 soil masses, something else happens. Because of its mass, the planet opens a gap in the protoplanetic disk. When material passes through that gap, it may come close enough to the planet that the planet's gravity dominates the host star's gravity. That material is then captured in a circumplanetary disk (CPD) that rotates around the planet, like a disk in a disk.
Much of the material within a circumplanetary disk is accreted in the forming plane. But not everything. The same forces that created planets out of the circumstellar disk go to work. They can create moons from the material that rotates in the disk around the earth.
Now, a team of astronomers has discovered this circumplanetary disk and moons form in it, for the first time.
The main author of the study describing these findings is Andrea Isella, an astronomer at Rice University in Houston, Texas. The results were published in The Astrophysical Journal letters and are called "Continuous Submillimeter Emissions Detection Associated with Candidate Protocols".
"Planets are formed from disks of gas and dust around newly formed stars and if a planet is large enough, it can form its own disc as it collects material in its orbit around the star, Isella says." Jupiter and its moons are, for example, a small planet system within our solar system, and it is believed that Jupiter moons were formed from a circumplanetary disk when Jupiter was very young. "
It happens all around the star PDS 70. That star was in the news about a year ago when astronomers captured the first The image of a newly created planet in a floppy disk. That planet is called PDS 70b. This discovery was of great curiosity about time, for good reason.
PDS 70b is not the only planet that orbits the star. There is another planet, PDS 70c, also in circulation, and they are both gas giants. Both of these planets were discovered by the European Southern Observatory (ESO) The Very Large Telescope (VLT) in optical and infrared. The warm glow of hydrogen accreting into the planet plane is what gave them away.
The team combined VLT observations with new radio observations from the Atacama Large Millimeter / Sub-Millimeter Array (ALMA.) The result is convincing evidence of a protoplanetary disk around the outermost star, PDS 70c.
"For the first time, we can completely see the telltale signs of a circumplanetary disk that helps support many of the current theories of planetary formation," says Andrea Isella, lead author.
"By comparing our observations with infrared and optical images at high resolution, we can clearly see that a differently enigmatic concentration of small dust particles is actually a planetary layer plate, the first feature ever observed," he said. According to the researchers, this is also the first time that a planet has clearly seen in these three distinct light bands.
A question answered, another question
PDS 70b and c shows different properties, and the team behind this study is not exactly sure what it means.
PDS 70c, the couple's ultimate star, is so far from its star that Neptune is from the sun. It is in exactly the same place as an obvious knot of dust seen in ALMA data. Because this planet shines so strongly in infrared and hydrogen bands of light, astronomers can convincingly say that a whole-shaped planet is already in circulation there. The light infrared and hydrogen bands show that nearby gas is still adapted to the surface of the planet, ending its teenage growth spurt.
Astronomers estimate that the PDS 70c is approximately 1 to 10 times the Jupiter mass. "If the planet is on the larger end of that estimate, it is quite possible that there may be planetary storms in the formation around it," noted Isella.
But PDS 70b has something else going on. These planets, which are about the same distance from their star as Uranus, are from the sun, have a lot of dust behind them as a tail behind them. And the astronomers are not sure how it fits in.
"What this is and what it means for this planetary system is not yet known," says Isella. "The only decision we can say is that it is far enough from the planet to be an independent function."
Astronomers are quite sure that the process they can look like playing around the PDS 70c is the same process that worked to create Jupiter moons. However, it is worth noting that the other gas giant of our solar system differs from Jupiter. Saturns were probably created as a result of a circumplanetary disk, but the icy rings were probably created by comets and other rocky bodies that crash into each other.
These exoplanetary systems are notoriously difficult to observe in optical and infrared light. The energy from the star in these parts of the spectrum extracts the light from planets. But not for ALMA.
ALMA focuses on radio waves and stars only emit radio waves weakly. The team says they can continue to observe the PDS 70 system with ALMA to watch as it changes and develops.
"That means we will be able to come back to this system at different time periods and more easily map the planet's path and dust concentration in the system," concluded Isella. "This will give us unique insights into the orbital properties of the solar systems in the very first stages of development."
The discovery of this circumplanetary disk and the probable moon formed in it is interesting in itself, but how the team found that the disc also promises for the future. While others have been found, this study is the most compelling.
"There are a handful of candidate planets that have been discovered in discs, but this is a whole new field, and they are still debating," Isella said. "(PDS 70 b and PDS 70 c) are among the most robust since there have been independent observations with different instruments and techniques."
In the end of their paper, the authors say "We claim that optical, NIR, and (sub) millimeter observations are very complementary because they probe different aspects of planning excretion processes and are affected by various systematic errors." They also note that ALMA alone does not can do the work. By combining the various observations, they have opened these exoplanets and their disks up to a more detailed study.
From the study: "As ALMA and existing optical telescopes reach their full-fledged ability, forthcoming observations of nearby circumstellar disks characterized by voids and gaps as those observed in the PDS 70 may reveal more newborn planets that interact with their native disk. Such observations are fundamental to investigating processes responsible for the formation of planetary systems. "