What does a baby solar system look like? A team of astronomers using the Spitzer Space Telescope, may have found out.
In the Sept. 10 issue of Astrophysical Journal Letters, astronomers from the University and various other universities announced the detection of what could be planets around two very young stars. The discovery defies some assumptions of the timeline of planet formation.
Stars form when giant clouds of interstellar gas, composed mostly of hydrogen, collapse under their own gravity. As the cloud collapses, the center heats up drastically and forms a star while the rest of the rotating cloud picks up speed and flattens into a disk.
The astronomers used the Spitzer Space Telescope’s InfraRed Spectrograph, essentially a prism for separating out the wavelengths of infrared light, to study the light coming from two stars: GM Aurigae and DM Tauri.
Both of these stars were emitting less energy than expected at certain infrared wavelengths. “This hinted that there was missing material in the disk,” said Nuria Calvet, University astronomy professor and lead author of the paper. “Then you have to ask: ‘what is producing that gap?’ The most natural explanation is that there is a planet there.”
Current astronomical theories explain that a planet can clear out a space in the disk, in two ways. First, part of the disk accumulates to form the planet. Then, the planet’s gravity tugs on the gas in the disk, speeding it up or slowing it down. Because of the disk’s rotation, the result of this tug is that the planet appears to “repel” gas and dust in the disk. This same effect is seen in the rings of Saturn, where small moons within the rings cause gaps to form.
Calvet said for the star DM Tauri, it appears that the entire center of the disk has been swept away. GM Aurigae is more interesting. With a mass only slightly largen than the sun, it is a near-clone of our most familiar star.
Astronomers believe it may provide clues to how our solar system formed. GM Aurigae shows signs of an inner disk, a clear gap, and an outer disk.
“These are million-year-old objects. They’re very young,” Calvet said. The possibility of planets around such young stars challenges the school of thought that planets form over many millions of years from the accumulation of dust in the star system.
The more likely scenario is that the planets formed in only a few hundred thousand years from early instabilities in the disk. Just as a star forms when part of a massive nebula becomes slightly more dense and collapses under its own gravity, a similar process acts to rapidly form planets.
Even a small increase in the density of a region in the disk could have a runaway effect, quickly attracting more gas and putting it on the fast track to forming a planet. Because any theory must agree with observations, GM Aurigae and DM Tauri allow theorists to improve their models of planet formation.
With this discovery, researchers are bringing us closer to understanding the origin of our own solar system. “We have a very rapidly changing, evolving universe,” Calvet said. “We are discovering new planets that may become similar to those in our own solar system. The thing is that we aren’t special.”