March 7, 2014
Infrared Mystery Surrounding Forming Planets Explained
Brett Smith for redOrbit.com - Your Universe Online
Almost a decade ago, scientists using NASA's Spitzer Space Telescope found that planet-forming disks around young stars are heated by starlight and glow with infrared light. However, these scientists found that additional infrared light was originating from an unknown source.
Now, new models developed by NASA have revealed why these stars emit more infrared light than expected – gas and dust magnetically suspended above the disks absorb the starlight and glow with infrared light.
"If you could somehow stand on one of these planet-forming disks and look at the star in the center through the disk atmosphere, you would see what looks like a sunset," said Neal Turner of NASA's Jet Propulsion Laboratory, Pasadena, Calif.
The NASA researchers said their new models show how planet-forming material around stars eventually coalesces into future planets, asteroids and comets.
The magnetic atmospheres are very similar to the magnetic system set up on the surface of our sun, where shifting magnetic field lines initiate tremendous solar prominences to appear in big loops.
Stars are created out of shrinking pockets of immense clouds of gas and dust, revolving as they reduce in size under the draw of gravity. As a star increases in size, more material pours down toward it from the cloud. Eventually, the rotation compresses this material out into a tumultuous disk, allowing planets to clump together from the disk material.
In the 1980s, the Infrared Astronomical Satellite mission began finding far more infrared light than anticipated around emerging stars. Utilizing additional observations, astronomers pieced together the presence of dusty disks of planet-forming material. However, it gradually became clear the disks alone weren't enough to account for the infrared light being seen – especially in the case of stars a few times the mass of the sun.
One theory introduced the concept that rather than a disk, the stars were encompassed by a massive dusty halo, which received the star's light and re-radiated it at infrared wavelengths. More recent observations implied that both a disk and a halo were needed for the levels of radiation being seen.
Finally, recent computer modeling of the turbulence in the disks confirmed that the disks should have fuzzy surfaces, with tiers of low-density gas sustained by magnetic fields, comparable to the way solar prominences are sustained by the sun's magnetic field.
The new work brings these theories together by determining how the starlight falls over the disk and its fuzzy atmosphere. This means that the atmosphere absorbs and re-radiates enough to explain all the extra infrared light.
The researchers said their work represents the first time these magnetic atmospheres have been linked to the mystery of excess infrared light seen with Spitzer.
"The starlight-intercepting material lies not in a halo, and not in a traditional disk either, but in a disk atmosphere supported by magnetic fields," Turner said. "Such magnetized atmospheres were predicted to form as the disk drives gas inward to crash onto the growing star."
The NASA team said they plan to test these ideas by using giant ground-based telescopes linked together as interferometers – a device that processes data from multiple telescopes.