Reason Why The Stars Give Off More Infrared Light Than Expected

In the 1980s, the Infrared Astronomical Satellite mission began finding more infrared light than expected around young stars. Using data from other telescopes, astronomers pieced together the presence of dusty disks of planet-forming material. But eventually it became clear the disks alone weren't enough to account for the extra infrared light, especially in the case of stars a few times the mass of the Sun. However, Researchers using NASA's Spitzer Space Telescope to study developing stars may have found the reason why the stars give off more infrared light than expected.


The planet-forming disks that circle the young stars are heated by starlight and glow with infrared light, but Spitzer detected additional infrared light coming from an unknown source. A new theory, based on three-dimensional models of planet-forming disks, suggests that gas and dust suspended above the disks on gigantic magnetic loops like those seen on the Sun 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 centre through the disk atmosphere, you would see what looks like a sunset," said Neal Turner of NASA's Jet Propulsion Laboratory in a statement.

The new models better describe how planet-forming material around stars is stirred up, making its way into future planets, asteroids and comets.

While the idea of magnetic atmospheres on planet-forming disks is not new, this is the first time they have been linked to the mystery of the observed excess infrared light. The magnetic atmospheres are similar to what takes place on the surface of our Sun, where moving magnetic field lines spur tremendous solar prominences to flare up in big loops.

One theory introduced the idea that instead of a disk, the stars were surrounded by a giant dusty halo, which intercepted the star's visible light and re-radiated it at infrared wavelengths. Then, recent observations from ground-based telescopes suggested that both a disk and a halo were needed. Finally, three-dimensional computer modeling of the turbulence in the disks showed the disks ought to have fuzzy surfaces, with layers of low-density gas supported by magnetic fields, similar to the way solar prominences are supported by the Sun's magnetic field.

The new work brings these pieces together by calculating how the starlight falls across the disk and its fuzzy atmosphere. The result is that the atmosphere absorbs and re-radiates enough to account for all the extra infrared light.

"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," said Turner. "Such magnetized atmospheres were predicted to form as the disk drives gas inward to crash onto the growing star.

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source : www.sen.com