Secrets of the Orion nebula

Astronomers have spotted a number of young stars in the Orion nebula changing right before their very eyes.

The colorful specks – developing stars strung across the image – are rapidly heating up and cooling down, illustrating the turbulent process of reaching full stellar adulthood.

Nicolas Billot, an astronomer at the Institut de Radioastronomie Millimétrique (IRAM), explains that the rainbow of colors represent different wavelengths of infrared light captured by both NASA’s Spitzer Space Telescope and the European Space Agency’s Herschel Space Observatory.

Indeed, Spitzer is designed to observe shorter infrared wavelengths than Herschel. By combining their observations, astronomers are able to formulate a more complete picture of star formation.
 In the picture of the Orion nebula, the telescopes’ infrared vision reveals a host of embryonic stars concealed in gas and dust clouds, which are at the very earliest stages of evolution.

A star forms as a clump of this gas and dust collapses, creating a warm glob of material fed by an encircling disk. In several hundred thousand years, some of the forming stars will accrete enough material to trigger nuclear fusion at their cores, and then blaze into stardom.

Herschel mapped this particular region of space once a week for six weeks in the late winter and spring of 2011. To monitor for activity in protostars, Herschel’s Photodetector Array Camera and Spectrometer probed long infrared wavelengths of light that trace cold dust particles, while Spitzer gauged the warmer dust emitting shorter infrared wavelengths.

Astronomers subsequently noticed that several of the young stars varied in their brightness by more than 20 percent over just a few weeks. As this twinkling comes from cool material emitting infrared light, the material must be far from the hot center of the young star, likely in the outer disk or surrounding gas envelope. At that distance, it should take years or centuries for material to spiral closer in to the growing starlet, rather than mere weeks.

A couple of scenarios under investigation could potentially account for this short span. One possibility is that lumpy filaments of gas funnel from the outer to the central regions of the star, temporarily warming the object as the clumps hit its inner disk. Or, perhaps material occasionally piles up at the inner edge of the disk and casts a shadow on the outer disk.

“Herschel’s exquisite sensitivity opens up new possibilities for astronomers to study star formation, and we are very excited to have witnessed short-term variability in Orion protostars.
.. Follow-up observations with Herschel will help us identify the physical processes responsible for the variability,” Billot added.