Peeking into the dusty core of a dark cloud seemingly devoid of stars, astronomers have found a faintly glowing body that could be the earliest glimmerings ever recorded from a newborn star. If the object, spied by the infrared eye of the orbiting Spitzer Space Telescope, is indeed a fledgling star, it’s the least massive star ever observed. It weighs in at less than one-thousandth the mass of the sun.
Astronomers aren’t certain how to classify the object, which resides 6,000 light-years from Earth in a dense core of gas and dust. The body may someday accumulate enough gas and dust to become a bona fide star. Another possibility is that the supply of material will run out before the object can achieve starhood, and it will become a brown dwarf instead, says Neal J. Evans of the University of Texas at Austin. It’s also possible that the object is neither star nor brown dwarf, but something more exotic, he adds.
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Evans’ team presented the findings this week in Pasadena, Calif., at a meeting devoted to Spitzer results.
Viewed previously by visible-light telescopes and a now-defunct infrared satellite, the core of dust and gas known as L1014 looked completely dark. Last December, however, Evans and his collaborators trained the newly launched Spitzer on the core to investigate conditions that might set the stage for star formation. To their surprise, the researchers detected a glimmer that Evans likens to “a big, red, bloodshot eye.” The infrared light is probably generated by dust heated by an energetic object in the core, the team reports in a September supplement of the Astrophysical Journal.
At the time of publication, the astronomers were concerned that their observation might have another explanation: The faint light might come from another core known to lie along the same line of sight as L1014 but 10 times as far from Earth. In that case, the glimmer would look faint only because its source is so remote.
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New observations with ground-based near-infrared telescopes have ruled out that scenario, says Evans. Team member Tracy L. Huard of the Harvard-Smithsonian Center for Astrophysics in Cambridge, Mass., and his colleagues found a fan-shaped glow coinciding with the puzzling object. That glow is too feeble to have come from the more distant core and “strongly suggests the source is embedded in the L1014 core,” Huard reported at the Spitzer conference.
The faint signal seen by Spitzer implies a “very slow and gentle” accumulation of material in L1014 that may indicate “a new way of forming stars,” Evans says. The Spitzer team has found other candidates for young stars in several supposedly starless cores.
Star modeler Alan P. Boss of the Carnegie Institution of Washington (D.C.) says the low mass and luminosity inferred from the Spitzer observations are “quite consistent” with current ideas about the birth of stars. Says Boss: “Spitzer has found a good example of the earliest phase of star formation seen to date.”