An international group of astronomers using NASA’s Hubble and Spitzer Space Telescopes has discovered a mysterious protostar that behaves like a flashing light.
This infrared image shows the protostellar object LRLL 54361 (NASA / ESA / J. Muzerolle / STScI)
The object, labeled LRLL 54361, unleashes a burst of light every 25.34 days. The heart of the fireworks is hidden behind a dense disk and envelope of dust. Astronomers propose that the light flashes are due to material suddenly being dumped onto the growing stars, known as protostars, unleashing a blast of radiation each time the stars get close to each other in their orbit. This is the so-called pulsed-accretion model. The phenomenon has been seen in later stages of star birth but never in such a young system, nor with such intensity and regularity.
“This protostar has large brightness variations with a precise period that is very difficult to explain,” said Dr James Muzerolle of the Space Telescope Science Institute in Baltimore, lead author of a paper reporting the discovery in the journal Nature.
LRLL 54361 was discovered by the Spitzer Space Telescope as a variable object inside the star-forming region IC 348, located 950 light-years away. Its infrared spectrum has the typical signature of a protostar. These stars are estimated to be no more than a few hundred thousand years old, based on statistical analysis.
The Hubble was used to confirm the Spitzer observations and revealed the detailed structure around the protostar. Hubble resolved two cavities that are traced by light scattered off their edges above and below a dusty disk. The cavities were likely blown out of the surrounding natal envelope of dust and gas by an outflow launched near the central stars.
By capturing multiple images over the course of one pulse event, the Hubble observations uncovered a spectacular movement of light away from the center of the system, an optical illusion known as a light echo.
The astronomers hypothesized that a pair of stars lie in the center of the dust cloud, moving about each other in a very eccentric orbit. As the stars approach each other, dust and gas are dragged from the inner edge of a surrounding disk. The material ultimately crashes onto one or both stars, which triggers a flash of light that then illuminates the circumstellar dust. The system is rare because close binaries account for only a few percent of our galaxy’s stellar population.
The team plans to continue monitoring LRLL 54361 using other facilities including the Herschel Space Telescope, and hopes to eventually obtain more direct measurements of the binary star and its orbit.
“This system continues to surprise us, and we can’t wait to see what happens next!” Dr Muzerolle concluded.
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Bibliographic information: James Muzerolle et al. 2013. Pulsed accretion in a variable protostar. Nature 493, 378–380; doi: 10.1038/nature11746
