SpaceTelescope.org: The Twin Jet Nebula, or PN M2-9, is a striking example of a bipolar planetary nebula. Bipolar planetary nebulae are formed when the central object is not a single star, but a binary system, Studies have shown that the nebula’s size increases with time, and measurements of this rate of increase suggest that the stellar outburst that formed the lobes occurred just 1200 years ago.
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Astronomy Picture Of The Day: Explanation: The yellowish star near center in this remarkable telescopic skyview is T Tauri, prototype of the class of T Tauri variable stars. Nearby it is a dusty yellow cosmic cloud historically known as Hind’s Variable Nebula (NGC 1555). Over 400 light-years away, at the edge of a molecular cloud, both star and nebula are seen to vary significantly in brightness but not necessarily at the same time, adding to the mystery of the intriguing region. T Tauri stars are now generally recognized as young (less than a few million years old), sun-like stars still in the early stages of formation. To further complicate the picture, infrared observations indicate that T Tauri itself is part of a multiple system and suggest that the associated Hind’s Nebula may also contain a very young stellar object. The naturally colored image spans about 4 light-years at the estimated distance of T Tauri.
The small open star cluster Pismis 24 lies in the core of the NGC 6357 nebula in Scorpius, about 8,000 light-years away from Earth. The brightest object in the center of this image is designated Pismis 24-1 and was once thought to weigh as much as 200 to 300 solar masses. This would not only have made it by far the most massive known star in the galaxy, but would have put it considerably above the currently believed upper mass limit of about 150 solar masses for individual stars.
However, Hubble Space Telescope high-resolution images of the star show that it is really two stars orbiting one another that are each estimated to be 100 solar masses.
In addition, spectroscopic observations with ground-based telescopes further reveal that one of the stars is actually a tight binary that is too compact to be resolved even by Hubble. This divides the estimated mass for Pismis 24-1 among the three stars. Although the stars are still among the heaviest known, the mass limit has not been broken due to the multiplicity of the system.
The images of NGC 6357 were taken with Hubble’s Wide Field and Planetary Camera 2 in April 2002.
ImageCredit: NASA, ESA, and J. Maíz Apellániz (Instituto de Astrofísica de Andalucía, Spain)