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V4334 Sagittarii

V4334 Sgr, also known as Sakurai's Object, is a cousin to last week's LCOTW, FG Sagittae.  The star was discovered by Y. Sakurai in 1996 as a possible nova in Sagittarius, but it soon became clear that this object wasn't an accreting white dwarf undergoing a thermonuclear runaway.  Instead, it was a very young white dwarf, still on the fence between being an asymptotic giant branch star and being a dead stellar remnant.  Its rapid brightening was caused by thermonuclear fusion, but of a more controlled kind -- namely a thermal pulse.  At very late stages of stellar evolution stars can cycle between being dormant objects whose light comes purely from cooling of the inert stellar core to being more typical "stars" whose light comes from thermonuclear fusion, in this case from helium burning inside the core.  Evolution models suggest that these pulses happen several times late in the lives of stars, and that the pulses are probably connected with episodic mass loss as well.  It's this mass loss that generates the planetary nebulae that mark the final passing of stars into their final white dwarf stage.

Although V4334 Sgr remained bright for a few months, it faded in short order, and has been invisible to optical observers for nearly a decade.

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