The Hubble Space Telescope has obtained these images of the expansive halo of light surrounding the star V838 Monocerotis, a rather unusual red supergiant. It is about 20,000 light years away, towards the constellation of Monoceros (the Unicorn). In full explosion, it reached 600,000 times the luminosity of our Sun. In fact, it became one of the brightest stars in the entire Milky Way, until its brightness declined again.
The so-called "light echo" of a cloud of dust around the star has revealed remarkable structures since the star suddenly increased in brightness at the beginning of 2003 for several weeks. Hubble monitored the evolution of the echo through several photos showing the eddies caused by turbulence in the dust and gas near the star. This material would have been ejected in some previous explosion some tens of thousands of years ago. The surrounding dust remained invisible until the bright explosion of the central star illuminated it.
The event showed similarity in some aspects to the novae, which suddenly increase their brightness due to thermonuclear explosions on their surfaces. However, some details of V8383 Mon, in particular its extremely red color, have little to do with any previously known nova. Nor did it expel its outer layers, but grew enormously in size, while lowering its surface temperature. The process of inflating to immense sizes without shedding the outer shell is not very usual, and not at all similar to what happens in a nova. It presents a rare combination of stellar properties never seen that, perhaps, represent a transitional state in stellar evolution rarely observed in the Universe.
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