MEISSA (Lambda Orionis).
One of the fainter stars to carry a proper name, Meissa is
the Lambda star of Orion. At faint
third magnitude, Meissa is not important in star-lore for its
brightness, but for its position, as (with a pair of other
stars) it marks the head of the ancient Hunter. Its name, apparently
something of a mistake, seems to have been taken from an older (no
longer much used) name for
Alhena in Gemini (Gamma Geminorum),
showing how confused star names can be. More confusing, the
significance of the name is rather mysterious, possibly meaning
(from Arabic) "the Proudly Marching One." Who that might be is not
known. The star may not immediately overwhelm the eye, but it
certainly does its surroundings. Meissa is a double that consists
of a hot (35,000 Kelvin!) fourth magnitude class O star four
seconds of arc away from a still-pretty-warm sixth magnitude B star
("only" 27,000 Kelvin). Though both stars (easily seen in a small
telescope) are white, various observers have seen lovely colors,
showing how the eye can be fooled. From its distance of 1000 light
years, we find the hot, bright component to radiate 65,000 times
more energy than our Sun
(including its ultraviolet radiation),
while the other one radiates about 5500 times the solar light.
Meissa is also the luminary of a small cluster. But it is most-
famed for a huge surrounding ring of gas an amazing 150 light years
across that is illuminated (ionized) by the star, showing the
immense power of these (fortunately very rare) hot class O stars.
This structure is set within an even larger ring of interstellar
dust and molecules. The rings may be leftover material from which
Meissa formed, compressed by the action of the O star. It is also
possible that the rings were created from the blast of another star
that exploded in the neighborhood of Meissa a few million years
ago. No one really knows. With an immense mass nearly 25 times
that of the Sun, explosion is almost certain to be the fate of
Meissa's brighter component. The fainter one, however, is right at
the edge of those that explode and those that turn into heavy white
dwarfs, condensed stars about the size of the Earth. The explosion
of the more-massive star, however, will outdo even that, as its
stellar remnant will collapse to the size of a small town and
perhaps appear to future astronomers as a rapidly spinning neutron
star, or pulsar. (Thanks to Monica Shaw, who helped research this star.)