Gum 19恒星形成星云的亮面与暗面

Gum 19 is located in the direction of the constellation¹（星座，荟萃） Vela (the Sail) at a distance of approximately 22 000 light years. The Gum 19 moniker（绰号，名字） derives² from（源于，来自） a 1955 publication by the Australian astrophysicist（天体物理学家） Colin S. Gum that served as the first significant survey of so-called HII (read "H-two") regions in the southern sky. HII refers to hydrogen gas that is ionised（电离） , or energised（供给……能量） to the extent that the hydrogen atoms lose their electrons（电子） . Such regions emit light at well-defined wavelengths³ (or colours), thereby⁴ giving these cosmic clouds their characteristic glow. And indeed, much like terrestrial（陆地的，陆生的） clouds, the shapes and textures⁵ of these HII regions change as time passes, though over the course of eons（万古，永世） rather than before our eyes. For now, Gum 19 has somewhat of a science fiction-esque（似……的） , "rip in spacetime" look to it in this image, with a narrow, near-vertical bright region slashing⁶ across the nebula⁷（星云） . Looking at it, you could possibly see a resemblance to a two-toned angelfish（扁鲨，神仙鱼） or an arrow with a darkened point. This new image of the evocative（唤起的） Gum 19 object was captured by an infrared⁸ instrument called SOFI, mounted on ESO's New Technology Telescope (NTT) that operates at the La Silla Observatory⁹ in Chile. SOFI stands for Son of ISAAC, after the "father" instrument, ISAAC, that is located at ESO's Very Large Telescope observatory at Paranal to the north of La Silla. Observing this nebula in the infrared allows astronomers¹⁰ to see through at least parts of the dust.

The furnace（火炉，熔炉） that fuels Gum 19's luminosity（光度，光辉） is a gigantic, superhot star called V391 Velorum. Shining brightest in the scorching¹¹（灼热的，激烈的） blue range of visible light, V391 Velorum boasts a surface temperature in the vicinity of 30 000 degrees Celsius¹². This massive star has a temperamental nature, however, and is categorised as a variable star accordingly. V391 Velorum's brightness can fluctuate（动摇，波动） suddenly as a result of strong activity that can include ejections of shells of matter, which contribute to Gum 19's composition and light emissions¹³.

Stars on the grand scale of V391 Velorum do not burn bright for long, and after a relatively¹⁴ short lifetime of about ten million years these titans blow up as supernovae（超新星） . These explosions, which temporarily rival whole galaxies¹⁵ in their light intensity¹⁶, blast heated matter in surrounding space, an event that can radically¹⁷ change the colour and shape of its enclosing（封闭，围合） nebula. As such, V391 Velorum's death throes may well leave Gum 19 unrecognisable.

Within the neighbourhood of this fitful supergiant, new stars nonetheless continue to grow. HII regions denote sites of active star formation wherein great quantities of gas and dust have begun to collapse¹⁸ under their own gravity. In several million years — a blink of an eye in cosmic time — these shrinking knots of matter will eventually reach the high density¹⁹ at their centres necessary to ignite（点燃，燃烧） nuclear fusion²⁰. The fresh outpouring（流露，流出） of energy and stellar winds（恒星风） from these newborn stars will also modify the gaseous²¹ landscape of Gum 19.