Dusty nebula hides a super-hot star

The Gum 19 nebula

The Gum 19 nebula glows under influence of a 30,000° Celsius star.

The little-known Gum 19 nebula seems to have a dual nature.

On one side, hydrogen gas is lit up by a supergiant blue star called V391 Velorum. On the other, new stars are being formed within a ribbon of luminous and dark material.

Gum 19 is located approximately 22,000 light years away in the direction of the constellation Vela (the Sail). The name comes from a 1955 catalogue produced by Australian astrophysicist Colin S. Gum, who made the first significant survey of so-called HII (“H-two”) regions in the southern sky.

HII refers to hydrogen gas that is ionised, or energised to the extent that the hydrogen atoms lose their electrons. Such regions emit light at well-defined wavelengths (or colours), thereby giving these clouds their characteristic glow.

This new image of Gum 19 was captured by an infrared instrument called SOFI, mounted on the European Southern Observatory’s (ESO) New Technology Telescope (NTT) that operates at the La Silla Observatory in Chile. Observing the nebula at infrared wavelengths allows astronomers to “see through” at least some of the dust.

Fuelling Gum 19’s glow is the gigantic, super-hot star V391 Velorum, which boasts a surface temperature of around 30,000 degrees Celsius. This massive star has a temperamental nature, however, and is categorized as a “variable star” – its brightness can fluctuate suddenly as a result of activity such as ejections of shells of gas.

Stars like V391 Velorum don’t burn brightly for long, and after a relatively short lifetime of about ten million years blow up as supernovae. These explosions blast heated matter into surrounding space, an event that can radically change the colour and shape of the enclosing nebula. When this happens to V391, the Gum 19 nebula will change dramatically.

Within Gum 19, new stars continue to grow. HII regions are sites where huge quantities of gas and dust have begun to collapse 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 density at their centres necessary to ignite nuclear fusion…new stars.

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