European Southern Observatory’s Very Large Telescope (VLT) has captured the final moments of a dying star [above] – a planetary nebula – in the form of a glowing bubble haunting darkness of space.
ESO 378-1, nicknamed Southern Owl Nebul, is a shimmering orb is a planetary nebula with a diameter of almost four light-years. The planetary nebula, which is also catalogued as PN K 1-22 and PN G283.6+25.3, is located in the constellation of Hydra (The Female Water Snake). Though the phenomenon is quite short-lived on cosmic scale, it will last for tens of thousands of years. In comparison a typical star has a life of several billion years.
The release of this photo by ESA comes just days after NASA released a similar image of a dying star captured by Hubble. The image [below] is of a planetary nebula known as NGC 6565, which is a cloud of gas ejected from the star after strong stellar winds pushed the star’s outer layers away into space. These same colors can be seen in the famous and impressive Ring Nebula (heic1310), a prominent example of a nebula like this one.
Planetary nebulae are basically remnants of a dying star created out of the ejected and expanding gas. The requirement for a star to end up in a nebula is that its mass should be less than about eight times that of the Sun. Stars that are heavier than this limit will end their lives in dramatic fashion as supernova explosions.
As these stars, which are under the mass limit, grow old they start to lose their outer layers of gas to stellar winds. After most of these outer layers have dissipated, the remaining hot stellar core starts to emit ultraviolet radiation which then ionises the surrounding gas. This ionisation causes the expanding shell of ghostly gas to begin to glow in bright colours.
Although the nebulae are brilliant and intriguing objects in the initial stages of formation, these bubbles fade away as their constituent gas moves away and the central stars grow dimmer.
After the planetary nebula has faded away, the leftover stellar remnant will burn for another billion years before consuming all its remaining fuel. It will then become a tiny — but hot and very dense — white dwarf that will slowly cool over billions of years. The Sun will produce a planetary nebula several billion years in the future and will afterwards also spend its twilight years as a white dwarf.
Planetary nebulae play a crucial role in the chemical enrichment and evolution of the Universe. Elements such as carbon and nitrogen, as well as some other heavier elements, are created in these stars and returned to the interstellar medium. Out of this material new stars, planets and eventually life can form. Hence astronomer Carl Sagan’s famous phrase: “We are made of star stuff.”