When a Sun-like star nears the end of its lifetime, it expels its outer gaseous layers, forming a huge glowing cloud of gas and dust, known as the planetary nebula (since some of these nebulae are round and pale, resembling the planets Uranus and Neptune, when viewed through the telescope). The blazing core of the dying star, which has been producing the star’s prodigious radiation throughout its evolution, becomes exposed. Then, it gradually develops into a white dwarf, a small very dense stellar object. The white dwarf cools and fades slowly.
A Sun-like star is a star whose mass and surface temperature are similar to those of the Sun.
The European Southern Observatory (ESO) recently published an exquisite infrared image (Fig. 1) of the Helix Nebula, one of the brightest and nearest planetary nebulae. Interestingly, from our Earth-based view, this nebula appears as if we were looking through a helix. The image was obtained by ESO’s VISTA telescope, at the Paranal Observatory in Chile. It shows fine details of the Helix Nebula that are not detectable in visual light.
The Helix is located about 700 light-years away from Earth. Its core, now called the central star, is visible in image’s center, as a tiny bluish point. It is evolving into a white dwarf star. Its energetic ultraviolet emission causes the surrounding nebula to shine.
The light year is a unit of measuring stellar and large astronomical distances. It is approximately equal to 10,000 billion km.
The Helix Nebula has a complex structure. Its main ring is about two light-years wide, roughly half the distance between the Sun and the nearest star to the Solar System. However, the entire nebula spans at least four light-years. The Helix’s extent is clearly shown in Fig. 1, as red molecular gas can be seen across much of the image.
The sensitive detectors and strong light grasp of the 4.1-meter VISTA telescope have allowed imaging fine detail in the Helix’s rings and a rich background of stars and galaxies.
Intriguingly, astronomers estimate the Sun will produce its planetary nebula, when it reaches the final stages of its evolution, about 5 billion years from now.
References
ESO Press Release
http://www.eso.org/public/news/eso1205/
Wikipedia