Showing posts with label CRL 2688. Show all posts
Showing posts with label CRL 2688. Show all posts

Tuesday, November 25, 2014

The Egg Nebula

The Egg Nebula (CRL 2688)
Copyright Credit: NASA/ESA/Hubble Heritage Team (STScI/AURA). Acknowledgment: W. Sparks (STScI) & R. Sahai (JPL)
 
This colourful image shows a cosmic lighthouse known as the Egg Nebula, which lies around 3000 light-years from Earth. The image, taken with the NASA/ESA Hubble Space Telescope, has captured a brief but dramatic phase in the life of a Sun-like star.

The Egg Nebula is a ‘preplanetary nebula’. These objects occur as a dying star’s hot remains briefly illuminates material it has expelled, lighting up the gas and dust that surrounds it.

These objects will one day develop into planetary nebulas which, despite the name, have nothing at all to do with planets. They gained their rather misleading title because when they were discovered in the 18th century they resembled planets in our Solar System when viewed through a telescope.

Although the dying star is hidden behind the thick dust lane that streaks down the centre of this image, it is revealed by the four lighthouse-like beams clearly visible through the veil of dust that lies beyond the central lane.

The light beams were able to penetrate the central dust lane due to paths carved out of the thick cloud by powerful jets of material expelled from the star, although the cause of these jets is not yet known.

The concentric rings seen in the less dense cloud surrounding the star are due to the star ejecting material at regular intervals – typically every hundred years – during a phase of the star’s evolution just prior to this preplanetary nebula phase. These dusty shells are not usually visible in these nebulas, but when they are it provides astronomers with a rare opportunity to study their formation and evolution.

The fleeting nature of this phase in a star’s life – which occupies only a few thousand of the star’s few billion years of existence – and the fact that they are fairly faint make it rare to capture them in action. In fact, the Egg Nebula, the first of its kind to be identified, was discovered only 40 years ago.

This image was taken with Hubble’s Advanced Camera for Surveys. Artificial colours are used to represent how the light from the star reflects off the dust – this can tell scientists about the physical properties of the dust.

The image combines observations with three different polarising filters, each showing light vibrating at a specific orientation. The three filters have been coloured red, blue and green, and all three observations were made at a wavelength of 0.606 microns. The image spans 1.2 light-years.  North is to the right and east is up.

This image was previously published on the NASA Hubble Heritage website.


Source: ESA

 

Monday, April 23, 2012

Hubble Images Searchlight Beams from a Preplanetary Nebula

Egg Nebula
Credit: ESA/Hubble & NASA

The NASA/ESA Hubble Space Telescope has been at the cutting edge of research into what happens to stars like our Sun at the ends of their lives (see for example Hubblecast 51). One stage that stars pass through as they run out of nuclear fuel is the preplanetary, or protoplanetary nebula. This Hubble image of the Egg Nebula shows one of the best views to date of this brief but dramatic phase in a star’s life.

The preplanetary nebula phase is a short period in the cycle of stellar evolution — over a few thousand years, the hot remains of the star in the centre of the nebula heat it up, excite the gas, and make it glow as a planetary nebula. The short lifespan of preplanetary nebulae means there are relatively few of them in existence at any one time. Moreover, they are very dim, requiring powerful telescopes to be seen. This combination of rarity and faintness means they were only discovered comparatively recently. The Egg Nebula, the first to be discovered, was first spotted less than 40 years ago, and many aspects of this class of object remain shrouded in mystery.

At the centre of this image, and hidden in a thick cloud of dust, is the nebula’s central star. While we can’t see the star directly, four searchlight beams of light coming from it shine out through the nebula. It is thought that ring-shaped holes in the thick cocoon of dust, carved by jets coming from the star, let the beams of light emerge through the otherwise opaque cloud. The precise mechanism by which stellar jets produce these holes is not known for certain, but one possible explanation is that a binary star system, rather than a single star, exists at the centre of the nebula.

The onion-like layered structure of the more diffuse cloud surrounding the central cocoon is caused by periodic bursts of material being ejected from the dying star. The bursts typically occur every few hundred years.

The distance to the Egg Nebula is only known very approximately, the best guess placing it at around 3000 light-years from Earth. This in turn means that astronomers do not have any accurate figures for the size of the nebula (it may be larger and further away, or smaller but nearer).

This image is produced from exposures in visible and infrared light from Hubble’s Wide Field Camera 3.

Source: ESA/Hubble - Space Telescope