Hubble images searchlight beams from a preplanetary nebula: 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.

Name: Egg Nebula
Type: Milky Way : Nebula : Type : Planetary
Category: Nebulae
Constellation: Cygnus
Distance: 3000 light years
Release date: 23 April 2012, 10:00
Credit: ESA/Hubble & NASA

The eye of the storm: This image from the NASA/ESA Hubble Space Telescope could seem like a quiet patch of sky at first glance. But zooming into the central part of a galaxy cluster — one of the largest structures of the Universe — is rather like looking at the eye of the storm. Clusters of galaxies are large groups consisting of dozens to hundreds of galaxies, which are bound together by gravity. The galaxies sometimes stray too close to one another and the huge gravitational forces at play can distort them or even rip matter off when they collide with one another. This particular cluster, called Abell 1185, is a chaotic one. Galaxies of various shapes and sizes are drifting dangerously close to one another. Some have already been ripped apart in this cosmic maelstrom, shedding trails of matter into the void following their close encounter. They have formed a familiar shape called The Guitar, located just outside the frame of this image. Abell 1185 is located approximately 400 million light-years away from Earth and spans one million light-years across. A few of the elliptical galaxies that form the cluster are visible in the corners of this image, but mostly, the small elliptical shapes seen are faraway galaxies in the background, located much further away, in a quieter area of the Universe.

Name: Abell 1185
Type: Early Universe : Galaxy : Grouping : Cluster
Category: Cosmology
Constellation: Ursa Major
Distance: z=0.032 (redshift)
Release date: 30 April 2012, 10:00
Credit: ESA/Hubble & NASA

Edge-on beauty: Visible  in the constellation of Andromeda, NGC 891 is located approximately 30  million light-years away from Earth. The NASA/ESA Hubble Space Telescope  turned its powerful wide field Advanced Camera for Surveys towards this  spiral galaxy and took this close-up of its northern half. The galaxy's  central bulge is just out of the image on the bottom left. The  galaxy, spanning some 100 000 light-years, is seen exactly edge-on, and  reveals its thick plane of dust and interstellar gas. While initially  thought to look like our own Milky Way if seen from the side, more  detailed surveys revealed the existence of filaments of dust and gas  escaping the plane of the galaxy into the halo over hundreds of  light-years. They can be clearly seen here against the bright background  of the galaxy halo, expanding into space from the disc of the galaxy. Astronomers  believe these filaments to be the result of the ejection of material  due to supernovae or intense stellar formation activity. By lighting up  when they are born, or exploding when they die, stars cause powerful  winds that can blow dust and gas over hundreds of light-years in space. A  few foreground stars from the Milky Way shine brightly in the image,  while distant elliptical galaxies can be seen in the lower right of the  image. NGC 891 is part of a small group of galaxies bound together by gravity. A version of this image was entered into the Hubble’s Hidden Treasures Image Processing Competition by contestant Nick Rose. Hidden Treasures is an initiative to  invite astronomy enthusiasts to search the Hubble archive for stunning  images that have never been seen by the general public.

Name: NGC 891
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Andromeda
Distance: 35 million light years
Release date: 14 May 2012, 10:00
Credit: ESA/Hubble & NASA Acknowledgement: Nick Rose