Stars that go out with a whimper: This NASA/ESA Hubble Space Telescope  image shows the planetary nebula IC 289, located in the northern  constellation of Cassiopeia. Formerly a star like our Sun, it is now  just a cloud of ionised gas being pushed out into space by the remnants  of the star’s core, visible as a small bright dot in the middle of the  cloud. Weirdly  enough, planetary nebulae have nothing to do with planets. Early  observers, when looking through small telescopes, could only see  undefined, smoky forms that looked like gaseous planets — hence the  name. The term has stuck even though modern telescopes like Hubble have  made it clear that these objects are not planets at all, but the outer  layers of dying stars being thrown off into space. Stars  shine as a result of nuclear fusion reactions in their cores,  converting hydrogen to helium. All stars are stable, balancing the  inward push caused by their gravity with the outwards thrust from the  inner fusion reactions in their cores. When all the hydrogen is consumed  the equilibrium is broken; the gravitational forces become more  powerful than the outward pressure from the fusion process and the core  starts to collapse, heating up as it does so. When  the hot, shrinking core gets hot enough,  the helium nuclei begin to fuse into carbon and oxygen and the collapse  stops. However, this helium-burning phase is highly unstable and huge  pulsations build up, eventually becoming large enough to blow the whole  star’s atmosphere away. A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Serge Meunier.

Name: IC 289
Type: Milky Way : Nebula : Type : Planetary
Category: Nebulae
Constellation: Cassiopeia
Release date: 8 July 2013, 10:00
Credit: ESA/Hubble & NASAAcknowledgement: Serge Meunier

A stranger in the crowd: The constellation of Virgo (The Virgin) is the largest of the Zodiac constellations, and the second largest overall after Hydra (The Water Snake). Its most appealing feature, however, is the sheer number of galaxies that lie within it. In this picture, among a crowd of face- and edge-on spiral, elliptical, and irregular galaxies, lies NGC 4866, a lenticular galaxy situated about 80 million light-years from Earth. Lenticular galaxies are somewhere between spirals and ellipticals in terms of shape and properties. From the picture, we can appreciate the bright central bulge of NGC 4886, which contains primarily old stars, but no spiral arms are visible. The galaxy is seen from Earth as almost edge-on, meaning that the disc structure — a feature not present in elliptical galaxies — is clearly visible. Faint dust lanes trace across NGC 4866 in this image, obscuring part of the galaxy’s light. To the right of the galaxy is a very bright star that appears to lie within NGC 4886’s halo. However, this star actually lies much closer to us; in front of the galaxy, along our line of sight. These kinds of perspective tricks are common when observing, and can initially deceive astronomers as to the true nature and position of objects such as galaxies, stars, and clusters. This sharp image of NGC 4866 was captured by the Advanced Camera for Surveys, an instrument on the NASA/ESA Hubble Space Telescope. A version was entered into the Hubble’s Hidden Treasures image processing competition by contestant Gilles Chapdelaine.

Name: ngc 4866
Type: Local Universe : Galaxy : Type : Lenticular
Category: Galaxies
Constellation: Virgo
Distance: 80 million light years
Release date: 15 July 2013, 10:00
Credit: ESA/Hubble & NASAAcknowledgement: Gilles Chapdelaine

A mysterious old spiral: This striking cosmic whirl is the centre of galaxy NGC 524, as seen with the NASA/ESA Hubble Space Telescope. This galaxy is located in the constellation of Pisces, some 90 million light-years from Earth. NGC 524 is a lenticular galaxy. Lenticular galaxies are believed to be an intermediate state in galactic evolution — they are neither elliptical nor spiral. Spirals are middle-aged galaxies with vast, pinwheeling arms that contain millions of stars. Along with these stars are large clouds of gas and dust that, when dense enough, are the nurseries where new stars are born. When all the gas is either depleted or lost into space, the arms gradually fade away and the spiral shape begins to weaken. At the end of this process, what remains is a lenticular galaxy — a bright disc full of old, red stars surrounded by what little gas and dust the galaxy has managed to cling on to. This image shows the shape of NGC 524 in detail, formed by the remaining gas surrounding the galaxy’s central bulge. Observations of this galaxy have revealed that it maintains some spiral-like motion, explaining its intricate structure. A version of this image was entered into the Hubble’s Hidden Treasures image processing competition by contestant Judy Schmidt.

Name: NGC 524
Type: Local Universe : Galaxy : Type : Lenticular
Category: Galaxies
Constellation: Pisces
Distance: 90 million light years
Release date: 22 July 2013, 10:00
Credit: ESA/Hubble & NASAAcknowledgement: Judy Schmidt

A spiral galaxy crowned by a star: Another treasure unearthed from the Hubble archives, this beautiful image shows a spiral galaxy named NGC 4517. Slightly bigger than our Milky Way, it is seen edge-on, crowned by a very bright star. The star is actually much closer to us than the galaxy, explaining why it appears to be so big and bright in the picture. NGC 4517 is located approximately 40 million light-years away in the constellation of Virgo (The Virgin). It has a bright centre, but this is not visible in this Hubble image. Its orientation has led to it being included in many studies of globular clusters, clumps of stars that orbit the centres of galaxies like satellites. The galaxy was discovered in 1784 by William Herschel, who described this region as having “a pretty bright star situated exactly north of the centre of an extended milky ray”. Of course the “milky ray” seen by Herschel is actually this spiral galaxy, but with his 17th century observing gear he could only tell that there a fuzzy, blurry structure below the much brighter star. This image is composed from visible and infrared light gathered by NASA/ESA Hubble Space Telescope. A version of this image was entered into the Hubble’s Hidden treasures image processing competition by contestant Gilles Chapdelaine.

Name: ngc 4517
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Virgo
Distance: 40 million light years
Release date: 29 July 2013, 10:00
Credit: ESA/Hubble & NASAAcknowledgement: Gilles Chapdelaine