A collection of ancient stars: The  NASA/ESA Hubble Space Telescope has produced this beautiful image of  the globular cluster Messier 56 (also known as M 56 or NGC 6779), which  is located about 33 000 light years away from the Earth in the  constellation of Lyra (The Lyre). The cluster is composed of a large  number of stars, tightly bound to each other by gravity. However,  this was not known when Charles Messier first observed it in January  1779.  He described Messier 56 as “a nebula without stars”, like most  globular clusters that he discovered — his telescope was not powerful  enough to individually resolve any of the stars visible here, making it  look like a fuzzy ball through his telescope’s eyepiece. We clearly see  from Hubble’s image how the development of technology over the years has  helped our understanding of astronomical objects. Astronomers  typically infer important properties of globular clusters by looking at  the light of their constituent stars. But they have to be very careful  when they observe objects like Messier 56, which is located close to the  Galactic plane. This region is crowded by “field-stars”, in other  words, stars in the Milky Way that happen to lie in the same direction  but do not belong to the cluster. These objects can contaminate the  light, and hence undermine the conclusions reached by astronomers. A  tool often used by scientists for studying stellar clusters is the  colour-magnitude (or Hertzsprung-Russell) diagram. This chart compares  the brightness and colour of stars – which in turn, tells scientists  what the surface temperature of a star is. By  comparing high quality observations taken with the Hubble Space  Telescope with results from the standard theory of stellar evolution,  astronomers can characterise the properties of a cluster. In the case of  Messier 56, this includes its age, which at 13 billion years is  approximately three times the age of the Sun. Furthermore, they have  also been able to study the chemical composition of Messier 56. The  cluster has relatively few elements heavier than hydrogen and helium,  typically a sign of stars that were born early in the Universe’s  history, before many of the elements in existence today were formed in  significant quantities. Astronomers  have found that the majority of clusters with this type of chemical  makeup lie along a plane in the Milky Way’s halo. This suggests that  such clusters were captured from a satellite galaxy, rather than being  the oldest members of the Milky Way's globular cluster system as had  been previously thought. This  image consists of visible and near-infrared exposures from Hubble’s  Advanced Camera for Surveys. The field of view is approximately 3.3 by  3.3 arcminutes. A version of this image was entered into the Hubble’s Hidden Treasures Image Processing Competition by  contestant Gilles Chapdelaine. 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. The competition has now  closed and the results will be published soon.

Name: M 56, NGC 6779
Type: Milky Way : Star : Grouping : Cluster : Globular
Category: Star Clusters
Constellation: Lyra
Distance: 35000 light years
Release date: 20 August 2012, 10:00
Credit: NASA & ESA Acknowledgement: Gilles Chapdelaine

Spotting a supernova in NGC 5806: A  new image from the NASA/ESA Hubble Space Telescope shows NGC 5806, a  spiral galaxy in the constellation Virgo (the Virgin). It lies around 80  million light years from Earth. Also visible in this image is a  supernova explosion called SN 2004dg. The  exposures that are combined into this image were carried out in early  2005 in order to help pinpoint the location of the supernova, which  exploded in 2004. The afterglow from this outburst of light, caused by a  giant star exploding at the end of its life, can be seen as a faint  yellowish dot near the bottom of the galaxy. NGC  5806 was chosen to be one of a number of galaxies in a study into  supernovae because Hubble’s archive already contained high resolution  imagery of the galaxy, collected before the star had exploded. Since  supernovae are both relatively rare, and impossible to predict with any  accuracy, the existence of such before-and-after images is precious for  astronomers who study these violent events. Aside  from the supernova, NGC 5806 is a relatively unremarkable galaxy: it is  neither particularly large or small, nor especially close or distant. The  galaxy’s bulge (the densest part in the centre of the spiral arms) is a  so-called disk-type bulge, in which the spiral structure extends right  to the centre of the galaxy, instead of there being a large elliptical  bulge of stars present. It is also home to an active galaxy nucleus, a  supermassive black hole which is pulling in large amounts of matter from  its immediate surroundings. As the matter spirals around the black  hole, it heats up and emits powerful radiation. This  image is produced from three exposures in visible and infrared light,  observed by Hubble’s Advanced Camera for Surveys. The field of view is  approximately 3.3 by 1.7 arcminutes. A version of this image was entered into the Hubble’s Hidden Treasures Image Processing Competition by contestant Andre van der Hoeven (who won second prize in the  competition for his image of Messier 77). 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. The  competition has now closed.

Name: NGC 5806, SN 2004dg
Type: Local Universe : Star : Evolutionary Stage : SupernovaLocal Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Virgo
Distance: 80 million light years
Release date: 27 August 2012, 10:30
Credit: ESA/Hubble & NASA

Ancient orbs: This  sparkling picture taken by the NASA/ESA Hubble Space Telescope shows  the centre of globular cluster M 4. The power of Hubble has resolved the  cluster into a multitude of glowing orbs, each a colossal nuclear  furnace. M  4 is relatively close to us, lying 7200 light-years distant, making it a  prime object for study. It contains several tens of thousand stars and  is noteworthy in being home to many white dwarfs — the cores of ancient, dying stars whose outer layers have drifted away into space. In  July 2003, Hubble helped make the astounding discovery of a planet  called PSR B1620-26 b, 2.5 times the mass of Jupiter, which is located  in this cluster. Its age is estimated to be around 13 billion years —  almost three times as old as the Solar System! It is also unusual in  that it orbits a binary system of a white dwarf and a pulsar (a type of  neutron star). Amateur  stargazers may like to track M 4 down in the night sky. Use binoculars  or a small telescope to scan the skies near the orange-red star Antares  in Scorpius. M 4 is bright for a globular cluster, but it won’t  look anything like Hubble’s detailed image: it will appear as a fuzzy  ball of light in your eyepiece. On  Wednesday 5 September, the European Southern Observatory (ESO) will  publish a wide-field image of M 4, showing the full spheroidal shape of  the globular cluster. See it at www.eso.org on Wednesday.

Name: M 4, Messier 4, NGC 6121
Type: Milky Way : Star : Grouping : Cluster : Globular
Category: Star Clusters
Constellation: Scorpius
Distance: 7000 light years
Release date: 3 September 2012, 10:00
Credit: ESA/Hubble & NASA