Cosmic riches: This dazzling image shows the globular cluster Messier 69, or M 69 for short, as viewed through the NASA/ESA Hubble Space Telescope. Globular clusters are dense collections of old stars. In this picture, foreground stars look big and golden when set against the backdrop of the thousands of white, silvery stars that make up M 69. Another aspect of M 69 lends itself to the bejewelled metaphor: As globular clusters go, M 69 is one of the most metal-rich on record. In astronomy, the term “metal” has a specialised meaning: it refers to any element heavier than the two most common elements in our Universe, hydrogen and helium. The nuclear fusion that powers stars created all of the metallic elements in nature, from the calcium in our bones to the carbon in diamonds. Successive generations of stars have built up the metallic abundances we see today. Because the stars in globular clusters are ancient, their metallic abundances are much lower than more recently formed stars, such as the Sun. Studying the makeup of stars in globular clusters like M 69 has helped astronomers trace back the evolution of the cosmos. M 69 is located 29 700 light-years away in the constellation Sagittarius (the Archer). The famed French comet hunter Charles Messier added M 69 to his catalogue in 1780. It is also known as NGC 6637. The image is a combination of exposures taken in visible and near-infrared light by Hubble’s Advanced Camera for Surveys, and covers a field of view of approximately 3.4 by 3.4 arcminutes.

Name: M 69
Type: Milky Way : Star : Grouping : Cluster : Globular
Category: Star Clusters
Constellation: Sagittarius
Distance: 30000 light years
Release date: 1 October 2012, 10:00
Credit: ESA/Hubble & NASA

Galaxy in a spin: NGC 3344 is a glorious spiral galaxy around half the size of the Milky Way, which lies 25 million light-years distant. We are fortunate enough to see NGC 3344 face-on, allowing us to study its structure in detail. The galaxy features an outer ring swirling around an inner ring with a subtle bar structure in the centre. The central regions of the galaxy are predominately populated by young stars, with the galactic fringes also featuring areas of active star formation. Central bars are found in around two thirds of spiral galaxies. NGC 3344’s is clearly visible here, although it is not as dramatic as some (see for example heic1202). The high density of stars in galaxies’ central regions gives them enough gravitational influence to affect the movement of other stars in their galaxy. However, NGC 3344’s outer stars are moving in an unusual manner, although the presence of the bar cannot entirely account for this, leaving astronomers puzzled. It is possible that in its past NGC 3344 passed close by another galaxy and accreted stars from it, but more research is needed to state this with confidence. The image is a combination of exposures taken in visible and near-infrared light, using Hubble’s Advanced Camera for Surveys. The field of view is around 3.4 by 3.4 arcminutes, or around a tenth of the diameter of the full Moon.

Name: NGC 3344
Type: Local Universe : Galaxy : Type : Spiral
Category: Galaxies
Constellation: Leo Minor
Distance: 20 million light years
Release date: 15 October 2012, 10:00
Credit: ESA/Hubble & NASA

Violent star formation episodes in dwarf galaxies: The NASA/ESA Hubble Space Telescope has imaged the faint irregular galaxy NGC 3738, a starburst galaxy. The galaxy is in the midst of a violent episode of star formation, during which it is converting reservoirs of hydrogen gas harboured in the galaxy’s centre into stars. Hubble spots this gas glowing red around NGC 3738, one of the most distinctive signs of ongoing star formation. Lying in the constellation of Ursa Major (The Great Bear), NGC 3738 is located about 12 million light-years from the Sun, and belongs to the Messier 81 group of galaxies. This galaxy — first observed by astronomer William Herschel  back in 1789 — is a nearby example of a blue compact dwarf, the faintest type of starburst galaxy. Blue compact dwarfs are small compared to large spiral galaxies — NGC 3738 is around 10 000 light-years across, just one tenth of the size of the Milky Way. This type of galaxy is blue in appearance by virtue of containing large clusters of hot, massive stars, which ionise the surrounding interstellar gas with their intense ultraviolet radiation. They are relatively faint and appear to be irregular in shape. Unlike spirals or elliptical galaxies, irregular galaxies do not have any distinctive features, such as a nuclear bulge or spiral arms. Rather, they are extremely chaotic in appearance. These galaxies are thought to resemble some of the earliest that formed in the Universe and may provide clues as to how stars appeared shortly after the Big Bang. This image was created by combining visual and infrared images taken with the Wide Field Channel of the Advanced Camera for Surveys aboard the Hubble Space Telescope. The field of view of the Wide Field Channel is approximately 3.4 by 3.4 arcminutes wide.

Name: NGC 3738
Type: Local Universe : Galaxy : Size : Dwarf
Category: Galaxies
Constellation: Ursa Major
Distance: 12 million light years
Release date: 22 October 2012, 10:00
Credit: ESA/Hubble & NASA

An unexpected population of young-looking stars: The  NASA/ESA Hubble Space Telescope offers an impressive view of the centre  of globular cluster NGC 6362. The image of this spherical collection of  stars takes a deeper look at the core of the globular cluster, which  contains a high concentration of stars with different colours. Tightly  bound by gravity, globular clusters are composed of old stars, which,  at around 10 billion years old, are much older than the Sun. These  clusters are fairly common, with more than 150 currently known in our  galaxy, the Milky Way, and more which have been spotted in other  galaxies. Globular  clusters are among the oldest structures in the Universe that are  accessible to direct observational investigation, making them living  fossils from the early years of the cosmos. Astronomers  infer important properties of globular clusters by looking at the light  from their constituent stars. For many years, they were regarded as  ideal laboratories for testing the standard stellar evolution theory.  Among other things, this theory suggests that most of the stars within a  globular cluster should be of a similar age. Recently,  however, high precision measurements performed in numerous globular  clusters, primarily with the Hubble Space Telescope, has led some to  question this widely accepted theory. In particular, certain stars  appear younger and bluer than their companions, and they have been  dubbed blue stragglers. NGC 6362 contains many of these stars. Since  they are usually found in the core regions of clusters, where the  concentration of stars is large, the most likely explanation for this  unexpected population of objects seems to be that they could be either  the result of stellar collisions or transfer of material between stars  in binary systems. This influx of new material would heat up the star  and make it appear younger than its neighbours. NGC  6362 is located about 25 000 light-years from Earth in the  constellation of Ara (The Altar). British astronomer James Dunlop first  observed this globular cluster on 30 June 1826. This  image was created combining ultraviolet, visual and infrared images  taken with the Wide Field Channel of the Advanced Camera for Surveys and  the Wide Field Camera 3. An image image of NGC 6362 taken by the  MPG/ESO 2.2-metre telescope will be published by the European Southern  Observatory on Wednesday. See it on www.eso.org from 12:00 on 31 October.

Name: NGC 6362
Type: Milky Way : Star : Grouping : Cluster : Globular
Category: Star Clusters
Constellation: Ara
Distance: 25000 light years
Release date: 29 October 2012, 10:00
Credit: ESA/Hubble & NASA