ESO WFI: Beautiful image of the open Wild Duck Cluster, Messier 11

The Wide Field Imager (WFI) on the MPG/ESO 2.2-meter telescope at the La Silla Observatory in Chile has taken this beautiful image of the open Wild Duck Cluster, Messier 11, or NGC 6705. 

The blue stars in the centre of the image are the young, hot stars of the cluster. 

The surrounding redder stars are older, cooler background stars. 

Credit: ESO

The Wide Field Imager on the MPG/ESO 2.2-meter telescope at ESO's La Silla Observatory in Chile has taken this beautiful image, dappled with blue stars, of one of the most star-rich open clusters currently known, Messier 11, also known as NGC 6705 or the Wild Duck Cluster.

Messier 11 is an open cluster, sometimes referred to as a galactic cluster, located around 6000 light-years away in the constellation of Scutum (The Shield).

It was first discovered by German astronomer Gottfried Kirch in 1681 at the Berlin Observatory, appearing as nothing more than a fuzzy blob through the telescope.

It wasn't until 1733 that the blob was first resolved into separate stars by the Reverend William Derham in England, and Charles Messier added it to his famous catalogue in 1764.

Messier was a comet hunter and the catalogue came into being as he was frustrated by constantly observing fixed, diffuse objects that looked like comets (for example, objects that we now know to be clusters, galaxies and nebulae).

He wanted a record in order to avoid accidentally observing them again and confusing them with possible new comets.

This particular stellar cluster was noted down as the eleventh such object, hence the name of Messier 11.

Open clusters are typically found lying in the arms of spiral galaxies or in the denser regions of irregular galaxies, where star formation is still common.

Messier 11 is one of the most star-rich and compact of the open clusters, being almost 20 light-years across and home to close to 3000 stars.

Open clusters are different to globular clusters, which tend to be very dense, tightly bound by gravity, and contain hundreds of thousands of very old stars, some of which are nearly as old as the Universe itself.

Studying open clusters is great way to test theories of stellar evolution, as the stars form from the same initial cloud of gas and dust and are therefore very similar to one another, they all have roughly the same age, chemical composition, and are all the same distance away from Earth.

However, each star in the cluster has a different mass, with the more massive stars evolving much faster than their lower mass counterparts as they use up all of their hydrogen much sooner.


This video takes you on a journey to the open cluster Messier 11 as seen with the Wide Field Imager (WFI) on the MPG/ESO 2.2-metre telescope at the La Silla Observatory. 

Credit: ESO/N. Risinger (skysurvey.org)/J. Bohanon

In this way, direct comparisons between the different evolutionary stages can be made within the same cluster: for example, does a 10 million year old star with the same mass as the Sun evolve in a different way to another star that is the same age, but half as massive?

In this sense, open clusters are the closest thing astronomers have to "laboratory conditions".

Because the stars within open clusters are very loosely bound to one another, individuals are very susceptible to being ejected from the main group due to the effect of gravity from neighbouring celestial objects.

NGC 6705 is already at least 250 million years old, so in a few more million years it is likely that this Wild Duck formation will disperse, and the cluster will break up and merge into its surroundings.

This image was taken by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO's La Silla Observatory in northern Chile.

More information: 
Research papers on NGC 6705: adsabs.harvard.edu/cgi-bin/bas… h=NGC+6705&version=1

ESO VLT Image: IC1295 the Ghostly Green Nebula

This intriguing picture from ESO's Very Large Telescope shows the glowing green planetary nebula IC 1295 surrounding a dim and dying star. 

It is located about 3300 light-years away in the constellation of Scutum (The Roman Shield). 

This is the most detailed picture of this object ever taken. 

Credit: ESA/ESO

Stars the size of the Sun end their lives as tiny and faint white dwarf stars but as they make the final transition into retirement their atmospheres are blown away into space.

For a few tens of thousands of years they are surrounded by the spectacular and colourful glowing clouds of ionised gas known as planetary nebulae.

The Constellation of Scutum
This new image from the VLT shows the planetary nebula IC 1295, which lies in the constellation of Scutum (The Roman Shield).

The small constellation Scutum was discovered in 1684 by Polish astronomer Johannes Hevelius (Jan Heweliusz), who originally named it Scutum Sobiescianum (Shield of Sobieski) to commemorate the victory of the Polish forces led by King John III Sobieski (Jan III Sobieski) in the Battle of Vienna in 1683. Later, the name was shortened to Scutum.

IC1295 has the unusual feature of being surrounded by multiple shells that make it resemble a micro-organism seen under a microscope, with many layers corresponding to the membranes of a cell.

Space Bubbles
These bubbles are made out of gas that used to be the star's atmosphere. This gas has been expelled by unstable fusion reactions in the star's core that generated sudden releases of energy, like huge thermonuclear belches.

The gas is bathed in strong ultraviolet radiation from the aging star, which makes the gas glow. Different chemical elements glow with different colours and the ghostly green shade that is prominent in IC 1295 comes from ionised oxygen.

Ionised Oxygen

 Ivan Engler

Ionised Oxygen is used for medical operations here on Earth and it´s use is attributed to the surgeon Ivan Engler.

At the centre of the IC1295 image, you can see the burnt-out remnant of the star's core as a bright blue-white spot at the heart of the nebula.

The central star will become a very faint white dwarf and slowly cool down over many billions of years.

Stars with masses like the Sun and up to eight times that of the Sun, will form planetary nebulae as they enter the final phase of their existence.

The Sun is 4.6 billion years old and it will likely live another four billion years.

Planetary Nebula
Despite the name, planetary nebulae have nothing to do with planets. This descriptive term was applied to some early discoveries because of the visual similarity of these unusual objects to the outer planets Uranus and Neptune, when viewed through early telescopes, and it has been catchy enough to survive.

These objects were shown to be glowing gas by early spectroscopic observations in the nineteenth century.

ESO VLT and FORS
This image was captured by ESO's Very Large Telescope, located on Cerro Paranal in the Atacama Desert of northern Chile, using the FORS instrument (FOcal Reducer Spectrograph).