A Living Fossil.

It seems the more we know the more we find out. In the natural world there are creatures nick-named ‘living fossils.’ The phrase was first used by Charles Darwin and relates to living things that have remained largely unchanged for millions of years. Two very different examples are Ctenophores and Gingko Biloba.

Ctenophores are also known as comb jellyfish. They propel themselves through the sea using lots of tiny hairs known as cilia. They are believed to have first appeared on Earth 700 million years ago which could mean that humans descended from them!

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A Ctenophore.

Gingko Biloba, or the maidenhair Tree, is the only one of its kind. It has neither ancestors nor evolved descendants. It is a truly ancient plant with fossil records of it dating back to the Permian era some 270 million years ago. It is much used today for its healing and soothing properties.

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A fossilised Gingko leaf.

So what has this to do with Astronomy? Well Astronomers have been looking at one of the globular clusters that are attached to the Milky Way, and have concluded that it is a living fossil from the earliest times of the galaxy: Terzan 5 is 19 000 light-years away and orbits the central bulge of the galaxy. It appears at the moment to be coming towards us at about 90Km/s.

The Milky Way is a spiral galaxy, with most of its stars to be found at the centre where they form a bulge. If you imagine our galaxy as two fried eggs put back to back the yolks represent the bulge.milky-wayHow our galaxy might look from afar.

It was only discovered in 1968 by French astronomer Agop Terzan. It lies in the constellation Sagittarius and is obscured by the number of stars in the area making it hard to find. Astronomers noticed in 2005 to have two distinct populations of stars with an age gap of 7 billion years. It was thought that Terzan 5 might have been the remnant of a dwarf galaxy that got too close to ours and was disrupted (broken up) by the gravity of the Milky Way.

Peering through the thick dust clouds of the galactic bulge an international team of astronomers has revealed the unusual mix of stars in the stellar cluster known as Terzan 5. The new results indicate that Terzan 5 is in fact one of the bulge's primordial building blocks, most likely the relic of the very early days of the Milky Way. This picture is from the Multi-Conjugate Adaptive Optics Demonstrator (MAD), a prototype adaptive optics system used to demonstrate the feasibility of different techniques in the framework of the E-ELT and the second generation VLT Instruments. The star colours are from the Hubble image of the same star field.

This picture is from the Multi-Conjugate Adaptive Optics Demonstrator (MAD), a prototype adaptive optics system used to demonstrate the feasibility of different techniques in the framework of the E-ELT and the second generation VLT Instruments. The star colours are from the Hubble image of the same star field.

It has now been discovered that this is not the case. Using instruments on the Hubble Space telescope, the WM Keck telescope and the ESO’s Very Large Telescope (VLT) in Chile Astronomers have been taking another look at these two lots of stars. They found that as well as the age gap they are made up of very different elements. This age gap indicates that the star formation process in Terzan 5 was not continuous, but was dominated by two distinct bursts of star formation.

This means its ancestor must have had large amounts of gas for a second generation of stars, something along the size of at least 100 million times the mass of the Sun! It had to be massive for it to have survived the 12 billion years since the galaxy formed without being disrupted They have also found that he stars in Terzan 5 have very similar properties to those found in the galactic bulge.

These unusual properties, which are uncommon amongst globular clusters, are why Astronomers are calling it a living fossil. The current theory of how galaxies form requires vast clumps of gas and stars to interact and then merge and dissolve to form the primordial bulge of the Milky Way in the process. Some of Terzan 5s characteristics “…resemble those detected in the giant clumps we see in star-forming galaxies at high-redshift, [that is galaxies far away from us] suggesting that similar assembling processes occurred in the local and in the distant Universe at the epoch of galaxy formation.” according to lead Astronomer Francesco Ferrari.

The research presents a possible route for astronomers to unravel the mysteries of galaxy formation, and offers an unrivalled view into the complicated history of the Milky Way.

If you want to know where Terzan 5 is, here is a map; the region (Sagittarius) is visible form the UK but the cluster itself, well that is a different matter!

This chart shows the rich constellation of Sagittarius. Among the many star clusters in this part of the Milky Way lies Terzan 5, a stellar cluster which resembles a globular cluster. This picture plots most of the the stars visible on a dark clear night with the naked eye.

This chart shows the rich constellation of Sagittarius. Among the many star clusters in this part of the Milky Way lies Terzan 5, a stellar cluster which resembles a globular cluster. This picture plots most of the the stars visible on a dark clear night with the naked eye.

 

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Published in: on September 8, 2016 at 16:17  Leave a Comment  
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