Best Ever Image of a Cometary Globule: Also What is a Cometary Globule?

The best ever image of a Cometary Globule has been released by the European Southern Observatory (ESO) from the Very Large Telescope (VLT) in the Atacama desert in Chile.

Cometary Globule CG4, in the constellation Puppis. Credit: ESO

It looks a lot like a nebula right? In actuality a cometary globule is a very specific type of nebula.  It’s very faint, and it’s formation is a matter of debate among the astronomical community.  A cometary globule is small, containing the mass of a few suns worth of material.  Compare this to a typical nebula, which has enough material to form thousands or even hundreds of thousands of stars.

The globule glows due to reflection of the light from hot OB stars, but is generally opaque, making it difficult to capture in astrophotography.  It is also very small, it’s head only 1.5 light-years in diameter, with an 8 light-year long tail.  You can see the full structure of it in the image below, which makes it clear to see why we call it a ‘cometary’ globule.

Image of cometary globule CG4 from 1976. Obtained from http://www.montgomerycollege.edu/

It looks a lot like a crazy monster about to devour the galaxy in the above image, but unfortunately for the monster, the Galaxy is a few hundred Million light-years further away, and far too large for an 8 light-year long monster to devour.

The debate among astronomers concerns the formation and evolution of such strange objects (yes there are others).  Some believe the globules used to be spherical nebulae whose shape was altered by a supernova explosion.  Others see it as an end point to the evolution of star-forming nebulae, where stellar winds from hot O and B stars have blown away the material.

In order to study the globules further, astronomers need to obtain spectral data from the faint clouds, in order to determine the mass, density, temperature, and velocity of the material that composes them.  In the next few years, we should start to see answers to these questions, giving us another piece of the galactic puzzle.

The globule is 1,300 light-years away in the constellation of Puppis in the southern hemisphere.

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