Thirteen thousand light-years from Earth, deep inside the Gum Nebula, lies cometary globules — a group of comet-like objects that, despite the name and appearance, have nothing to do with comets. They are small nebulous globules of gas and dust, and their exact nature remains a bit of a mystery.
This type of nebula, which is a sub-type of what is known as a Bok globule — a very compact, very dense, very cold nebula — is the smallest type of dark nebula, only a light-year or two across. Inside that region is a mass that can roughly vary between two and 100 times the mass of our sun.
These globules often appear as dark patches in the sky, emanating no light (which makes them very difficult to detect and study). And although they are some of the coldest objects we have seen in the universe, inside often burns a very warm core — a forming star, or multiple stars.
CG4, also known as God’s Hand, is a cometary globule — a Bok globule on which one side has been blown outwards into a long tail, resembling a comet. It is just one of several such cometary globules located in the Gum Nebula, all with their tails trailing away from the Vela supernova remnant, which may indicate that the exploding star is what caused the tails.
Another hypothesis is that the shape is caused by stellar winds and ionizing radiation from very hot, very large OB stars nearby. These, astronomers believe, could initially form the structures known as elephant trunks — structures like those seen in the Pillars of Creation in the Eagle Nebule — and eventually cometary globules.
In the stunning new observation by the ESO’s Very Large Telescope (VLT), CG4 shows off its intricate detail, and its dusty “mouth” can be seen. Compared with the surrounding nebula, this Bok globule is very small, but in reality, its dimensions would dwarf the solar system. The head of the globule is 1.5 light-years across and its faint tail stretches eight light-years long. CG4 and other cometary globules nearby generally point away from the Vela supernova remnant in the center of the Gum Nebula (which is nearly 1,000 light-years wide).
The picture actually shows the head part of the nebula, which is a thick cloud of gas and dust. It can only be seen because it is lit up by the light of nearby stars.
And while those stars make it possible to see the nebula, they’re gradually destroying it. The radiation that comes from them is slowly eroding the particles that scatter the starlight and make it look so bright.
[Image via Independent]