A stunning new image of the cometary globule CG4 has been obtained by a group of astronomers using ESO’s Very Large Telescope.
This image shows the cometary globule CG4; although it looks huge and bright in this image it is actually a faint nebula and not easy to observe; the exact nature of CG4 remains a mystery. Image credit: ESO.
Cometary globules are faint, small clouds of gas and dust within our Milky Way Galaxy.
These objects were first recognized in 1976 on pictures taken with the UK Schmidt Telescope in Australia and their faintness makes them particularly challenging targets for color photography.
The cometary globule CG4, sometimes referred to as God’s Hand, is located in the constellation of Puppis, about 1,300 light-years away.
Its head is some 1.5 light-years in diameter, and its tail is about 8 light-years long. The dusty cloud contains enough material to make several Sun-sized stars.
The head of the nebula is itself opaque, but glows because it is illuminated by light from very hot stars. Their energy is gradually destroying the dusty head of the globule, sweeping away tiny particles that scatter the starlight as a faint, bluish reflection nebula.
CG4 also shows a faint red glow, probably from excited hydrogen, and seems about to devour an edge-on spiral galaxy, which in reality is hundreds of millions of light years away, far beyond the globule.
Why CG4 and other cometary globules have their distinct form is still a matter of debate among astronomers and two theories have developed.
Cometary globules, and therefore also CG4, could originally have been spherical nebulae, which were disrupted and acquired their new, unusual form because of the effects of a nearby supernova explosion.
Some astronomers suggest that cometary globules are shaped by stellar winds and ionizing radiation from hot, massive OB stars. These effects could first lead to the bizarrely named formations known as elephant trunks and then eventually cometary globules.
To find out more, scientists need to find out the mass, density, temperature, and velocities of the material in the globules.
These can be determined by the measurements of molecular spectral lines which are most easily accessible at millimeter wavelengths – wavelengths at which telescopes like the Atacama Large Millimeter/submillimeter Array (ALMA) operate.
