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16 April, 2018

A Key Element to Life is Lacking in the Crab Nebula

Work by Jane Greaves and Phil Cigan from Cardiff University, UK suggests there may be a cosmic paucity of a chemical element essential to life. Greaves has been searching for phosphorus in the universe, because of its link to life on Earth. If this element is lacking in other parts of the cosmos, then it could be difficult for extra-terrestrial life to exist.

She explains "Phosphorus is one of just six chemical elements on which Earth organisms depend, and it is crucial to the compound adenosine triphosphate (ATP), which cells use to store and transfer energy. Astronomers have just started to pay attention to the cosmic origins of phosphorus, and found quite a few surprises. In particular, phosphorus is created in supernovae - the explosions of massive stars - but the amounts seen so far don't match our computer models. I wondered what the implications were for life on other planets if unpredictable amounts of phosphorus are spat out into space, and later used in the construction of new planets."

The team used LIRIS on the William Herschel Telescope (WHT) to observe infrared light from phosphorus and iron in the Crab Nebula, a supernova remnant around 6,500 light-years away in the constellation of Taurus.

A composite of infrared (shown as red), visible (green) and ultraviolet (violet) images of the Crab Nebula, with IR enhanced and visible/UV balanced to yield neutral star colours. Composite image made with the Cosmic Coloring Compositor. Credit: NRAO. Large format: [ PNG ].

Cigan, an expert on these stellar remnants, says: "This is only the second such study of phosphorus that has been made. The first looked at the Cassiopeia A (Cas A) supernova remnant, and so we are able to compare two different stellar explosions and see if they ejected different proportions of phosphorus and iron. The first element supports life, while the second is a major part of our planet's core. We are eager for a chance to come back and use LIRIS again to complete our study of how phosphorus abundance changes across the Crab Nebula".

Spectrum of one position near the centre of the Crab Nebula, taken with LIRIS at the WHT. The overlaid dotted line is a synthetic representation of how the phosphorus line would appear if the Crab Nebula had the same ratio of phosphorus to iron as the median value in Cas A, the only other supernova remnant where phosphorus was studied previously. Credit: Jane Greaves and Phil Cigan. Large format: [ PNG ].

These preliminary results suggest that material blown out into space could vary dramatically in chemical composition. Greaves remarks "The route to carrying phosphorus into new-born planets looks rather precarious. We already think that only a few phosphorus-bearing minerals that came to the Earth - probably in meteorites - were reactive enough to get involved in making proto-biomolecules."

She adds: "If phosphorus is sourced from supernovae, and then travels across space in meteoritic rocks, I'm wondering if a young planet could find itself lacking in reactive phosphorus because of where it was born? That is, it started off near the wrong kind of supernova? In that case, life might really struggle to get started out of phosphorus-poor chemistry on another world otherwise similar to our own."



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Last modified: 16 April 2018