The key ingredients of life appear in unexpected places.

One of the key ingredients for life like Earth to arise has been found in the least expected place: the "outskirts" of the Milky Way .

According to Sicence Alert, the key ingredient for life is phosphorus.

"To create phosphorus, you need some violent event. It's thought that phosphorus is created in supernova explosions, and to do that, you need a star that's at least 20 times the mass of the Sun," said astronomer and chemist Lucy Ziurys from the Steward Observatory at Arizona State University.

But where they found it , the phosphorus is located far from the massive stars or supernova remnants in the dense disk of light of the Milky Way .

The habitable zone of the galaxy containing Earth may extend to the very edge - (Photo: NASA).

"The phosphorus we found is on the edge of the galaxy, where it shouldn't be. That means there must be another way to make phosphorus," said co-author Lilia Koelemay from Arizona State University.

There are two leading explanations for how life-related elements appeared there.

One is the hypothetical 'galactic fountain' model , in which supernovae create shock waves so powerful that they shoot material from the main disk of a galaxy all the way into the surrounding halo. This material then cools and 'rains' back down into the galactic disk.

This is thought to be unlikely because there is little evidence of "galactic fountains" or the ability for them to propel matter so far.

The second possibility is related to a discovery a few years ago: Low-mass stars also produce phosphorus.

Instead of being created directly like a giant star, phosphorus in a microstar explosion is formed when isotopes of silicon "trap" extra neutrons, which then turn into phosphorus.

Whatever way this "backbone" of life was created, it confirms that it could be present in the Milky Way in many other ways, possibly including ways previously unknown.

This also addresses the possibility of extending the Milky Way's "habitable zone" to its very edges. Because wherever life-supporting NCHOPS elements are present - nitrogen, carbon, hydrogen, oxygen, phosphorus and sulfur - there is a good chance that alien life will be present, which we'd all like to see.