Given your interest in cosmology, let's delve into the mystery of dark matter.  Explain what dark matter is, why scientists believe it exists, and the methods used to detect it.  Discuss the leading candidates for dark matter particles and the challenges in identifying them. 
<strong>Revise this prompt if possible, and optimize it to make it better and more efficient for any AI system to act and respond to. 
If possible run your optimized version.</strong>