It MIGHT 'baryonic dark matter'
I.e. it is made of normal matter BUT non luminous ...There are many lines of evidence that baryonic dark matter is only responsible for a small fraction of the estimated dark matter out there. There are a LOT of theories about what the remaining NON- baryonic dark matter is- I believe that it is now generally accepted that it is weakly interacting with light and normal matter- in other words its only observable by its gravitational effects on 'normal' matter... (since only %4 of the universe is what we call 'normal' matter, normal is relative)