Black sooty moldy? stuff covering leaves

[Dinamight]

Over the last 3 - 4 weeks a lot of the leaves on our palms have become covered in a black substance. I can scrape it off with my finger nail, it looks like dirt but the rain does not wash it away. It seems to have appeared quite suddenly.

Is this "sooty mold?" I haven't noticed a lot of ants around which I am told is responsible for spreading it. Is it dangerous to the tree? What should I be doing to stop it and get rid of it?

Thank you!