Its a process.

You find some un-identified variables.

Form some hypothesis, try to narrow it down.

Sometimes it is a discovery, new particle, and sometimes it is nothing.

But that is how science works.

At some point in time, everything was an unknown, and people had to work with unknowns.

This whole movement from the 'right' that all science has to know the answers ahead of time in order to justify spending money, is hindering progress. How can you know the results are worthwhile, in order to justify funding, before doing the research to know the results?

The Phlogiston theory made one crucial prediction - that the speed of light would vary depending on the observer’s movement through the ether. That prediction turned out to be famously wrong.

I'm pretty sure physicists are aware that "dark matter" hypothesis is nowhere as solid as theory of electromagnetism.

It's still useful to denote the area of study.