Dark Universe

Clusters of galaxies hold the prestigious title of "largest gravitationally bound structures in the universe," which is no small feat.

The XENON1T detector hasn't detected any dark matter particles yet. But it has carried out a 30-day science run, and project scientists are optimistic about the future.

Despite how far science has come, so many questions remained unanswered.

But scientists still don't know what the mysterious stuff is.