B737-800 Captain reported encountering wake turbulence while 8 miles in trail of another heavy aircraft on descent into MIA.

Narrative

While descending on the CSTAL 2 Arrival; after a frequency change to Miami Approach; the controller requested we slow to 280 KIAS. I responded that we were currently flying 280 KIAS as assigned by the previous controller. When the ATC explained that we were following Aircraft Y 8 NM ahead; we volunteered to slow further as well as our willingness to accept a delay vector. We were told that slowing further was not possible as there was an aircraft behind us as well on the arrival and that a turn wouldn't be necessary. Shortly thereafter; less than 5 minutes; we encountered wake turbulence presumably from Aircraft Y in front of us. We maintained control of the aircraft but definitely encountered both roll and pitch consistent with wake/moderate turbulence. We informed the controller and were given vectors immediately. We then made a PA to the passengers explaining what happened. Everyone was already seated as we had prepared the cabin for landing earlier. We landed uneventfully. No one was injured to our knowledge. Everyone seemed fine as I said goodbye to the passengers as they disembarked.Tight aircraft spacing; approximately 8 miles; on arrival behind Aircraft Y. Consider additional requirements or increased emphasis on adherence to aircraft spacing requirements/regulations to provide more conservative safety margins… i.e.; increase aircraft spacing all phases of flight.