Black pepper is not necessary for turmeric to be effective, but it can be helpful. Black pepper contains a compound, piperine, which inhibits the metabolic breakdown of turmeric compounds in the gut and the liver. This allows higher levels of turmeric compounds to remain in the body (i.e., it increases its bioavailability), which may increase the effects of turmeric. Keep in mind that this can also affect the breakdown of other compounds, including certain drugs. You can get more details about this in the Turmeric (Curcumin) Supplements Review
Be aware that the biggest problem with turmeric is making sure that its compounds are absorbed
from the gut. You will absorb little if turmeric is not taken with along with fats or oils, which is why it's best to take turmeric and curcumin with a meal containing fats or oils. Black pepper does not help with absorption. Special formulations of turmeric and curcumin supplements have been developed to increase absorption and bioavailability of turmeric compounds. Details about these are also found Turmeric (Curcumin) Supplements Review, noted above.