That is a new paper by Linda Schilling and Harald Uhlig, here is the abstract:
How do Bitcoin prices evolve? What are the consequences for monetary policy? We answer these questions in a novel, yet simple endowment economy. There are two types of money, both useful for transactions: Bitcoins and Dollars. A central bank keeps the real value of Dollars constant, while Bitcoin production is decentralized via proof-of-work. We obtain a “fundamental condition,” which is a version of the exchange-rate indeterminacy result in Kareken-Wallace (1981), and a “speculative” condition. Under some conditions, we show that Bitcoin prices form convergent supermartingales or submartingales and derive implications for monetary policy.
In this framework, I would attribute the volatility of the recent Bitcoin price to a) sometimes being in the speculative equilibrium or uncertainty about such, b) regulatory uncertainty, and c) uncertainty about the hedging or store of value properties of Bitcoin and other cryptoassets. If you are interested in other considerations, here is a good Jimmy Song essay on why Bitcoin might be special. And see this paper by Garratt and Wallace, though unlike with Schilling and Uhlig I am less sure how they are modeling the black/gray market uses for Bitcoin as a transactions medium.