The accumulation of gas by the core is initially a slow process but after the forming protoplanet reaches about 30 Earth masses ( M ) it accelerates and proceeds in a runaway manner .
A slow process continues for several million years .
The accumulation of gas by the core is initially a slow process , which continues for several million years , but after the forming protoplanet reaches about 30 Earth masses ( M ) it accelerates and proceeds in a runaway manner .