The wood dried and shrank. Wood dries more quickly out the ends since the cell structure of a tree is basically intended to transmit water lengthwise. The centers of the two planks were not as dry as the ends, and the glued up assembly separated at the center as they shrank. If the glue line is stronger than the wood, and most good glue lines are, the wood itself will crack. You could fill the crack; but if the wood is not done drying, it will just crack some more.
It is striking looking wood. It needs to dry before you can do anything with it. The old rule of thumb for air drying is 1 year per inch of thickness. It is a good place to start for most woods in most climates. Someone with a moisture meter might be able to tell you more accurately.