Thanks for taking such beautiful photos!  This is a hornet nest, and it is not permanent, but it will continue to grow over the summer - usually causing the most issues in late summer / early fall.  If it is in an area of the yard you can avoid, you can leave it alone - the colony will die in winter.   If it is an area of the yard that you generally are using, then you may want to consider removal.  

Hornets (like bumble bees) have a lifecycle where the queen over winters by herself, and will start a nest in the spring.  She raises a lot of workers, and the nest grows over the summer, and later in the summer they will raise a reproductive generation (queens and males). That generation will mate, and all the rest of the workers and males will die off and the queens will overwinter again.  We get a lot of calls about these in late summer - often people don't notice them until they are large.