BLACK STAR?

No - it's just a ring of mini clamps gluing the "kerf". The "kerf" has two purposes. Primarily It's to facilitate the gluing grip of the top & the back to the sides. Secondarily, it helps to stiffen the sides which are pretty flimsy.

Working in a workshop as chaotic as this you need to be hyper-observant to keep track of your tools - & lo & behold - there's my orange plastic "dead-head" hammer! In its head there's a cylinder half filled with lead shot which ensures that when you hit - it never bounces!