Why there is a start (*) after Nodegroup:0 in MySQL cluster? What does it means?
It shows which node is master. It is internal thing and probably the only visible effect of it is when exactly half of the nodes goes down. Then if one of the remaining nodes is master - cluster keeps working. If not - cluster aborts.

http://dev.mysql.com/doc/refman/5.1/en/faqs-mysql-cluster.html#qandaitem-B-10-1-8

Updated link:
http://dev.mysql.com/doc/refman/5.1/en/faqs-mysql-cluster.html#faq-cluster-what-show-nodegroup-star