Hala's sun was a medium size star in the Hala system in the Othala galaxy.
History[]
In order to destroy the Replicators, the Asgard artificially increased the mass of the star and collapsed it into a black hole thus destroying the planet Hala and most of the Replicators present there. However a small bunch of them were able to escape. (SG1: "New Order, Part 1")