There’s a new celebrity in town. But unlike some celebrities, this one deserves your attention. A painting — no wait, come back! — by one of the most important artists in history is on loan to the Speed Art Museum. Jan van Eyck was famous in his day (that would be 15th-century Belgium). He’s best known for “The Arnolfini Portrait” and the “Ghent Altarpiece,” and there’s a good chance he invented oil painting, or, at least, he was one of the first to use it. His painting, “Virgin and Child with Saints and Donor,” is on loan from the Frick Collection in New York City. Van Eyck’s the complete package: an artist who excels technically while grabbing viewers with powerful images and storytelling.