Madonna was criticized for her performance of "Like a Virgin" at the first 1984 MTV Video Music Awards (VMA). She appeared on stage atop a giant wedding cake, wearing a wedding dress and white gloves. The performance is noted by MTV as an iconic moment in VMA history. In later years, Madonna commented that she was terrified of the performance. The next hit was "Material Girl" promoted by her video, a mimicry of Marilyn Monroe's performance of the song "Diamonds Are a Girl's Best Friend" from the 1953 film Gentlemen Prefer Blondes. While filming this video, Madonna started dating actor Sean Penn. They married on her birthday in 1985. Like a Virgin was certified diamond by the Recording Industry Association of America and sold more than 25 million copies worldwide. In February 1984, according to the film director Sir Richard Attenborough, Madonna auditioned at the Royale Theatre on Broadway for a dance role in his movie version of A Chorus Line using her birth-name of Ciccone, but he rejected her.

Answer this question, if possible (if impossible, reply "unanswerable"): When did Madonna married Sean Penn?
on her birthday in 1985