There is no definitive answer, but there are a few theories about how Obi-Wan Kenobi could have destroyed the Death Star without the help of the stormtroopers. One theory suggests that he may have used the Force to cause a reactor malfunction. Another theory suggests that he may have sabotaged the Death Star's reactor in some way. There is also speculation that he may have used a hidden transmitter to call for help from Luke Skywalker and the Rebel Alliance.