Susan Aldridge, president of the University of Maryland, University College, went on unexpected and indefinite leave Wednesday. State university system officials did not disclose the reason.

In a letter sent Wednesday to the university community, state university Chancellor William “Brit” Kirwan wrote:

I am writing to inform you that, beginning today, President Susan Aldridge will be on leave for an undetermined period of time. During her absence, Javier Miyares, senior vice president for institutional effectiveness, will serve as acting president. I know that I can count on the entire UMUC community to provide Javier with its support so that UMUC may continue its exemplary education service to Maryland and our nation.

I asked university system spokeswoman Anne Moultrie whether there would be a customary news release. She replied, in an e-mail, “No, no release. The information is that Dr. Aldridge is on leave and Chancellor Kirwan has appointed Javier Miyares as acting president of UMUC.”

UMUC is essentially a 21st century version of night school: a sprawling, global campus operated by the state university system, offering mostly online classes to 90,000 students.

UMUC is one of the largest public colleges in the nation and claims to be the largest among state colleges, although it is not a traditional college.

Aldridge has been president since 2006. She holds a doctorate from the University of Colorado and is well-known in online higher-education and distance-learning circles.