The Hercules Text by Jack McDevitt

The classic first-contact science fiction novel that launched the career of Jack McDevitt, the national bestselling author of Coming Home—now revised from the original edition, and featuring a new foreword.
From a remote corner of the galaxy a message is being sent. The continuous beats of a pulsar have become odd, irregular.artificial. It can only be a code.
Frantically, a research team struggles to decipher the alien communication. And what the scientists discover is destined to shake the foundations of empires around this world—from Wall Street to the Vatican.