Help identify an unknown airborne object
My best guess is you saw a high altitude aircraft flashing its landing lights.

Landing lights serve a number of purposes. Besides illuminating the landing surface, they can also be used to signal other planes as they are so bright. To experience how bright they are, stand near the approach or departure path of a busy airport at night.

The reason for the pilots flashing the landing lights in your scenario is unknown. It could be signaling another plane on a potential collision course, or just a way of saying hello to other traffic (hey, cruising a commercial airliner is kinda bored, huh?).

Without any visual reference, judging distances on a nighty sky can be tricky. Flashing a light is a convenient way of saying "hey I'm here!" to other planes. It is likely that your judgment of the flying object's distance was also impaired by the night environment. The only reliable observation I would pick is that you did not hear any sound, which suggests the object was very far away.