If the expansion of the universe continues and it stays in its present form, eventually all but the nearest galaxies will be carried away from us by the expansion of space at such a velocity that the observable universe will be limited to our own gravitationally bound local galaxy cluster. In the very long term (after many trillions—thousands of billions—of years, cosmic time), the Stelliferous Era will end, as stars cease to be born and even the longest-lived stars gradually die. Beyond this, all objects in the universe will cool and (with the possible exception of protons) gradually decompose back to their constituent particles and then into subatomic particles and very low-level photons and other fundamental particles, by a variety of possible processes.