What about the most “permanent” objects in the universe? Could it be that they are just borrowing time? Cosmic doom has long been safely distant, stars would exhaust themselves, black holes would linger and the universe would sink into an imaginedly slow death. A series of calculations of Radboud University replaces that intuition with a much more focused shot that still has the final state infinitely, but with a more general type of decay than many readers are used to associating with black holes alone.
It all began with the realization by Stephen Hawking in the 1970s that empty space is not indeed empty. Quantum field theory This is what can be generated by fluctuations that can temporarily create pairs of particles and the fact that the spacetime is not flat may not allow those pairs to simply cancel in the normal way. Hawking said that close to a black hole, such a discrepancy can manifest itself as a trickle of radiation, which evaporates the mass of the black hole on mind-defying time scales. That suggestion put the old relativistic image of black holes as sinks of energy in a queasy state: should radiation radiate away, then even a black hole can theoretically radiate away.
Heino Falcke, Michael Wondrak and Walter van Suijlekom expand the scope of the mechanism by indicating that besides an event horizon is not the only stage on which particle creation can be separated into “escape” and “capture.” The most important element in their treatment is the curvature of spacetime. Should it be possible to separate by means of curvature, then the dense horizonless remnants, which are neutron stars and white dwarfs, would also be long-term emitters in a Hawking-like process sometimes referred to as a gravitational pair production. The practical payoff is a new limit on the duration of time during which the universe will be populated by long-lasting remnants of stellar evolution.
The original figure in the headline is startling in its own terms: there is a maximum of 1078 years to the continued existence of the last stellar remains, much less than the older calculations which were as much as 101100 years. It is not that the cosmos suddenly “speeds up”; it is that now more objects are permitted to be involved with the same sluggish spurt of mass-energy. White dwarfs cool cores of Sun-like stars take up the deadline, simply as they are numerous, long-lived, and in this context they do not remain indefinitely inert, but eventually dissolve.
However, the unexpected finding is that neutron stars and stellar-mass black holes are found to lie approximately on the same evaporation timescale, which is approximately 1067 years. Density is the parameter that is in control and black holes are not necessarily the losers in the “evaporate fastest” contest. Because, in the calculations of the team, a black hole can effectively reclaim a portion of its production, to the effect that it slows its net loss, Wondrak noted that “a black hole has no surface”, which is important since, in their accounting, a black hole is able to effectively recapture part of its production.
Sanity checks of boundary-pushing are also included in the paper. Similarly to the engineers who operate a model outside its normal operating range, the authors approximate evaporation durations of familiar objects: a human and the Moon emerge with similar numbers of approximately 1090 years using the same process, which is intended to investigate the mathematics and not predict any practical outcome. The underlying claim that is highlighted in those thought experiments is that curvature-driven particle production is not an exceptional feature of black holes but rather a more general effect of quantum fields residing on a curved background.
The attraction turns out to be the unification rather than the countdown as an editorial consequence of fundamental physics. The development of the work by associating long-term cosmic evolution with one cosmetic curvature-induced leakage reduces the conceptual gap between black holes and other compact objects, and leaves the most fundamental question unanswered: how does quantum theory and gravity count books in the most extreme environments.
