For decades, neutron stars and white dwarfs have stood as cosmic monuments to stellar death. They are the cold, dense remnants left behind after massive stars collapse or fade. Unlike black holes, which eventually radiate themselves into nonexistence through Hawking radiation, neutron stars and white dwarfs were believed to be stable over incomprehensibly long time periods, bound by gravity and preserved by quantum pressure. Recent work by physicists Heino Falcke, Michael Wondrak, and Walter van Suijlekom introduces a very different scenario. Their findings point to a stark and surprising reality: even these stellar remnants are subject to decay. The force responsible may be spacetime itself.
The research reveals a fundamental and previously underestimated mechanism: gravitational pair production. This process has no need for an event horizon. Yet it allows stellar remnants, including neutron stars, white dwarfs, and even massive compact objects without the extreme characteristics of black holes, to emit particles and lose mass over time. The key to this process lies in the extreme curvature of spacetime that surrounds these dense bodies.
Traditionally, Hawking radiation was understood as arising only from black holes. Virtual particle-antiparticle pairs pop into existence near the event horizon, and one particle falls in while the other escapes. This imbalance extracts mass from the black hole, slowly evaporating it. What Falcke and colleagues show is that a similar process can take place anywhere spacetime curvature is strong enough. For neutron stars and other compact remnants, this effect emerges not from the presence of an event horizon, but from the intense gravitational field around them.
In this new framework, the curvature of spacetime itself separates virtual particle pairs before they annihilate. These separated particles can then materialize as real emissions, robbing the star of energy and mass. The decay this process causes does not require temperature, nuclear fusion, or collisions. It is a quantum mechanical effect rooted in the structure of spacetime.
This leads to an upper bound on the lifetime of any such compact object. The decay time depends on density, following a simple but powerful relation: τ ∝ ρ⁻³ᐟ². That is, the higher the density, the faster the decay. For neutron stars, with densities reaching over 10¹⁴ g/cm³, the predicted lifetime is on the order of 10⁶⁸ years. This is roughly comparable to the decay time expected for a low-mass stellar black hole. White dwarfs, which are less dense, can endure for much longer—around 10⁷⁸ years. Supermassive black holes such as the one in galaxy M87 are expected to last roughly 10⁹⁶ years.
Even seemingly mundane objects like the Moon or human bodies would decay through this process, though the timescales become truly astronomical. A Moon-sized body would have a lifetime of around 10⁸⁹ years. For a typical human body, the number is even more absurd. And yet, the math holds. Spacetime does not discriminate.
Importantly, this form of radiation occurs both outside and inside the object. For neutron stars and white dwarfs, which are optically thick and absorbing, any particles produced within are absorbed and reradiated thermally from the surface. For black holes, the situation is different. Their event horizon traps internal emissions, meaning only externally produced particles can escape.
The model used to develop these predictions relies on the effective action from quantum field theory in curved spacetime. The imaginary part of this action, representing the probability that vacuum remains vacuum, is non-zero in the presence of curvature. This means real particles emerge from what would otherwise be quantum fluctuations. In simple terms, the spacetime around a neutron star constantly pokes at the quantum vacuum, prompting it to release particles. Over time, this results in a net energy loss from the star.
The rate of mass loss is slow, unimaginably slow, but persistent. It resembles radioactive decay: continuous and irreversible. The process continues until the star’s mass falls below a minimum threshold. For neutron stars, that threshold is about 0.1 solar masses. When this point is reached, the star can no longer support itself against gravity. A catastrophic event occurs—a final burst of particles and neutrinos that signals the star’s end.
The implications are broad. It means there is no such thing as a truly permanent stellar remnant. Everything, from the most massive black holes to the smallest compact objects, is subject to eventual decay. The universe’s end may not be populated by inert, frozen remnants, but by their gradual disappearance. If any objects survived from a prior cosmic cycle, their decay could still be underway. Given the lifetimes involved, most stars formed in our universe will not live long enough to reach these endpoints. But remnants from a universe older than our own could, in theory, be approaching their expiration.
Could such decaying remnants produce observable effects? The radiation is far too weak for current detectors. For example, the effective temperature of a decaying white dwarf is estimated at mere picokelvin. But the end-stage explosion of a neutron star at its critical mass might produce a flash of energy detectable across great distances. It might appear as an unexplained high-energy burst, perhaps not unlike the short gamma ray bursts sometimes attributed to magnetars or unknown merger events.
The work also hints at possible future extensions. If gravitational curvature is enough to drive particle emission, then this process could apply across many contexts, from dense stars to early-universe scenarios. It adds a new layer to long-term astrophysical evolution and challenges the idea that only black holes radiate due to quantum effects.
While speculative detection scenarios are premature, this theory introduces a profound revision to stellar evolution. There is no forever. Not even for the most tightly packed balls of degenerate matter. They will all lose mass. They will all decay. And in the end, they will all vanish.
The decay timescales derived in this research provide an upper limit. They represent the absolute longest such objects could survive, barring other decay channels. For instance, proton decay, if it exists, or pycnonuclear fusion inside white dwarfs, could shorten the lives of such stars. But even in the absence of these effects, gravity alone appears sufficient to destroy them.
A neutron star’s structure is defined by intense forces: degeneracy pressure, nuclear matter, and curved spacetime. Its compactness is close to the theoretical maximum. Yet this very trait makes it vulnerable to decay through the gravitational pair production mechanism. The same field that holds the star together becomes the source of its undoing.
The gravitational field strips energy from the vacuum and bleeds it into reality, one particle at a time. This leak continues across trillions upon trillions of years. The result is an invisible death, driven not by collisions or decay of particles, but by the geometry of the universe itself.
This redefines the lifespan of stellar corpses, removes the absolute stability once assigned to neutron stars, and places them on the same mortal scale as black holes. All compact remnants fall into a single framework. They all face dissolution. The difference is time.
In the farthest future, the universe will not be filled with dark, dense stars. It will be filled with silence.
Source:
Falcke, H., Wondrak, M. F., & van Suijlekom, W. D. (2025). An upper limit to the lifetime of stellar remnants from gravitational pair production. Journal of Cosmology and Astroparticle Physics. https://arxiv.org/abs/2410.14734
A real brain-stretcher. It's good to make yourself think about complex and universe-sized problems.
ps - perhaps irrelevantly I always liked Larry Niven's story collection 'Neutron Star.'-greenman
Re: Fascinating
Posted by Christopher Blackwell on May 12, 2025, 6:21 pm, in reply to "Fascinating"
Greenman, it is.
Later I will post some of the weirder more question able stuff, paranormal, alien abduction and alternate history. Even here, it does more research than these subjects usually get.
I am a sucker for a good story, whether I believe it or not. ChristopherBlackwell
on May 12, 2025, 4:16 pm
