Neutron Stars vs. Black Holes: Which is Stranger?

Degenerate Systems, Degenerate Matter, and the Gravitational Collapse of Massive Objects in Universe

When stars a lot bigger than our sun are done with their nuclear lives, they don’t just fade out, quietly whimpering like small stars, they explode under the influence of their own gravity. Both are spawned by the same cataclysmic supernova explosions, but what happens next couldn’t be more different. The other leads to a spinning, city-size core of exotic material; the other, an invisible gravitation abyss that nothing, not even light, can escape. But which is really the stranger of the two?

Neutron Stars: The Stronghold of Quantum Forces

Neutron stars are the remnants of medium-heavy weight stars for which the core collapses to form a degenerately neutron-rich ball. They are only 10–15 km wide, but can be twice as massive as the Sun. Gravitational pressure becomes so great that the electrons and protons are smashed together so hard that they combine to form neutrons, creating an ultra-dense core. This is stopped by neutron degeneracy pressure, which is the quantum mechanical degeneracy pressure which prevents further collapse—temporarily at least.

Aside from their form, neutron stars are pretty wild. Many of the pulsars spin at extraordinary rates — hundreds of times a second — spitting out regular pulses of radiation. Some theorists suggest that still further inside, the neutrons may melt into free quarks — or even something even stranger, like an exotic particle that we can’t replicate in any laboratory on Earth.

Black Holes: The Other Side of Infinity

Beyond 3 solar masses, even neutron degeneracy pressure is unable to resist the gravity associated with the core-collapse of a massive star. The result: a black hole. All matter is condensed, or crushed, to a point of infinite density at the center. The event horizon is encircled, a one-way point of no return, beyond which nothing comes out

Black holes are not equipped with surfaces, produce no light and can’t be observed directly. But they rule their surroundings, warping the light of background stars and gobbling up surrounding material in bruising accretion disks. They range in size from ones that are a few times the mass of the Sun to supermassive holes that tether entire galaxies. The most baffling aspect? At bottom, our laws of physics — quantum mechanics and general relativity — come into conflict, leaving us with more questions than answers.

Degenerate Matter: The Quantum Line in the Sand

The actual line between neutron stars and black holes is really the idea of degenerate matter. In the case of white dwarfs, it’s electrons that oppose collapse. In neutron stars, it’s neutrons. But beyond a certain point, no force we are familiar with can halt gravity. This is the point of no return during gravitational collapse, which will result in a black hole.

 Remarkably, this principle is also what supports neutron stars. But even this rule is defeated by a sufficiently hefty star — where gravity wins out over the universe’s most recalcitrant quantum rule.

Taking the Measure of the Titans: Size, Mass and Mystery

Black holes are all escape, with no surface and no direct visibility — but their gravitational pull and tumultuous accretion disks announce their existence. Owing to their size, small black holes are in some cases the size of neutron stars, supermassive ones millions up to billions of times the sun.

Neutron stars are weird because of what we can study: exotic states of matter, extreme magnetic fields, superfast spin. Black holes are stranger that way, for what we can’t — that is beyond an event horizon, the true nature of singularities, the final fate of information.

Which Is Stranger? A Matter of Perspective

So, which is it, stranger: neutron stars, or black holes? One task is to build as many of them as possible and study their properties, as their behavior stretches the limits of our knowledge of quantum mechanics, nuclear physics and magnetism. But black holes, enigmas that they are, point to a deep mystery at the heart of how spacetime and information are connected.

Neutron stars take the cake for complexity and weirdness that you can actually observe. Black holes, though, are more cryptic — burrowing deep underground and hiding their secrets in the dark, possibly for eternity. In the grand theater of cosmic oddities, neutron stars are the most illusion-beclouded objects that we can see, while black holes are the most perplexing since we can’t see them at all.