Black holes have always been interesting to us humans, especially the scientists. But it also attracted the attention of those who are not interested in science. Interstellar movie is one of those things that made people even more curious. We picture black holes as eternal, cosmic vacuum cleaners that sucks everything in. Scientists also thought that once a star forms and dies and creates a black hole, it was permanent. But do black holes evaporate? Do they really live forever, or do black holes die? The universe rarely follows such simple rules.
Check this article out, too: Could Black Holes Lead to Parallel Universes?
How can something with so much gravity evaporate, though? Stephen Hawking discovered something in 1947 – we now call it Hawking Radiation. It changed all our understanding of the lifespan of black holes. We now know that black holes die; they evaporate very slowly. I want to give a brief look into this, how do black holes evaporate, what changed after Hawking’s discovery, and some fun facts.
The Classical View: Why We Thought They Were Forever
Let’s first start from the beginning. When we discovered that black holes evaporate and die, it was revolutionary, but why? It’s because of how we looked at them before, our understanding was much different (and limited). According to Albert Einstein’s General Theory of Relativity, a black hole is defined by its event horizon, the point of no return. It’s the edge of a waterfall where the current becomes faster than you can swim. Once you cross that line, all paths lead downward, and you become spaghetti.
In classical physics, nothing can move faster than the speed of light. Since the gravitational pull inside the event horizon is strong enough to trap light, absolutely nothing should be able to get out. This logic created a “one-way membrane.” Matter and energy could fall in, adding to the black hole’s mass, but nothing could ever come out. Therefore, a black hole could only do one thing: grow. It could get bigger by eating gas, dust, stars, or merging with other black holes, but it could never get smaller. Under these rules, a black hole was permanent. Never dies. But in the 1970s, physicists began mixing the rules of the subatomic world (quantum mechanics) into the rules of the massive world (general relativity), and the picture changed completely.
Stephen Hawking’s Discovery: How Do Black Holes Evaporate?
In 1974, Stephen Hawking made that legendary discovery. He was trying to study the properties of matter near the event horizon, and he realized (discovered) that black holes emit radiation. This contradicted the “black holes are black” rule. This was the first step, and this was what created the “Hawking radiation” that we still use today. It suggests that black holes aren’t completely black. They glow faintly with thermal radiation, and they have a temperature. Do you know what this means? This means that Radiation is escaping a black hole’s gravity. A place where we thought nothing could escape. Now, the second step was to understand how radiation can escape where not even light can? The answer doesn’t come from inside the black hole, but from the empty space right at the edge.
The Quantum Vacuum: It’s Not Empty
The most important thing to understand about Hawking Radiation is that “empty space” is not truly empty. According to the Heisenberg Uncertainty Principle, energy levels in space can fluctuate. “Virtual particles” constantly pop into existence and then annihilate each other. They appear in pairs: a particle and its antiparticle (like an electron and a positron). Usually, they exist for a fraction of a nanosecond, collide, and vanish, returning their energy to the vacuum. That’s what happens in “empty space.” It’s a constant brew of activity. It’s like taking out a bank loan and repaying it instantly. The net result is zero. This happens everywhere in the universe, all the time, usually without consequence. But when it happens right on the edge of a black hole, there are consequences.
Separation at the Event Horizon
Imagine a pair of these particles popping into existence at the event horizon. In normal space, they would attract each other and annihilate. But here, gravity stops that. If one particle of the pair forms just inside the horizon (or gets sucked in immediately) while the other forms just outside, they get separated. The one outside no longer has a partner to annihilate with. It becomes a real particle and escapes into the universe. To an observer far away, it looks like the black hole has just spit out a particle.
The tricky thing is that logic dictates that energy cannot be created from nothing. The particle that escaped has positive energy (mass). Nature demands that the energy books be balanced. Therefore, the particle that fell in must be treated as having “negative energy” relative to the outside universe. When this negative energy particle hits the black hole’s singularity, it subtracts mass from the black hole. The particle that moves away from the black hole is what Hawking saw and labelled as “Hawking radiation.”
So, for every photon or particle that radiates away as Hawking Radiation, the black hole loses a tiny bit of its mass. It is paying the “bill” for the created particle. Over time, this slow leak causes the black hole to shrink. The bigger the mass, the longer the time it takes to evaporate.
The Physics of Evaporation: Temperature and Time
Now, you know that black holes do evaporate. They leak mass, so they shrink over time. As you also learned just now, we are talking about an extremely small mass leakage every time it happens. Considering that black holes are massive (some are bigger than our universe), it takes time. But have any vanished, or considering the universe is old, why didn’t most of them vanish? The answer is in the thermodynamics of black holes.
In our everyday world, hot things tend to be big and full of energy. But black holes behave in the exact opposite way: The more massive a black hole is, the colder it is, and the slower it evaporates. Conversely, the smaller a black hole gets, the hotter it becomes, and the faster it radiates energy.
Why Size Matters
The temperature of a black hole is inversely proportional to its mass. A supermassive black hole, like Sagittarius A* at the center of our galaxy (which is 4 million times the mass of the Sun), has a Hawking temperature that is almost absolute zero. It is incredibly cold.
This is important because of the Cosmic Microwave Background (CMB). The “empty” space of the universe has a temperature of about 2.7 Kelvin (leftover heat from the Big Bang). Because large black holes are colder than space itself, heat flows into them from the universe. Right now, almost every black hole we know of is absorbing more energy from the cosmic background than it is emitting in Hawking Radiation.
So, do black holes evaporate currently? Technically, the process exists, but for stellar-mass and supermassive black holes, they are growing faster than they are shrinking. They won’t truly start losing net mass until the universe expands and cools down enough (billions of years from now) that the background temperature drops below the black hole’s temperature.
The Unimaginable Timeline
The timeframe for a black hole to evaporate completely is mind-blowing. It is not a process measured in human lifetimes or even the age of stars. For a black hole with the mass of our Sun to evaporate completely, it would take approximately 10^{67} years. That is a 1 followed by 67 zeros. To put that in perspective, the current age of the universe is only about 1.38 \times 10^{10} years. For the largest supermassive black holes, the time scale is closer to 10^{100} years. This means that while black holes do evaporate, probably there will be nothing to see that. Long after the last star has burned out and galaxies have drifted apart, black holes will still be sitting there, slowly leaking Radiation.
The Life Cycle of a Black Hole
Just like a living organism, a black hole has a life cycle, birth, a long stable middle age, and death. However, the “death” of a black hole is not a quiet event, it’s violent (from our expectations, it didn’t really happen in real life, yet).
Primordial Black Holes: Have Any Evaporated Yet?
If big black holes take a long time to evaporate and die, are there any in the process of evaporating? This brings us to Primordial Black Holes. These are hypothetical black holes created not by collapsing stars, but by density fluctuations in the split-second moments after the Big Bang.
Some of these primordial black holes could have formed with very small masses when the universe was created. We are talking about masses roughly equivalent to a mountain or an asteroid. Remember the rule: smaller black holes evaporate faster. If a primordial black hole formed with a specific initial mass, the math suggests it would be reaching the end of its life right now. As I said above, we don’t have proof that it happened or is happening. Currently, we are searching for flashes of gamma rays that may indicate the process. It’s probably the only option we have to have real-life proof.
The Final Moments
The evaporation process is a runaway feedback loop. As a black hole loses mass, it gets smaller. When it gets smaller, it gets hotter. As it gets hotter, it radiates energy faster, which makes it lose mass even quicker. For billions of years, a black hole might lose mass at a snail’s pace. But in the last few seconds of its life, it goes critical. When the black hole shrinks to the size of an atom, it releases its remaining energy in a fraction of a second. This final explosion would be equivalent to the detonation of millions of nuclear hydrogen bombs at once. It would release a burst of high-energy gamma rays and particles. This is the violence I mentioned.
Black Hole Information Paradox
The discovery that black holes evaporate solved one problem, entropy. Before Hawking’s breakthrough, they seemed to break fundamental physics rules by swallowing entropy forever, but now we know they are not gone. It gives it back, balancing the entropy. The radiation emission gives them their own temperature and entropy. However, this created a massive new problem. We call it the Black Hole Information Paradox. This is arguably the biggest unsolved problem in theoretical physics today.
The issue comes down to a conflict between the pillars of physics. Quantum mechanics states that “information” (the quantum state of particles) is never destroyed. If you burn a book, the information isn’t technically lost; if you could gather every molecule of ash and photon of light, you could theoretically reconstruct the book. However, if a black hole evaporates completely, what happens to the stuff that fell inside? This also messes with the entropy of the universe. If stuff gets destroyed, we are talking about negentropy, the opposite of entropy (I’m SO lucky I wrote an article about this because it’s a fun topic and very complicated). It should increase the order in the universe, but negentropy is not a concept with proof. Can the universe of the entropy increase where we see high entropy vs low entropy areas? Or overall’s universe’s entropy decreasing? Does that make this ‘real’?
So, where is it? Lost or hidden?
According to Hawking’s original calculations, the Radiation that comes out is random heat. It carries no “memory” of what the black hole ate. If you throw an encyclopedia into a black hole, and the black hole eventually disappears, leaving only random Radiation, the information in that encyclopedia seems to be erased from the universe forever.
This violates the rules of quantum mechanics. Does the information get destroyed (proving quantum mechanics wrong)? Is it hidden in the Radiation in a way we don’t understand (like our understanding of physics is not there yet)? Or is it left behind in a microscopic “remnant”? Recent research suggests the universe might be like a hologram, where the information is stored on the 2D surface of the event horizon rather than inside the 3D volume, allowing it to “leak” back out as the black hole dies. This is a very early theory, nothing concrete behind it yet. It’s just fun to mention it.
Conclusion
So, do black holes evaporate? Yes, technically. They are not the forever beings we once imagined. Black holes are dynamic, radiating objects that interact with the quantum vacuum of space. They do live long, though. We are talking about longer than any other thing that has existed, exists, or will exist. They will be the last things to die.
It’s important to mention, though, that all these are theoretical. This is one of the many other astronomy topics that fall under theoretical astronomy (or physics). We are trying hard to find the real-life proof, like looking for the gamma ray signals of primordial black holes, but we’ll see if we’re lucky enough in our lifetime.
FAQ
What is Hawking Radiation?
Hawking Radiation is a theoretical process proposed by physicist Stephen Hawking. It suggests that black holes are not completely black but can emit a faint glow of particles due to quantum effects near their event horizon. This process causes them to slowly lose mass over immense timescales.
How long does it take for a black hole to evaporate?
The timescale is astronomically long. A black hole with the mass of our Sun would take far longer than the current age of the universe to evaporate. The process’s speed gets faster as the object loses mass, but for most of these things, their lifespan is effectively eternal from our perspective.
What happens at the end of a black hole’s life?
Theoretical physics suggests that as a black hole evaporates, it shrinks and gets hotter. In the final moments, we anticipate a tremendous release of energy, a very violent end, an explosion. The exact nature of this endpoint is a major open question because we don’t have any proof.
Do all black holes evaporate?
According to the theory, yes, all black holes are subject to this process. However, for the supermassive black holes at the centers of galaxies, the rate of evaporation is so slow that they will likely exist for timescales that are almost incomprehensible.