Is the Sun really a giant hydrogen bomb? Where does its energy come from?

When it comes to the sun, everyone is familiar with it. However, do we really know it and understand it? Why does it emit light and heat? Why hasn't it burned out after billions of years? Can Einstein's E = mc² explain all this? Is it really a big hydrogen bomb? Let's talk about it today.

Tuchong Creative

01

The sun is cold

I believe many people know that the sun shines and heats by nuclear fusion. According to calculations, the sun can produce 386 trillion joules of energy per second, which is equivalent to 1.8 billion Tsar hydrogen bombs exploding per second. The quick impression given is that the sun is a giant hydrogen bomb.

So the question is: Which is hotter, the core of the sun or a hydrogen bomb?

The answer is that the hydrogen bomb wins! The core of the sun is only 15 million degrees, far lower than the hundreds of millions of degrees of high temperature of a hydrogen bomb, and not even high enough to ignite a hydrogen bomb (a hydrogen bomb needs the high temperature of an atomic bomb to detonate).

Or, let's calculate from another perspective: the volume of the sun is 141 trillion cubic kilometers, and nuclear fusion occurs almost entirely in the core, which accounts for 8‰ of this volume. So,

386 trillion watts ÷ (141 trillion cubic kilometers × 0.008)

≈34 watts/m3

Doesn't this number remind people of a light bulb, not a hydrogen bomb? Of course, the core of the sun is not uniform, and the core of the core is more efficient, but at most it is only 277 watts per cubic meter.

What is the concept of 277 watts per cubic meter? The basal metabolism of an adult is about 1400 kcal per day, and the power converted to the International System of Units is 1400×1000×4.2 (kcal→cal→joule) ÷ 24 ÷ 3600 (day→second) = 68 watts. The volume of the human body is about 0.06 cubic meters, and 68 watts/0.06 cubic meters is 1134 watts/cubic meter. The maximum production capacity of the sun's core is only one-fourth of this number. That is to say, if a person uses the same volume of the sun's core as energy, even if he lies flat on the spot and does nothing, he will be frozen to death. Four sets of such core materials are just enough to feed one person. In other words, if we only calculate the efficiency of energy generation per unit volume, our efficiency for eating a few meals a day is far higher than that of solar nuclear fusion...

So what went wrong? Is the calculation formula wrong? Is there a problem with the unit conversion? Everyone uses a calculator to calculate and will get the same result. In fact, there is nothing wrong. The sun is just so "cold" (relatively speaking). It is not a giant hydrogen bomb at all, but a giant nuclear reactor with extremely low efficiency. It burns very quietly. Since its birth, it has only lost less than 0.03% of its mass. Its huge energy is due to its size, not its production efficiency. If hydrogen bombs work according to the way the sun works, they will not be terrifying thermonuclear weapons, but the controlled nuclear fusion that humans have always dreamed of - of course, we still hope that its production capacity is slightly higher, otherwise we should just eat rice.

Tuchong Creative

02

How did the temperature of 15 million degrees Celsius come about?

You may be wondering: How does the core of the sun, with such low energy efficiency, heat itself to 15 million degrees Celsius?

In fact, **the high temperature in the core of the sun is the cause of nuclear fusion, not the result. Nuclear fusion occurs only after the high temperature, not because of the high temperature baked out by nuclear fusion. **This high temperature is generated by the laws of thermodynamics. Even if there is no nuclear fusion, if we gather together gases of the same mass and composition as the sun and let this large mass of cold gas shrink under the action of gravity, the compressed gas core will inevitably have a high temperature.

So, what is the role of nuclear fusion? The heat it produces compensates for the radiation dissipation of this mass of gas (to be precise, such a hot state should be called "plasma"), making the particles move more violently, thereby resisting the gravitational force and preventing our original star from continuing to shrink.

This is a very interesting self-regulating equilibrium state: if the star continues to shrink, or the heat generated by fusion is difficult to dissipate, the core will heat up, the fusion efficiency will increase, and more heat will be generated to expand the core. If the core expands too much, the core will become cold, the fusion efficiency will decrease, and gravity will regain the upper hand and compress the core back. It sounds like an oscillating process, but in fact, after reaching an equilibrium point, the temperature and size of each layer of the star will stabilize, just like our sun. The energy of nuclear fusion is neither accumulated nor overdrawn, and 100% is radiated from the surface into space.

If this mass of gas is very stubborn and refuses to ignite nuclear fusion, it will directly enter the star's flameout state and continue to shrink. If the mass is small, it will become a white dwarf, and if the mass is large, it will continue to shrink into a neutron star or even a black hole.

There is a phenomenon in the universe that can demonstrate to us the supporting role of nuclear fusion in the structure of stars. At the end of the life of a particularly large star, the star goes out of flames suddenly due to the exhaustion of nuclear fuel. At this time, the star loses its internal support and collapses like a building in a directional explosion, blooming a big firework in the universe, releasing energy that is equivalent to the total energy released by the sun in its lifetime. This is the phenomenon of supernova explosion.

To sum up, it is not accurate to compare our sun to a hydrogen bomb. It is actually a giant nuclear reactor with low efficiency. It is precisely thanks to the sun's gentleness (relative to the earth) that colorful life can evolve on earth.