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Can a star turn into a planet?

Can Stars Become Planets?

Have you ever been gazing at the stars on a clear night, you wondered if stars could be planets? Before we answer this question, let's first find out the difference between stars and planets!

How do stars die and what happens after their death? Let's take our Sun as an example. The sun belongs to a category of stars known as the main sequence. Stars of this category generate their energy through the nuclear fusion process of hydrogen in their cores to form helium. This energy is released in the form of heat and light.

The energy generated from the nuclear fusion process also allows stars to maintain the pressure of gravity trying to pull them in, so these stars don't collapse. In general, stars will be in the main sequence category for about ten billion years.

For us, ten billion years may be a very long time. But on a cosmic scale, that is a short time. Main sequence stars have a limited amount of hydrogen in their cores. Once all the hydrogen is used up, the nuclear fusion process at the core of the main sequence can stop.

Can a star turn into a planet?


The loss of nuclear fusion makes the pressure that maintains gravity disappears. Gravity prevails and the star's core begins to collapse inward, causing the temperature to rise even hotter.

As the core gets hotter, the main sequence star expands and the outer layer cools (lower temperature), causing it to emit a reddish glow. The main sequence star, at this stage, has already evolved into a red giant.

The red giant stage will last for about 1 billion years. During this phase, the star will try to generate more energy to stay alive through complex nuclear reactions that will deplete the helium it contains.

This helium fusion reaction can only support the star temporarily. Gradually, the red giant star will become unstable, so it will begin to lose more and more of its outer layer.

Low-mass stars like our Sun will go through this process until all of their outer layers are detached and leaving their core behind. At this stage, the star's core will be referred to as a white dwarf, and will slowly cool and dim.

Can Stars Become Planets?

However, it is different for massive stars. Stars with masses more than 1.4 times the mass of our Sun, when they run out of all their fuel and leave iron, their cores collapse inward and then explode in giant explosions, called supernova explosions.

A supernova releases so much energy that it can shine brighter than all the stars in the galaxy for several weeks. Such a massive explosion would leave the star's core as a neutron star or black hole.

How Are Planets Formed?

When a star forms, there is often a disk of gas, dust, and debris left over from that star formation surrounding it, much like the rings around Saturn.

The dust particles in this disk are the building blocks of rocky planets. The particles in this disk can collide with each other, sticking together due to the gravitational pull. If the collision wasn't too chaotic, these particles stuck together, continuing until they formed a large object known as a planetesimal.

These planetesimals can still collide and merge until eventually, they become the forerunners of planets known as proto-planets, which over time will become fully-fledged planets.

Oh yes, if the distance between the planetesimal and its parent star is far enough, the core of the planetesimal can be as cold as ice, which over time will develop into a gas planet.

Now, back to the question, can star turn into planets directly? The answer to that question is… yes! Stars can turn into planets, but this only applies to a certain category of stars, known as brown dwarfs.

What is a Brown Dwarf?

Brown dwarfs are often referred to as failed stars. They are cosmic objects that are too small to be stars, but too big to be planets. Interestingly, they also feature a mixture of stars and planets.

Brown dwarfs themselves range in size from 2 times to 90 times the mass of Jupiter. Like ordinary stars, brown dwarfs are commonly found to have planets orbiting them. Unfortunately, they don't have enough gravitational force to support the nuclear fusion of hydrogen in their cores, so they are dim because they don't glow.

Although the brown dwarf cannot support hydrogen fusion, it can still carry out the nuclear fusion of heavy hydrogen (deuterium). So, early in their life, brown dwarfs get energy from this deuterium fusion reaction, which also makes them give off heat and light, like ordinary stars.

However, the amount of deuterium available is limited. As a result, brown dwarfs will use up deuterium fuel very quickly. Once they are all used up, all fusion reactions stop, and the brown dwarf will stop emitting heat and light. The brown dwarf will also dim and cool and begin to resemble a gas giant planet like Jupiter.

To date, approximately 3,000 brown dwarfs have been discovered. Indeed, this number is very little because finding brown dwarfs is also quite difficult for astronomers.


For most of their life, brown dwarfs have cool, dark temperatures, which makes them difficult to spot with conventional telescopes. It is thought that the number of brown dwarfs in the universe may be equivalent to the number of ordinary stars. 

It is even possible that brown dwarfs can make a small but substantial contribution to dark matter's mysterious identity.

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