You may have heard many times about white dwarf stars. But how about the black dwarfs? They are not the opposite of white dwarfs. They are formed from white dwarfs, theoretically.
It was speculated that the white dwarfs are not the final stage of medium stars’ evolution. Astronomers hypothesized that the white dwarfs will cool down further and become black dwarfs. In this article, we’ll going to learn more about black dwarfs. Let’s get into it.
Black Dwarf Star Evolution
We all know stars die, and their death could take on different routes i.e. supernova, black hole, white dwarf, etc. Those stars that end up or will end up as white dwarfs will eventually undergo the next stage – the black dwarf’s stage.
The black dwarf star’s evolution is purely theoretical. This is what scientists predict about what will happen to the white dwarfs in the future. Those black dwarfs have still not come into existence yet. You won’t find any black dwarfs in space.
This kind of evolution starts with medium to low-mass stars exhausting their nuclear fuel, depleted of hydrogen, expanding, and becoming a red giant. In the next stage, the star would shed its outer layers, leaving behind a hot and dense core. That core is a white dwarf, and it no longer has any nuclear fusion.
Without the nuclear reaction to sustain its luminosity, the hot and dense white dwarf will gradually cool down and become a black dwarf. This cooling process is theorized to take longer than the current age of the universe. This is why no black dwarfs are believed to exist yet.
What Is a Black Dwarf Star Made Of?
The composition of a black dwarf star is largely dictated by its progenitor, the white dwarf. White dwarfs are primarily made of electron-degenerate matter, consisting of carbon and oxygen. In some cases, they also have helium or even iron. The material compositions depend on the mass and evolutionary history of the original star.
As a white dwarf cools and transitions into a black dwarf, its composition remains largely unchanged. However, the lack of thermal energy means that the electron degeneracy pressure is now maintained at an incredibly low temperature.
As it cools, the material within a white dwarf (primarily carbon and oxygen) is expected to crystallize into a diamond. This astronomical-sized diamond would be incredibly stable, allowing the black dwarf to exist in this state for trillions of years. It is also possible for it to exist until the end of the universe.
What Is the Size of a Black Dwarf Star?
The size of a black dwarf star is predicted to be similar to that of its precursor, the white dwarf. Generally, the size of white dwarfs is about the size of Earth. Despite their small size, black dwarfs and white dwarfs, are incredibly dense. A teaspoon of black dwarf material could weigh as much as an elephant. However, the exact size could be varied a bit based on the mass of the original star and the details of its cooling process.
What Is the Temperature of a Black Dwarf Star?
In the early stage, white dwarfs are extremely hot. The temperatures could be reaching up to 100,000 Kelvin. However, as they emit their stored thermal energy over trillions of years, their surface temperature gradually decreases.
In theory, a black dwarf star would have a temperature close to that of the cosmic microwave background radiation. The temperature is about 2.7 Kelvin (-270.45°C or -454.81°F). Due to the very low temperature, the star no longer emits significant heat or light. In the end, it will blend into the cosmic background and become virtually invisible in the blackness of space.
Will Our Sun Become a Black Dwarf?
Maybe you have wondered if our Sun will eventually become a black dwarf. Yes, it will, according to the theoretical prediction. The Sun is a middle-aged star of about 4.6 billion years. It is expected to exhaust its nuclear fuel in about 5 billion more years, and then expand into a red giant.
Eventually, it will shed its outer layers and leave behind a white dwarf core composed primarily of carbon and oxygen. Later in a trillion years, this white dwarf will gradually cool, and transform into a conceptualized black dwarf.
Therefore, the fate of our Sun is indeed to become a black dwarf. However, this transformation will occur far beyond the time scale of human existence and even the current age of the universe itself.
Summary
The concept of a black dwarf star offers a poignant reflection on the inevitable fate of many celestial bodies, including our own Sun. Although the universe is not old enough for any black dwarfs to exist yet, their theoretical presence provides invaluable insights into stellar dynamics and the ultimate destiny of the universe. Here are the main points about a black dwarf star:
- They’re stars that used to be white dwarfs and have cooled down so much that they’ve turned black. This is just a theory though, because the universe isn’t old enough for any black dwarfs to exist yet.
- Even as they cool down to become black dwarfs, they’re still made of the same stuff as white dwarfs – mainly carbon and oxygen. Over time, they might turn into something like a giant diamond.
- Black dwarfs would be about as big as Earth, but way, way heavier. A tiny bit of a black dwarf would weigh as much as an elephant!
- They get really cold, almost as cold as space itself, which is why we can’t see them. They blend in with the background of space.
- One day, billions of years from now, our Sun will also turn into a black dwarf. But that’s going to take so much time that it’s hard to even imagine.
Disclaimer:
While we strive to provide accurate and reliable information, please be aware that the content of this blog post is subject to a margin of error. The probability of absolute accuracy is not guaranteed.
