What is a Black Dwarf: Definition, Facts & Characteristics

In theory, a black star is a stellar remnant that indicates a white dwarf star is ending its life. If you want to learn what is a black dwarf is, read this article for a detailed explanation of this theoretical concept. Black dwarf stars are theoretical remnants of other stars, more specifically, the last life cycle of white dwarfs.

The latter are low to medium stars that no longer have any nuclear fuel and leave a hot, dense cover behind after shedding their outer layers. With time, white dwarfs cool down and eventually fade away to become black dwarfs. In other words, black dwarfs are just dead stars that no longer emit any heat or light. Their density is high, and they have the same mass as the original star but compressed into a smaller volume. Since they lack nuclear fusion, black stars are dark and cold, and thus, they don’t generate any energy.

How long does a black dwarf last?

According to some estimations, a 1.24 solar masses black dwarf may collapse and turn into a supernova after 10¹⁶⁰⁰ years, but this is only a theoretical calculation. The black dwarf size determines the time of its disintegration. Before it becomes a black dwarf, this type of star is first a protostar, then a main sequence star, a red giant, a planetary nebula, and a white dwarf. When the life of a black dwarf ends, this one-time star experiences decay and eventually evaporates into a hydrogen form. In 2012, scientists discovered two white dwarfs that are a bit over 11 billion years old, so they could, one day, become black dwarfs.

What are black dwarfs made of?

A hypothetical astronomical object, a dead star is fused with all its original helium and hydrogen fuel into carbon, nitrogen, and oxygen. As a result, radiation causes this star to lose its remaining energy. The black dwarf temperature is under 600K on the surface and even 5 degrees kelvin sometimes. These objects don’t emit any visible light, but they do emit faint infrared radiation. It can’t support heat or light like an orbiting planet. Since they have a high mass and are small, they also have a very high density, more than one million times the Sun’s density. As a reminder, the very black dwarf meaning is a stellar remnant –  a white dwarf that cooled enough and no longer emits any significant light or heat.

What happens after a black dwarf?

Our knowledge of physics doesn’t indicate what happens with black dwarves because none of them have appeared yet. But humanity didn’t cancel the hypotheses, so it seems these theoretical stars may emit particles, gradually losing energy and mass because of the Hawking radiation. But this process may take trillions to quadrillions of years.

Calculations are saying that far in the future, the Universe will have sextillions of black dwarfs that will eventually explode like supernovae. Representing the last things that the Universe can do, this won’t happen for a very long time. By analyzing their possible cooling rates, astronomers can estimate how old some stars are and understand more about cosmic evolution.

What are the properties of a black dwarf?

To better understand this whole concept, let’s examine some (theoretical) black dwarf properties. When a star exhausts its nuclear fuel, it becomes a red giant before it sheds its outer layers and leaves behind a white dwarf core. In the beginning, white dwarfs are very luminous and hot, but after a few billion years, they eventually cool down and turn into black dwarfs.

They are also incredibly dense and have almost the same mass as the Sun yet compressed into a smaller volume. Their density gives them a gravitational pull stronger than the Sun’s. Since they lack nuclear fusion, black dwarfs don’t emit any heat or light. They are cold and dark in space. They don’t produce energy either, but they can still exert gravitational influence on objects nearby, contributing to their surrounding stellar systems’ dynamics.

Giving a specific black dwarf example is not possible because no such star has been observed yet. In fact, scientists believe that our Universe is too young to support black dwarf existence, but they may form – one day, in trillions of years.

Can black dwarfs outlast the other stars in the Universe?

As soon as they form, black dwarfs are expected to have incredibly long lifespans but whether they will surpass that of other stars is the question of each star formation time. Black dwarfs are also stars, after all – and all stars will eventually run out of fuel and go through different stellar evolution phases.

Since black dwarfs have completely cooled down and no internal nuclear reactions take place, they don’t emit any electromagnetic radiation such as infrared, radio waves, or any visible light. More importantly, these objects take such a long time to form that we, as a race, will unlikely ever discover one – according to scientists’ theoretical calculations.