When Will The Universe Get Its First ‘Black Dwarf’ Star?

The Big Bang transpired around 13.8 billion years ago, and it likely took about 50 to 100 million years for the initial stars to emerge. Since that moment, the universe has been awash in starlight. When sufficient matter—primarily hydrogen and helium—comes together, nuclear fusion ignites in the core, marking the birth of a star.

Over time, however, stars exhaust their nuclear fuel. Some massive stars may engage in additional fusion processes, but eventually, all fusion must cease. Even after a star's demise, its remnants can continue to emit light. Notably, aside from black holes, every remnant that has formed continues to shine. This leads us to the question: how long until the universe witnesses its first dark star?

The journey starts with clouds of gas. When a molecular gas cloud collapses under its own gravity, certain regions become slightly denser than their surroundings. These denser areas effectively draw in more matter, accelerating the gravitational collapse. Though this process may span millions of years, the transition from dense gas to a cluster of new stars occurs in a mere few hundred thousand years.

Stars come in a myriad of colors, sizes, and brightness levels, with their life cycles and ultimate fates determined at birth. The most visually striking stars are the massive, bright ones, boasting up to hundreds of times the mass of our Sun, and shining millions of times more brightly.

However, these dazzling stars are exceedingly rare, constituting less than 1% of all known stars and consuming their nuclear fuel in just 1 to 2 million years.

Upon exhausting their fuel, these massive stars undergo a spectacular type II supernova. During this event, the inner core collapses into a neutron star or a black hole, while the outer layers are expelled into space. This enriched material then plays a crucial role in the formation of future stars, contributing essential elements for rocky planets and possibly life. The molecular gas cloud from which our Sun and Solar System formed is believed to have been influenced by at least six previous generations of stars.

Black holes transition to darkness almost instantaneously, forming an event horizon where all light is trapped. Once the core collapses enough to create this boundary, any residual energy becomes part of the singularity's mass. The only light emitted will be through Hawking radiation during its decay, alongside energy from the surrounding accretion disk.

Conversely, neutron stars tell a different tale. Formed from the remnants of a supernova, a neutron star experiences rapid compression, causing an immense rise in temperature. Within mere moments, a core that could span hundreds of thousands of miles collapses to roughly 10 miles in diameter, resulting in extreme density and temperature.

Neutron stars radiate an enormous amount of energy, primarily in X-ray form, due to their incredibly hot surfaces. The question remains: how long will it take for a neutron star to cool?

The cooling duration hinges on neutrino physics, which is still not fully understood. Neutron stars might cool out of the visible spectrum in as little as 10¹? years, or possibly take longer, up to 10²?-to-10²² years, indicating a lengthy wait.

In contrast, most stars—over 99%—do not explode as supernovae. Instead, they shrink into white dwarfs at the end of their lives. Although this process spans tens to hundreds of thousands of years, it's rapid relative to supernova timelines.

White dwarfs contain heat within a volume significantly larger than neutron stars, allowing them to cool more efficiently. These stars can achieve temperatures exceeding 20,000 K but will cool at a rate of roughly 10¹?-to-10¹? years, ultimately reaching just above absolute zero.

After approximately 10 trillion years—a thousand times the current age of the universe—a white dwarf may cool enough to become invisible, marking the emergence of a black dwarf star.

However, no black dwarfs exist today; the universe is far too young. Current estimates suggest the oldest white dwarfs have only lost about 0.2% of their heat since their formation, indicating that they remain incredibly hot.

As we envision a universe filled with stars clustered in galaxies, by the time the first black dwarf forms, galaxies will have merged into a single entity, and only the faintest, dimmest stars will remain. In this distant future, darkness will prevail, as dark energy will have pushed galaxies beyond reach.

Ultimately, a new cosmic entity will arise, even if we will never observe it ourselves. Understanding their existence and formation process illustrates one of science's most profound capabilities: predicting the far-off future yet to unfold.

Starts With A Bang is now on Forbes and republished on Medium thanks to our Patreon supporters. Ethan has authored two books, Beyond The Galaxy, and Treknology: The Science of Star Trek from Tricorders to Warp Drive.