Stars shining today will look different in the distant future
Looking into the universe’s future suggests a broad pattern: stars shine for long periods, galaxies change, and stellar remnants gradually become more common. Stars that live far longer will remain after stars like the Sun end their lives. As the gas available for making new stars dwindles, stellar birth is expected to become increasingly rare.
Astronomers observe stars of different ages and masses, galaxies where stars are forming actively, and galaxies rich in old stars. Comparing their properties with calculations based on physical laws helps reveal how these objects change over time. Extending those calculations far beyond the present allows astronomers to estimate their future.
The Sun will swell and leave a small remnant
Today, the Sun shines through nuclear fusion in its core, where hydrogen nuclei combine to form helium nuclei. As the hydrogen available to sustain this process in the core dwindles, the star’s internal structure also changes. Stellar evolution models predict that the Sun will continue fusing hydrogen in its core for about another 5 billion years, then head toward the red giant stage, when its outer layers expand enormously.
The enlarged Sun will greatly alter the environments of nearby planets. The heat they receive will depend on how much stronger the Sun’s light becomes and how far its outer layers expand. When Earth becomes difficult for life to inhabit and whether Earth eventually falls inside the Sun are separate questions.
The Sun is then expected to shed its outer material into space, leaving a small, hot core. This is a white dwarf. The remnant will also shine for a long time as it releases its remaining heat. About 5 billion years refers to the time from now during which the Sun is expected to sustain core hydrogen fusion, not the date it becomes a white dwarf or loses all its light.
Small, faint stars can shine much longer than the Sun
Other stars can keep shining after the Sun becomes a white dwarf. A star’s lifetime depends not only on how much hydrogen it has but also on how quickly it uses that hydrogen. Red dwarfs, which have less mass than the Sun, release energy at a low rate, so they can shine longer even with less fuel.
In stars of particularly low mass, heated material rises and cooled material sinks, mixing much of the interior. This motion is called convection. It brings hydrogen from farther out into the core, allowing the star to make use of more of its hydrogen. Some models of low-mass stars predict lifetimes of trillions of years.
One trillion years is ten thousand times one hundred million years. That is far longer than the universe’s current age of about 13.8 billion years. This is why it has not yet been possible to observe such a long-lived star pass through its entire life, from birth to the end.
After hydrogen inside a very low-mass red dwarf has turned into helium over a long period, the star may follow a path in which its surface becomes hotter. This is called the theoretical blue dwarf stage. It is a future state that has not yet been observed, and not every red dwarf can be assumed to follow the same path.
Galaxies have less gas available for making new stars
The Hubble and ALMA telescopes have found evidence of a shortage of cold gas in distant galaxies that form very few new stars. These observations are not photographs of future galaxies, but they provide clues to the material and conditions needed for stellar birth.
Stellar birth requires conditions that allow cold gas to gather in one place. Some gas enters stars and stays there for a long time, with some material remaining in remnants after the stars’ lives end. Light and outflows from stars can also heat some gas or push it out of a galaxy, making it harder for that gas to gather again.
Stars return some of their material to space during their lives. If it cools and gathers again, it can become material for new stars. But not all of the original gas returns each time. Long-term models in which the universe keeps expanding for sufficiently long predict that stellar birth becomes rarer, while long-lived stars and remnants make up a growing share of the population.
Not every galaxy changes in the same way. As galaxies pass close to each other or merge, their gas can be compressed, temporarily increasing the formation of new stars. There is therefore no timetable on which stellar birth stops in every galaxy on the same day.
When the Milky Way and Andromeda might merge is also unsettled. The results depend on measurements of their motions and how the gravity of neighboring galaxies is included. A 2025 study and a 2026 follow-up give different merger probabilities. This is why the event is not marked as certain to happen on a particular future date.
The white dwarfs left behind cool for a very long time
Not every object disappears after stellar death. Remnants such as white dwarfs, neutron stars, and black holes can remain. A white dwarf gradually grows dimmer as it releases stored heat, after its time as a star powered by fusion in the core has ended.
Extending this cooling into the very distant future suggests a white dwarf that gives off almost no light. This theoretical state is called a black dwarf. The universe is not thought to be old enough for white dwarfs to have cooled that much, and no black dwarfs have been found.
Giving off almost no light does not mean reaching exactly absolute zero. Changes inside the material and energy received from the surroundings also affect cooling. This makes it difficult to assign one exact number to the time needed to become a black dwarf.
Unknown conditions matter more in the more distant future
Predictions that the Sun will become a giant and leave a remnant are checked against observations of many stars and stellar evolution theory. To study stars trillions of years from now, or remnants that have cooled for even longer, scientists must examine how physics tested today would work over far greater spans of time. Both kinds of prediction rely on calculations, but the extent to which they can be compared directly with observations differs.
How the expansion of the universe changes in the future is another important condition. The nature of dark energy, introduced to explain the accelerating expansion, remains unknown. Questions such as whether the particles that make up matter remain stable forever can also affect calculations about remnants in the very distant future.
The scenes in this article are therefore neither photographs of a certain future nor a timeline with equal intervals. They are explanatory models that start with objects observed today and show the changes expected and the conditions that need further examination. Beyond the changes in stars and galaxies, the final state of the universe as a whole remains a separate question.
Sources
- NASA Science — The Sun’s remaining main-sequence lifetime and types of stars
- Laughlin and colleagues — A model of the evolution of a very low-mass star
- NASA Science — Galaxy interactions and star formation
- NASA Hubble — Observations of galaxies short of cold gas
- ESA Gaia — White dwarf cooling and internal changes
- Adams and Laughlin — Long-term evolution of astronomical objects and model assumptions
- Sawala and colleagues — Uncertainty in a Milky Way–Andromeda merger
- Wu and colleagues — A 2026 follow-up on galaxy merger predictions
- NASA Science — Dark energy and unresolved conditions for future expansion