Why the smaller the star, the longer it lives?

(ORDO NEWS) — Some heavenly bodies live for millions of years, while others live for tens of billions, like the star Methuselah, writes Al Jazeera. To calculate the lifespan of a star, you need to take into account many indicators, including its mass and the rate of energy consumption.

The actual lifespan of stars depends on their mass, as well as how quickly they use up their nuclear fuel. Large stars die faster, while small ones live very long.

How old are the stars? What causes their death? Why do small stars live longer than big ones? Such questions may come to your mind. So what does the science say?

In fact, the lifespan of stars depends on their mass, as well as how quickly they use up their nuclear fuel. The smaller the star, the longer it lives.

In other words, the larger the star, the faster it burns its own supply of nuclear fuel, while smaller stars consume fuel over a longer period. If the largest stars burn up and explode after only a few million years, celestial bodies with a mass equal to the Sun can continue to use hydrogen for about ten billion years.

If a star is very young and less than one-tenth the mass of the Sun, it can continue to fuse hydrogen for hundreds of billions of years. This is longer than our Universe, which is 13.7 billion years old, has existed.

Stellar energy consumption

According to the scientific website Live Science, the size of some stars is 7% of the solar mass, but can be equal to 250 solar masses. At the same time, larger stars have more fuel, and it burns stronger and brighter, which makes the star shine in the sky.

Why the smaller the star the longer it lives 2
Star Methuselah (HD 140283) in the starry sky

The larger the star, the more gravity pulls its matter into the core, so nuclear reactions occur at a higher speed and consume available fuel faster. The age of large stars does not exceed several hundred million years.

Smaller stars, less than 10% of the mass of the Sun, have much less fuel for nuclear reactions, so they can store small amounts of energy for hundreds of billions of years.

According to Ryan French, a physicist at University College London (UCL) in the UK, the universe formed only 13.8 billion years ago, so the young star simply did not have enough time to grow old.

Determining the age of stars is not easy at all: to calculate, astronomers use special measurements of the mass, brightness and speed of a star in space compared to others, and then resort to computer simulations.

According to Scientific American, throughout its life, a star is in a very finely balanced state, the so-called “hydrostatic equilibrium”, when the gravity that pulls the star inward is balanced by the external pull caused by nuclear reactions in the star’s core.

This outward push occurs when hydrogen nuclei fuse to form helium nuclei, producing a burst of energy that maintains the star’s shape and brightness. This nuclear fusion takes place inside the hot and dense core of the star, where the temperature reaches 20 million degrees.

The energy generation rate of a star is very sensitive to both the temperature and the gravitational pressure of its outer layers. Once all of the star’s hydrogen has been melted, nuclear reactions no longer occur. An irreversible path to death begins.

When we look up into the night sky, the stars we see are mostly brighter and more massive than the Sun and therefore die quickly. Most of the stars that exist longer and fainter than the Sun are not bright enough to be seen without the aid of a telescope.

The oldest star in the universe

According to French, one of the oldest stars ever discovered is the star Methuselah, located 190 light-years from planet Earth and named after a biblical character who lived for almost a thousand years.

The current age estimate for this star is 13.7 billion years, which means it formed shortly after the Big Bang.

Astronomers have discovered another type of star. We are talking about protostars that are still in the process of formation and are less than 500,000 years old.

The sun is in the middle, having been around for nearly five billion years and has enough nuclear fuel to last that long.

When do stars die?

The death of a star also depends on its mass. It dies only when the core runs out of energy.

The most massive stars quickly deplete their fuel reserves and explode in supernovae. Some of the most powerful explosions in the universe occur, and supernova radiation can easily exceed that of the rest of the host galaxy, even if only for a short time.

The remaining stellar core forms a neutron star or a black hole, depending on how much mass there was before the explosion.

As for intermediate stars like the Sun, they face a less bizarre fate: when they run out of hydrogen, they grow in size, turning into red giants, after which their outer layers fall off and leave a naked core – a white dwarf.

It is assumed that the white dwarf eventually turns into a black one. However, the formation of black dwarfs has not yet been observed, since the disappearance of a White dwarf takes more time than our Universe exists.

As for the small stars, which have a very long life, not one of them has yet died. Stars with a mass less than one tenth that of the Sun burn so slowly that they can live up to 100 billion years, which is much longer than the universe exists.

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