Why the universe is running out of new stars (and what that means for its existence)

Stars are essentially giant balls of hot gas that began life in the same way.

They form huge clouds of cosmic dust called nebulae. Gravity brings the gases together, which eventually heats up and becomes a baby star, or as it is called, a protostar.

As the star’s heart heats up to millions of degrees Celsius, the hydrogen atoms within it begin to melt into helium through a process called nuclear fusion. This reaction emits light and heat and the star is now in a stable “main sequence phase”.

Astronomers estimate that main sequence stars, including our own sun, make up about 90% of all stars in the universe. The range varies between a tenth and 200 times the mass of our Sun.

Ultimately, these stars use up their fuel and can take different paths on their way to death.

Stars with small masses like our Sun enter a fading process that can take billions of years.

For larger “sister” stars, those at least eight times the size of the Sun, their end is more dramatic: They are destroyed in a massive explosion called a supernova.

In 2013, an international team of astronomers dedicated to studying trends in star formation found that 95% of all stars born in the history of the universe had already done so.

“We live in a universe dominated by old stars,” study author David Sobral said at the time in an article published in the journal Subaru Telescope.

On the universe’s timeline, it appears that peak star production occurred about 10 billion years ago, during a period known as “cosmic noon.”

“Galaxies are converting gas into stars at a decreasing rate,” explains Professor Douglas Scott, a cosmologist at the University of British Columbia in Canada.

Scott is co-author of a yet-to-be-published report analyzing data from the European Space Agency’s Euclid and Herschel telescopes.

He and his team of space researchers were able to study nearly 2.6 million galaxies simultaneously, which was possible thanks to the 3D map of the universe created by the Euclid mission.

Astronomers were particularly interested in the heat that stars give off. Galaxies with higher star formation rates tend to contain hotter cosmic dust because they contain larger, hotter stars.

The team found that temperatures in galaxies have been falling over the past billion years.

“We are past the peak of star formation and there will be fewer and fewer new star formations in the universe,” Scott adds.

Although the death of old stars can lead to the formation of new stars from the same material, it is not that simple.

Let’s say we have a pile of building materials and build a house out of them. If we want to build a new one, we can recycle things from an old house, but not everything will be useful.

“That means we can only build a smaller house. Every time we demolish, there are fewer useful materials until nothing can be built,” Scott says.

This is what happens to stars.

“Each generation of stars must use less fuel, and at some point there will no longer be enough fuel to create a star,” he adds.

And he concludes: “We already know that less massive stars are more common in the universe than massive stars.”

Scientists have long theorized that the universe will one day end. You just can’t be sure how or when.

One of the most widely accepted theories currently is thermal death.

Also known as the Big Freeze, it predicts that as the universe continues to expand, energy will spread until it eventually becomes too cold to support life. Stars get further and further away, they run out of fuel and no new ones are formed.

“The amount of energy available in the universe is finite,” Scott explains.

But before you look wistfully at the sky, the disappearance of the stars would take an astronomically long time.

Scott estimates that new stars will continue to emerge over the next 10 to 100 billion years, long after our sun is likely gone.

As for the Big Freeze, it could last even longer: earlier this year, astronomers at Radboud University in the Netherlands estimated that the end would come in about a trillion years, or a one followed by 78 zeros.

So there is enough time to admire the stars on the next clear night.

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