Is the Universe running out of new stars?

Astronomers estimate that main sequence stars, including our Sun, make up about 90% of all stars in the Universe. Their size varies from a tenth to 200 times the mass of the Sun.

Eventually, these stars run out of fuel and may take different paths on their journey to death.

Lower mass stars, like our Sun, undergo a process of decline over billions of years.

For the larger “sisters”, which are at least eight times the mass of the Sun, the end is more dramatic: they explode in a huge explosion called a supernova.

In 2013, an international team of astronomers studying star formation trends said that 95% of all stars that will ever exist have already been born.

“Clearly, we live in a universe dominated by old stars,” said the study’s lead author, David Sobral, in an article published at the time on the Subaru Telescope website.

In the timeline of the Universe, it appears that peak star formation occurred around 10 billion years ago, during a period known as cosmic noon.

“Galaxies convert gas into stars, and do so at a decreasing rate,” says Professor Douglas Scott, a cosmologist at the University of British Columbia in Canada.

Professor Scott is co-author of a pre-publication study, currently undergoing peer review, which analyzed data from the European Space Agency’s Euclid and Herschel telescopes.

He and an international team of researchers managed to study more than 2.6 million galaxies simultaneously, which was made possible thanks to Euclid’s mission to create a huge 3D map of the Universe.

Astronomers were particularly interested in the heat given off by stardust. Galaxies with a higher star formation rate tend to have hotter dust, because they host larger, hotter stars.

The team found that the galaxies’ temperatures gradually decreased over several billion years, according to Scott.

“We are already well past the maximum time for star formation, and there will be fewer and fewer new stars with each generation of star formation,” he says.

It is true that the death of old stars can lead to the formation of new stars using the same material, but things are not that simple.

Let’s say we have a bunch of building materials and we use them to build a house. If you want to build a new one, you can certainly try to recycle the old building, but not everything will be useful.

“That means we can only build a smaller house. Every time we demolish it, there will be fewer useful materials until I can no longer build a new house,” says Scott.

This is practically what happens to stars.

“Each generation of stars has less fuel to burn and, eventually, there will not be enough fuel to form a star,” explains the cosmologist.

“We already know that low-mass stars are much more common than high-mass stars in the Universe.”

Scientists have long hypothesized that the Universe will one day end. They just don’t know how and when.

One of the most accepted theories today is that of thermal death.

Also called the Great Freeze, it predicts that as the Universe continues to expand, energy will disperse until it becomes too cold to support life. The stars move away from each other, run out of fuel, and no new ones form.

“The amount of energy available in the Universe is limited,” explains Scott.

But before taking a nostalgic look at the sky, it is important to remember that it would take an astronomical amount of time for the stars to disappear.

Professor Scott estimates that new stars will continue to emerge for the next 10 to 100 trillion years, long after our Sun is likely gone.

As for the Great Freeze, it could take even longer: earlier this year, astronomers at Radboud University in the Netherlands estimated that the final end would occur in about a billion and a half years, or 1, followed by 78 zeros.

So you’ll have plenty of time to enjoy the stars the next time you have a clear night.