Nothing lasts forever, not even our universe. Over the past two decades, astronomers have been noticing clues that the cosmos may be past its prime. One of those signs is that fewer stars have been born.
Now, that doesn’t mean the universe is running out of stars. There are estimates that there are at least one septillion of them – that’s a number followed by 24 zeros.
But astronomers believe the production of new stars is slowing.
The current scientific consensus is that the universe is 13.8 billion years old. The first stars formed shortly after the Big Bang..
In fact, the year before, the James Webb Space Telescope found a trio of stars in our galaxy, the Milky Way, which is believed to be close to 13 billion years old.
Stars are essentially giant balls of hot gas who started their lives the same way.
They form in huge clouds of cosmic dust known as nebulae. Gravity brings the gases together, which eventually heats up and becomes a baby star, or as it is known, a protostar.
As the heart of the star heats up to millions of degrees Celsius, the hydrogen atoms contained there begin to churn to form 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 from one tenth to 200 times the mass of our Sun.
Eventually those 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 last billions of years.
For larger “sister” starsat least eight times the size of the Sun, its ending is more dramatic: They are destroyed in a large explosion known as a supernova.
In 2013, an international team of astronomers studying trends in star formation stated that of all the stars that were going to be born in the history of the Universe, 95% 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 timeline of the universe, it appears that its peak star production occurred about 10 billion years ago, in a period known as the “Cosmic Noon.”
“Galaxies are converting gas into stars and they are doing so at a decreasing rate,” explains Professor Douglas Scott, a cosmologist at the University of British Columbia in Canada.
Scott is the co-author of a report, not yet published, that analyzes data from the European Space Agency’s Euclid and Herschel telescopes.
He and his team of space researchers were able to simultaneously study nearly 2.6 million galaxies, which was possible thanks to the 3D map of the universe created by the Euclid mission.
Astronomers were particularly interested in the heat emitted by stars. Galaxies with higher star formation rates tend to have hotter cosmic dust as they contain larger, hotter stars.
The team found that galaxy temperatures have been decreasing over the past billion years. “We have already passed the time of greatest star formation, and there will be less and less new star formation in the universe”Scott adds.
It’s true that the death of old stars can lead to the formation of new ones using the same material, but it’s not that simple.
Let’s assume we have a pile of building materials and we use it to make a house. 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 make a smaller house. Each time we do demolition, there will be fewer materials that are useful until nothing can be built,” Scott says. That’s what happens with stars.
“Each generation of stars has less fuel to spend and eventually there will not be enough fuel to make a star,” he adds. And he concludes: “We already know that less massive stars are more common than massive stars in the universe.”
Scientists have long theorized that the universe will one day come to an end.. They just can’t be sure how or when.
One of the most accepted theories currently is thermal death.
Also known as the “Big Freeze,” it predicts that as the universe continues to expand, energy will spread out until it eventually gets too cold. to sustain life. Stars move further and further away, they run out of fuel and new ones do not form.
“The amount of energy available in the universe is finite,” explains Scott.
But before you look wistfully at the sky, the disappearance of the stars would take an astronomical amount of time.
Scott estimates that new stars will continue to appear for the next 10 to 100 billion years, long after our Sun is likely gone.
As for the “Big Freeze,” it could take even longer: Earlier this year, astronomers at Radboud University in the Netherlands estimated that the end would come in approximately a quintillion yearsthat is, a one followed by 78 zeros.
There’s plenty of time, then, to appreciate the stars the next time there’s a clear night.
