During the early 2000s, the Hubble Space Telescope observed an enormous planet around a very old star that was 2.5 times larger than Jupiter.

It formed in the Milky Way about 13 billion years ago, which is less than a billion years after the birth of the universe. Soon, more discoveries of other ancient planets followed.

Scientists were puzzled because stars in the early universe should be made up of mostly light elements like hydrogen and helium.

They rarely contain heavier elements such as carbon and iron. This implied that some planet formation occurred when the universe was super young.

That means those planets had time to develop and grow to large sizes, bigger than Jupiter, inside their primordial disks. The question of how that could happen has hung in the air for over 20 years.

Astronomers believed that the disks of gas and dust surrounding stars with light elements should have been dispersed within a couple of million years, leaving nothing behind with which to make a planet.

They also thought the heavy elements needed to build a planetary disk around a star did not exist until supernova explosions created them later on.

Now, the James Webb Space Telescope (JWST) has solved the mystery of how ancient stars can host massive planets.

Its observations confirmed that there were a few heavy, metallic elements that made planetary disks last a lot longer than previously believed.

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"We see that these stars are indeed surrounded by disks and are still in the process of gobbling material, even at the relatively old age of 20 [million] or 30 million years," said Guido De Marchi, the lead author of the study and an astronomer at the European Space Research and Technology Center in Noordwijk, Netherlands.

"This also implies that planets have more time to form and grow around these stars than in nearby star-forming regions in our own galaxy."

Researchers used Webb to study stars in a nearby galaxy called the Small Magellanic Cloud, which is 199,000 light-years away from Earth.

The stars they observed were from the cluster named NGC 346. The conditions in the cluster are similar to those in the early universe, with mainly light elements and some heavier elements.

The light and electromagnetic waves emanating from these stars and their nearby surroundings showed that they host long-lasting planetary disks. There are two theories that could explain this phenomenon.

The first is that stars consisting of light elements do not contain many elements going through radioactive decay.

The lack of radiation means the star does not have as much strength to push the planetary disk away, so it might last a lot longer than a disk around a star with heavier elements.

Another possibility is that a star that was formed from light elements must have done so from an extremely gigantic cloud of gas and dust. The cloud would've left behind a disk around the newborn star and take a long time to blow away.

"With Webb, we have a really strong confirmation of what we saw with Hubble, and we must rethink how we model planet formation and early evolution in the young universe," said De Marchi.