NASA’s James Webb Space Telescope (JWST) Finds Planet-Forming Disks Lived Far Longer in Early Cosmos

By proving a controversial finding made more than 20 years ago using NASA’s Hubble Space Telescope, NASA’s newer space telescope JWST just solved a conundrum. In the year 2003, Hubble provided evidence of a gigantic planet around a very old star, almost as old as the cosmos. Such stars possess very small amounts of heavier elements that are basically the building blocks of planets. This implied that some planet formation occurred when our cosmos was very young, and those planets had enough time to form and grow big inside their primordial disks, even larger than Jupiter. But how? This was perplexing.

To answer the above-mentioned question, scientists used JWST to study stars in a nearby galaxy that, much like the early cosmos, lacks large amounts of heavy elements. They found out that not only do some stars there have planet-forming disks, but that those disks are far longer-lived than those seen around young stars in our very own galaxy Milky Way. “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 study leader Guido De Marchi of ESTEC, Noordwijk, Netherlands.

In the early cosmos, stars formed from mostly helium and hydrogen, and very few heavier elements such as iron and carbon, which came later on through supernova explosions. “Current models predict that with so few heavier elements, the disks around stars have a short lifetime, so short in fact that planets cannot grow big,” said co-investigator Elena Sabbi (chief scientist for Gemini Observatory at the National Science Foundation’s NOIRLab in Tucson). “But Hubble did see those planets, so what if the models were not correct and disks could live longer?”

To test this idea, researchers trained JWST on the Small Magellanic Cloud, a dwarf galaxy that is one of the Milky Way’s nearest neighbours. In particular, they examined the colossal, star-forming cluster NGC 346, which also has a comparative lack of heavier elements. The cluster served as a nearby proxy for studying stellar environments with similar conditions in the early, faraway universe.

Hubble observations of NGC 346 from the mid-2000s exposed many stars about 20 to 30 million years old that seemed to still possess planet-forming disks around them. This went against the common belief that such disks would dissipate after 2 or 3 million years.

“The Hubble findings were controversial, going against not only empirical evidence in our galaxy but also against the current models,” said De Marchi. “This was intriguing, but without a way to obtain spectra of those stars, we could not really establish whether we were witnessing genuine accretion and the presence of disks, or just some artificial effects.”

Now, owing to Webb’s sensitivity and resolution, researchers have the first-ever spectra of forming, Sun-like stars and their immediate environments in a nearby galaxy.

“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 or 30 million years,” said De Marchi. “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.”