Webb captures long-lived disks of world formation in the distant universe

Dec. 16 () –

The NASA/ESA/CSA James Webb Space Telescope has just solved a puzzle by demonstrating a controversial finding made with the NASA/ESA Hubble Space Telescope more than 20 years ago.

Webb has discovered that planet-forming disks lived longer in the early days of the Universe, with data that refutes current theories in this regard.

In 2003, Hubble provided evidence of the existence of a massive planet around a very old star, almost as old as the Universe. These stars possess only small amounts of heavier elements that are the building blocks of planets. This implied that some planet formation occurred when our Universe was very young.and those planets had time to form and grow within their primordial disks, even larger than Jupiter. But how?

To answer this question, the researchers used Webb to study stars in a nearby galaxy that, like the early Universe, lacks large amounts of heavy elements. They discovered that some stars not only have planet-forming disks, But these disks have a longer life than those seen around young stars in our galaxythe Milky Way.

“With Webb we have a really strong confirmation of what we saw with Hubble, and we need to rethink how we model planet formation and early evolution in the young Universe,” he said. in a statement study leader Guido De Marchi from ESA’s European Space Research and Technology Center in Noordwijk, the Netherlands.

In the early Universe, stars formed mainly from hydrogen and helium, and very few heavier elements such as carbon and iron, which arrived later through supernova explosions.

“Current models predict that with so few heavier elements, the disks around stars are short-lived, so short that planets cannot grow,” said Webb study co-investigator Elena Sabbi, chief scientist at the Observatory. Gemini at NOIRLab. “But Hubble did see those planets, so, What if the models were not correct and the disks could live longer?”

To test this idea, scientists trained Webb in the Small Magellanic Cloud, a dwarf galaxy that is one of the Milky Way’s closest neighbors. In particular, they examined the huge star-forming cluster NGC 346, which also has a relative lack of heavier elements. The cluster served as a close surrogate for studying stellar environments with similar conditions in the early and distant Universe.

Hubble observations of NGC 346 in the mid-2000s revealed many stars between 20 and 30 million years old that appeared to still have planet-forming disks around them. This was going contrary to the conventional belief that such disks would dissipate after 2 or 3 million years.

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

Now, thanks to Webb’s sensitivity and resolution, scientists have for the first time spectra of Sun-like stars in formation and their immediate surroundings in a nearby galaxy.

“We see that these stars are surrounded by disks and They are still in the process of devouring materialeven at a relatively old age of 20 or 30 million years,” De Marchi said. “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. “.

This finding refutes previous theoretical predictions that when there are too few heavier elements in the gas around the disk, the star would quickly blow up the disk. Therefore, the life of the disk would be very short, even less than a million years. But if a disk doesn’t stay around the star long enough for dust grains to stick together and form pebbles and become the core of a planet, How can planets form?

TWO MECHANISMS

The researchers explained that there could be two different mechanisms, or even a combination, for planet-forming disks to persist in environments scarce in heavier elements.

First, in order to eject the disk, the star applies radiation pressure. For this pressure to be effective, elements heavier than hydrogen and helium would have to reside in the gas. But the huge star cluster NGC 346 only has about ten percent of the heaviest elements that are present in the chemical composition of our Sun. Perhaps it simply takes a star in this cluster longer to disperse its disk.

The second possibility is that, for a star like the Sun to form when there are few heavier elements, it would have to start from a larger cloud of gas. A larger gas cloud will produce a larger disk. Therefore, there is more mass in the disk and therefore it would take more time to eject it, even if radiation pressure worked the same way.

“With more matter around stars, the accretion lasts longer,” Sabbi said. “Disks take ten times longer to disappear. This has implications for how a planet forms and the kind of system architecture you can have in these different environments. This is very exciting.”

The scientific team’s article appears in the December 16, 2024 issue of The Astrophysical Journal.