On December 27, 2024, the James Webb Space Telescope (JWST) made significant strides in understanding the formation of massive planets around ancient stars, solving a mystery that has persisted for two decades.
In 2003, the Hubble Space Telescope identified the oldest known planet, a gas giant 2.5 times the size of Jupiter, formed in the Milky Way approximately 13 billion years ago, shortly after the universe's birth.
This discovery raised questions as many ancient planets were detected, challenging the notion that early stars primarily consisted of light elements like hydrogen and helium, with minimal heavy elements necessary for planet formation.
Previously, scientists believed that the dust and gas disks surrounding these stars would dissipate due to stellar radiation within a few million years, leaving insufficient material for planet formation. They thought that heavy elements needed for long-lasting protoplanetary disks were only produced later by supernova explosions.
However, JWST's observations of an ancient star model indicated that Hubble's findings were accurate. A recent study published in The Astrophysical Journal revealed that protoplanetary disks can endure much longer than previously thought, even around stars with low heavy element content.
Guido De Marchi, the study's lead author and an astronomer at the European Space Research and Technology Centre in Noordwijk, Netherlands, stated, "We observe that these stars are indeed surrounded by disks and are still in the process of accreting material, even at relatively old ages of about 20 to 30 million years. This implies that planets can form and grow around these stars for an extended period compared to regions of star formation in our galaxy."
JWST analyzed spectra from stars in the star cluster NGC 346, which mirrors conditions in the early universe, containing abundant light elements and few heavy ones. This cluster is located in the Large Magellanic Cloud, approximately 199,000 light-years from Earth.
The emitted light and electromagnetic waves from these stars revealed the presence of long-lived protoplanetary disks. Scientists proposed two main explanations: first, the absence of radiation from heavy elements, as stars composed of light elements do not produce significant radiation through radioactive decay, allowing the disks to persist longer. Second, stars formed from massive clouds of dust and gas leave behind substantial disks, which take longer to disperse.
This discovery opens new avenues for understanding planet formation in the early universe and provides insights into the evolution of planetary systems in environments rich in light elements.