Astronomers have long thought that the swirling disks of gas and dust that form planets around young stars only last about 10 million years. However, a groundbreaking discovery shows that for some low-mass stars, these disks can last much longer - up to 30 million years.

Shown here is a less massive star surrounded by a planet-forming disk of gas and dust. The planet formation process can cause gaps in the astrolabe, not shown in this diagram. Streamlines near the center show that material in the disk is still falling onto the star. Image source: NASA/CXC/M. Weiss

Observations using NASA's James Webb Space Telescope reveal stable, gas-rich environments around such stars, raising the intriguing possibility of long-term planet formation. This could have major implications for our understanding of planetary evolution and the possibility of life beyond Earth, especially in systems like TRAPPIST-1 where planets may have had more time to form in the habitable zone.

If the universe had a photo album, it would probably contain images of swirling disks of gas and dust that form around young stars - planetary nurseries. These planet-forming disks are thought to be a common but short-lived stage in the lives of most young stars, providing the raw materials needed to build planets.

Typically, these disks last about 10 million years before dissipating—a short-lived existence in cosmological terms. However, researchers at the University of Arizona made a startling discovery: Some astrolabes have been around for far longer than expected. Their results show that around very small stars, those with a mass of one-tenth the Sun or less, these disks survive much longer than previously thought.

In a study published in the Astrophysical Letters Journal, a team led by Feng Long of the University of Arizona's Lunar and Planetary Laboratory made detailed observations of a protoplanetary disk that is 30 million years old—three times older than scientists typically expected. Using NASA's James Webb Space Telescope, they conducted the first detailed chemical analysis of a long-lived disk, providing new clues about the formation of planets and the potential for habitable worlds outside our solar system.

"In a sense, protoplanetary disks provide us with the prototype of planetary systems, including a glimpse of what the solar system looked like in its infancy," said Lang, the paper's first author and a Sagan researcher at the Lunar and Planetary Laboratory.

As long as the star has a certain mass, the high-energy radiation from the young star will blow the gas and dust out of the disk, making it no longer available as raw material for building planets.

The team observed a star, officially known as WISE J044634.16-262756.1B - more conveniently J0446B - located in the constellation Columbus (Latin for "dove"), about 267 light-years from Earth. Researchers found that its planet-forming disk lasted about three times longer than expected.

Although we know that most star disks dissipate within 10 million to 20 million years, we have found that for certain types of stars, their disks can last much longer. Since the material in the astrolabe provides the raw materials for the planets, the lifetime of the astrolabe determines how much time the system has to form planets.

Although small stars retain their disks longer, their disk chemistry does not change significantly. The chemical composition is similar regardless of age, suggesting that the chemical composition does not change drastically even when the astrolabe reaches a very high age. This long-lived, stable chemical environment could give planets around low-mass stars more time to form.

By analyzing the gas content in the disk, the researchers ruled out the possibility that the disk around J0446B is a so-called debris disk, a long-lasting disk composed of second-generation material produced by collisions of asteroid-like objects.

"We detected gases such as hydrogen and neon, which tells us that the original gas remains in the disk around J0446B."

The confirmed existence of long-lived, gas-rich star disks has implications for life outside the solar system, the authors say. Of particular interest to researchers is the TRAPPIST-1 system, which is 40 light-years from Earth and consists of a red dwarf star and seven Earth-sized planets. Three of the planets are in the "habitable zone," where conditions allow the existence of liquid water, making life possible, at least in principle.

The co-authors say that because stars with long-lived planetary disks are of similar mass to the central star in the TRAPPIST-1 system, the presence of long-lived planetary disks is particularly interesting for the evolution of planetary systems.

"In order to form the specific orbital arrangement we see in TRAPPIST-1, the planets need to migrate within the disk, and this process requires the presence of gas," said Ilaria Pascucci, professor of planetary science at LPL. "The long-term presence of gas we find in these disks may be responsible for the unique arrangement of TRAPPIST-1."

Long-lived disks have not yet been discovered in high-mass stars such as our Sun, because stars in such systems evolve more quickly and planets form in shorter periods of time. The authors note that although our solar system followed a different evolutionary path, long-lived astrolabe could tell researchers a lot about the universe, since low-mass stars are thought to far outnumber Sun-like stars.

Better understanding of how low-mass star systems evolve and obtaining snapshots of long-lived star disks could help pave the way to filling in the gaps in the cosmic album.

Compiled from /scitechdaily