James-Webb and Spitzer telescopes reveal ongoing changes in a young neighboring solar system

According to the model most commonly believed by scientists, a star typically arises from a giant cloud of interstellar gas composed primarily of hydrogen and helium, the two most abundant elements in the universe. Small changes in density within the cloud lead to gravitational collapse: the cloud begins to collapse in on itself, pulling gases toward the center to form a young star. If a large proportion of the gases in the cloud are found concentrated in the center, in the star (our Sun alone represents 99% of the solar system’s mass), the rest of the gases begin to swirl around, creating what astronomers call protoplanetary. Disc. Over a few million years, the gases and dust that make up the protoplanetary disk begin to coalesce through successive collisions. The dust expands into larger and larger blocks, until it becomes planetesimals – embryonic planets that grow into a protoplanetary disk.

According to scientists, this is the same scenario that appears to have occurred about 4.6 billion years ago, when our Sun was born from an interstellar cloud. The resulting protoplanetary disk formed over a few million years the planets we know today in our Solar System, and all the ingredients that later formed the Earth (and allowed the appearance of life) were already within this disk. were present; But our understanding of the formation and evolution of our solar system remains very vague. To try to better understand its origins, astronomers want to observe emerging stellar systems in the universe, to make possible analogies with ours.

This animation shows the evolution of a protoplanetary disk around a star. As planets form, holes appear, which collect gas and dust. © ExploreAstro

The birth of a star system a few hundred light years away from us

If the James-Webb Space Telescope is today the star of space observatories peering to the periphery of the universe, other telescopes preceded it, and the discoveries made by it have not been eclipsed by those made thanks to its older brother. This is especially the case for the Spitzer Space Telescope (Space Infrared Telescope Facility) from NASA, launched in 2003, which, among other things, made the first live observations of the process of planet formation in a protoplanetary disk around Sun-like stars. Among these observed newborn star systems, astronomers noticed the young star SZ Chamaeleontis (SZ Cha), which is located about 500 light years away from us in the Chameleon constellation and is surrounded by a disk of dust – a protoplanetary disk.

If the formation of planetary systems is not rare in the universe, then detecting the formation of a planetary system is an achievement, and observing the events occurring there is valuable to astronomers. By analyzing data collected by the Spitzer Space Telescope in 2008 when it observed SZ Chamaeleontis, scientists discovered the surprising presence of Neon III, one of the natural isotopes of neon. They presented their analysis in 2013 in the journal The Astrophysical Journal, Scientists were surprised by their discovery because, out of sixty protoplanetary disks characterized at the time, SZ Chamaeleontis was the only disk to present such a high concentration of Neon III, while the other systems had much less. The team of scientists concluded that the presence of Neon III in the SZ Chamaeleontis system was an indication that the protoplanetary disk was bombarded primarily by ultraviolet radiation, unlike other systems dominated primarily by X-rays.

An indicator of the life expectancy of a protoplanetary disk

The type of radiation to which the protoplanetary disk is subjected is important for its evolution: according to numerical simulations, disks dominated by X-rays decay much faster than those dominated by ultraviolet radiation. The planets are in a kind of race against time to be able to form before the disk disappears. However, in the SZ Chamaeleontis system, numerical models indicated that the dominance of ultraviolet radiation gave at least another million years for planet formation before the disk of gas and dust evaporated forever.

If SZ Chamaeleontis was already revealed during observations by the Spitzer telescope, scientists were surprised: Looking at the young star again, this time using the James-Webb Space Telescope, astronomers were surprised to see Only fifteen years after the observations made by the Spitzer telescope, the presence of Neon III in the system had almost disappeared. They present their new results in the journal The Astrophysical Journal, Since both telescopes were highly efficient, scientists had ruled out the possibility of measurement error.

Previously dominated by ultraviolet radiation, the protoplanetary disk is now dominated by X-rays, limiting the time available for planet formation there. Researchers believe that the neon signature differences in the SZ Cha system are the result of a variable wind, which, when present, absorbs UV light and repels X-rays. Winds are actually common in systems with newly formed and energetic stars; But it is possible to observe the system during quiet, windless periods – something the Spitzer telescope did fifteen years ago. Researchers are already planning to make further observations of the system as well as other young planet systems to better understand their formation processes. According to them, brief periods of quiescence may be common in protoplanetary disks affected by ultraviolet radiation, but have rarely been observed.