The Orion Nebula is a vibrant and changing astronomical spectacle that consists of a group of young stars and the gas and dust around them. In this nebula, some stars have unfriendly neighbors, and the ultraviolet radiation they emit can damage the protoplanetary disks around other stars, thus hindering the formation of planets. This is a surprising discovery using the latest observations from the James Webb Space Telescope (JWST) that gives us a deeper understanding of the evolution of stars and planets.
Protoplanetary disks are rotating disks of gas and dust that orbit newborn stars and are the cradles of planet birth. In the protoplanetary disk, dust particles will gradually aggregate into rocks, which will further merge into planetary embryos, eventually forming planets. However, not all protoplanetary disks are successful in giving birth to planets, and some protoplanetary disks are destroyed or depleted before the planets can form.
There is such an unfortunate protoplanetary disk in the Orion Nebula, which is named D203-506 and is located about 1300 light-years away from us. Its central star is a red dwarf star with only 10 to 20 percent of the mass of the Sun and 1% of the Sun's brightness. The protoplanetary disk around this star is very compact, with a diameter of only 20 astronomical units (1 astronomical unit is equal to the average distance from the Earth to the Sun, which is about 1.).500 million km). This protoplanetary disk is about a few million years old, equivalent to a newborn baby, and our solar system is already 4.6 billion years old.
D203-506's neighbors are a group of massive stars that make up the trapezoidal cluster at the center of the Orion Nebula and are the primary source of light for the entire nebula. These stars are more than 10 times more massive and 100,000 times brighter than the Sun, and they emit ultraviolet radiation that is so intense that it can penetrate the surface layer of the protoplanetary disk, heating the gas in it, freeing it from the gravitational constraints of the disk and escaping into space. That's why D203-506's protoplanetary disk loses a large amount of hydrogen every year, which is the main component of the protoplanetary disk.
A new study suggests that D203-506's protoplanetary disk is disappearing at an alarming rate, and if this continues, it will completely dissipate within a million years. This means that this protoplanetary disk may not have enough time and matter to form large planets, such as gas giants similar to Jupiter. Current planetary formation models suggest that it would take at least a million years for a planet the size of Jupiter to coalesce from the protoplanetary disk, so the protoplanetary disk of D203-506 is facing competition with planetary formation.
Olivier Bernet, lead author of the new study and research scientist at France's National Centre for Scientific Research (CNRS), said:"The future of this protoplanetary disk is very bleak, and it may never be able to form planets, or it may only form some small rocky planets, like Mercury and Mars in our solar system. "
The study was made using JWST's near-infrared spectrometer (NIRSPEC) observations of the protoplanetary disk of D203-506, one of JWST's four main scientific instruments, which can simultaneously measure thousands of wavelengths of spectra to obtain physical and chemical information about stars and protoplanetary disks. By analyzing the emission lines of hydrogen in the protoplanetary disk, researchers can estimate the temperature, density, and flow rate of hydrogen to calculate the rate of material loss from the protoplanetary disk.
The researchers found that the protoplanetary disk of D203-506 loses about 01% hydrogen, which is equivalent to 3 Earth-mass hydrogen being blown away every year. This number may not seem like much, but for one there is only 001 solar mass of protoplanetary disks, however, is very impressive. The researchers also found that the temperature of the gases in the protoplanetary disk was as high as 10 000 K, which was due to the heating effect of ultraviolet radiation. These results are consistent with previous observations of the same protoplanetary disk using the Hubble Space Telescope (HST) and the Large Millimeter Submillimeter Array (ALMA), indicating that JWST is very observant.
In addition to hydrogen, there are other components in the protoplanetary disk, such as oxygen, carbon, nitrogen, etc., which can form molecules such as water, carbon dioxide, methane, etc., which are essential for the existence of life. However, these molecules are also affected by UV radiation, which can be destroyed or escape. According to a related article published by the same research team in the journal Nature Astronomy on February 23, 2024, the protoplanetary disk of D203-506 loses the equivalent of the entire Atlantic Ocean each month due to ultraviolet attacks.
The loss of these molecules affects not only the formation of planets, but also the planet's climate and biosphere. For example, water is a fundamental condition for carbon-based life and an important regulator of planetary surface temperatures. If a planet doesn't have enough water, it can turn into an arid desert, or an icy permafrost. Carbon dioxide and methane are greenhouse gases that enhance the absorption of solar radiation by the planet's atmosphere, thereby raising the planet's surface temperature. If a planet doesn't have enough greenhouse gases, it can turn into a cold snowball, or a hot oven.