The James Webb Space Telescope, a joint project of NASA, the European Space Agency and the Canadian Space Agency, continues to reveal hidden corners of the universe with its infrared instruments. In a new image it showed many stars that were previously invisible because of dense dust clouds in NGC 7129, a star-forming region in the constellation Cepheus, about 3,300 light-years from us. The image is already helping to better understand how new stars are born and evolve.
A star's life cycle begins in dense molecular clouds made of cold dust and gas, known as nebulae. Inside such "cocoons", matter gradually clumps together, gains mass and eventually contracts under gravity, which gives rise to a new star. Because of dust, young stars often cannot be seen by telescopes that do not detect infrared light. Thanks to Webb's sensitivity to the near- and mid-infrared range, astronomers were able to look inside NGC 7129 and see many stars less than 1 million years old.
More than 130 stars have been identified in this cluster. They are at different stages of development depending on their mass: more massive stars evolve faster and leave the main sequence earlier - the stage at which a star shines steadily through thermonuclear reactions. The most massive and mature star in this region is the central LkH(alpha) 234, which has not yet reached the main sequence and has a mass of roughly 5 to 8 solar masses. Such stars have mostly finished accreting mass and will soon begin burning hydrogen in their cores.
This raises their temperature, heats the surrounding gas and dust and makes them bright enough for astronomers to look inside the cloud. In the image, hot atomic hydrogen appears as a golden region on the left. Cooler gas, heated by shock waves from outflows from still-forming stars (protostars), is shown in red on the right, and smaller clouds are visible in the upper left. Outflows caused by the birth of LkH(alpha) 234 also created a cavity visible in the left part of the image. Shock waves from these outflows mostly dispersed the hydrogen gas, but also compressed some regions, leading to the formation of new stars inside the cavity.
Some of these stars have also not yet reached the main sequence and emit a stellar wind - a stream of charged particles. It creates arc-shaped shock waves nearby that lead to the appearance of other small cavities. The stellar wind also presses on the cooler, denser gas outside the cavity, forming a sharp ridge visible in the upper part of the image. Outside the cavity, this pressure creates a boundary known as a photodissociation region, where hydrogen molecules break apart into individual atoms.
In the upper left, a bright blue nebula is lit by a protostar surrounded by a torus-shaped disk of matter, with outflows also visible nearby. Webb's high resolution has also revealed many complex structures in this star-forming region, continuing research begun by the Spitzer Space Telescope, which has already been retired. Further study of the region will help understand how these stars and protostars shape their surroundings and over time gradually destroy molecular clouds.