How are stars formed? From a cloud of dust to a luminous ball

Many conditions must be met for new stars to form. On the one hand, scientists have been modeling theories describing star formation processes for decades, and on the other hand, they have been observing the formation of young stars and planetary systems in space. While observing the formation of planetary systems around young stars is relatively “easy,” star formation itself is a serious challenge because of the environment in which it occurs.

Also read: The evolution of stars continues all the time. What are the stages of a star’s life?

All stars in the universe form in dense, opaque clouds of cold dust and gas. From observations made in our immediate neighborhood, i.e. in the Milky Way, these clouds are often found in spiral arms. Over time, or under the influence of external factors, such as a shock wave hitting the cloud after a nearby supernova explosion, the cloud begins to shrink under the influence of its own gravity and breaks into pieces. From these parts, protostars are formed. This is also the reason why the stars are not created by themselves, but create – at least at first – what are called groups or open associations of several hundred stars. The cloud must be large and massive enough for its fragments to collapse under the influence of gravity. If the cloud has enough mass to form a single star, it will not collapse due to gravity. Thus, cloud-forming stars have similar ages and chemical compositions that reflect the chemical composition of the cloud from which they formed.

Observing this process is a challenge for astronomers, because individual parts of the cloud of dust and gas, which initially collapse under gravity, become denser. At some point, it is so dense that energy can no longer escape from such a cloud, and the temperature inside it begins to rise. Over time, the increase in pressure also stops and a small protostar forms in the center of the cloud. However, it is not visible from the outside, because it is still enclosed in a very thick cocoon of dust.

How do stars form from clouds of dust?

Despite years of research, scientists are still not sure what exactly triggered the onset of gravitational cloud collapse and what would form from it. Researchers from the University of St Andrews I decided to check what happens when two clouds of gas and dust collide with each other. It turns out that in such a situation, the numerous disturbances and shock waves appear in the newly formed larger cloud. All these disturbances lead to the separation of small parts from the larger whole, which quickly collapse under the influence of their own gravity, thanks to which we get a relatively fast star cluster.

What is interesting, however, is that the environment of the cloud of dust and gas has the greatest influence on star formation, more so than the properties of the cloud itself. Simulations show that if a cloud of dust and gas is present in a relatively dense interstellar medium (10 times thinner than a cloud), then the cloud fragments are more massive and less, albeit more massive, from which stars form. Likewise, when the interstellar medium is thinner, stars that are larger and less massive are formed from the cloud.

In the coming years, astronomers will certainly expand our knowledge of star formation. After all, the James Webb Space Telescope, which observes the universe in infrared light, is perfectly designed to observe what has hitherto been hidden behind a thick blanket of dust.