What happens when we stop assuming what can't be assumed?
Astrophotography by GrandpaJunkrat - ----- YSO's
Cosmology from my armchair..............................
I do it metric .............................................................. Location:
bastion@protonmail.com The Netherlands
Bortle 7 - 9
Young Stellar Objects: the birth of stars under the laws of gravity and pressure
Stars do not appear suddenly; they emerge slowly from cold, dense clouds of gas and dust that drift through interstellar space. These clouds exist in a delicate balance between two opposing forces: gravity, which pulls the material inward, and internal pressure, which pushes outward. This balance is fragile. When a region of the cloud exceeds a critical threshold known as the Jeans mass, the internal pressure can no longer support the gas against its own weight. The cloud becomes gravitationally unstable, collapses, and the earliest stage of a new star is set into motion.
As the collapse proceeds, the temperature in the centre rises. Density increases, pressure builds, and the forming object continuously searches for a new equilibrium that it never fully attains. The energy it emits at this stage does not come from nuclear fusion but from the release of gravitational potential energy as the material contracts. Around the young object, a rotating disk of gas and dust forms, feeding material inward while outflows and jets clear the surrounding envelope. In this transitional state we speak of a Young Stellar Object, a broad term encompassing everything between the first gravitational collapse and the moment a star reaches the main sequence.
In regions such as NGC 7129, these stages coexist side by side. Some objects remain deeply embedded in their dusty cocoons, invisible in optical light. Others have already emerged and shine through the surrounding nebula.
T Tauri objects represent the young, low‑mass population: still accreting, magnetically active, and often highly variable. Their surfaces host hotspots, cool spots, and accretion shocks that imprint rapid changes in brightness. Herbig Ae/Be objects are their more massive counterparts. Hotter and more luminous, they illuminate their surroundings with reflection nebulae and strong emission lines, signalling that accretion and disk interaction are still ongoing even as they approach the onset of stable hydrogen fusion.
Among the most striking phenomena in star‑forming regions are the Herbig–Haro objects. These glowing knots arise where high‑velocity jets collide with the surrounding medium. The shocks heat and ionise the gas, producing bright emission features that slowly drift through the nebula. They are unmistakable signatures of a star that is still shedding angular momentum and adjusting to its internal structure — a star that has not yet reached equilibrium.
The research presented on this website focuses on this rich and dynamic population of young stars in NGC 7129. By combining data from multiple surveys — optical, infrared, and astrometric — a coherent picture emerges of how these objects appear, evolve, and interact with their environment. The emphasis lies on understanding the physical processes that govern their behaviour: the interplay between gravity and pressure, the role of temperature and density, the influence of disks and jets, and the way variability and embeddedness reveal the ongoing struggle toward stability.
Star formation is, at its core, a search for balance. A Young Stellar Object is an object that has not yet found that balance, but is steadily moving toward a state in which gravity and pressure finally match. That moment marks the true birth of a star. Everything before it is motion, change, and growth — and it is precisely this restless evolution that makes YSOs some of the most fascinating objects in astrophysics.
