Distribution of Water in the Universe

The majority of the water in Earth’s atmosphere and crust is saltwater, seawater, with fresh water accounting for less than 1% of the total. The great majority of water on Earth is saline or salt water, with an average salinity of 35 (or 3.5 percent, or around 34gm of salts in 1 kg of saltwater), though this varies slightly depending on the quantity of runoff absorbed from surrounding land. Over 97 percent of the water on Earth comes from marginal seas and oceans, saltwater and saline groundwater, closed lakes, albeit no closed lake holds a globally significant amount of water. Except when evaluating water quality in arid places, saline groundwater is rarely considered. The remaining water on the world is the planet’s fresh water supply. Fresh water is typically described as water having a salinity of less than 1% of that of the oceans, or less than 0.35. Water with a salinity between this and one is known as marginal water, as it is inappropriate for many applications by both humans and animals, On Earth, the ratio of salt water to fresh water is roughly 50 to 1.

Star formation

Star formation is the collapse and production of stars in dense regions within molecular clouds in interstellar space, often known as “stellar nurseries” or “star-forming regions.” Star formation is a discipline of astronomy that studies the interstellar medium (ISM) and giant molecular clouds (GMC) as precursors to star formation, as well as protostars and young stellar objects as immediate products of the process. It’s linked to planet formation, which is another discipline of astronomy. In addition to accounting for the birth of a single star, star formation theory must also account for binary star statistics and the starting mass function. The majority of stars develop as part of a group of stars known as a stellar cluster. 

Stellar Nurseries

A molecular cloud, also known as a stellar nursery (if star formation is taking place within it), is a type of interstellar cloud whose density and size allow for the creation of absorption nebulae, molecules (most often molecular hydrogen, H₂), and H (II) regions. In contrast, some parts of the interstellar medium are mostly made up of ionised gas. Because infrared and radio measurements of molecular hydrogen are difficult, carbon monoxide is the most commonly employed molecule to determine the existence of H₂ (CO). Although there are reasons to challenge this assumption based on observations of other galaxies, the ratio of CO brightness to H₂ mass is assumed to be constant. Clumps are high-density regions within molecular clouds that include a lot of dust and a lot of gas cores. If gravitational forces are strong enough to drive the dust and gas to collapse, these clusters constitute the start of star formation.

Protostar

As long as the gravitational binding energy can be removed, a protostellar cloud will continue to collapse. The majority of the surplus energy is lost by radiation. However, the collapsing cloud will eventually become opaque to its own radiation, necessitating another method of energy removal. The dust within the cloud heats up to temperatures of 60–100 K, and these particles emit at far infrared wavelengths where the cloud is transparent. As a result, the dust acts as a buffer between the cloud and additional collapse. The cloud’s density rises towards the centre during collapse, making the centre region the first to become optically opaque. When the density is at 1013 g / cm³, this happens. The collapse is effectively halted in a core region known as the first hydrostatic core. The virial theorem predicts that the temperature will continue to rise. When gas falls toward this opaque zone, it collides with it, causing shock waves that heat the core even more.

Quasar

A quasar is a tremendously bright astronomical object found in the centres of some galaxies that is fueled by gas spiralling at great speed into an exceptionally big black hole. Even at billions of light-years away, the brightest quasars can outshine all of the stars in the galaxy in which they dwell, making them visible. Quasars are the furthest and brightest objects known. The term quasar comes from how these objects were first found in the 1950s during the first radio surveys of the sky. Most radio emitters were detected with otherwise normal-looking galaxies away from the Milky Way’s plane. However, certain radio sources coincided with objects that looked to be extraordinarily blue stars, despite the fact that photos of some of these objects revealed that they were surrounded by faint, fuzzy halos. They were named “quasi-stellar radio sources” because of their almost starlike appearance, which was reduced to “quasar” by 1964.

Interstellar Clouds

In our and other galaxies, an interstellar cloud is a collection of plasma, gas, and dust. To put it another way, an interstellar cloud is a region of the interstellar medium (ISM) that is denser than average. The ISM is the matter and radiation that lies in the space between the star systems in a galaxy. The hydrogen in a cloud can be neutral, forming a H I zone; ionised, or plasma, forming a H II region; or molecular, forming molecular clouds, or sometimes dense clouds, depending on the size, density, and temperature of the cloud. Clouds that are neutral or ionised are sometimes referred to as diffuse clouds. The gas and dust particles from a red giant’s later life form an interstellar cloud.

Conclusion

Stars are developed within the molecular clouds, that are present at high concentrations of interstellar gas and dust. These areas are generally severely cold (with a temperature of about 10 to 20K, which is just above absolute zero). Gases are able to become molecular at these temperatures, i.e. their atoms bind together. The most common compounds in interstellar gas clouds are CO and H₂. The extreme cold environment also results in  the gas to cluster together at extremely higher densities. Stars develop completely when the density reaches a particular level. Dark nebulae are dense regions that are opaque to visible light due to their density. We must explore them using infrared and radio telescopes because they do not glow by optical light.