Matter exists in different forms, known as states, depending on conditions like temperature and pressure. On Earth, we commonly encounter matter as solids, liquids, and gases. Water, for instance, can be ice (solid), liquid water, or steam (gas), demonstrating these transformations. These familiar states represent how atoms and molecules arrange and behave under various energy levels. However, when considering the entire cosmos, a different state of matter predominates.
The Dominant Phase
The most common phase of matter in the universe is plasma, often referred to as the fourth state of matter. Unlike solids, liquids, or gases, plasma is an ionized gas, meaning its atoms have been stripped of one or more of their electrons. This process leaves behind a collection of free-moving electrons and positively charged ions. While the overall charge of plasma remains roughly neutral due to an equal number of positive and negative charges, its constituent particles are electrically charged.
Plasma exhibits unique properties because of these charged particles. It is an excellent electrical conductor and responds strongly to electric and magnetic fields. This behavior distinguishes it significantly from a neutral gas, where particles are not electrically charged. The formation of plasma typically requires high energy input, such as extreme temperatures, which causes atoms to ionize.
Where Plasma Thrives
Plasma’s prevalence throughout the cosmos stems from the extreme conditions found in most astronomical environments. High temperatures, often millions of degrees, are necessary to ionize atoms and maintain matter in the plasma state. Such conditions are common in the vastness of space.
Stars, including our Sun, are composed almost entirely of plasma, with their immense heat driving nuclear fusion reactions within this plasma. Beyond stars, plasma extends into interstellar and intergalactic space, albeit at much lower densities. The solar wind, a continuous stream of particles emanating from the Sun, is also a form of plasma that fills interplanetary space. Additionally, nebulae, vast clouds of gas and dust where stars are born, contain significant amounts of plasma. This pervasive distribution means that plasma constitutes approximately 99% of the ordinary matter in the universe.
Beyond Plasma
While plasma dominates the universe, other familiar states of matter—solids, liquids, and gases—are rare on a cosmic scale. These states require specific conditions, such as moderate temperatures and pressures, found on planetary surfaces or within cooler celestial bodies. For example, liquid water, a common substance on Earth, exists within a narrow temperature range that is uncommon in the broader universe.
More exotic states of matter, such as Bose-Einstein condensates or neutron star matter, exist under even more extreme conditions. Bose-Einstein condensates, for instance, form at temperatures near absolute zero and have been created in laboratories. Neutron star matter, found within the dense cores of collapsed stars, represents another specialized state. These forms of matter highlight the diversity of phases possible, yet their occurrence remains rare compared to plasma.