New Insights on Quarks and Quark Matter in Stars and Clusters

Context

A recent study revealed that three-quark clusters are more prone to formation compared to two-quark clusters, particularly in scenarios where other particles densely surround a specific type of quark. 

Challenging Particle-Physics Models: Insights into Heavy Quarks Clusters

• Challenge to Traditional Particle-physics Models: The researchers noted that this finding challenges the traditional particle-physics models, which assume that quark consolidation occurs independently of the particle environment.
• Cluster of Heavy Quarks: Another study reported the observation of clusters consisting exclusively of heavier quarks. 
• Difficulty in Studying Heavy Quarks: Heavy-quark clumps are very short-lived and harder to study, requiring more sophisticated tools and computing power. 
  • However, understanding them is important for understanding all quarks shedding light on their impact on phenomena such as nuclear fusion and the evolution of stars.

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Composition of Matter

All matter comprises atoms, with protons and neutrons forming the nucleus while electrons orbit outside. However, unlike electrons, protons, and neutrons, which constitute composite particles, consist of quarks.

Stages of Star/Life Cycle of Stars

• Equilibrium of Forces: A star represents a sphere of matter that achieves equilibrium between two opposing forces. 
  • Gravity,  arising from the star’s mass, encourages the star to collapse inward. Conversely, the nuclear force expressed in the explosive energy released by fusion reactions at its core, pushes the star to blow up and outwards. 
  • Within a star, these two forces are in perfect balance, resulting in its luminous presence in the sky.
• Collapse of Star: When a star exhausts its fusion fuel, nuclear fusion diminishes, allowing gravity to gradually overpower the outward pressure. Eventually, the star will reach the end of its life cycle and undergo collapse or implosion. 
• Post-Life Fate Determination Based on Size and Mass: The destiny of the star in its post-life phase is determined by its initial size and mass, leading to the formation of a white dwarf, a neutron star, or a black hole.
  • Scientists have estimated that if the Sun were 20-times more massive, it may collapse into a black hole when it dies. If it were only eight-times heavier, it could become a neutron star. 

Neutron Stars

In neutron stars, the strength with which the core collapses will fuse all protons and electrons inside into neutrons.

• Extreme Density and Novel Matter States in Neutron Stars: The interior of neutron stars exhibits extreme density, with the equivalent mass of two Suns compressed into a sphere just 25 kilometers wide. 
  • This immense pressure may lead to the formation of a novel state of matter.
• Study of Neutron Properties: The Tolman-Oppenheimer-Volkoff(TOV)equation is used to calculate the bulk properties of neutron stars. It assigns a probability to the presence of quarks within neutron stars. 
  • The TOV equation is widely used in the study of properties of compact stars.
• Magnetic Moments of Protons and Neutrons: Protons are positively charged and therefore have a magnetic moment (a turning force exerted by a magnetic field) associated with them. 
  • Neutrons also have a magnetic moment but they are neutrally charged. 
• Quest for Quark Matter in Neutron Stars: A longstanding question in physics concerns whether this state could involve quark matter, where neutrons are no longer present, only quarks.
• Evidence for Quark Matter: As per a recent journal Nature Communications, the interiors of the most massive neutron stars may consist predominantly of quark matter, with an estimated likelihood of 80-90%.
  • However, the astrophysical observations were small in number, meaning the result is not so reliable. Astrophysicists need more observational data to understand quark matter and how exactly it forms.
• Challenges with Neutron Study: While their properties are well-theorized, direct experimentation on them is impossible in earthly laboratories.
  • Additionally, crucial data on the masses and radii of most neutron stars remain unknown, sparking intense interest among astrophysicists.

Understanding Quark Stars

• Discovery of Quarks: Physicists in the 1960s figured neutrons must be made of smaller particles that gave rise to the magnetic moment but whose electric charges cancel themselves out. 
  • Gell-Mann called them quarks and their existence was confirmed in the 1970s.
• Classification of Quarks and Antiquarks: Quarks, fundamental particles, come in six varieties: up, down, top, bottom, strange, and charm. There exist antiquarks also, which are the antimatter counterparts of quarks. 
• Meson Formation: When a quark and an antiquark combine, they form a meson, with examples including up + anti-down. 
• Baryon Formation: Three-quark clusters are referred to as baryons, constituting the ordinary matter that surrounds us.
• Quarks Binding by Gluons: Quarks are further held together by another set of particles called gluons. 
  • Since nuclear forces are very strong, quarks are always tightly bound to each other and are not free, even in the vacuum of empty space.
•  Quantum Chromodynamics Theory: It explains the nuclear force that holds quarks together.
  • It predicts that at sufficiently high energies, nuclear matter can become ‘deconfined’ to create a new phase of matter in which quarks don’t have to exist in clusters.

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• Evidence of Confinement: Physicists have provided evidence of deconfinement through experiments involving the collision of lead ions at extremely high energies, such as those conducted at the Large Hadron Collider. 
• Existence of Quark-gluon Plasma: These experiments have revealed the existence of a state of matter known as quark-gluon plasma, where quarks briefly exist independently, signifying the ‘plasma’ phase. 
  • According to the Big Bang theory, the early universe was filled with this plasma before particles aggregated to form the first matter clusters.
• Clues to discover Quark stars: This process of particle aggregation may release energy or induce alterations in the surrounding environment, providing astrophysicists with potential clues to identify and eventually discover quark stars. 
  • Until then, the existence of quark stars remains one of the unresolved mysteries in physics.

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