Updated: Oct 8
Author: Dhruv Hegde
Image Credit: NASA Goddard Space Flight Center/CI Lab
This paper seeks to address the universal ramifications that have been observed by Strange Matter, along with the theoretical bounds that have been conceived with the notion of Strange Matter itself. Through an astrophysical perspective, this paper will address the properties of strange matter and the way by which it operates without alignment to the Bodmer-Witten Assumption; the discussion of cosmological entities, both theorized and observed, will be included to explain the presence of strange matter within neutron stars, quark stars, and, even, strange stars. For the sake of understanding, quarks will also be described – both in their high-energy quark-gluon plasma state and within their standard hardon state. Given that strange matter is still highly theoretical in concept, this paper will contextualize the research completed in the field so far and refer to the developments being done to bring it to modern application; quarks are a fundamental unit and their standard manipulation could possibly lead to a greater understanding of fundamental particle interaction and the formation of quark matter in high quantities.
Introduction to Strange Matter
In order to properly understand the nature of strange matter within chromodynamic interactions with the universe, we must first properly familiarize ourselves with the overarching establishment of Quark Matter. Those who have a background in physics are likely to know about the existence of Quarks, minute subatomic particles that, alongside gluons, form into protons and neutrons. As part of the 17 fundamental particles of Quantum Mechanics, Quarks are a defining force with 6 different types – up, down, bottom, top, charm, and strange – that all encapsulate different charges and exhibit universal properties. Of the 6 categorizations of quarks, there are 3 minute sub-groups that exhibit similar properties, simply in opposing directions; for example, the up quark, a positively charged particle, and the down quark, a negatively charged particle, complement one another. Alongside the up quark, top and charm are also positively charged, whilst strange and bottom are both negatively charged.
In the actuality of Quark Matter, the quarks that we previously discussed are moving independent of a rigid structure, which they are generally enclosed within; this seemingly disordered structure of quarks and gluons is typically known as quark-gluon plasma. The plasma portion of this name refers to the high-energy state that quark matter is constantly in, without which it would revert back into an organized and triangular structure to form a hadron particle. The reason it needs to maintain such a high-energy state is due to the fact that quarks are generally held by the strong nuclear force as well, gaining additional force and making it difficult for the quark to escape the confinement of the hadron state. Quark matter is not readily found or observed due to temperatures near or exceeding 10^(12) Kelvin, but it is found in high-density and high-temperature regions, with a neutron star code being an ideal condition. A neutron star, which is the collapsed and compressed core of a former supergiant star, exhibits one of the greatest energy densities found on any deep-space object and maintains the ideal conditions for a soup of quark matter to be harbored.
Now, before attempting to describe the fundamentals of strange matter, which you might have gained a preconceived notion by this point, the discussion on Fermi Liquids is necessary. The Fermi liquid model is one that utilizes the theoretical work of Enrico Fermi and Paul Dirac in order to describe the resting state of fermions. Fermions, a category of particles similar to and that overlaps with Hadrons, describes particles that have a half-integral spin and are subatomic; some common examples of Fermions are Protons, Neutrons, Electrons, and Neutrinos. Since Protons and Neutrons, which are also Hadrons due to their composition of quarks, quark matter can be expected to operate by the Fermi Liquid model under certain conditions. To simplify the notion of a Fermi liquid and the behaviors that it exhibits, think of common metals that you encounter in your day-to-day life. For example, the iron spoon that you might have eaten breakfast with or a gold ring that you might wear. These common metals, in their resting state at standard chemical conditions, are examples of Fermi liquids. However, the highly unstable platform of high-energy quarks also comes under the same category. The reason that two eminently polarizing pieces of matter can be grouped under the same category is due to the theoretically expressed properties of Fermi liquid, such as low-lying excitations and a majorly rigid structure.
Finally, moving forth into the concept of Strange Matter, you might have been able to piece together that Strange Matter is composed of strange quarks, which is the reason that it is a subsection within Quark Matter. As previously discussed, each quark exhibits varying properties, and the strange quark particle provides an eminently differentiating force in comparison to the other quarks. Like the other quarks, the strange quark still exhibits the same physical outlook, in terms of size, elementary spin, and external forces; the difference arises in how the composition of strange quarks come together to form strange matter. As we’ve previously discussed, under high-pressure conditions, hadrons deconstruct in order to form an unstable pool of independent quarks. However, the strange quark differs in that it is the only type of quark that is able to remain stable even in such high-pressure conditions. Utilizing their intense stability, strange quarks interact with up and down quarks and form a semi-fluid bond with these other quarks, creating another triangular connection between them. However, since there is no baryon to form from this connection, there are no interatomic forces for them to operate to, allowing the entities to float around with no defined structure. For this reason, strange matter has such a loosely defined or understood structure, despite being the same mere quark connections that we observe within atoms.
Whilst on the topic of quark matter, we discussed the natural occurrence of the substance in neutron stars. Nevertheless, one key detail in the quark matter that is found within neutron stars is that it does not ideally include strange quarks to any degree. This was a recent finding that spurred the development of a theoretical framework to define both a quark star and a strange star. For the sake of simplicity, let us first undertake the mission of understanding the quark star. A quark star, simply defined, is a compact and high-density star that is composed completely out of quark and quark-based particles; however, this doesn't tell the full story of the formation and properties of a quark star. Compared to a neutron star, a quark star is theorized to be eminently denser and having a greater pressure, for a neutron star is to form a quark star under the most critical conditions. When the neutrons in a neutron star begin to be subject to such great amounts of pressure, the neutrons begin to deconstruct into their quark counterparts, creating the continuous quark matter substance that we know of. Quark stars could also possibly be formed directly, where neutron degeneracy can be achieved outside of the neutron star state; the most plausible situation where this could arise comes with the natural collapse of a Type II supernova. Although, as we move forth into the study of strange stars, the assumptions begin to become arbitrarily theoretical. A neutron star and a strange star would be almost indifferentiable, for a strange star involves the top layer still being of neutron star material and the internal layers being of the differing strange matter, which is composed entirely of strange quarks and the strangelets. A strangelet is simply the technical term for the combination of a strange, up, and down quark as we previously discussed. This precise combination of strangelets and strange quarks creates an almost perfectly stable and dense material that is resistant to outside forces and exerts a strong unifying force itself; this strong force is overwhelmingly strong to external particles, meaning that strange quarks are able to draw in additional particles into creating strange matter. As a result of this, strange matter is able to replicate and increase in quantity through conversion of mass; this poses a great danger to external objects, which might succumb to the pressure of strange matter and transform itself.
Observations of Strange Matter Properties
As we discussed in the introduction, strange matter, especially within highly pressurized and dense locations such as within the core of a neutron star, is immensely stable and carries conditional characteristics that are able to overcome the forces of other particles and envelop them to develop further. As neutrons come into contact with the strange quark particles, the nuclear force that these particles exhibit causes degeneracy of neutrons eminently faster than natural degeneracy, bringing about a greater release of quarks to be held by the strange quarks. However, what we failed to discuss regards the spread of release of strange matter and the properties that it exhibits outside of critical conditions.
Within the core of a neutron star, this highly-dense state that provides for such critical conditions remains for 10 billion years, which is highly unfavorable for the release of strange matter; moreover, within this natural decay process, the logical successor to a neutron star is a black hole, an even more concentrated core that causes a seemingly endless vertical distortion of the space time fabric, which would disintegrate the strange matter into a more raw form of energy. Given that this natural decay process would essentially “destroy” the strange matter, there is only one process by which strange matter can be released to form an independent strange star or fabricate concentrated clumps that move in space: neutron star merger. When two neutron stars attract one another in a spiral and eventually collapse into one another, jets, similar to ones in blazars or quasars, are released with nuclear material that includes strangelets. These strangelets, which contain concentration amounts of strange quarks and other quark combinations, then can combine with other strangelet particles or meet another source of matter which it could possibly envelop. When it is not in a high-energy or high-density state, the strange matter can be eminently more stable and can interact with other pieces of strange matter to combine and eventually form a complete strange star.
Developments in Strange Matter
While practical applications using strange matter can be quite dire or minimal in our current state, getting a greater understanding of the properties of strange matter and the way by which strange quarks might interact with other particles of quarks can help develop our understanding of quantum interaction. The extent to which strange matter is able to manipulate other forms of matter is a capability that could help lead change in quantum reconstruction within teleportation and in forms of nanotechnology. The danger of strange matter is also eminent and while it might not afflict our world within our given lifespan, it does have the possibility of seeping through the universe in a vast conversion wave, possibly even leading to the death of the current universe; understanding strange matter, how it emerged, and the properties that it exhibits can help pave the way for a new field in experimental physics and can also drive out understanding of particle interactions.
Alcock, Charles, Edward Farhi, and Angela Olinto. 1986. “Strange Stars.” The Astrophysical Journal 310 (November): 261. https://doi.org/10.1086/164679
“Electron Degeneracy Pressure | COSMOS.” Astronomy.swin.edu.au. https://astronomy.swin.edu.au/cosmos/E/electron+degeneracy+pressure
Nave, R. 2010. “Quarks.” Gsu.edu. 2010. http://hyperphysics.phy-astr.gsu.edu/hbase/Particles/quark.html
Pappas, Stephanie. “Physicists See ‘Strange Matter’ Form inside Atomic Nuclei.” Scientific American. https://www.scientificamerican.com/article/physicists-see-strange-matter-form-inside-atomic-nuclei/
“Strange Quark - an Overview | ScienceDirect Topics.” www.sciencedirect.com. Accessed June 19, 2023. https://www.sciencedirect.com/topics/chemistry/strange-quark
“The Strange Quark.” The Pasayten Institute. https://pasayten.org/the-field-guide-to-particle-physics/strange-quark
Weber, Fridolin, Milva Orsaria, Hilario Rodrigues, and Shu-Hua Yang. 2012. “Structure of Quark Stars.” Proceedings of the International Astronomical Union 8 (S291): 61–66. https://doi.org/10.1017/s1743921312023174