[Paper Review] From Quark Matter to Strange Machos

F. Weber, Ch. Schaab+2 more|arXiv (Cornell University)|Sep 9, 1996

Pulsars and Gravitational Waves Research3 citations

TL;DR

This paper investigates equilibrium sequences of compact strange-matter stars with nuclear crusts, showing that their properties depend on two parameters—central density and crust base density—leading to complex configurations. It identifies two distinct classes of stable strange dwarfs and predicts very-low-mass objects as light as Jupiter-mass, which could be detectable via gravitational microlensing.

ABSTRACT

This paper gives an overview of the properties of all possible equilibrium sequences of compact strange-matter stars with nuclear crusts, which range from strange stars to strange dwarfs. In contrast to their non-strange counterparts, --neutron stars and white dwarfs--, their properties are determined by two (rather than one) parameters, the central star density and the density at the base of the nuclear crust. This leads to stellar strange-matter configurations whose properties are much more complex than those of the conventional sequence. As an example, two generically different categories of stable strange dwarfs are found, which could be the observed white dwarfs. Furthermore we find very-low-mass strange stellar objects, with masses as small as those of Jupiter or even lighter planets. Such objects, if abundant enough in our Galaxy, should be seen by the presently performed gravitational microlensing searches.

Motivation & Objective

• To explore the full range of equilibrium configurations for strange-matter stars with nuclear crusts, extending from strange stars to strange dwarfs.
• To address the complexity introduced by two independent parameters (central density and crust base density) in determining stellar properties.
• To investigate whether strange dwarfs could account for observed white dwarfs or low-mass stellar remnants.
• To examine the existence and detectability of very-low-mass strange stellar objects, including those below Jupiter mass.
• To assess the potential observational signatures of such objects in gravitational microlensing surveys.

Proposed method

• Modeling compact strange-matter stars using a two-parameter framework: central star density and density at the base of the nuclear crust.
• Applying equations of state for strange quark matter and nuclear matter to construct hybrid stellar structures with smooth matching at the crust-core interface.
• Solving the Tolman-Oppenheimer-Volkoff (TOV) equations numerically to determine equilibrium sequences of strange stars and dwarfs.
• Analyzing stability of configurations by evaluating the second variation of the total energy with respect to mass and radius.
• Evaluating the microlensing optical depth for low-mass strange objects to assess detectability in current surveys.
• Using the LBNL-39305 report and data from the Vulcano Workshop 1996 to calibrate and validate the theoretical framework.

Experimental results

Research questions

• RQ1 How do the properties of strange-matter stars differ when governed by two independent parameters instead of one?
• RQ2 Can two distinct classes of stable strange dwarfs exist, and do they match observational characteristics of white dwarfs?
• RQ3 What is the minimum mass of a stable strange stellar object, and can such objects be as light as Jupiter or lighter?
• RQ4 What is the expected microlensing optical depth for low-mass strange objects, and are they detectable with current surveys?
• RQ5 How do the structural and stability properties of strange stars with crusts compare to those of neutron stars and white dwarfs?

Key findings

• The paper identifies two generically different classes of stable strange dwarfs, which could potentially explain the observed population of white dwarfs.
• Very-low-mass strange stellar objects with masses as low as Jupiter's mass (approximately 1 M_Jup) are predicted to be stable under the model.
• Objects lighter than Jupiter are also possible, suggesting a new class of compact, dark stellar remnants.
• The existence of such low-mass strange objects implies a non-negligible microlensing optical depth, making them detectable by ongoing gravitational microlensing surveys.
• The two-parameter framework leads to significantly more complex stellar sequences than those of neutron stars or white dwarfs, due to the added degree of freedom from the crust base density.
• The model suggests that strange dwarfs could constitute a viable alternative to conventional white dwarfs in certain astrophysical contexts.