arXiv subjects

Sarah Louisa Pitz

Publications and source records attributed to Sarah Louisa Pitz.

3 recordsLinked to original sources

arXiv2026

Ultra-compact twin stars with hybrid equations of state from bosonic dark matter

The properties of compact stars with a strong first-order phase transition to quark matter and with an additional fluid of self-interacting bosonic dark matter (DM) are studied. We find that the inclusion of DM changes considerably the stability of mass-radius configurations relative to the naive one-fluid criterion. For compact star configurations with similar masses and different radii, so-called twin stars, the presence of DM removes the unstable segment between the hadronic and the hybrid branch, so that the stable mass-radius sequence becomes continuous after the onset of the phase transition to quark matter. We furthermore find stable ultra-compact objects (UCOs), defined by a total compactness $C = M_\text{tot}/R_\text{grav} \ge 1/3$. We observe two distinct classes of UCOs: a DM-halo class with $f_\text{DM} \gtrsim 0.9$, and a DM-core class at $f_\text{DM} \lesssim 0.02$. The two classes can be separated by the surface redshift of the normal matter, which reaches $z=0.73$--$0.77$ for the DM-core class and stays below $0.45$ for the DM-halo class. Finally, we find hybrid star solutions of 'ultimate twins' with similar mass and visible radius, but different dark matter content, leading to different tidal deformabilities and surface redshifts. Future X-ray and gravitational measurements of ultra-compact neutron stars with radii and masses outside the allowed neutron star range can thereby probe the presence and the properties of DM in addition to a first-order phase transition to quark matter.

astro-ph.HE↗

arXiv2024

Generating ultra-compact neutron stars with bosonic dark matter

In this work we investigate the properties of neutron stars admixed with selfinteracting scalar bosonic dark matter. The dark matter interaction is described by a generalized $ϕ^n$ power-law potential. We perform a stability analysis of these two-fluid objects by studying the onset of the unstable radial modes. We find ultra-compact neutron star-dark matter configurations where the neutron star matter is confined to a core radius of values below $7$ km which is unreachable for pure neutron stars. The total gravitational maximum mass of these ultra-compact configurations can have values of $3.4 \, M_\odot$. With our general ansatz of the power-law potential we show that the compactness of these solutions can be extreme, i.e. the compactness is $C = 1/3$ or even larger, making them compact enough to have a light-ring mimicking black holes. These ultra-compact objects are stable and possess a dark matter halo while having a hadronic matter core. With the addition of dark matter to neutron stars recent unusual mass-radius measurements of compact stars can be explained. We conclude that apparently contradictory measurements of neutron star masses and radii could be not only an indication of the presence of dark matter around a the hadronic matter core which is stabilized by the gravitational potential of dark matter but could also serve to disentangle the selfinteraction strength of dark matter. Our work points to a stiff equation of state for the dark matter fluid, rather than a soft one.

astro-ph.HE↗

arXiv2024

Generating ultra compact boson stars with modified scalar potentials

The properties of selfinteracting boson stars with different scalar potentials going beyond the commonly used $ϕ^4$ ansatz are studied. The scalar potential is extended to different values of the exponent $n$ of the form $V \propto ϕ^n$. Two stability mechanism for boson stars are introduced, the first being a mass term and the second one a vacuum term. We present analytic scale-invariant expressions for these two classes of equations of state. The resulting properties of the boson star configurations differ considerably from previous calculations. We find three different categories of mass-radius relation: the first category resembles the mass-radius curve of selfbound stars, the second one those of neutron stars and the third one is the well known constant radius case from the standard $ϕ^4$ potential. We demonstrate that the maximal compactness can reach extremely high values going to the limit of causality $C_\text{max} = 0.354$ asymptotically for $n\to\infty$. The maximal compactnesses exceed previously calculated values of $C_\text{max}=0.16$ for the standard $ϕ^4$-theory and $C_\text{max}=0.21$ for vector-like interactions and is in line with previous results for solitonic boson stars. Hence, boson stars even described by a simple modified scalar potential in the form of $V \propto ϕ^n$ can be ultra compact black hole mimickers where the photon ring is located outside the radius of the star.

astro-ph.HE↗