Year: 2026
Type: preprint
Abstract: 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 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 $z = 0.734 - 0.808$ for the DM-core and extreme values of $z = 2 - 3.468$ for the DM-halo class, allowing us to use their redshift as a way to disentangle the two classes. Furthermore, the high redshift of the DM-halo UCOs could serve as a signal of DM since their redshift exceeds the Buchdahl limit of $z = 2$. Finally, we find hybrid star solutions of ``ultimate twins" with similar masses and visible radii, 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.
Source: arXiv (Cornell University)
Institution: Goethe University Frankfurt
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7208761377