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We present a comprehensive, two-decade, multiwavelength variability study of the blazar PKS 1510 - 089, one of the most prominent and extensively monitored flat-spectrum radio quasars. Using Fermi-LAT γ-ray data together with Swift-XRT and UVOT observations spanning 2005─2024, we trace the long-term evolution of its flux, interband correlations, and spectral behaviour across the optical, X-ray, and γ-ray bands. We find that all flux distributions prefer a double-log-normal fit. In case of the optical bands, this may be due to contributions from the accretion disk. The range of fluxes in a given band, as well as the fractional variability values are in-line with the expectations that high-energy parts of a given spectral component are more variable than low-energy parts. No obvious cross-correlations exist between the bands over the 20 years of observations. The X-ray and γ-ray spectra are variable, but do not show any trend with flux. These results are suggestive of different zones being active in the jet of PKS 1510 - 089 at any given time. In a previous paper, we used the same techniques to study the high-frequency-peaked BL Lac object PKS 2155 - 304. Both sources follow the aforementioned trend on the energy-dependent variability of the spectral components, as well as the lack of significant cross-correlations between the studied bands. While PKS 2155 - 304 exhibits a harder-when-brighter behaviour in its high-energy part of the synchrotron component, no such behaviour could be found in PKS 1510 - 089. Both sources show orphan flares, which can seemingly happen in any band. In summary, the long-term studies of these two sources reveal that the underlying physics is similar in these apparently different source classes, even though variability patterns keep changing and remain unpredictable.

We investigate the gravitational wave spectrum from first-order QCD phase transitions using the parity doublet model at finite baryon chemical potential. The model incorporates the chiral invariant mass <inline-formula><mml:math><mml:msub><mml:mi>m</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:math></inline-formula>, representing the portion of nucleon mass that persists even when chiral symmetry is restored. Within the model, we identify two first-order phase transition regions: the nuclear liquid-gas transition and the chiral phase transition. By solving the bounce equation and computing the Euclidean action <inline-formula><mml:math><mml:msub><mml:mi>S</mml:mi><mml:mn>3</mml:mn></mml:msub><mml:mo>/</mml:mo><mml:mi>T</mml:mi></mml:math></inline-formula>, we obtain the gravitational wave spectra from both transitions. The liquid-gas transition yields transition strength <inline-formula><mml:math><mml:mi>α</mml:mi><mml:mo>∼</mml:mo><mml:mi>O</mml:mi><mml:mo>(</mml:mo><mml:mn>1</mml:mn><mml:mo>)</mml:mo></mml:math></inline-formula> and inverse duration of the phase transition <inline-formula><mml:math><mml:mi>β</mml:mi><mml:mo>/</mml:mo><mml:mi>H</mml:mi><mml:mo>∼</mml:mo><mml:mi>O</mml:mi><mml:mo>(</mml:mo><mml:mn>10</mml:mn><mml:mo>)</mml:mo><mml:mi>─</mml:mi><mml:mi>O</mml:mi><mml:mo>(</mml:mo><mml:mn>100</mml:mn><mml:mo>)</mml:mo></mml:math></inline-formula> near the end point of the first-order line, producing signals with peak frequencies from the millihertz to the nanohertz band that can fit the existing data. In contrast, the chiral transition produces signals suppressed by approximately five orders of magnitude, well below the sensitivity of all current and planned detectors. These results establish, within the parity doublet model, a quantitative link between first-order QCD phase transitions and their gravitational wave signatures, and provide a concrete framework for relating gravitational wave observations to the chiral invariant mass <inline-formula><mml:math><mml:msub><mml:mi>m</mml:mi><mml:mn>0</mml:mn></mml:msub></mml:math></inline-formula> and thus to the origin of nucleon mass.