Testing the cosmological principle with quasars

¹ School of Physics and Technology, Xinjiang University, Urumqi 830046, China
² School of Physics and Electronics, Henan University, Kaifeng 475004, China
³ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, Urumqi 830011, China
⁴ School of Physics and Astronomy, China West Normal University, Sichuan 637002, China

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Received: 22 August 2025
Accepted: 9 March 2026

Abstract

The cosmological principle posits that the universe is homogeneous and isotropic on the large scales. In history, the cosmological principle was confirmed by various cosmological observations from CMB to large scale structure. However, several new challenges to the cosmological principle were reported in recent years, particularly in radio observations from overdispersed radio source counts to quasars. Here, we firstly present studies on the peculiar velocity of large-scale anisotropy by measuring the dipole signal from the DESI DR1 catalogue with a sample of 1 176 570 quasars (0.8 < z < 3.0). Our analysis reveals the peculiar velocity of |v| = 443.8 ± 204.1 km/s towards (l, b) = (107.4° ±86.8° ,28.4° ±45.2° ) in Galactic coordinates. The motion direction deviates from the CMB dipole (264.02°, 48.253°). The inferred velocity is consistent at the 1.56σ level with the value of 370 km/s from a purely kinematic interpretation of the CMB dipole. Based on the motion direction component analysis, we have not found any significant deviation from cosmological principle in current released quasars data.