Missing Beats: Dark Matter Silences Short-Period Cepheids in the Galactic Center

TL;DR

The study demonstrates that DM annihilation heating can reshape Cepheid evolution in dense galactic nuclei by suppressing blue loops for low-mass Cepheids. Using a capture–annihilation framework and an interpolated DM profile, the authors implement DM heating in the MESA stellar evolution code and show that at ρ_DM ≈ 10^5 GeV cm^−3, 3–6 $M_\odot$ Cepheids fail to develop blue loops, eliminating short-period Cepheids in the inner parsecs. This establishes a potentially observable DM signature: the unexpected absence or paucity of short-period Cepheids in the Galactic Center, testable with upcoming near-infrared facilities. The work highlights GC Cepheids as a complementary probe of DM properties, offering constraints complementary to direct detection and other astrophysical tests.

Abstract

Upcoming near-infrared facilities (e.g., JWST/NIRCam, ELT/MICADO) will dramatically increase the detectability of galactic center Cepheids despite extreme extinction at optical wavelengths. In this work, we study the impact of dark matter (DM) annihilation on Cepheid stars in the inner parsec of the Milky Way. We show that at densities $ρ\sim 10^5 \, \text{GeV} \, \text{cm}^{-3}$, blue-loop evolution can be suppressed, preventing the formation of low-mass ($3$-$6 \, M_\odot$) short-period ($1$-$6$ days) Cepheids. A dearth of such variables could provide indirect evidence for DM heating. Notably, this effect occurs at lower DM densities than required to impact main-sequence stars. Future surveys will thus offer a novel, complementary probe of DM properties in galactic nuclei.

Figures (6)

• Figure 1: Vanishing blue loops: the evolution of $6$--$7~{\rm M}_\odot$ stars in the SM (black, solid) and with DM annihilation (red, dashed) with $m_{\rm DM}=1$ GeV, $\rho_{\rm DM}=10^5$ GeV/cm$^3$, and $v_{\rm DM}= 50$ km/s . The gray region shows the instability strip.
• Figure 2: Hertzsprung-Russell Diagram of the evolution of a $6~{\rm M}_\odot$ star with metallicity $Z=0.02$ and initial helium abundance $Y=0.29$, consistent with galactic center stars. The gray region is the Cepheid instability strip.
• Figure 3: Capture fraction for a $5.5~{\rm M}_\odot$ Cepheid of radius $50 \,R_\odot$, assuming spin-dependent interactions and $70.6\%$ hydrogen by mass, computed using Asteria Leane:2023woh. Dashed lines indicate direct detection constraints from CRESST CRESST:2022dtl and LUX LUX:2017ree.
• Figure 4: Evolution of $6$--$11~{\rm M}_\odot$ stars for the SM (black, solid) and under DM annihilation (red, dashed) with $m_{\rm DM}=1$ GeV, $\rho_{\rm DM}=10^5$ GeV/cm$^3$, and $v_{\rm DM}= 50$ km/s. The gray region shows the instability strip.
• Figure 5: Kippenhahn diagrams showing the $^4$He mass fraction for $6~{\rm M}_\odot$ stars during the dredge up and the start of the blue loop. The x-axis proceeds monotonically in time, and the y-axis shows the enclosed stellar mass within a shell. Both a SM star (upper) and a star evolving under DM energy injection (lower) are shown. The DM plot uses $m_{\rm DM}=1$ GeV, $\rho_{\rm DM}=10^5$ GeV/cm$^3$, and $v_{\rm DM}=50$ km/s. The blue dashed lines indicate the location of the helium core.