What Physical Cause Makes Cepheid Variables Pulsate Regularly?

💡 The Answer

• Pulsations are driven by the κ-mechanism, where helium opacity changes with temperature.
• As the star contracts, helium becomes more opaque, trapping radiation and heating the interior.
• This increased pressure drives expansion, after which the cycle repeats.
• The star's mass and metallicity determine the exact period and stability of pulsation.