Astronomers determine a star’s age using starquakes through a technique called asteroseismology. The basic idea is that a star’s internal structure changes in a predictable way as it ages, and starquakes let us “listen” to those changes.
Here’s how it works, step by step.
1. What a starquake is
Starquakes are sound waves that resonate inside a star. They are driven by turbulence near the surface (in Sun-like stars) or by opacity changes deeper inside (in some evolved stars). These waves make the star very slightly expand and contract, producing tiny, regular brightness or surface-velocity changes.
Each star supports many oscillation modes, each with a very precise frequency.
2. Oscillation frequencies probe the interior
Different oscillation modes travel through different parts of the star:
- Some sample the outer layers
- Others penetrate deep into the core
The exact frequencies depend on:
- Density profile
- Temperature profile
- Chemical composition (especially hydrogen vs helium)
All of these evolve as the star ages.
3. The key age indicator: the core
As a star gets older:
- Hydrogen in the core is converted into helium
- The mean molecular weight increases
- The core becomes denser and more compact
This changes the sound speed in the core, which shifts specific oscillation frequencies in a measurable way.
In particular, astronomers look at:
- Frequency separations between modes (called large and small separations)
- Mixed modes in subgiants and red giants, which are extremely sensitive to core evolution
These seismic fingerprints are strong age indicators.
4. Comparing observations with stellar models
The process is:
- Measure oscillation frequencies (from missions like Kepler, TESS, or ground-based spectroscopy)
- Compare them to theoretical stellar evolution models
- Find the model that best matches the observed frequency pattern
Since stellar evolution is time-dependent, the best-fit model gives the star’s age.
5. Why this is powerful
Without asteroseismology:
- Ages of single field stars are very uncertain (often ±50–100%)
With starquakes:
- Sun-like stars can have ages measured to ~5–10% precision
- Red giants can be dated to specific evolutionary stages (shell burning vs core burning)
For example, the Sun’s age (≈4.57 billion years) is confirmed to high precision using helioseismology.
6. In one sentence
Starquakes reveal a star’s internal sound-speed structure, which changes predictably as nuclear fuel is burned, allowing astronomers to infer the star’s age by matching observed oscillation frequencies to stellar evolution models.