https://en.wikipedia.org/wiki/Binary_star
聯星（Binary star）是兩顆恆星組成的恆星系統，它們圍繞著共同的質心，在軌道上互繞。
A binary star or binary star system is a system of two stars that are gravitationallybound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in which case they are called visual binaries. Many visual binaries have long orbital periods of several centuries or millennia and therefore have orbits which are uncertain or poorly known.
According to binary star, there must be two suns, why we cannot see it? （ChatGPT, 2024-62)
The term "binary star" refers to a system where two stars orbit a common center of mass due to their mutual gravitational attraction. While binary stars are quite common in the universe, not all star systems are binary. Our Sun, for instance, is a single star system, known as a "singleton."
However, if you are asking about why, in binary star systems, we might not always see both stars, there are several reasons why one of the stars in a binary system might not be visible:
### 1. **Distance and Brightness**
- **Brightness Discrepancy**: In many binary star systems, the two stars can have vastly different brightness levels. If one star is significantly brighter than the other, the light from the dimmer star can be overwhelmed by the brighter star's light, making the dimmer star hard to detect.
- **Distance from Earth**: Binary stars can be very far from Earth. If they are distant and the dimmer star is relatively faint, our telescopes might not have the resolution to distinguish it from the brighter star.
### 2. **Orbital Configuration**
- **Line of Sight**: The orientation of the binary system relative to Earth can affect visibility. If the stars are aligned in such a way that one star passes in front of the other, the secondary star might be hidden from view periodically. This is particularly true in eclipsing binary systems.
- **Close Orbit**: In some binary systems, the stars are so close to each other that their light blends together when viewed from Earth. These systems can often only be resolved as binary through their spectral lines (spectroscopic binaries) or other indirect methods.
### 3. **Types of Stars**
- **Non-Luminous Companions**: In some binaries, one of the components might be a type of object that doesn’t emit much light, such as a white dwarf, neutron star, or black hole. These companions are difficult to see directly but can be inferred through their gravitational effects on the visible star.
- **Infrared and X-ray Binaries**: Some stars emit primarily in non-visible wavelengths like infrared or X-rays. These stars might not be visible in optical light but can be detected by telescopes sensitive to those wavelengths.
### 4. **Technological Limitations**
- **Resolution Limits**: The resolution of telescopes can limit our ability to see both stars in a binary system, especially if the stars are very close together or if one star is much fainter.
- **Detection Methods**: Many binary stars are discovered through indirect methods, such as observing periodic variations in a star's brightness (eclipsing binaries) or Doppler shifts in their spectral lines (spectroscopic binaries).
### Conclusion
Not all star systems have two suns. Our own Solar System, for example, has only one star. In binary star systems where there are indeed two stars, several factors can affect our ability to see both stars, including differences in brightness, distance, orbital configuration, and the type of stars involved. Advances in technology and observational techniques continue to improve our ability to detect and study binary star systems, revealing more details about their nature and dynamics.
