60017 is or answer ok you got it
There is synthesis
decomposition
double displacement
single displacement
combustion
metathesis
so i guess you could say 6
1. it is difficult to search for it . Because infrared rays will never penetrate through earth atmosphere.
2. we are unaware of how it looks like and we only know it is red and will glow . A damaged star also looks like this.
3. Dust also makes is hard to detect Dyson spheres . So we will get confused between Dyson sphere and a star surrounded by dust.
