its not about stars its about mass and he proposed that mass can be converted into energy
Um... yes? Light is a form of energy. Energy has mass.
In the beginning of the 20th century. He proposed mass-energy equivalence in 1905, and set out to mathematically express this. E = mc2 shows that energy can be converted into mass, and mass into energy. Thus, we no longer say that mass is conserved, or energy is conserved. But rather, we say that mass-energy is conserved.
No. Sound is mechanical energy. Mechanical energy does not have mass. And no form of energy has mass. But energy has a mass equivalent per E=mc2 thanks to Albert Einstein.
Light does not have mass. It is a form of energy.
Matter is indeed another form of energy, as proposed by Einstein with his famous equation e=mc^2.
The Law of conservation of Energy applies to mass as mass is a form of energy, E=mc2.
One instance, when a particle is accelerated with sufficient kinetic energy, that energy can change into mass in the form of subatomic particles.
It's because they emit radiation, and radiation is a form of energy and energy is a form of mass.
A gravitational field affects everything that has energy (or mass, but mass is a form of energy). As such it affects virtually everything.
It isn't. This is a popular statement, but it is complete incorrect. Both mass and energy are conserved. Energy: The energy was already available previously, but in another form (nuclear energy, which is a type of potential energy). Mass: The heat or light that is produced is energy; it has an associated mass. For example, the photons (light) that leave the Sun not only take energy, but also mass, away from the Sun. This mass is exactly equal to the "missing" mass.
No. Nor can you convert mass into energy. In any reaction - including nuclear reactions - both the amount of mass and the amount of energy remain the same, before and after the reaction. For example, the energy that escapes from a nuclear reaction also has a corresponding mass. On the other hand, the energy existed before the reaction as well, in the form of (nuclear) potential energy.