We present a general star formation law where star formation rate depends upon efficiency \alpha , timescale \tau of star formation , gas component \sigma _ { g } of surface mass density and a real exponent n .
A given exponent n determines \tau which however yields the corresponding star formation rate .
Current nominal Schmidt exponent n _ { s } for our model is 2 < n _ { s } < 3 .
Based on a gravitational instability parameter Q _ { A } and another dimensionless parameter f _ { P } \equiv ( P / G \sigma _ { c } ^ { 2 } ) ^ { 1 / 2 } , where P = pressure , \sigma _ { c } = column density of molecular clouds , we suggest a general equation for star formation rate which depends upon relative competence of the two parameters for various physical circumstances .
We find that Q _ { A } emerges to be a better parameter for star formation scenario than Toomre Q-parameter .
Star formation rate in the solar neighbourhood is found to be in good agreement with values inferred from previous studies .
Under closed box approximation model , we obtain a relation between metallicity of gas and the efficiency of star formation .
Our model calculations of metallicity in the solar neighbourhood agree with earlier estimates .
We conclude that metallicity dispersion for stars of same age may result due to a change in efficiency through which different sample stars were processed .
For no significant change of metallicity with age , we suggest that all sample stars were born with almost similar efficiency .