International Journal of Astrophysics and Space Science 2021; 9(3): 45-50 http://www.sciencepublishinggroup.com/j/ijass doi: 10.11648/j.ijass.20210903.12 ISSN: 2376-7014 (Print); ISSN: 2376-7022 (Online) Density, Alternative Determinant of Star Formation Efficiency of the Milky Way GMCs: Core Reason for Low Star Formation Efficiency Okezuonu Patrick Chinedu, Ogwo Jemima Ngozi Department of Industrial Physics, Faculty of Physical Science, Abia State University, Uturu, Nigeria Email address: To cite this article: Okezuonu Patrick Chinedu., Ogwo Jemima Ngozi. Density, Alternative Determinant of Star Formation Efficiency of the Milky Way GMCs: Core Reason for Low Star Formation Efficiency. International Journal of Astrophysics and Space Science. Vol. 9, No. 3, 2021, pp. 45-50. doi: 10.11648/j.ijass.20210903.12 Received: October 11, 2021; Accepted: November 5, 2021; Published: November 24, 2021 Abstract: The overall efficiency with which Milky Way Giant Molecular Clouds (GMCs) is forming stars was determined by deriving an equation using density of cloud (i.e. stellar density/ total cloud density), which is the core parameter that determines star formation other than the mass of cloud, and comparing with mass (i.e. stellar mass/ total gas mass) as was propounded by previous researchers, to ascertain the reasons the observed star formation efficiency of Milky Way Giant Molecular Clouds ( ) is low. This will aid understanding the physical factors behind the formation of stars from interstellar gas and develop a predictive theory of star formation and evolution of galaxies. A total of 191 star formation complexes-giant molecular cloud (SFC-GMC) complexes was used in estimating the following cloud parameters: density as 93.8218 solar mass/parsec squared, average stellar density as 2.67872 solar mass/parsec squared, average luminosity as 9.87E24 solar luminosity, average effective temperature as 498,647 solar temperature, average stellar radius as 51.4522 parsec and average cloud radius as 325507 parsec as well as the total mass in stars M harbored by the individual clouds (20,831 solar mass), which was inferred from Wilkinson Microwave Anisotropy probe (WMAP) free-free. Finally, the overall efficiency with which Milky Way Giant Molecular Clouds is forming star gave 0.0289573 which is less than the previous estimate as 0.030849, showing that not all the masses of the cloud were present at the end of the star formation, and this reduction in mass are caused by magnetic field, supersonic turbulence, self-regulation and unbound states of its internal structure, which are the reasons the observed star formation efficiencies are low. Keywords: Galaxies, Star Formation Efficiency, Cloud Density, Stellar Mass, Gas Mass 1. Introduction Everything known about galaxy, such as its observations, definition etc. is through its stellar contents. Therefore, any theory of galaxy formation has to start by addressing how stars’ form, the main processes that drive star formation and what mass fraction of a gas cloud can be converted into stars (star formation efficiency (SFE or )). Star formation on the other hand is the process by which interstellar medium of gas and dust collapse and form stars in its dense region known as molecular clouds or star-forming region [24]. “Lee et al and Murray N. defined star formation efficiency of the GMCs ( ) as the fraction of the GMC that is converted into stars over the lifetime of the GMCs [16, 22]”. Mathematically is defined as the total mass in stars, produced over the life time of the GMC, divided by the overall GMC mass which also includes the total mass in those stars (1) where is the total mass of the individual stars inside the clouds, is the total mass of the remaining cloud that does not finally convert to star and is the total mass of the cloud. After thorough examination on this parameter (Mass) found in equation (1), it was found that using mass to calculate the efficiency of clouds in forming stars cannot provide the exact value for the prescribed efficiency because some of these masses of the clouds have been destroyed by both internal and