astronomy Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest includ ...

, the Kennicutt–Schmidt law is an empirical relation between the surface gas density and star formation rate (SFR) in a given region.The name "Schmidt law" is now commonly used for a general relation between volume gas density and star formation rate, and the Kennicutt-Schmidt law for the surface gas density and star formation rate. The relation was first examined by

Maarten Schmidt Maarten Schmidt (28 December 1929 – 17 September 2022) was a Dutch-born American astronomer who first measured the distances of quasars. He was the first astronomer to identify a quasar, and so was pictured on the March cover of ''Time'' mag ...

in a 1959 paper where he proposed that the SFR surface density scales as some positive power

n

of the local gas surface density. i.e. :

\Sigma_ \propto (\Sigma_)^n

. In general, the SFR surface density

(\Sigma_)

is in units of solar masses per year per square parsec

(M_\odot  ~\textrm^ \textrm^)

and the gas surface density in grams per square parsec

(\textrm~\textrm^)

. Using an analysis of gaseous helium and young stars in the solar neighborhood, the local density of

white dwarfs A white dwarf is a stellar core remnant composed mostly of electron-degenerate matter. A white dwarf is very dense: in an Earth sized volume, it packs a mass that is comparable to the Sun. No nuclear fusion takes place in a white dwarf; what ...

and their

luminosity function A luminous efficiency function or luminosity function represents the average spectral sensitivity of human visual perception of light. It is based on subjective judgements of which of a pair of different-colored lights is brighter, to describe re ...

, and the local helium density, Schmidt suggested a value of

n \approx 2

(and very likely between 1 and 3). All of the data used were gathered from the Milky Way, and specifically the solar neighborhood. In 1989, Robert Kennicutt found that the H

\alpha

intensities in a sample of 15 galaxies could be fit with the earlier Schmidt relations with a power law index of

n = 1.3 \pm 0.3

. More recently, he examined the connection between surface gas density and SFR for a larger set of galaxies to estimate a value of

n = 1.4 \pm 0.15

References

{{DEFAULTSORT:Kennicutt-Schmidt law Stellar astronomy Galaxies Star formation