Star formation rate

The star formation rate (also: star formation rate , English Star formation rate - abbreviated as SFR ) describes the time profile of the star formation in a galaxy . It is an important parameter for understanding galaxy evolution . The star formation rate is usually given in terms of solar masses per year.

A related quantity is the areal density of the star formation rate. It indicates how many stars are formed per year and per unit area of ​​a disk galaxy: ${\displaystyle \Sigma _{\text{SFR}}}$

${\displaystyle \Sigma _{\text{SFR}}={\frac {SFR}{A}}}$

and is therefore given in solar masses per year and square parsec .

Relationships with the density of the interstellar medium

The empirical relationship between the star formation rate and the density of the interstellar medium is used in simulations of galaxy evolution. ${\displaystyle \rho }$

Schmidt law

In 1959, the Dutch astronomer Maarten Schmidt found the empirical connection for the sun's environment in the Milky Way :

${\displaystyle SFR\propto \rho ^{n}}$

The observed star formation rate at high gas densities is described very well with an exponent . With low gas densities, however, it must be taken into account that a minimum density is required for star formation. ${\displaystyle n\approx 1{,}3}$

Schmidt-Kennicutt law

The Schmidt law was carried over to other galaxies by Robert Kennicutt in the form of the Schmidt-Kennicutt law. It describes the relationship between the areal density of the star formation rate and the gas density accumulated in the line of sight (in grams per square parsec): ${\displaystyle \Sigma _{\text{gas}}}$

${\displaystyle \Sigma _{\text{SFR}}\propto (\Sigma _{\text{gas}})^{n}}$

The exponent is independent of the star formation history, the metallicity or the population composition of the galaxies. ${\displaystyle n=1{,}45\pm 0{,}2}$

The Schmidt-Kennicutt law applies at least five billion years in the past, an extension to even higher redshifts (i.e. age groups) is assumed. Starburst galaxies that show a temporarily higher star formation rate due to an interaction with other galaxies show a strong deviation from Schmidt-Kennicutt's law .

Web links

• Astronomers discover the cause of the high birth rate in the young universe
• The Rate of Star Formation , by Maarten Schmidt
• astronews.com: Radio data reveals star formation rate February 22, 2017

Individual evidence

1. ↑ S. Komugi et al .: The Schmidt-Kennicutt Law of matched Age Star Forming Regions; Pa-alpha Observations of the early-phase Interacting Galaxy Taffy I . 2012, arxiv : 1208.0315v1 .
2. ↑ Maarten Schmidt: The Rate of Star Formation . In: The Astrophysical Journal . tape 129 , 1959, pp. 243 , doi : 10.1086 / 146614 .
3. ^ Robert C. Kennicutt, Jr .: The Global Schmidt Law in Star-Forming Galaxies . In: The Astrophysical Journal . tape 498 , 1998, pp. 541 , doi : 10.1086 / 305588 , arxiv : astro-ph / 9712213 .
4. ↑ B. Fuchs, H. Jahreiss, C. Flynn: A Schmidt-Kennicutt law for star formation in the Milky Way disk . 2008, arxiv : 0810.1656v1 .
5. ^ J. Freundlich et al .: Towards a resolved Kennicutt-Schmidt law at high redshift . 2013, arxiv : 1301.0628v2 .
6. ↑ Médéric Boquien, Ute Lisenfeld, Pierre-Alain Duc, Jonathan Braine, Frédéric Bournaud, Elias Brinks, Vassilis Charmandaris: Studying the spatially resolved Schmidt-Kennicutt law in interacting galaxies: the case of Arp 158 . 2011, arxiv : 1107.0969v1 .