Stellar initial mass function varies with metallicity and age of stars, say astronomers

Within the huge and various universe, the preliminary mass distribution on the delivery of a brand new inhabitants of stars determines the destiny of galaxies. This relationship is described by the preliminary mass perform (IMF). For greater than half a century, astronomers have assumed that the IMF is a common relationship, i.e., it’s uniform all through the universe.

Nonetheless, in recent times, some indications counsel that in some galaxies the place star formation is especially lively, the IMF could also be of a distinct kind than is usually assumed within the Milky Way. However to totally confirm these outcomes, astronomers might want to discover extra direct observational proof within the Milky Way.

Now, based mostly on the Massive Sky Space Multi-Object Fiber Spectroscopic Telescope (LAMOST, often known as the Guo Shou Jing telescope), a analysis staff led by Prof. Liu Chao from the Nationwide Astronomical Observatories of the Chinese language Academy of Sciences (NAOC) has discovered a vital piece of direct proof on how the IMF varies with completely different environments.

This research was revealed in Nature on Jan. 18.

“The IMF varies with ranges of metallic components, and populations of stars born earlier within the universe’s historical past include fewer low-mass stars than youthful populations,” mentioned Li Jiadong, a Ph.D. pupil at NAOC and first creator of the research.

Counting stars in a given quantity is a direct and classical option to measure the IMF of low-mass (red dwarf) stars, whose mass distribution doesn’t evolve with time; this strategy is basically unbiased of fashions or assumptions.

“Though many earlier research utilized star counting to derive the IMF, two issues haven’t been solved. One is that solely a small variety of stars have been counted in earlier work. The second is that earlier research didn’t measure the metallicity of stars,” mentioned Prof. Zhang Zhiyu, co-author of the research.

LAMOST has supplied spectra that include details about the chemical composition, temperature and luminosity of thousands and thousands of stars, enabling the researchers to measure the metallicity of close by red dwarf stars.

By deciding on about 93,000 red dwarf stars in catalogs from each LAMOST and the Gaia survey, the researchers have been in a position to group stars based on their metallicity and calculate the distribution of stellar mass in every group.

The research has revealed the variable abundance of low-mass stars in our galaxy, the Milky Way, and established a robust benchmark for fashions of star formation. The findings might also have an effect on the outcomes of fashions of chemical enrichment of distant galaxies, in addition to estimates of galaxy mass and the effectivity of planet formation.

“As an example, the total stellar mass of galaxies is usually estimated by assuming that the IMF is invariant, but when the IMF is variable, this might change the total mass estimates of galaxies and probably alter the sector of Galactic astronomy,” mentioned Prof. Liu.

Prof. Pavel Kroupa, an authority on the IMF on the College of Bonn, Germany, commented on the outcomes: “On the premise of a big ensemble of well-observed stars, the authors report that the IMF of late-type stars within the native Galactic disk is metallicity- and age-dependent. These outcomes are extremely necessary for addressing how common the stellar IMF is and allow an in-depth understanding of the attainable shifts in stellar populations that shaped at completely different instances and underneath completely different situations within the Galaxy.”