Observations of 140 000 distant galaxies have shown that the stars in them are, on average, larger than those in the Milky Way and the Local Group galaxies.
Since astronomers realised that the most distant luminaries gather into their own galaxies, separate from our own, it has been assumed that their stellar populations are not markedly different. Of course, some galaxies may be older, so many stars in them have already evolved. But the initial mass function (IFM) - the proportion of large, medium and small stars at birth - is assumed to be universal.
However, University of Copenhagen professor Charles Steinhardt and his colleagues recently conducted a new analysis of observations of more than 140,000 distant galaxies. The work has shown that their NFMs are, on average, larger than those of the Milky Way and neighbouring galaxies. The scientists write this in an article published in the latest issue of The Astrophysical Journal.
The mass of stars is perhaps their most important characteristic. It is what determines the character and entire evolution of a star, right up to its death. Thus, small luminaries become dull, almost 'immortal', white dwarfs, while large ones may go supernova to become a neutron star, or even a black hole. This is why knowing the distribution of stellar masses is so important in understanding the composition and dynamics of galaxies.
But to determine the mass of a distant star, you need to at least see it, and other galaxies are so distant that only the most powerful instruments can discern the brightest stars within them. Such data collected in the large-scale catalogue COSMOS (Cosmic Evolution Survey), Danish astrophysicists together with colleagues from the USA.
For the work they used records more than a million observations on the stars of more than 140 thousand distant galaxies - both relatively close, and are on very large distances, up to 12 billion light years. Note that these are not as distant as the oldest galaxies known to date.
The authors looked at the spectrum of these observations because it depends a lot on the mass of the stars: say, larger ones emit more intensely in the blue part of the spectrum, and smaller ones in the yellow-red part. Statistics have shown that the mass of stars in distant galaxies is on average greater than in the Milky Way and its local surroundings, and this difference only increases with distance.
Interestingly, the difference in the nature of star formation also corresponds to this trend. Galaxies full of massive stars produce "inner resources" faster and stop giving birth to new luminaries, while relatively moderate galaxies continue this process for a long time.
