Ask Astro: How many stars are born each year in the Milky Way?

Doug Kaupa 

Council Bluffs, Iowa 

There are a lot of methods to estimate the star-formation fee of the Milky Way, starting from counting younger stars on to measuring the brightness of gasoline and dust which can be not directly heated by radiation from these stars. Though every of those strategies entails considerably unsure assumptions, encouragingly all of them converge on related values of about 1 to 2 solar plenty of stars forming per yr. After all, not all of this mass goes right into a single star. Most stars that kind are low-mass stars with plenty smaller than that of our Solar — the commonest stars in our galaxy are crimson dwarfs. So, on common, we count on that roughly six to seven new stars kind within the Milky Way yearly.

Whereas this might sound small, the star-formation fee of the Andromeda Galaxy (M31) has been estimated to be even smaller at roughly 0.4 solar mass per yr (or only one to 2 stars on common). Taking a look at different spiral galaxies within the close by universe, we see a spread of star-formation charges, but it surely looks like the charges measured for the Milky Way and Andromeda are pretty typical general.

What in the end controls the star-formation fee in a galaxy is the quantity of gasoline obtainable. New stars kind from chilly, dense molecular gasoline; this gasoline is primarily manufactured from hydrogen but in addition incorporates some hint quantities of heavier components and appreciable quantities of dust. Over time, the provision of this chilly molecular gasoline has been step by step depleted as stars crammed the Milky Way. If we might rewind the clock to 10 billion years in the past and consider our galaxy in its youth, we’d see it forming stars at a extra vigorous tempo!

Annette Ferguson 

Professor of Astrophysics, College of Edinburgh, Scotland