10 Facts About The Universe That Make Your Brain Hurt

9. Up To 4800 Stars Are Born Every Second

It's an educated guess of course, but how realistic is that? More to the point, how would you go about working something like that out? It's a lot of stars and does it account for the universe getting bigger, or expanding all the time? The expansion of the universe is due to other factors; however, if we keep focus on those stars being reformed out of existing material then we can see a way to work it out. The question then becomes how much dust and gas becomes stardust each year. Yes, it's true to say that it takes a long time to make a star, eons in fact, but what we sometimes lose sight of is that the process is continuous. In the Milky Way the star formation rate is about 3 solar masses per year and one solar mass is equal to the mass of our Sun = 2x1027kg. It's another way of saying that enough basic material to construct three suns is used every year. That's only on average remember, since every star varies in size and mass from the next. Our sun is a pretty common size, so it's fair to say we get three per year. Now we know other facts such as the number of observable galaxies there are and the density of the universe immediately following the Big Bang, (back to that Planck density we mentioned at the introduction). From this astronomers extrapolate the number of probable galaxies in existence to around 50 billion. Already the numbers are getting pretty awesome and it's easy to see where all this star raw material comes from. Just as there are many different types of star there are three different types of galaxy with a few subdivisions in the classification: spiral, irregular, elliptical. Similarly, the same logic as for suns also applies to galaxies. If ours is average then through extrapolation we can also reasonably suggest that 3 per galaxy x 50 billion = 150 billion is accurate enough. That's 400 million stars born per day, or 4800 per second!