Guide to the Cosmos

Making the Wonders of our Universe Accessible to Everyone.

 Newsletter: Stars Just Ain’t What They Used To Be

The heavens were once a blaze with young, brilliant megastars. But those days are long gone.


The production rate of new stars in our universe is now 30 times less than in the heyday, 11 billion years ago. So concluded the largest ever study of star formation.


Our juvenile universe was nearly devoid of carbon and fraught with withering radiation and cataclysmic explosions from frenzied, short-lived, monster stars. It probably could not support life.


The elderly universe will slowly fade to black. Accelerating expansion will carry distant galaxies ever farther and aging stars will eventually twinkle their last. With ever-fewer new stars, the universe will become progressively colder and less habitable.


We exist in the prime of our universe — after the fire, and before the ice.


An international team of astronomers from Portugal, UK, Japan, Italy, and the Netherlands measured the amount of ionized hydrogen in star-forming galaxies at various epochs in our universe’s history. When stars form, their intense radiation ionizes nearby hydrogen atoms, separating their electrons and protons. Later these recombine and emit light of a characteristic wavelength called Hα, the hydrogen alpha line.


Using the UK Infrared, the ESO/VLT, and the Subaru telescopes, the team studied Hα emissions from two areas of the sky covering 2 square degrees, about 4 times the area covered by our Moon. They identified 3701 Hα-emitting, star-forming galaxies at distances out to redshift z=2.23, corresponding to 10.6 billion light-years.


If a galaxy’s light has traveled 10.6 billion light-years to reach Earth, that light reveals the galaxy as it was 10.6 billion years ago, when the light we see today began its journey. Hence, as astronomers look at ever-farther distances they view progressively earlier periods in our universe’s history. We don’t have to guess what happened in the cosmic past; we see the past in our telescopes.


The expansion of our universe is due to the stretching of space. As it stretches so do the wavelengths of light passing through it — the light is redshifted. A redshift of z=2.23 means light’s wavelength is now 3.23 times longer, and the universe is now 3.23 times larger in each direction, than when the light was emitted. From Einstein’s General Relativity and cosmological measurements, we can compute how long ago that was.


Star formation rates were measured at four redshifts, z=0.40, 0.84, 1.47 and 2.23, corresponding to 4.2, 7.0, 9.2 and 10.6 billion years ago. They found a 30-fold decline in star formation rate, as shown below on a logarithmic scale. The study didn’t mention this, but the 30-fold decline happens to match the universe’s 30-fold volume expansion and 30-fold decline in matter density over the same period.



Astronomers believe the first stars formed about 300 million years after the Big Bang, or about 13.5 billion years ago. Some of the first stars were hundreds of times more massive and millions of times brighter than our Sun. These monsters were short-lived, exploding within a million years in spectacular supernovae. Subsequent stars were less massive and burned more slowly. Smaller stars can live for billions or even trillions of years. Our Sun is now 4.6 billion years old, and will probably burn for another 5 to 6 billion years.


This study says half the stars in our universe are between 9 and 11 billion years old; those that are Sun-like are now at the end of their lives. Team leader David Sobral of the University of Leiden said: “If the measured decline continues, then no more than 5% more stars will form over the remaining history of the cosmos, even if we wait forever.”


Billions of years ago, our universe was probably uninhabitable, as it will be again billions of years from now.


This is the Golden Age, my friends; enjoy life while the good times last.


Best Regards,
June 18, 2013


Note: Previous newsletters can be found on my website.


Below are my latest eBooks in the Everyone’s Guide Series.  They are all available for Kindle on and for Nook on Barnes&, for $2.99 each


(Click on each cover for more information.)




Dr. Robert L. Piccioni

Guide to the Cosmos


Author of

"Everyone's Guide to Atoms, Einstein & the Universe"

"Can Life be Merely an Accident?"


"A World Without Einstein"