Podcaster:  Pamela Quevillon

Title:  The Circle of Life

Organization: Speak Easy Narration

Link ;

Featured image credited to : ESO

Description:  This is the 2nd audio from Space Scoop, a product of “Universe Awareness”. Our goal is to inspire every child with our wonderful cosmos.

Bio: Pamela Quevillon is a voice actress who most often lends her voice to science and science fiction content. You can find her work on the “Escape Pod” and “365 Days of Astronomy”, as well as on her site

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by — no one. We still need sponsors for many days in 2013, so please consider sponsoring a day or two. Just click on the “Donate” button on the lower left side of this webpage, or contact us at


Hello and Welcome to 365 Days of Astronomy for June 4. In today’s episode, we bring you another Space Scoop in collaborations with the European “Universe Awareness” project, which seeks to inspire every child with our wonderful cosmos.

Today’s edition is titled: The Circle of Life

Looking up at the night sky it’s hard to believe that stars don’t live forever. Most of the little twinkling lights we see scattered across the night sky have been there for the entirety of human history. But in reality, like humans, stars are born, they live, they grow old and eventually die. How they die, though, depends on their mass. Small stars gently puff out of existence, like blowing out a candle. Massive stars die in dramatic explosions, billions and billions of times more powerful than an atomic bomb!

Until recently, Astronomer’s believed that we’d pretty much figured out the exact life-cycle of stars that have around the same mass as our Sun. It was expected that stars like the Sun would blow off much of their atmosphere into space near the end of their lives. This material then goes on to form the next generation of stars. Like the circle of life on Earth.

A new study, however, has shaken the world of space science. A study of the ancient stars living in a globular cluster (which is a huge group of stars) shows that many Sun-sized stars never go through this stage of life at all!

The results of the study were a big surprise. It turns out that up to 70% of ancient stars skip this mass loss phase altogether! Instead they evolve directly into retirement as white dwarf stars. While these stars are similar in size to our sun, they are made of of a different combination of ingredients, and it appears that how much sodium is in the star helps to determine how it dies.

Here’s a Cool Fact
Do you know why no-one has ever seen what happens when a low-mass star dies? Well, the Universe is around 13.8 billion years old. Stars with about 10 times less mass than our Sun have enough energy to live for six to twelve trillion years. That’s longer than the Universe has even existed, yet!

The stars astronomers observed in this project are located in a distant globular cluster called NGC 6752 that is in the constellation Pavo, the Peacock. Visible to southern hemisphere observers, this collection of stars was made into an official constellation in 1603 by German celestial cartographer Johann Bayer. It is one of several celestial birds in this region, including Apus, Tucana, Grus and Phoenix. In mythology the peacock was sacred to Juno, goddess of the heavens from whose breast the Milky Way sprang.

While all stars seem to form in clusters, not all the clusters stay bound together through the eons the way NGC 6752 is bound together. Most regions of star formation that you can see in the sky are in a different type of cluster, called an open cluster, that will fall apart as it orbits our galaxy.

If you go outside in late October, it is possible to see a variety of star forming regions doting the sky. The easiest to find set is the Orion Nebula in Orion’s sword, the Pleiades cluster near Orion, and the Hyades cluster that is around the eye of Taurus the bull. You can see these stellar nurseries from most regions on the Earth.

Each of these systems is the home of young stars, but while the Orion nebula is very much a stellar nursery, with stars just 10 million years old or younger, the Pleiades, is more like a day care center with stars 100 million years old or younger. At the same time, Hyades is more like an afterschool program for stars 730 million years old or younger. All these systems are filled with celestial children. In their youth these stars still gather in clumps. But, as they age, the stars will drift apart until, as adults, they have no memory of the place they were born. Our Sun is one of these solitary stars and every time I introduce my students to these three open clusters, they ask what happened to the open cluster where our Sun was born. (Image Credit: NASA,ESA, M. Robberto (Space Telescope Science Institute/ESA) and the Hubble Space Telescope Orion Treasury Project Team)

The truth is, the cluster and our Sun had a falling out.

Once upon a time, somewhere in our galaxy, our Sun’s atoms were part of a giant molecular cloud. Approximately 7 billion years ago, that molecular cloud was bumped. Exactly what did the bumping no one knows. That anonymous bump so shocked the dark molecular cloud that in recoiled and collapsed in on itself. At first this inward spiral wasn’t at all dramatic, and an imaginary space traveler looking at this shocked cloud with her imaginary eyes might not have perceived the motion. Over time, however, momentum built up, and the collapse gained speed, with the densest parts of the cloud pulling themselves into fragments, as more ethereal parts were left behind to collapse more slowly. In one of these collapsing regions a womb of gas and dust that was neither too big nor too small began to glow as a single star exhaled its first breath of heat. As it grew and began to illuminate its surroundings, a disk formed; a disk containing just enough stardust to someday form 8 planets and a lot of harder to categorize smaller bits.

While this star, which would come to be called “The Sun,” was busy forming, its nursery mates were similarly busy growing, glowing, and in some cases even going an extra step and exploding. This stellar nursery was filled with screaming stars that wept radio waves and threw off high energy jets as they tried to find their way onto the main sequence. While these stars wailed and grabbed at matter, they also traveled as a pack around the galaxy. While we can’t do more than guess at the Sun’s original orbital position, we know that today it takes about 135 million years for the Sun to orbit the galaxy. Let’s assume for a minute that the Sun emerged from the center of of that cluster. This would put it in a position to watch some of its nursery mates race ahead around the galaxy, take less time to orbit, while other of its nursery mates slowly fell behind, taking longer to orbit (and a few just explode themselves into oblivion as supernovae). After a few orbits and a few hundreds of millions of years, these differences in speed caused the fastest (and slowest) stars to fall out of the cluster, as their positions no longer made it possible for the casual observer to match them up with their cluster of origin. Over time, differences in orbital velocities drew more and more of the stars away from their siblings. Eventually, it became impossible to tell exactly which stars made up those sibling stars to the Sun.

The Sun, like its sisters and brothers, simply fell out of the cluster as it raced around the galaxy, just as a runner might fall away from the pack.

We are an orphan system, alone in the galaxy. Unlike the majority of stars, our Sun has no companion. Having escaped the chaos of our home, we are now simply alone.

This has been “The Circle of Life.” If you’d like to learn more about this science, or about the Universe Awareness project, check out the links on

End of podcast:

365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by the New Media Working Group of the International Year of Astronomy 2009. Audio post-production by Preston Gibson. Bandwidth donated by and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at or email us at In the new year the 365 Days of Astronomy project will be something different than before….Until then…goodbye.