“Change, like sunshine, can be a friend or a foe, a blessing or a curse, a dawn or a dusk.” -William Arthur Ward
Few things are as essential to our world as we know it as the primary source of our light, heat, and all the life that flourishes on Earth as the Sun itself.
And yet, there are two things that may strike you as very important when it comes to our Sun. One may be the fact that, at 150 million kilometers (93 million miles) distant, the Sun is so much closer to us than even the next closest star: Proxima Centauri.
At forty trillion kilometers distant, Proxima Centauri is over 200,000 times farther away than our Sun, giving you an idea of the great distances between the stars in our sky, and how fortunate the Earth is to be bound to our Sun.
The other thing that’s striking, once you learn a bit about the timeline of the Universe, is that even though the Sun has been around for billions of years, the Universe existed for over nine billion years before the Sun came into existence! So where, then, did our Sun come from?
The Sun, like all stars, didn’t simply pop into existence. And what’s more: the environment it formed in is dramatically different from the environment we live in now.
In order to form any sort of collapsed object, you need to start with a more diffuse set of matter that will contract down to a more compact configuration. All throughout the galaxy, we find molecular clouds that are doing exactly that.
This is what’s going on inside the Great Orion Nebula, above. Molecular gas clouds, composed of a combination of pristine gas untouched since the Big Bang as well as recycled material expelled from previous generations of stars, contract down under the relentless force of gravity.
In order to do so, these clouds must be huge: much more massive than the material required to form a single star. And when you accumulate enough of this diffuse matter in one location, and it begins to contract, there are inevitably some regions that become densest the fastest. And — because that’s how gravity works — these places that become denser pull progressively more matter in atop themselves, limited only by how quickly they can dissipate the energy associated with this gravitational contraction. If we peer deeply into the dark depths of these clouds — like the Horsehead Nebula — what is it that we find?
There are stars forming in there! In fact, this is how stars form throughout not only our own galaxy, but all galaxies in which new stars are observed to form: in clusters. Typically containing thousands of stars separated only by maybe twenty light years, this is what these dusty, contracting nebulae will turn into as the effects of gravity run its course.
And over enough time, all of the gas will either form stars or be stripped away from heat, pressure, or interactions with other galactic material in relatively short order. Stars are still actively forming in NGC 3603 above, making it one of the places we’re optimistically hoping will soon bring us a supernova within our own galaxy. But when the dust is all gone, no new stars form, and all we can do is watch as the heaviest, most massive stars die off. What’s left behind is known as an open star cluster, like the Wild Duck Cluster (Messier 11), below.
Messier 11 is 220 million years old: less than 5% the age of our Sun. Yet it is not young for an open cluster; all of the brightest, most massive O-stars (and most of the B-stars) have already died, spending all of their fuel. Although in extremely rare instances, open star clusters can hold together for billions of years, most star clusters get ripped apart by the gravitational influence of our galaxy!
Nearly three times the age of the Wild Duck Cluster, the Hyades is down to maybe 200-400 stars, about a third of which are in the process of gravitational escape from the cluster. We can also see a number of stars that have just finished escaping from the Hyades: there’s a star stream that’s at least partially left behind by the cluster!
In fact, based on the velocities of the stars, we can extrapolate back in time and find that the Hyades was a more massive, tightly-bound cluster in the past!
Over the 4.5 billion years since our Sun formed in an open cluster, all of the stars that formed along with it were scattered throughout the galaxy, and unlike the stars in, say the Big Dipper, there is no star stream or moving group that we appear to be associated with; our history — like that of all old field stars — is lost to the ages.
But don’t let our forgotten ancestry get you down; our skies are filled with a huge number of easily visible, young star clusters, including this beauty: The Double Cluster in Perseus!
With more than 300 B-type stars in each of these young clusters, dated at 5.8 and 3.2 million years old, respectively, even these two infants are too old to have those extremely short-lived O-stars in them! Find the double cluster on a dark night with your naked eye, just between the constellations of Perseus and Cassiopeia, or grab a pair of binoculars (or a small telescope) and see that it is, in fact, two separate clusters!
What you’ll see is a glimpse of where all our galaxy’s stars once lived: in a stellar nursery. And that’s where the Sun comes from!