Twinkle, Twinkle, Little Stars…We are Stardust

One of the first poems we learnt as kids as we looked at the shining stars was ‘Twinkle, Twinkle Little Stars…how I wonder what you are….’
I have often wondered having known the working of our human body, whether we are calling out and remembering longingly our ancestors high up in the distant sky as we sing this poem. Also Joni Mitchell reminds us in her song ‘Woodstock’ (1970s) ‘…We are stardust, We are golden, And we’ve got to get ourselves, Back to the garden…’ is she reminding us that we- humans are stardust.
Here is the fascinating and highly improbable story of why both these lines of thought are true…scientifically speaking


One of the most fundamental basis of many higher life forms on planet Earth is the ability to  pick up oxygen molecules from the atmosphere and through a series of process present it to the billions of tiny microscopic cells in our organ for energy production. It is true when someone said, ‘if we do not inspire (breathe oxygen in), we expire.’ In other words, oxygen is the elixir of life for us.

Central to moving atmospheric oxygen and provide it to every cell in our body is the iron
molecule. It lies at the center of the blood hemoglobin (pictured here)  where its slightest movement  of 0.4 Angstrom (1 angstrom =one ten-billionth of a meter) of the iron molecule is the difference between the ability to pick up or offload oxygen.

One would think as highly improbable and absurd that this iron, central to our existence came from distant stars as stardust and made it into the heart of the hemoglobin molecule.

Indeed, we are stardust…here is this amazing story…improbable but true…

The story starts some 13.7 billion years back when the Big Bang created our universe. Ever since that time, stars across the galaxy have undergone an endless life cycle of birth and death.

In the birth of a star, all matter first is in the form of hydrogen and helium. A relative abundance of hydrogen compared to helium led to an uneven distribution in space which allowed gravity to “clump” these elements together to form nascent stars called protostar.

At the core of these protostars, where the temperature is the highest, matter exists in a soupy mix (plasma) of electrons lying separated from their nuclei. Then, a “flash point” moment is reached. The strong forces cause the nuclei to undergoing fusion-a process that released tremendous amounts of energy. The lightest element hydrogen (H) is the first to reach this flashpoint moment. The H nuclei fuse to form a helium (He) nucleus (process known as hydrogen burning). During most of a star’s lifetime this is the primary fusion reaction that powers the star. The jostling of the outward flow of energy (thermal pressure) released balances the collapsing force of gravity, and this determines a star’s size.
As time passes the fusion process causes more and more He to accumulate in the core. This He uncle now starts to interfere with the H nuclei collisions and reduce the rate of H fusion (sometimes called “helium poisoning”). This process reduces the thermal pressure, and the star begins to contract. The more massive He nuclei are drawn to the center of the core by gravity which is now surrounded by a ‘shell’ of H where nuclear fusion continues. The continued hydrogen burning further boosts the temperature of the He core until a point when He nuclei now start to undergo fusion and through a series of reaction a carbon nuclei is formed.

The tremendous increase in energy produced in the H shell boosts the thermal pressure of the core to the point where it overcomes gravity, and the size of the overall star increases. The increase in the surface area grows at a faster rate than the increase in released energy, so the surface actually cools even though the star is giving off more energy. This causes the star to glow red, and the star is referred to as a red giant.

At this point the star has a central core of He being fused into Carbon (C), surrounded by a shell that has H being turned into He. As the C nuclei are produced, they are pulled toward the center, just as the He nuclei were earlier, and a C core is created. In larger stars, with a mix of increasing temperature, density, and massive gravitational forces the C nuclei fuses into Neon nuclei. This pattern of the central core collapsing and increasing temperature continues by adding cores/shells involve neon being converted to oxygen, oxygen fusing to silicon, and finally, silicon giving rise to nickel which ultimately decays to form iron. Stars that reach this stage are called red supergiants.

The formation of iron represents a critical inflection point in a star’s life. Nuclear fusion of elements until iron is formed releases energy. To make nuclei heavier than iron, however, requires an expenditure of energy. Using resources much faster than can be replenished, the star is now perched on the edge of disaster. The formation of increasing amounts of iron sows the seeds for a violent death of the star.

As energy release declines, the intense forces of gravity takes over which alongwith a decrease in the internal pressure makes the collapse of the core more intense.  For massive stars disaster takes the form of a supernova explosion.

The core collapses inward in just one second to become a neutron star or black hole. The material in the core is as dense as that within a nucleus and cannot be compressed any further. When even more material falls from the outside into this hard core, it rebounds like a train hitting a wall. A wave of intense pressure traveling faster than sound —a sonic boom— thunders across the extent of the star. When the shock wave reaches the surface, the star suddenly brightens and explodes. For a few weeks, the surface shines as brightly as a billion suns while the emitting surface expands at several thousand kilometers per second. The abrupt energy release is comparable to the total energy output of our Sun over its entire lifetime.
Exploding stars eject their outer layers thus belching helium that was formed from
hydrogen burning and launches the carbon, oxygen, sulfur and silicon that have accumulated from further burning into the gas in their neighborhood. These are sprayed into the universe as stardust and overtime some reached Earth. More than 40,000 tons of cosmic dust fall on Earth every year. Here it formed the building blocks of life on Earth. The intense heat enables nuclear reactions that leads to the creation of new elements heavier than iron behind the outgoing shockwave of the supernova (picture showing a bright supernova star on the periphery of a galaxy)

The center the Neutron stars are the collapsed cores of stars that have exploded in a  supernova. The force of gravity is so intense within the neutron star such that a teaspoon full of neutron-star material would weigh, on Earth, about 5 billion tons even though the size of the neutron star may be a few miles in dimension. Most of the neutron stars are solitary wanderer’s but some are paired up, as remnants of binary stars and may collide with each other. In the Milky Way galaxy, with hundreds of billions of stars, such a neutron-star collision is likely to happen about once every 100,000 years. Gold, platinum, lead and uranium, are now considered not to have their origins in supernova explosions but from something even more exotic: the collisions of ultra-dense objects called neutron stars.

Five billion years from now our Sun, a small star, will also undergo a similar fate as its hydrogen fuel is depleted. It will expand to form a huge ‘red giant’ engulfing its planets, including Earth.

Four billion years ago, when the earth was new but before life appeared on it, there was no free oxygen in the air. Instead, earth’s atmosphere contained mostly water vapor, nitrogen, methane and ammonia. The first organisms to develop, probably about 3.8 billion years ago, used these materials for food and energy. Shortly afterwards (as geologic time goes), somewhere between 3.3 and 3.5 billion years ago, there appeared single-celled organisms called cyanobacteria (formerly called blue-green algae), which had the ability to convert energy from the sun into chemical energy through photosynthesis.

Then, sometime between one and two billion years ago, an amazing thing happened. Photosynthetic bacteria learned a new trick. Instead of carrying out photosynthesis with H2S, they used water. And instead of producing sulfur, this process produced molecular oxygen.

This remarkable event transformed the earth and all of the life on it. The oxygen so produced was released into the atmosphere. Many new organisms appeared that acquired the chemical wherewithal to manage and make use of the oxygen. This led to the formation of the porphyrin ring- a part of our hemoglobin molecule to enhance the ability to carry oxygen.

Approximately 450–500 million the hemoglobin molecule was formed with iron from the distant dying stars at the center of our hemoglobin molecule. Similarly, the calcium and phosphorus in our bones all came from distant dying stars.

Now we know why when our kids sing ‘Twinkle, Twinkle Little Stars…how I wonder what you are….’ we may be calling out to our ancestors.

We are stardust! We just have to realize we are special!



Featured Image is Heart of Steel (Hemoglobin) (2005) by Julian Voss-Andreae. The images show the 5′ (1.60 m) tall sculpture right after installation, after 10 days, and after several months of exposure to the elements.