Astronomy: Cosmic bling

Published: September 15, 2013

When two dead stars collide, gold is created.

The announcement was short. It lasted only a fraction of second — a blink of an eye. But a spacecraft in Earth’s orbit, keeping an eye on such events, captured it on June 3 this year. The announcement may have been brief, but it told us that two exotic dead stars, called neutron stars, have collided with each other. This is a relatively rare event, but it bears good news for the merchants in the Sona bazaar. This collision has created gold — lots of it.

But before you head over to Sona bazaar, you should know that this particular collision happened in a galaxy so far away that it has taken light — traveling at a stupendous speed of 186,000 miles every second — four billion years to reach us! In astronomical terms, this collision happened in a galaxy four billion light-years away. In comparison, light from our Sun gets to us in 8 minutes, and is therefore only 8 light-minutes away. The distance of billions of light-years doesn’t intimidate astronomers, as they routinely study events and objects that are even farther away than this particular galaxy. The significance of this event, however, resides in the fact that for the first time, astronomers have been able to study light from collisions that may help us understand the way elements like gold are created in the universe.

Before we get too caught up in the cosmic glamour, we should remember that almost all of the elements that make our bodies were cooked up inside the stars: the carbon in our DNA, oxygen in our lungs, and iron in our blood. Hydrogen in the water molecule, on the other hand, is a leftover from processes in the early history of the universe. The classic quote from the late astronomer Carl Sagan is indeed true: “We are made up of star stuff”.

But for years, astronomers had been seeking an explanation for elements like gold, lead, platinum etc. It was thought that most of them formed when large stars — stars that are ten times the size of our Sun — die in large explosions called Supernovae. However, calculations showed that supernovae in the universe could only account for a fraction of these elements. There must be another way to make gold in the universe.

Now we know how.

Here is the recipe: You take two stars that are orbiting each other. This is not as hard as it seems. Nearly half of all stars in our own Galaxy have at least one other star in its system. But make sure that both of these stars are at least 10 times bigger than our Sun. Then wait about 10 million years. This is the average lifetime of big stars. They will eventually exhaust all their fuel and explode in their individual supernovae. All that will be left of them will be their cores, called neutron stars. These are some of the strangest objects in the universe. Each of the neutron star contains mass equal to that of our Sun, but all packed in a size no greater than a city like Karachi. This means that they have very high density. A teaspoon of neutron star material would weigh as much as a mountain. Now you have two of these neutron stars orbiting each other. But orbits for such exotic objects are unstable. The two stars will eventually collide with each other — and this collision will result in the creation of gold and other rare elements.

However, in an act of ultimate charity, these elements are spread into the surrounding space.

By the time our Solar system was born, many such collisions had enriched our Galaxy with gold (and other elements). The gas cloud that formed the Sun and the Earth already contained these elements. Some of this gold became part of the Earth. Four-and-a-half billion years later, this rare element caught the attention of bipedal species and it became an object of desire and envy.

So the next time when you wear a gold ring or necklace, pause for a minute and appreciate how the cosmos gave us bling.

Salman Hameed is associate professor of integrated science and humanities at Hampshire College, Massachusetts, USA. He runs the blog Irtiqa at irtiqa-blog.com

Published in The Express Tribune, Sunday Magazine, September 15th, 2013.

Reader Comments (3)

  • Galba
    Sep 15, 2013 - 2:06PM

    I ve been a astronomy follower all my life but lately I ve realized that at times it becomes a bit too fictional! I mean, studying and inferring from stuff happening 4bn LY is bit too distant from the very rationality and logic science is founded upon. Most of these endeavours are to prove something that helps negates creationism and rationalize everything. Most of it is fascinating yet far from reality and they call it ‘logic’.

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  • Philip de Louraille
    Sep 15, 2013 - 6:21PM

    You must have missed when the article said “However, calculations showed that supernovae in the universe could only account for a fraction of these elements. There must be another way to make gold in the universe.”

    In other words, a “normal” supernova, while generating all the elements, did not produce enough to explain the amount found on Earth. Out of mathematical calculations.

    Hence physicists, rather than wave their hands and said ‘and magic happens here’, had to think hard enough to come up with an idea to explain the abundance and with a lot of calculations on fast computers realized that it took 2 neutron stars to collide to come up with the numbers we see on Earth. They also had to compute the expected rate of such neutron star collisions to make sure it is not so rare as to make it improbable. And so on and so forth. Science is based on facts or on assumptions that are validated by solid arguments and scrutiny is welcome.
    However, what you find too fictional is not what I would call good scrutiny. You would have to validate this with substance.

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  • Sep 15, 2013 - 6:55PM

    Galba,
    Two things: a) It has to do with our ability to analyze light. If we can get light (and this where large telescopes come in), then we can analyze it. How can we say something about the elements in a galaxy so far away? Spectroscopy! (this is the just like the way a prism divides up light into its different components). It is this tool that allows us know the composition of the Sun and other stars. The key is that elements – all elements – have very specific light signatures (like fingerprints). If you have a spectrograph on a large telescope, you can identify those elements – even if a galaxy is located 4 billion light years away!

    b) Actually, the farthest objects that astronomers have observed lie much farther than 4 billion light years. In fact, we can trace galaxies only a few hundred million years after the Big Bang – that happened 13.8 billion years ago. The fact that we can identify the age of the universe so precisely has to do with the analysis of the light that was emitted only a few hundred thousand years – 380,000 years to be precise – after the Big Bang. This light is the Microwave Background Radiation that was discovered in 1965 and garnered Nobel Prize for its discoverers.

    So – rationality and logic is still solidly in place.

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