Sky Matters: Neutron stars are very rare and are amongst the densest objects known in the universe

There’s a popular programme called ‘Who Do You Think Your Are?’ which charts the genealogy of individuals, usually celebrities, perhaps as far back as a few hundred years.

These are often fascinating stories, but they really only scratch at the surface of the real story about our origins. 

To appreciate this, ask yourself the question — where did the atoms in my body come from and how old are they?

Finding the answer to this fundamental question has been one of the greatest achievements of modern science. 

Take the water in your body. It is composed of two hydrogen atoms and one oxygen atom. 

We now know the hydrogen was created about 13.7 billion years ago during the creation of the universe itself. 

The oxygen was created millions to billions of years later by massive stars as they exploded at the end of their lives in violent supernova explosions.

By contrast, the carbon which makes up much of the sophisticated molecules in our bodies (including much of the DNA molecule that encodes life) likely came from stars like our Sun as they gently expanded and shed their outer layers towards the end of their lives.

It’s fascinating to wonder whether all the oxygen or carbon (or other elements) in your body came from the same dying stars, and whether the stars that makes me who I am are also the stars that have made you.

And recently there has been a dramatic twist to this story. 

When massive stars explode, stars several times larger than our own sun, the explosion compresses the centres of the stars into incredibly dense material made up almost exclusively of neutrons and hence these are called neutron stars.

The matter we are all familiar with on Earth is composed of neutrons, protons and electrons. 

Neutron stars are very rare and are amongst the densest objects known in the universe — a teaspoon would weigh 10 billion kg, equivalent to 20% of the Earth’s population standing on that single teaspoon!

In August 2017 two distant neutron stars were observed colliding, resulting in an explosion of truly cataclysmic proportions. 

The light from this explosion was picked up by telescopes from across the globe and astronomers discovered that in the collision massive amounts of elements such as gold were produced, along with other elements including lead, and radioactive elements such as uranium.

This solved a long-standing mystery about how to make gold and other elements. (Contrary to the belief of alchemists of the 18th and 19th and possibly 20th century, you can’t make gold from lead in a beaker in a chemistry lab!)

So next time you look up at the sky have a thought about this. 

The stars which appear blue are massive and are likely to explode at the end of their lives generating elements such as oxygen, sodium and magnesium.

The stars which are more yellow in colour are likely to be similar to our Sun and they will eject elements such as carbon and nitrogen as they die. 

And the invisible neutron stars, lurking in the darkness to our unaided eyes, may end up generating gold, lead, uranium and other exotic elements in fantastically energetic explosions.

And writing of explosions, a larger-than-usual lump of rock crashed into the Earth’s atmosphere in December last over the Bering Sea, off Russia’s Kamchatka Peninsula, releasing 10 times the energy in the atom bomb dropped on Hiroshima.

A much less dangerous show of celestial fireworks is due on the evening of April 22 and into the morning of 23 when the Earth ploughs into the dust tail of comet Thatcher.

This annual meteor shower, known as the Lyrids, may not generate any new elements, but they’re worth a watch. 

Just give your eyes 20 minutes to fully adapt to the dark and you should see a meteor every few minutes.

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