A recent BFD article reported new research suggesting that the first stars may have shone much earlier than we thought. Now we have an insight into how at least one of those first-generation stars died.
Spectacularly, in a word.
Most of you will be familiar with novae. These occur when a particular type of star nears the end of its life and gravitational collapse and runaway fusion cause it to explode. The sudden increase in brightness (where the star was previously often invisible to the naked eye) leads to the term “nova”, meaning “new” star. Novae are relatively common: about ten occur every year. Really bright ones, several times a century.
Less common are the supernovae. These are novae on a colossal scale. At its peak, a supernova can (briefly) outshine an entire galaxy.
So, what could be bigger than a supernova? A hypernova.
Around 13 billion years ago a star died a violent death in a massive explosion that was much more powerful than a supernova.
Evidence of this cataclysmic event, known as a hypernova, is in the chemical pattern of a newly discovered star, which has elements that could only have been created by such a huge explosion.
You’ve probably heard the saying that “we are all stardust”. What this means is that the elements that make up every atom of the Earth, and us, were formed inside a star that later exploded.
The early universe was made up almost completely of light elements like hydrogen and helium. Those condensed into the first stars. Stars are gigantic nuclear fusion reactors: as the first generation of stars cooled and died, the hydrogen and helium in their cores fused into heavier elements.
When those stars exploded, they spewed out gigantic clouds of gas and dust full of those elements. Those clouds later condensed into new stars. The fusion cycle started again — and the second-generation stars fused even heavier elements.
And so the cycle went on.
The quantities of heavy elements in a star suggest which generation it belongs to. Our Sun is thought to be a third-generation star.
The composition of a newly-discovered star is quite unusual.
“We’ve never seen this particular pattern in a star before,” said study co-author David Yong, an astronomer at the Australian National University.
“These objects are very, very rare.”
Dr Yong and colleagues discovered the star located 7,500 light years away while searching for ancient stars using the SkyMapper telescope at Siding Spring Observatory in New South Wales[…]
Dubbed, SMSS J200322.54-114203.3, the star had a had an iron-to-hydrogen ratio around 3,000 times lower than the Sun, suggesting it formed around 13 billion years ago.
But the star also had very high levels of heavier elements than iron such as zinc, uranium, europium and possibly gold.
This combination of elements makes it extremely unusual for stars of its age.
While we know that elements as heavy as iron can be fused inside stellar cores, the origin of really heavy elements like uranium and gold remained a mystery. Enter the hypernovae.
Heavier elements were thought to be generated by the dead cores of massive stars, known as neutron stars, smashing together.
In 2017, scientists caught a glimpse of this process through the detection of gravitational waves produced by the collision.
But the chemical pattern of the newly discovered star doesn’t match those that are generated by neutron star mergers, Dr Stuart Ryder said[…]
The only explanation that fits is that the star got its unique chemical pattern from the destruction of a massive, whirling star called a magneto-rotational hypernova.
The only problem is that hypernovae are hyper-rare.
“These objects have been theorised, but they’ve never been observed.
“Now we have for the first time evidence that these objects may have existed in the early universe.”
ABC Australia
The speed of light means that looking further away in space is also looking further away in time. To look at the early universe, we have to look a long way. So far away that the objects are incredibly hard to detect. But space-based telescopes like Hubble are allowing us to do just that.
And we are discovering that the early universe was a very violent, yet creative, place.
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