If Stephen Smart is lucky, he may one day receive a message that will give astrophysicists a warning that one of the most unusual displays known to science is about to illuminate the night sky. Signals from automated telescopes and underground detectors will reveal that a star in our galactic neighborhood has just become a supernova.
A supernova occurs when a star destroys itself so completely that it can obscure the combined light of an entire galaxy. In the last thousand years, only five have been visible to the naked eye. Ironically, it all happened before the telescope was invented.
“We know about supernovae from their appearance in other galaxies and from debris left in our own galaxy,” said Smart, an astrophysicist at Queen’s University in Belfast. “But what we’d like to do is see one that appears quite close to us so we can study it with modern telescopes and detectors.”
If a supernova explodes within 10 parsecs of our planet, it is very likely to cause mass extinction, Prof. John Ellis, King’s College London
When a supernova erupts, it sprays space with heavy elements – so observing one nearby would provide valuable information about the creation of matter in our galaxy.
“Most elements heavier than oxygen were created in a supernova before being launched into space,” said Professor Mark Sullivan of the University of Southampton. “These atoms provide the galaxy with material necessary for life. The calcium in your bones and the iron in your blood – as well as the gold in your finger ring – are created by the explosion of supernovae.
This is an image that continues to attract writers and artists. According to Janet Winterson, astronomers have shown that our first real parent was actually a star, and that we are made up of elements that are “the longest-lived radioactive nuclear waste from a supernova explosion.” Or, as Johnny Mitchell put it, simply, “We’re stardust.”
The 16th-century Danish astronomer Tycho Brahe from the 1879 Barcelona edition of La Ciencia y sus Hombres by Luis Figie. Photo: PhotoStock-Israel / Alamy
The most common type of supernova occurs when a very large star runs out of fuel, stopping the fusion process that keeps it glowing. The outer layers of the star fall inward and the protons and electrons are crushed together to form neutrons, which are wrapped in a superdense ball. Matter continues to rain on this neutron ball before bouncing back, causing a shock wave that destroys the star.
All that is left behind is a neutron sphere, which is so dense that a matchbox will weigh about 3 billion tons. And if the original ancestor star that led to the supernova was particularly large, that neutron star will become so heavy that it will form a black hole from which nothing can escape, not even light.
It is a supernova with a collapse of the nucleus and can release more energy than our sun will release in its lifetime of 10 billion years. If a star in our galaxy, too far away to be seen with the naked eye on Earth, becomes a supernova, it will suddenly shine so brightly that it can be seen in daylight.
Scientists estimate that an average of about 20 supernovae appear in a galaxy like ours every thousand years. Yet only five have been observed in the last millennium. East Asian and Arab records show that there were supernovae in 1006, 1054 and 1181, while European documents recall those that occurred in 1572 and 1604.
The first of this last pair appeared in November 1572 and was observed by the Danish astronomer Tycho Brahe. “Suddenly a strange star appeared on top, shining with its light,” he recalled. “When I stood motionless, watching … When I made sure that no star of this kind had shone so far, I was so perplexed by the improbability of the thing that I began to doubt the faith of my own eyes.”
But if supernovae are so brilliant, why have we only discovered five in the last 1,000 years? Why haven’t we seen a number closer to 20 suggested by observations from other galaxies? The answer is clear, Sullivan said. “Our galaxy is like a flat plate and our solar system is about two-thirds of the way to its edge. A supernova that appears on the other side of the plate will simply be eclipsed by all the dust and stars that lie at the center of the galaxy.
Since then, astronomers have observed supernovae in other galaxies and studied the remains of those that appeared in our galaxy. These include the glowing threads of the Cancer Nebula, the remnants of the supernova that illuminated the night sky in 1054 AD. and which have since spread into space.
Galactic debris like this reveals the vast destruction that is being unleashed by supernovae. Yet these stellar convulsions are also important drivers of creation, scientists say. In addition to spraying space with heavy elements on which life depends, they also play a key role in the formation of planets and stars, says astrophysicist Cosimo Insera of Cardiff University.
“A supernova sends shock waves into a galaxy, and these clouds of gas and dust hit space, compressing them so that protostars begin to form in their centers. Eventually, nuclear fusion begins, which ignites the star’s hydrogen supply and it begins to shine. The planets form and orbit the star. That’s probably how our sun and solar system came to be. “
However, supernovae pose a threat. “If this happened within 20 parsecs – approximately 60 light-years – of Earth, its intense cosmic rays could destroy our protective ozone layer, which would allow elevated levels of ultraviolet radiation from the sun to reach us,” Sullivan said. . However, only one very close to Earth can have such an impact, and there are currently no candidate stars near us who seem ready to be destroyed in this way, he added.
On the other hand, it is also clear that supernovae have exploded near Earth in the past. As evidence, scientists point to the discovery of a radioactive isotope of iron – known as iron-60 – which was discovered in seabed deposits deposited 2.5 million years ago and in other deposits created about 7 million years ago. Iron-60 is made by supernovae, and these deposits suggest that at least two must have erupted near Earth in the last 10 million years, probably about 100 parsecs or 320 light-years away.
An image of the Cancer Nebula taken with the Hubble Space Telescope. Photo: Jeff Hester / AP Photo / Nasa / ESA
What effect this has had on the planet is uncertain. “You may have had an increase in the activity of cosmic rays, and this may have affected the formation of clouds on Earth or reduced the amount of solar radiation reaching the earth,” said Professor John Ellis of King’s College London. “This could cause climate change, which in turn could affect the course of human evolution.
Aside from the rather startling prospect that the emergence of Homo sapiens may have been shaped by local supernovae, these findings also suggest that there may have been enough of them to have had a real impact on life earlier in our planet’s history.
“If you find two that have happened quite close to Earth in the last 10 million years, that suggests that hundreds must have appeared in the last billion years,” Ellis said. “Some of them would be quite far away… but a few would be close, say 10 parsecs away. And we need to be clear: if a supernova erupted within 10 parsecs of our planet, it would very likely cause mass extinction.
Earth has experienced at least five mass extinctions, each of which destroyed thousands of species of animals, plants and sea creatures, and at least one of them was caused by an alien agent: an asteroid that hit Earth at the end of the Cretaceous 66 million years ago. before, destroying dinosaurs.
Other mass extinctions are blamed for earthquakes – such as large-scale volcanism. Now, however, scientists suspect that in another case it is a guilty event from another world. They point to rocks that formed at the end of the Devonian period 360 million years ago, when there was another mass extinction that destroyed ammonites, trilobites and other early life forms.
These rocks contain hundreds of thousands of generations of plant spores that appear to have been burned by ultraviolet light, evidence of a long-lasting ozone-depleting event, said astronomer Brian Fields of the University of Illinois at Urbana-Champaign. “We speculate that one or more supernova explosions, about 65 light-years from Earth, could be responsible for the long-term loss of ozone,” he said.
This explosion would first bathe the Earth with powerful X-rays and gamma rays before the debris from the explosion hit the planet, removing it from its protective ozone layer. This astronomical double blow would expose the planet’s surface to deadly radiation for up to 100,000 years and lead to mass extinction.
Further evidence for this idea is now being sought by scientists. They have given way to the demand for iron-60 atoms because they decay too quickly to survive 360 million years after Devon’s late mass extinction. Instead, they plan to look for atoms of the isotope plutonium-244, which is also produced by supernovae and can survive for several hundred million years. This study is ongoing.
Meanwhile, scientists are preparing to respond as quickly as possible to the first signs that a supernova has begun nearby. Most importantly, these first signals will not be flashes of light, but will come from underground detectors designed to detect the smallest insignia in the universe, the neutrino.
The main spectrometer of the tritium neutrino experiment in Karlsruhe (Katherine). The experiment, currently underway in Germany, is designed to measure the mass of an electron neutrino. Photo: Forschungszentrum Karlsruhe
“Neutrinos are the first thing that will appear …
Add Comment