The secrets of supernova star explosions may be hidden in dust scattered across the moon, and a team of scientists from the China Institute of Atomic Energy (CIAE) has developed a new way to uncover these clues of star death.
The research could help scientists get a clearer picture of how stars die and provide material for the next generation of stars, planets, moons, and sometimes even life (at least as far as Earth is concerned).
The technique is based on the advanced detection of a rare iron isotope found in infinite amounts in lunar dust. This type of iron was forged millions of years ago in the hearts of previous generations of massive stars. When these stars lost their millions (or billions) year-long “tug of war” with gravity and ended their lives in supernova explosions, the isotopes would be released and, scientists believe, dispersed throughout the cosmos. , on the Moon.
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“Our team agreed that the only way to accurately track historical supernova events is to push the limits of what our equipment can do,” team leader and CIAE researcher Bing Guo said in a statement. said.
How do supernovae contribute to cosmic recycling?
When the first generation of stars were born, 200 to 400 million years after the Big Bang, the universe was filled mostly with hydrogen and some helium. At the time, there were very few atoms of elements heavier than this, and astronomers (somewhat confusingly) called them “metals.”
This means that the first stars, paradoxically called Population III stars, were composed of hydrogen, some helium, and almost no metal. While these stars were alive, nuclear fusion processes that converted hydrogen into helium in their cores allowed them to shine brightly in the universe. This fusion process also provided outward radiation pressure that prevented the inward force of their own gravity from causing them to collapse.
But this meant that once the stars’ cores ran out of hydrogen, the balancing act between radiation pressure and gravity came to an end, with the latter becoming the clear winner. Thus, as the cores of these stars collapsed, their outer layers, where nuclear fusion was still continuing, flew away.
For stars with masses close to that of the Sun, this results in stellar cores collapsing into white dwarf stars, surrounded by a slowly dispersing and cooling cloud of once stellar material. But this is not the fate of stars with at least eight times the mass of the Sun.
When these massive stars collapse, the pressure built up in their cores triggers the nuclear fusion of helium with other heavy elements. For the most massive stars, this process is repeated until the core is filled with iron, the heaviest element a star can form.
The core of a massive star will then collapse again, triggering a supernova explosion. This explosion releases all the elements the star has produced throughout its life and distributes them to the surrounding galaxy. The star then becomes a dense stellar remnant; either a neutron star or a black hole in case of complete gravitational collapse.
But even this is not the end of the elements that the star creates during its life. These materials find their way into clouds of interstellar gas and dust, which can eventually collapse and give birth to stars and planets.
Subsequent generations of stars thus become increasingly “metal-rich” as time passes. All the dispersed material was also integrated into the newly developing planets orbiting these stars and any life forms that could exist on these worlds. Therefore, when scientists say “you are the stars” it is more than just pseudo-commitment; this is the truth.
The lunar dust monitoring team is interested in the tracer of this cosmic recycling process, which is a rare isotope formed during a supernova, not an element formed during the life of the star.
Iron-60: From Supernovae to the Moon
Atoms consist of three particles: the atomic nucleus contains positively charged protons and neutral neutrons, and negatively charged electrons “orbit” this nucleus.
Elements are defined by the number of protons in the atomic nucleus. In other words, an atom with six protons in its nucleus is always carbon. When you add another proton it becomes a nitrogen atom. However, elements have more flexibility when it comes to the number of neutrons in their nuclei.
A carbon atom can have six protons and six neutrons, or it can have six protons and seven neutrons, or it can have six protons and eight neutrons. These different variations of atoms of the same element are called “isotopes” of that element. The carbon atom with six protons and six neutrons is called “carbon-12”, while the carbon atom with six protons and seven neutrons is called the carbon isotope “carbon-14”.
Some of these isotopes, especially the heavier ones, are unstable and undergo a process called radioactive decay. The time required for half of a certain amount of radioactive isotope to decay is called “half-life”.
When supernovae explode in just a few seconds, they release as much energy as the Sun can radiate in billions of years. This provides the necessary conditions for the creation of heavy radioactive isotopes. The team aims to develop ways to search for a radioactive iron isotope called “iron-60” in lunar dust.
Iron-60 has an atomic nucleus containing 26 protons and 34 neutrons and its half-life is approximately 2.3 million years. While a supernova can create amounts of iron-60 equivalent to approximately 10 times the mass of Earth, production of this isotope in the solar system is negligible. Scientists estimate that supernovae in the entire Milky Way occur about three times every 100 years, while “nearby” star explosions occur even less frequently, once every 100 years. million years.
The presence of iron-60 on Earth or the Moon is a good indication of a supernova exploding relatively close to the solar system (e.g., about 100 light-years away) in the recent history of our 4.6 billion-year-old planet. says the research team.
However, the scarcity of iron-60 and the influence of other more common disruptive elements have made detection of its abundance extremely challenging for low-sensitivity spectrometers. To combat this, Guo and his colleagues made adjustments to CIAE’s HI-13 tandem accelerator facility. This involved the addition of a “Wein filter”, a device that can be used to select charged particles moving at specific speeds to perform “accelerator mass spectrometry” (AMS).
The team found that AMS could detect iron-60 in simulated samples with a sensitivity well beyond the technology typically used for these studies.
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The CIAE team believes that it is now possible to further improve the detection sensitivity of AMS systems; This is a breakthrough that could greatly improve our understanding of stars dying in supernova explosions, thus enabling us to survive.
“The installation of the Wien filter could be a game changer for us,” Guo said. “Our next goal is to optimize our entire AMS system to reach even lower detection limits. Every increased sensitivity opens up a universe of possibilities.”
The team’s research was published May 24 in the journal Nuclear Science and Techniques.