“All good things must come to an end.” This adage is true in space as well as on Earth.
We are aware that stars, like everything else, must die. When they run out of the fuel needed for nuclear fusion in their cores, stars of all sizes collapse under their own gravity, dying to form a dense cosmic remnant such as a white dwarf, neutron star, or black hole. black. Our star, the sun, will suffer this fate in about 5 billion years, initially swelling as a red giant and obliterating the inner planets, including Earth. After about 1 billion years, this phase will also end, leaving the sun’s core as a white dwarf ember surrounded by a cloud of cosmic ash in the form of cooling stellar material.
Scientists have developed the Hertzsprung-Russell diagram, a chart of stellar life, afterlife, and death. This diagram traces stars of all masses through their evolution from hydrogen-burning main sequence stars to dense cosmic debris.
However, new research has revealed that some stars at the heart of our galaxy may be putting their finger on our best models of stellar life and death. These stars can feed on dark matter, the most mysterious thing in the universe, to effectively give themselves cosmic immortality, necessitating the creation of a “dark Hertzsprung-Russell diagram.”
Connected: Across the universe, the annihilation of dark matter may be heating dead stars
“The Galactic Center of the Milky Way is a very extreme environment and very different from where we are in the Milky Way,” research team leader Isabelle John of the Kavli Institute for Particle Astrophysics and Cosmology told Space.com. “The stars closest to the Galactic Center, the so-called ‘S-group stars’, are very strange.
“They show a number of properties found nowhere else: It’s not clear how they got so close to the center, where the environment is thought to be quite hostile to star formation.”
John added that these S-cluster stars, which lie within about three light-years of the heart of our galaxy, also appear to be much younger than would be expected if the stars had migrated into this region from somewhere else in the galaxy. The Milky Way. “Even more mysteriously, not only do the stars look remarkably young, but there are fewer older stars than expected,” she continued. “Also, it seems like there are suddenly a lot of heavy stars.”
John and colleagues hypothesize that one reason for these unusual features may be that these stars collect large amounts of dark matter, which is then annihilated within them. This process could provide them with an entirely new and unexpected form of fuel.
“Our simulations show that stars can only survive on dark matter as fuel, and because there is an extremely large amount of dark matter near the Galactic Center, these stars become immortal,” John added. “This is quite fascinating because our simulations show results similar to observations of S-group stars: dark matter as fuel will keep the stars forever young.”
“The idea of immortal stars,” John continued, “could explain many of the unusual properties of S-group stars at once. If stars in the Galactic Center become immortal due to the high density of dark matter, this could be unusual reason for a large abundance of apparently young stars in the Galactic Center, while at the same time explaining the absence of older stars.”
Dark matter is its worst enemy
Dark matter is a problem for physicists because, accounting for about 85% of the universe, it is invisible to us because it does not interact with light. Furthermore, dark matter does not appear to interact with “ordinary matter”. This everyday matter consists of protons, neutrons and electrons and includes all the stars, planets, moons, asteroids, comets, gas, dust and living things in the universe.
Scientists can only infer the presence of dark matter because it interacts with gravity, and this interaction can affect ordinary matter and indeed light. However, if interactions between dark matter and ordinary matter do occur, these are rare and weak; Scientists do not believe that we have ever discovered such an interaction.
What is less certain is whether dark matter interacts with itself. To understand what this means, remember that ordinary matter particles all have an antimatter version of them. For example, there is a positively charged antiparticle called a positron for a negatively charged electron. And when matter and antimatter meet, they annihilate each other, releasing energy.
“The annihilation of dark matter is analogous to the annihilation of matter and antimatter: if a particle and its antiparticle meet, they annihilate and produce other particles, for example, photons. Similarly, dark matter particles can annihilate in such a way,” said John. . “In many dark matter models, dark matter particles are considered their antiparticles, meaning that any two dark matter particles can annihilate each other.”
However, we don’t see dark matter annihilation, so it must be quite rare. That means, John says, it would be more likely to happen in an environment where large amounts of dark matter can clump together. Perhaps the ultra-dense region at the heart of a star is where gravity, with which dark matter interacts, is strongest.
Can the sun also become immortal?
Main sequence stars burn hydrogen in nuclear fusion processes during their lifetime. This creates helium, most of the star’s energy, and the outward “radiation pressure” that balances the inward push of the star’s gravitational forces. This cosmic pull between radiation pressure and gravity lasts for millions or even billions of years and keeps these stars in stable equilibrium.
“For most of a star’s life, these processes occur primarily in the star’s core, where the gravitational pressure is highest,” John said. “We show that if stars collect a large amount of dark matter, which is then annihilated inside the star, it can also provide an external pressure, making the star stable due to the annihilation of dark matter rather than nuclear fusion, so stars can use dark matter as fuel instead of hydrogen.
“Stars use up their hydrogen, which will eventually cause them to die. On the other hand, dark matter can be continuously collected, which makes these stars immortal.”
So could the sun grant itself immortality by switching to this alternative fuel source? John thinks not. Located in the middle of one of the spiral arms of the Milky Way, it is in the wrong place in our galaxy to enter this dark fountain of youth.
“Stars need very large amounts of dark matter to efficiently replace fusion. Throughout most of the Milky Way, the density of dark matter is not high enough to significantly affect the stars. But in “At the Galactic Center, the density of dark matter is very high, potentially many billions of times higher than on Earth, which provides the amount of dark matter needed to make stars immortal,” Jon explained. “So our sun is not immortal.”
John added that the team’s findings potentially reveal many secrets about dark matter itself, as well as the immortal stars it can power.
“Our findings tell us that dark matter can be distributed with ordinary particles, which is required to slow down dark matter particles inside the star to capture them – also, that dark matter particles can be annihilated with one – the other,” she said. “By observing the distribution of immortal stars around the Galactic Center, we would also get some information about the distribution and density of dark matter around the Galactic Center.”
John explained that, to verify these findings, astronomers need more precise observations of the Milky Way’s innermost stars to determine whether these stars lie on a “dark main sequence,” which could hint at to their immortality.
They also aim to determine the effect of dark matter annihilation on different stars. Initial simulations show that lighter stars will become “bloated” and shed their outer layers as they pass through this dark fuel. This may explain the nature of the so-called “G-objects” found in the Galactic Center, which are stellar bodies that appear to be surrounded by clouds of gas.
“So far, our work has focused on main sequence stars. We also want to understand how dark matter affects stars at later evolutionary stages when they have left the main sequence and are undergoing various nuclear fusion processes,” said Johns. “Our results are exciting because they show that stellar observations provide an additional and unique way to study and understand the interactions of dark matter with ordinary matter.”
A pre-revised version of the team’s research is available in the paper’s arXiv repository.