Scientists are finally figuring out how much dark matter – the nearly imperceptible material that is said to attract everything but emit no light – really weighs.
The new estimate helps determine how heavy the particles could be – with implications for what the mysterious stuff actually is.
The study greatly narrows the potential mass of dark matter particles, from an estimated 10 ^ minus 24 electron volts (eV) and 10 ^ 19 Gigaelectron volts (GeV), to between 10 ^ minus 3 eV and 10 ^ 7eV – a possible range of masses many trillions or trillions times smaller than before.
The findings could help dark matter hunters focus their efforts on the indicated range of particle masses – or they could reveal that a previously unknown force is at work in the universe, said Xavier Calmet, a professor of physics and astronomy at the University. from Sussex in the United States. United Kingdom.
Related: The 11 Biggest Unanswered Questions About Dark Matter
Calmet, together with PhD student Folkert Kuipers, also from the University of Sussex, described their efforts in a new study published in the March issue of Physical letters B..
What is Dark Matter?
By some estimates, dark matter makes up about 83 percent of all matter in the universe. It is thought to interact with light and ordinary matter only through gravity, meaning it can only be seen through the way it bends light rays.
Astronomers discovered the first hints of dark matter when they gazed at a galactic cluster in the 1930s, and theories that galaxies are fringed and lined by huge halos of dark matter became mainstream after the 1970s, when astronomers realized that galaxies were swirling faster than otherwise should. , given how much visible matter they contain.
Related: The 12 Strangest Objects in the Universe
Possible candidates for dark matter particles include ghostly tiny particles known as neutrinos, theoretical dark, cold particles known as axions, and proposed weakly interacting massive particles, or WIMPs.
The new massive boundaries could help eliminate some of these candidates, depending on the details of the specific dark matter model, Calmet said.
Quantum gravity
What scientists do know is that dark matter appears to interact with light and normal matter only through gravity, and not through any of the other fundamental forces; and so the researchers used gravitational theories to arrive at their estimated ranges for the masses of dark matter particles.
Importantly, they used concepts from theories of quantum gravity, resulting in a much smaller range than the previous estimates, using only Einstein’s general theory of relativity.
“Our idea was very simple,” Calmet told Live Science in an email. “It’s amazing that people haven’t thought of this before.”
Einstein’s general theory of relativity is based on classical physics; it perfectly predicts how gravity usually works, but breaks down in extreme conditions where quantum mechanical effects become significant, such as in the middle of a black hole.
Theories of quantum gravity, on the other hand, try to explain gravity through quantum mechanics, which can describe all the other three known fundamental forces: electromagnetic force, the strong force that holds most matter together, and the weak force that holds radioactive decay. causes.
However, none of the quantum gravity theories has strong evidence to support them so far.
Calmet and Kuipers estimate the lower limit for the mass of a dark matter particle using values from general relativity, and estimate the upper limit of the lifetime of dark matter particles predicted by quantum gravity theories.
The nature of the values from general relativity also defined the nature of the upper bound, so that they could derive a prediction independent of a particular model of quantum gravity, Calmet said.
The study found that while quantum gravity effects were generally almost insignificant, they became important when a hypothetical dark matter particle took an extremely long time to decay and when the universe was about as old as it is today (about 13.8 billion years ), he said. .
Physicists previously estimated that dark matter particles needed to be lighter than the ‘Planck mass’ – about 1.2 x 10 ^ 19 GeV, at least 1000 times heavier than the largest known particles – yet heavier than 10 ^ minus 24 eV to fit with observations of the smallest galaxies known to contain dark matter, he said.
But so far, few studies had tried to narrow the range, even though great strides had been made in understanding quantum gravity over the past 30 years, he said. “Humans simply haven’t looked at the effects of quantum gravity on dark matter before.”
Unknown power
Calmet said the new limits for dark matter particle masses could also be used to test whether gravity interacts only with dark matter, which is widely believed, or whether dark matter is affected by an unknown force of nature.
“If we found a dark matter particle with a mass outside the range discussed in our article, we would not only have discovered dark matter, but also very strong evidence that … a new force outside of gravity is acting on dark matter. ,” he said.
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This article was originally published by Live Science. Read the original article here.