When the New Horizons probe reached the outer reaches of the Solar System, past Pluto, its instruments picked up a strange object.
At the very least, the space between the stars was bright and bright. This in itself was not unexpected; this light is called the cosmic optical background, the faint light from all light sources in the Universe outside of our galaxy.
The unusual part was the amount of light. There were more than scientists thought there should be – twice as much, in fact.
Now, in a new paper, scientists describe an explanation for the superluminal glow: it’s made up of some undetectable elements of dark matter.
“The results of this work,” writes a team of researchers led by astronomer José Luis Bernal of Johns Hopkins University, “provide a possible explanation for the number of astronomical objects allowed by independent constraints, and this may answer one of the causes much of what has long been known in cosmology: the nature of dark matter.”
We have many questions about the Universe, but dark matter is one of the most difficult. That’s the name we give to the unknown people in the Universe the responsibility of providing more gravity in a stable environment than it should.
For example, galaxies rotate faster than they would under the gravitational force created by the mass of visible matter.
The curvature of space-time around massive objects is greater than it should be if we can account for the curvature of space in terms of the mass of light objects.
But whatever is creating this, we cannot directly identify it. The only way we know it exists is that we can’t calculate this extra gravity.
And there’s more to it. About 80 percent of the matter in the Universe is dark matter.
There are speculations about what it might be. One of the candidates is the axion, which is part of a theoretical class of particles that was first proposed in the 1970s to address the question of why What is the atomic force of a solid obeys something called charge-parity symmetry when most models say it doesn’t.
As it turns out, axions in a particular mass group should also behave in the same way that we expect dark matter to behave. And there may be a way to find out – because theoretically, axions are expected to decay into pairs of photons in the presence of a magnetic field.
Several experiments are investigating where these photons come from, but they must also be traveling through space in large quantities.
The challenge is to separate them from all other sources of light in the Universe, and this is where the cosmic optical background comes in.
The background itself is very difficult to detect because it is very small. The Long Range Reconnaissance Imager (LORRI) aboard New Horizons is perhaps the best tool for this task. It is far from Earth and the Sun, and LORRI is much more sensitive than the instruments attached to the Voyager remote probes that were launched 40 years earlier.
Scientists have hypothesized that the mass detected by New Horizons may be made up of stars and galaxies that we cannot see. And that option is still on the table. The task of Bernal and his team was to examine whether dark matter like axions could be responsible for extraluminal light.
He did some math and concluded that axions with masses between 8 and 20 electronvolts can produce a visible signal under certain conditions.
That’s the amazing light of a particle, which we tend to measure in megaelectronvolts. But recent estimates place a hypothetical factor of one electronvolt, a number that would require axions to be smaller.
It is impossible to determine which explanation is correct based on the available data. However, by narrowing down the number of axions that could be responsible for the extra charge, the researchers laid the groundwork for future searches for larger particles.
The researchers write: “If this increase comes from the decay of dark matter to the photon line, there will be a big signal in the measurements of the energy map to come.”
In addition, the ultraviolet instrument in New Horizons (which will have good information and investigate different types of spectra) and future studies of high-energy gamma-ray attenuation will also test this idea and expand the search for dark matter. many frequencies.”
Research has been published in Physical Review Letters.
