The instruments of the probe picked up something strange when it reached the outer darkness of the solar system.
The space between the stars glowed with light. The light from all the light sources in the Universe is called the Cosmic Optical Background, and it was not a surprise.
There was a lot of light. Scientists thought there was less than they actually thought.
Scientists theorize that the optical light excess may be the result of an interaction of dark matter and light.
The results of this work provide a potential explanation for the optical background excess that is allowed by independent observational constraints and that may answer one of the most long-standing unknowns in the field of astronomy.
Dark matter is one of the most vexing questions about the universe. It's the name given to a mass in the Universe that provides far more gravity in concentrated spots than should be.
Galaxies are rotating faster than they should because of the mass of visible matter.
If we only took the amount of glowing material into account, the space-time around massive objects would be closer to what it should be.
We don't know if it is creating this effect or not. We can't account for the extra gravity so we're only able to know it's there.
There's lots of it. Dark matter makes up 80% of the matter in the universe.
Some people think it might be. The axion is a hypothetical class of particles that was first conceived in the 1970s to resolve the question of why strong atomic forces follow charge-parity symmetry.
Axions in a specific mass range should behave the same as dark matter. Axions are expected to decay into pairs of photons in the presence of a strong magnetic field.
Several experiments are looking for sources of these particles, but they should also be streaming through space.
It is difficult to separate them from all the other sources of light in the Universe.
Since it's so faint, it's hard to detect the background. The Long Range Reconnaissance imager is the best tool for the job at this time. It is far away from Earth and the Sun, and LORRI is more sensitive than the instruments attached to the more distant probes.
The product attributed to stars and galaxies that we can't see is what scientists think the excess detected by New Horizons is. There is still a lot on the table. The work of Bernal and his team was to determine if axion-like dark matter was to blame for the extra light.
The observed signal could be produced by axions with a mass between 8 and 20 electronvolts.
The particle tends to be measured in megaelectronvolts. Recent estimates put the piece of matter at a fraction of a single electronvolt.
The current data is not enough to tell which explanation is correct. The researchers narrowed down the mass of the axions that could be responsible for the excess.
There will be a signal if the excess arises from dark-matter decay to a photon line.
The search for dark matter will be expanded by future studies of very high-energy gamma-ray attenuation, as well as the ultraviolet instrument aboard New Horizons, which will have better sensitivity and probes a different range of the spectrum.
The research has appeared in a journal.
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