The New York Times website reported on December 8 that this may be the most unexpected news when the dark year is about to end. It was discovered by a group of astronomers who used the camera on the New Horizons probe (which visited Pluto) to measure the darkness of interplanetary space.

Todd Lauer of the National Optics-Infrared Astronomy Research Laboratory said: “There is something unknown. The universe is not completely dark, and we don’t fully know its composition yet.”

Raul and his colleagues found that in an open space about 6.44 billion kilometers away from the sun, far from bright planets and interplanetary dust scattering light, the brightness is about twice the expected.

He said the most likely explanation is that there are more galaxies or star clusters with very faint brightness that provide the background light of the universe than the model shows. Or, it may even be that the black holes at the centers of other galaxies are injecting extra energy into this vacuum, and these galaxies are otherwise unremarkable.

Raul said in an email that a less exciting possibility is, “We made a mistake and missed a light source or shooting artifact that should have been discovered. This is what I worry about the most.”

A more interesting speculative suggestion involves what can be called “cold dark matter.” It is believed that the universe is full of “dark matter” whose exact nature is unknown, but its gravity determines the visible universe. Some theories suggest that this material may be a cloud of bizarre subatomic particles that emit energy light during radioactive decay, collision, and self-annihilation, increasing the brightness of the universe.

Raul and his colleagues prefer to leave this speculation to particle physicists. He said in an email: “Our work only involves measuring flux itself. As observers, we are willing to dedicate our observations to people who can figure out how to explain.”

The research report was published online in November. Mark Postman, an astronomer at the US Space Telescope Science Institute, is one of the authors of the report. He said: “This is very important for estimating the total energy contained in the universe, and it helps us understand the entire universe history of star formation.”

They found that the extra light radiance in the universe is about 10 nanowatts per steradian per square meter. Steradian is the unit of measurement of solid angle, and 4π steradian can cover the entire sky sphere.

Raul compares this measurement to Sirius or the light from opening a refrigerator 1.6 kilometers away. He wrote in an email: “You can imagine lying in bed with the curtains open on a dark, moonless night. Maybe you are awake and staring at the wall. When Sirius appears from behind the mountain, or neighbors go to the refrigerator for something to eat , You will see the light in the room become brighter.”