The ‘X17’ particle: Scientists may have discovered the fifth force of nature

A new paper suggests that the mysterious X17 subatomic particle is indicative of a fifth force of nature.

The ‘X17’ particle: Scientists may have discovered the fifth force of nature
  • In 2016, observations from Hungarian researchers suggested the existence of an unknown type of subatomic particle.
  • Subsequent analyses suggested that this particle was a new type of boson, the existence of which could help explain dark matter and other phenomena in the universe.
  • A new paper from the same team of researchers is currently awaiting peer review.


Physicists have long known of four fundamental forces of nature: gravity, electromagnetism, the strong nuclear force, and the weak nuclear force.

Now, they might have evidence of a fifth force.

The discovery of a fifth force of nature could help explain the mystery of dark matter, which is proposed to make up around 85 percent of the universe's mass. It could also pave the way for a unified fifth force theory, one that joins together electromagnetic, strong and weak nuclear forces as "manifestations of one grander, more fundamental force," as theoretical physicist Jonathan Feng put it in 2016.

The new findings build upon a study published in 2016 that offered the first hint of a fifth force.

In 2015, a team of physicists at Hungary's Institute for Nuclear Research was looking for "dark photons," which are hypothetical particles believed to "carry" dark matter. To catch a glimpse of these strange forces at work, the team used a particle accelerator to shoot particles through a vacuum tube at high speeds. The goal was to observe the way isotopes decay after thrust into high-energy states — anomalies in the way particles behave could suggest the presence of unknown forces.

So, the team closely watched the radioactive decay of beryllium-8, an unstable isotope. When the particles from beryllium-8 decayed, the team observed unexpected light emissions: The electrons and positrons from the unstable isotope tended to burst away from each other at exactly 140 degrees. This shouldn't have happened, according to the law of conservation of energy. The results suggested that an unknown particle was created in the decay.

A new type of boson

A team of researchers at the University of California, Irvine (UCI), proposed that the unknown particle was not a dark photon, but rather a boson — specifically, a "protophobic X boson," which would be indicative of a fifth fundamental force. In simple terms, bosons are particles in quantum mechanics that carry energy, and function as the "glue" that holds matter together and controls the interactions between physical forces.

As Big Think's Robby Berman wrote in 2016:

"[In] the Standard Model of Physics, each of the four fundamental forces has a boson to go with it - the strong force has gluons, the electromagnetic force is carried by particles of light, or photons, and the weak force is carried by W and Z bosons. The new boson proposed by the UCI researchers is unlike others and as such may point to a new force. The new boson has the intriguing characteristic of interacting only with electrons and neutrons at short distances, while electromagnetic forces normally act on protons and electrons."

The X17 particle

In the new paper, published on the preprint archive arXiv, the Hungarian team observed similar evidence for a new boson, which they refer to as the X17 particle, as its mass is calculated to be about 17 megaelectronvolts. This time, however, the observations come from the decay of an isotope of helium.

"This feature is similar to the anomaly observed in 8Be, and seems to be in agreement with the X17 boson decay scenario," the researchers wrote in their paper. "We are expecting more, independent experimental results to come for the X17 particle in the coming years."

A 'revolutionary' discovery

The discovery of a fifth force of nature would provide a glimpse into the "dark sector", which in general describes yet-unobservable forces that can't readily be described by the Standard Model. Strangely, the subatomic particles in this hidden layer of our universe hardly interact with the more observable particles of the Standard Model.

A fifth force could scientists better understand how these two layers coexist.

"If true, it's revolutionary," Weng said in 2016. "For decades, we've known of four fundamental forces: gravitation, electromagnetism, and the strong and weak nuclear forces. If confirmed by further experiments, this discovery of a possible fifth force would completely change our understanding of the universe, with consequences for the unification of forces and dark matter."

Without Dark Matter, It's Unlikely That Any of Us Would Exist at ...

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This is what aliens would 'hear' if they flew by Earth

A Mercury-bound spacecraft's noisy flyby of our home planet.

Image source: sdecoret on Shutterstock/ESA/Big Think
Surprising Science
  • There is no sound in space, but if there was, this is what it might sound like passing by Earth.
  • A spacecraft bound for Mercury recorded data while swinging around our planet, and that data was converted into sound.
  • Yes, in space no one can hear you scream, but this is still some chill stuff.

First off, let's be clear what we mean by "hear" here. (Here, here!)

Sound, as we know it, requires air. What our ears capture is actually oscillating waves of fluctuating air pressure. Cilia, fibers in our ears, respond to these fluctuations by firing off corresponding clusters of tones at different pitches to our brains. This is what we perceive as sound.

All of which is to say, sound requires air, and space is notoriously void of that. So, in terms of human-perceivable sound, it's silent out there. Nonetheless, there can be cyclical events in space — such as oscillating values in streams of captured data — that can be mapped to pitches, and thus made audible.

BepiColombo

Image source: European Space Agency

The European Space Agency's BepiColombo spacecraft took off from Kourou, French Guyana on October 20, 2019, on its way to Mercury. To reduce its speed for the proper trajectory to Mercury, BepiColombo executed a "gravity-assist flyby," slinging itself around the Earth before leaving home. Over the course of its 34-minute flyby, its two data recorders captured five data sets that Italy's National Institute for Astrophysics (INAF) enhanced and converted into sound waves.

Into and out of Earth's shadow

In April, BepiColombo began its closest approach to Earth, ranging from 256,393 kilometers (159,315 miles) to 129,488 kilometers (80,460 miles) away. The audio above starts as BepiColombo begins to sneak into the Earth's shadow facing away from the sun.

The data was captured by BepiColombo's Italian Spring Accelerometer (ISA) instrument. Says Carmelo Magnafico of the ISA team, "When the spacecraft enters the shadow and the force of the Sun disappears, we can hear a slight vibration. The solar panels, previously flexed by the Sun, then find a new balance. Upon exiting the shadow, we can hear the effect again."

In addition to making for some cool sounds, the phenomenon allowed the ISA team to confirm just how sensitive their instrument is. "This is an extraordinary situation," says Carmelo. "Since we started the cruise, we have only been in direct sunshine, so we did not have the possibility to check effectively whether our instrument is measuring the variations of the force of the sunlight."

When the craft arrives at Mercury, the ISA will be tasked with studying the planets gravity.

Magentosphere melody

The second clip is derived from data captured by BepiColombo's MPO-MAG magnetometer, AKA MERMAG, as the craft traveled through Earth's magnetosphere, the area surrounding the planet that's determined by the its magnetic field.

BepiColombo eventually entered the hellish mangentosheath, the region battered by cosmic plasma from the sun before the craft passed into the relatively peaceful magentopause that marks the transition between the magnetosphere and Earth's own magnetic field.

MERMAG will map Mercury's magnetosphere, as well as the magnetic state of the planet's interior. As a secondary objective, it will assess the interaction of the solar wind, Mercury's magnetic field, and the planet, analyzing the dynamics of the magnetosphere and its interaction with Mercury.

Recording session over, BepiColombo is now slipping through space silently with its arrival at Mercury planned for 2025.

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