Five billion light-years from earth, there’s a massive galactic pileup unfolding in slow motion. As four clusters of galaxies plow into each other, thousands of individual galaxies are colliding—creating huge amounts of cosmic chaos and a lot of energy.
New images of this phenomenon—one of the largest galactic mergers on record—suggest it’s also producing more than just pretty pictures. It’s also serving as quite possibly the largest particle accelerator of all time, besting the exquisitely engineered Large Hadron Collider one million times over.
The discovery of the power of the collision, endearingly named MACSJ0717.5+3745, was revealed at a recent American Astronomical Society meeting by Reinout van Weeren of the Harvard-Smithsonian Center for Astrophysics. He and his team observed different types of radiation to peer into the complex interactions.
Radio-wave data from the Very Large Array show what seems to be radiation emitted by high-energy charged particles. According to X-ray data from the Chandra Observatory, there’s extremely hot (hundred-million-Kelvin-hot) gas in the same place the radiation is coming from. That combination of energetic particles and super-heated gas suggests that gases are colliding and spewing out high-energy particles.
Galaxies are mostly empty space, of course, and the likelihood of stars colliding is relatively small. But as Clara Moskowitz, writing for Scientific American, explains that the gases in galaxies’ interstellar spaces can interact violently:
When clouds of gas slam into one another, they warm up, causing a shock front where magnetic fields get compressed. These fields cause particles to travel back and forth over the front, picking up energy from the heat of the gas during every crossing. Eventually, the particles become so energetic that they escape and fly out into space.
This isn’t the first natural particle accelerator we’ve observed—supernova debris can create the same energy-amping shock fronts—but it seems to be one of the strongest. In millions of years, some of the particles could wind up as the cosmic rays that pelt the Earth.
The colossal mass of the four clusters has also created a very large gravity lens. The gravity the clusters exert bends the light originating from other galaxies, allowing us to see distant galaxies that would otherwise be invisible, just like a glass lens in a standard telescope. Later this year, in fact, astronomers will use another giant lens, the Hubble Space Telescope, which took the first optical images of this collision, to take advantage of the gravitational lensing to produce long-exposure images which peer deep into the cosmos. The combined powers of Hubble and MACSJ0717.5+3745 will produce what is “probably the best cosmic telescope on our sky,” Dan Coe of the Space Telescope Science Institute told Moskowitz.