Mysterious Cosmic Bridge Discovered Connecting Two Galaxy Clusters 10 Million Light-Years Apart

Our planet is one small part of the solar system, which is itself one infinitesimally small part of our galaxy, the Milky Way. The Milky Way, possibly containing as many as 400 billion stars, is part of the Local Group, two linked clusters of over 54 galaxies. The Local Group is, in turn, part of the Virgo Supercluster, which contains at least 100 galaxy clusters. A 2014 study found that the Virgo Supercluster may in fact be a part of an even larger structure, the Laniakea Supercluster, which contains roughly 100,000 galaxies. There are about 10 million superclusters in the observable universe. These superclusters form cosmic filaments—threads of millions of galaxies weaved through the void like fungal mycelium through the forest's soil. The resulting structure, what we believe the universe to look like, is called the Cosmic Web.

Until now, the Cosmic Web has been observed through the clusters and superclusters that, tied together by gravity, make up the cosmic filaments. A new study, however, has looked into the dark space between galaxy clusters and found a mysterious bridge of radio waves between two galaxy clusters almost 10 million light-years apart.

Abell 0399 and Abell 0401 are two galaxy clusters about 1 billion light-years from earth. They are slowly crashing together. Eventually they will merge into a larger structure, but considering there is 9.8 million light-years of space between them, it won't happen for a long time.

It turns out Abell 0399 and Abell 0401 are already interacting in a perplexing way however. According to a paper published earlier this month in the journal Science, astronomers have observed a stream of electrons spiraling around magnetic fields at close to light speed linking the two galactic clusters. This is the first time an electromagnetic link between two beads in the Cosmic Web has been observed.

The European telescope array LOFAR detected the radio waves emitted by this stream of electrons—a phenomenon called synchrotron emission. Astronomers now believe that this type of link is common between galaxy clusters, but is hard to detect with today's telescopes. According to astronomer Tracey Clarke of the U.S. Naval Research Laboratory:

“The signal detected in this study is a factor of up to a hundred times brighter than some theoretical predictions for the emission from the synchrotron web. This is likely because it is enhanced in this region between these merging clusters.”

As with everything spacey, one new discovery creates even more mysteries. For one, astronomers do not know how synchrotron emission could be produced over such a vast distance. Also, the mechanism for accelerating electrons to near light speed over 9.8 million light-years remains unknown. According to Tracey Clarke:

"This opens a whole new set of doors to begin exploring things like the particle distribution in the filaments, the magnetic field strength—and potentially its origin—as well as acceleration or reaccelerating processes at work within the filaments.”

Just as we keep seeing new complex interactions at the smallest levels, it seems we're finding new complex interactions at the largest levels. And the lower and upper limits on those levels seems to be changing all the time. The great thing about outer space is that it will most likely always be a mystery, an endless frontier of curiosity and wonder. You have to think of it that way, because it's either that, or sheer terror at how very, very small we really are.