An intense demolition derby of at least six galaxies smashing into one another has been found lurking in the early universe by the James Webb Space Telescope. This merger is also expected to fuel the growth of a supermassive black hole and trigger the formation of what will eventually become one of the most massive galaxies in the cosmos.
"What makes this special is that we can follow both the build-up of a giant galaxy and the growth of the black hole at its center," Huub Röttgering, an astronomer at the Netherlands' Leiden Observatory, said in a statement.
The discovery came after a tip-off from radio astronomers who had noticed emissions that seemed to be coming from an undiscovered active black hole. When the James Webb Space Telescope (JWST) looked closer, it found a surprise.
"We didn't find a single galaxy, but an entire complex of at least six galaxies," said Aayush Saxena of the University of Oxford.
These six galaxies sit at a redshift of 4.0, which equates to a time about 12 billion years ago, just 1.8 billion years after the Big Bang.
Through the vision of the JWST's Near-Infrared Camera the six galaxies appear fuzzy, reminiscent of a faraway version of Stephan's Quintet, which is a collection of five galaxies, four of which form a compact group that are on course to merge to become a giant elliptical galaxy.
Similarly, the six galaxies spotted by the JWST, and collectively termed TGSSJ1530+1049, will undergo a series of rapid mergers to become what is known as a 'brightest cluster galaxy,' which is an enormous elliptical galaxy of the kind found at the center of galaxy clusters.
"We call structures like this protoclusters: the precursors of the vast collections of galaxies we see today," said Leiden's Roderik Overzier. "These are places where matter came together very early on. We think we are seeing a rare moment when several massive galaxies still exist separately, but are already in the process of forming one much larger galaxy."
Already a supermassive black hole has formed at the heart of this galactic maelstrom, and radio observations with the European VLBI (very long Baseline Interferometer) Network and the U.K.'s e-MERLIN (enhanced Multi-Element Remotely Linked Interferometer Network) at a resolution on the scale of a 100 milliarcseconds have identified radio lobes and hotspots typical of an active black hole's jet interacting with the gas surrounding it.
"Using a network of connected radio telescopes, we were able to produce a very sharp image of TGSSJ1530+1049," said Krisztina Gabányi of Eötvös Loránd University in Budapest, Hungary. "The radio emission is produced as material falls into the black hole, while some of it is expelled again at high speed."
The jet doesn't seem to extend as far as all the galaxies in TGSSJ1530+1049 yet, implying that the black hole is still fairly young.
The six galaxies of TGSSJ1530+1049 span a volume only a few tens of thousands of light-years across, which is smaller than our Milky Way galaxy — and yet, they pack in a humungous amount of stars, equivalent to hundreds of billions of solar masses and a star-formation rate somewhere between 70–163 solar masses per year. That's a frenetic pace compared to the Milky Way, which produces much less than ten solar masses per year.
TGSSJ1530+1049 is one of the densest collections of heavyweight galaxies found in the early universe so far, and is giving exciting clues as to how the most massive galaxies, clusters and black holes in the universe formed.
The JWST observations are reported in The Open Journal of Astrophysics, while the radio measurements are described in a paper in Astronomy & Astrophysics.
