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| The composite image places PLCK G287 at its center, appearing as a dense cluster of white dots — individual galaxies — against a star-flecked black background. Surrounding it is a vast X-ray glow in gradated blues and purples, fading from deep blue at the edges to soft pink near the core. Two bright arcs in orange and yellow — the radio relics — flank the cluster’s top right and lower left, hinting at the immense forces at play in this cosmic environment. |
Astronomers have discovered the largest known cloud of energetic particles ever seen surrounding a galaxy cluster — a colossal formation stretching nearly 20 million light-years across. The finding, announced today at the 246th meeting of the American Astronomical Society (AAS), is rewriting what scientists thought they knew about how particles stay energized in deep space.
The discovery centers on PLCK G287.0+32.9, a massive galaxy cluster located about 5 billion light-years from Earth. First detected in 2011, the cluster has now been observed in unprecedented detail through a new composite image combining data from NASA’s Chandra X-ray Observatory (blue and purple), the MeerKAT radio telescope (orange and yellow), and the Pan-STARRS optical survey (red, green, and blue).
Unlike previous theories that linked such energetic regions to activity from nearby galaxies, this enormous halo appears to be powered by shockwaves and turbulence in the hot gas between galaxies. These shockwaves move through the intracluster medium — the vast expanse of plasma that fills the space between galaxies in a cluster — re-energizing particles and producing a faint but massive radio glow.
“This cloud is nearly 20 times the diameter of the Milky Way,” said lead researcher Kamlesh Rajpurohit of the Center for Astrophysics | Harvard & Smithsonian. “We’ve never seen anything like it.”
Earlier studies had identified two bright radio relics — immense shockwaves marking the cluster’s outer edges. But the latest observations reveal that the entire cluster is suffused in a vast, faint radio emission, setting a new record. The previous largest known particle cloud around a cluster — in Abell 2255 — spans roughly 16.3 million light-years.
The scale of this new structure opens up exciting opportunities to explore cosmic magnetic fields, one of the most elusive components of the Universe. These fields play a major role in galaxy formation and particle acceleration, but scientists still don’t fully understand how they arise or evolve.
NASA’s Marshall Space Flight Center manages the Chandra program, with science operations based at the Smithsonian Astrophysical Observatory in Cambridge, Massachusetts.