A ghostly jellyfish, raised from the dead

 Galaxy clusters are the largest known structures in the universe held together by gravity. In addition to harboring thousands of galaxies, they can contain huge clouds of hot gas and, at times, even the glowing ghost of a “jellyfish”. 

In the Abell 2877 cluster of galaxies, located about 300 million light years from Earth to the south, astronomers have discovered one such ghost. Visible only in a narrow range of radio light, the cosmic jelly is over 1 million light years across. According to a study published in March in The Astrophysical Journal, no such large structure had ever been seen in such a narrow range of light. For researchers, it could be that this cosmic jelly is, in fact, a “radio phoenix”. 

Image: Torrance Hodgson, ICRAR/Curtin University

 A cosmic structure born from a high-energy explosion (like a black hole explosion) disappears over millions of years as the structure expands and its electrons lose energy. Then, finally, it is re-energized by another cosmic cataclysm (like the collision of two galaxies), resulting in a massive structure that radiates brightly at certain radio frequencies but quickly dims at all others. It's a ghost, a jellyfish and a phoenix, all in one event!