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Within the last five years, astronomers have discovered a new type of astronomical phenomenon that exists on vast scales \u2013 larger than whole galaxies. They\u2019re called ORCs (odd radio circles), and they look like giant rings of radio waves expanding outwards like a shockwave. Until now, ORCs had never been observed in any wavelength other than radio, but according to a new paper released on April 30 2024, astronomers have captured X-rays associated with an ORC for the first time. <\/p>\n
<\/p>\n The discovery offers some new clues as to what might be behind the creation of an ORC.<\/p>\n While many astronomical events, like supernova explosions, can leave behind circular remnants, ORCs seem to require a different explanation.<\/p>\n \u201cThe power needed to produce such an expansive radio emission is very strong,\u201d said Esra Bulbul, lead author of the new paper. \u201cSome simulations can reproduce their shapes but not their intensity. No simulations explain how to create ORCs.\u201d<\/p>\n ORCs can be a challenge to study, in part because they are usually only visible in radio wavelengths. They haven\u2019t previously been associated with X-ray or infrared emissions, nor has there been any sign of them in optical wavelengths. Sometimes, ORCs surround a visible galaxy, but not always (eight have been discovered to date around known elliptical galaxies).<\/p>\n Using ESA\u2019s XMM-Newton telescope, BulBul and her team observed one of the nearest known ORCs, an object called the Cloverleaf, and found a striking X-ray component to the object.<\/p>\n \u201cThis is the first time anyone has seen X-ray emission associated with an ORC,\u201d said Bulbul. \u201cIt was the missing key to unlock the secret of the Cloverleaf\u2019s formation.\u201d<\/p>\n X-rays of the Cloverleaf show gas that has been heated and excited by some process. In this case, the X-ray emissions reveal two groups of galaxies (totaling about a dozen galaxies altogether) that have begun to merge inside the Cloverleaf.<\/p>\n The chaotic galaxy mergers are interesting, but they can\u2019t explain the Cloverleaf by themselves. Galaxies mergers happen all over the universe, while ORCs are a rare phenomenon. There\u2019s something unique going on to create something like the Cloverleaf.<\/p>\n \u201cMergers make up the backbone of structure formation, but there\u2019s something special in this system that rockets the radio emission,\u201d Bulbul said. \u201cWe can\u2019t tell right now what it is, so we need more and deeper data from both radio and X-ray telescopes.\u201d<\/p>\n That doesn\u2019t mean astronomers don\u2019t have any guesses.<\/p>\n \u201cOne fascinating idea for the powerful radio signal is that the resident supermassive black holes went through episodes of extreme activity in the past, and relic electrons from that ancient activity were reaccelerated by this merging event,\u201d said Kim Weaver, NASA project scientist for XMM-Newton.<\/p>\n In other words, ORCs like the Cloverleaf might require a two-part origin story \u2013 powerful emissions from active supermassive black holes, followed by galaxy merger shockwaves that give those emissions a second kick.<\/p>\n Learn More:<\/strong><\/p>\n E. Bulbul et. al. \u201cThe galaxy group merger origin of the Cloverleaf odd radio circle system.\u201d Astronomy and Astrophysics.<\/p>\n \u201cX-ray Satellite XMM-Newton Sees \u2018Space Clover\u2019 in a New Light.\u201d NASA.<\/p>\nLike this:<\/h3>\n