{"id":101161,"date":"2025-08-27T16:05:06","date_gmt":"2025-08-27T16:05:06","guid":{"rendered":"https:\/\/www.newsbeep.com\/ca\/101161\/"},"modified":"2025-08-27T16:05:06","modified_gmt":"2025-08-27T16:05:06","slug":"astrophysicists-find-no-hair-on-black-holes","status":"publish","type":"post","link":"https:\/\/www.newsbeep.com\/ca\/101161\/","title":{"rendered":"Astrophysicists Find No \u2018Hair\u2019 on Black Holes"},"content":{"rendered":"

In 2012, physicists showed that this paradox is tightly linked to the nature of the event horizon. They\u2019d known since the 1970s that black holes emit radiation, and that this radiation probably somehow carries the scrambled information about the stuff that fell into the hole. Now they imagined what would happen if an astronaut who was about to cross the horizon of an ancient black hole communicated with someone far away \u2014 an observer who had gathered the radiation emitted by the black hole over its lifetime. The result of the thought experiment was puzzling<\/a>: The astronaut and the faraway observer would end up with two copies of the same information, one recovered over the black hole\u2019s long lifetime and the other from close by. The extra copy is a problem, again spoiling the careful accounting of probabilities that quantum mechanics relies on. Some physicists concluded that something strange must happen just outside the horizon to disrupt the astronaut\u2019s information gathering.\u00a0<\/p>\n

Short Hair, Long Hair<\/p>\n

Attempts to address the information paradox usually add extra detail outside the event horizon, referred to as quantum hair. The researchers who came up with the thought experiment about the astronauts in 2012 suggested that a shell of extremely high-energy particles called a firewall might lie just outside the horizon, breaking the connection between the two observers. Alternatively, the physicist Samir Mathur argues that black holes don\u2019t have a horizon at all. Instead, he says that they are \u201cfuzzballs\u201d \u2014 each one a quantum combination, or superposition, of many different configurations of space-time, making the black hole\u2019s edges fuzzy.<\/p>\n

Other ideas include \u201cgravastars<\/a>\u201d that resemble black holes but are surrounded by shells of exotic matter, and so-called regular black holes<\/a> \u2014 reimagined versions of the objects that lack the infinitely dense points in their centers known as singularities.<\/p>\n

This zoo of proposals all introduce new effects outside the horizon that should change how a vibrating black hole emits gravitational waves.<\/p>\n

The proposed effects generally lie very close to the horizon, perhaps only within 10\u221233 centimeters \u2014 the so-called Planck length. Such close-cropped quantum hair would not be directly observable as a change in the signals from black hole collisions, but it might be visible in other ways. For example, unusual aftereffects<\/a> called echoes, generated as gravitational waves bounce off a firewall or other structure near the horizon, might appear after an initial signal.<\/p>\n

Searches for echoes have so far come up empty. These failed searches don\u2019t rule out the possibility of quantum hair, however, since it\u2019s unclear which kinds of quantum hair should give rise to echoes and which won\u2019t, or how exactly the echoes would appear.<\/p>\n

Meanwhile, physicists can also look for \u201clonger\u201d hair \u2014 more obvious deviations from Einstein\u2019s theory. There\u2019s less theoretical reason to expect this, but on the other hand, the highly curved space-times near black holes are a new environment for astronomers, and they can\u2019t be sure what they might find. Perhaps space-time curves differently under these conditions than general relativity predicts.<\/p>\n

\u201cI think it\u2019s a worthwhile exercise to go and test that,\u201d said Niayesh Afshordi<\/a>, an astrophysicist at the University of Waterloo in Canada.<\/p>\n

Math Meets Data<\/p>\n

Since the first detection of colliding black holes by the Laser Interferometer Gravitational-Wave Observatory, or LIGO, in 2015, physicists have been trying to use this data to test Einstein\u2019s theory. The project accelerated after additional observatories \u2014 Virgo in Europe and KAGRA in Japan \u2014 came online. But a substantial mathematical challenge stood in the way: The black holes that collide are always rotating, which greatly complicates calculations. The mathematician Roy Kerr calculated back in 1963 how rotating black holes behave in the framework of Einstein\u2019s equations. But what if that framework is wrong?<\/p>\n

A group of physicists at KU Leuven cracked the problem in 2023. They developed a technique<\/a> for understanding how fast-spinning black holes would behave if Einstein\u2019s theory were modified.<\/p>\n

Then, at a conference later that year, a graduate student in the Leuven group, Simon Maenaut<\/a>, met Gregorio Carullo<\/a>, a postdoctoral researcher in Copenhagen at the time who was an expert in analyzing gravitational wave signals. They realized that they could test the Leuven group\u2019s theories against Carullo\u2019s data, and they wasted no time. \u201cWe sort of jumped on a free desk and started coding together,\u201d said Carullo, who is now at the University of Birmingham.<\/p>\n","protected":false},"excerpt":{"rendered":"In 2012, physicists showed that this paradox is tightly linked to the nature of the event horizon. They\u2019d…\n","protected":false},"author":2,"featured_media":101162,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[24],"tags":[49,48,314,66],"class_list":{"0":"post-101161","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-physics","8":"tag-ca","9":"tag-canada","10":"tag-physics","11":"tag-science"},"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/101161","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/comments?post=101161"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/posts\/101161\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media\/101162"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/media?parent=101161"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/categories?post=101161"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/ca\/wp-json\/wp\/v2\/tags?post=101161"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}