The outer edges of a black hole might be "fuzzy" instead of neat and smooth.
- A recent study analyzed observations of gravitational waves, first observed in 2015.
- The data suggests, according to the researchers, that black holes aren't bounded by smooth event horizons, but rather by a sort of quantum fuzz, which would fit with the idea of Hawking radiation.
- If confirmed, the findings could help scientists better understand how general relativity fits with quantum mechanics.
ESO, ESA/Hubble, M. Kornmesser<p>In the 1970s, Stephen Hawking famously proposed that black holes aren't truly "black." In simplified terms, the theoretical physicist reasoned that, due to quantum mechanics, black holes actually emit tiny amounts of black-body radiation, and therefore have a non-zero temperature. So, contrary to Einstein's view that black holes are neatly defined and are not surrounded by loose materials, Hawking radiation suggests that black holes are actually surrounded by quantum "fuzz" that consists of particles that escape the gravitational pull.</p><p>"If the quantum fuzz responsible for Hawking radiation does exist around black holes, gravitational waves could bounce off of it, which would create smaller gravitational wave signals following the main gravitational collision event, similar to repeating echoes," Afshordi said.</p>
Credit: NASA's Goddard Space Flight Center/Jeremy Schnittman<p>A new study from Afshordi and co-author Jahed Abedi could provide evidence of these signals, called gravitational wave "echoes." Their analysis examined data collected by the <a href="http://www.virgo-gw.eu/" target="_blank">LIGO and Virgo gravitational wave detectors</a>, which in 2015 detected the first direct observation of gravitational waves from the collision of two distant neutron stars. The results, at least according to the researchers' interpretation, showed relatively small "echo" waves following the initial collision event.</p><p>"The time delay we expect (and observe) for our echoes ... can only be explained if some quantum structure sits just outside their event horizons," Afshordi told <em><a href="https://www.livescience.com/black-hole-echoes-unsettle-einstein-relativity.html" target="_blank">Live Science</a>.</em></p>
Afshordi et al.<p>Scientists have long studied black holes in an effort to better understand fundamental physical laws of the universe, especially since the introduction of Hawking radiation. The idea highlighted the extent to which general relativity and quantum mechanics conflict with each other. </p><p>Everywhere — even in a vacuum, like an event horizon — pairs of so-called <a href="https://www.scientificamerican.com/article/something-from-nothing-vacuum-can-yield-flashes-of-light/" target="_blank">"virtual particles"</a> briefly pop in and out of existence. One particle in the pair has positive mass, the other negative. Hawking imagined a scenario in which a pair of particles emerged near the event horizon, and the positive particle had just enough energy to escape the black hole, while the negative one fell in.</p><p>Over time, this process would lead black holes to evaporate and vanish, given that the particle absorbed had a negative mass. It would also lead to some interesting <a href="https://en.wikipedia.org/wiki/Black_hole_information_paradox#Recent_developments" target="_blank">paradoxes</a>.</p><p>For example, quantum mechanics predicts that particles would be able to escape a black hole. This idea suggests that black holes eventually die, which would theoretically mean that the physical information within a black hole also dies. This violates a key idea in quantum mechanics which is that physical information can't be destroyed.</p><p>The exact nature of black holes remains a mystery. If confirmed, the recent discovery could help scientists better fuse these two models of the universe. Still, some researchers are skeptical of the recent findings.</p><p>"It is not the first claim of this nature coming from this group," Maximiliano Isi, an astrophysicist at MIT, <a href="https://www.livescience.com/black-hole-echoes-unsettle-einstein-relativity.html" target="_blank">told</a> Live Science. "Unfortunately, other groups have been unable to reproduce their results, and not for lack of trying."</p><p>Isi noted that other papers examined the same data, but failed to find echoes. Afshordi told <em>Galaxy Daily</em>:</p><p>"Our results are still tentative because there is a very small chance that what we see is due to random noise in the detectors, but this chance becomes less likely as we find more examples. Now that scientists know what we're looking for, we can look for more examples, and have a much more robust confirmation of these signals. Such a confirmation would be the first direct probe of the quantum structure of space-time."</p>
One of Stephen Hawking's predictions seems to have been borne out in a man-made "black hole."
- Stephen Hawking predicted virtual particles splitting in two from the gravitational pull of black holes.
- Black holes, he also said, would eventually evaporate due to the absorption of negatively charged virtual particles.
- A scientist has built a black hole analogue based on sound instead of light.
What Hawking predicted<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTYwNjAyOS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTYzNTU2ODMyM30.WQZs1L8SuWHexiGKXj_uuH0eBlNFdSPtdW14TnctPK0/img.jpg?width=980" id="f6261" class="rm-shortcode" data-rm-shortcode-id="7467feaf63835aeb8733c46a05f28bf5" data-rm-shortcode-name="rebelmouse-image" />
Physicist Stephen Hawking.
Photo: Bruno Vincent/Getty<p>While it's known that photons can't escape the pull of a black hole, Hawking's equations, intolerant of absolute nothingness, suggested "empty" space is actually full of virtual quantum matter/antimatter pairs that blink into existence, and immediately annihilate each other thanks to their opposite electrical charges, quickly blinking out again.</p><p>Hawking proposed that when virtual pairs pop into existence near a black hole, though, they're torn apart by the pull of the black hole, with the antimatter being sucked in while the matter shoots off into space — at this point, they're no longer virtual, but real, particles. The negative charge belonging to the antimatter particles reduces the energy and mass of the black hole that's absorbed it by a tiny amount — however, when a black hole ingests enough of these, it evaporates. The positively charged particles fly away as what's now called "Hawking radiation." It would be very weak, but nonetheless there.</p><p>Hawking also predicted that the radiation emitted would exhibit a continuous thermal spectrum rather than discreet light wavelengths preferred by individual escaping photons. The temperature of the spectrum would be determined instead by the black hole's mass. </p><p>Part of the problem in testing Hawking's theories was summarized by physicist Silke Weinfurtner, who <a href="https://www.nature.com/articles/d41586-019-01592-x" target="_blank">has written</a>: </p><p style="margin-left: 20px;">"The temperature that is associated with Hawking radiation, known as the Hawking temperature, is inversely proportional to the mass of the black hole. And for the smallest observed black holes, which have a mass similar to that of the Sun, this temperature is about 60 nanokelvin. Hawking radiation therefore produces a tiny signal, and it would seem that the phenomenon cannot be verified through observation."</p>
The analogue black hole in Haifa<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTYwNjA0Ni9vcmlnaW4ucG5nIiwiZXhwaXJlc19hdCI6MTYyMjQyOTQ2Mn0.sN5CVbwsVQf3nYxKLDJhzwb2djqulfBmRTaShuYQOT0/img.png?width=980" id="18b44" class="rm-shortcode" data-rm-shortcode-id="9bf76ae01c1f55d620b63cb2e08bf1d1" data-rm-shortcode-name="rebelmouse-image" />
Physicist Jeff Steinhauer.
Image source: Technion–Israel Institute of Technology<p>Experimental physicist <a href="https://phsites.technion.ac.il/atomlab/" target="_blank">Jeff Steinhauer</a> of Technion–Israel Institute of Technology in Haifa, Israel, has been <a href="https://www.nature.com/news/one-man-band-the-solo-physicist-who-models-black-holes-in-sound-1.20437" target="_blank">working alone</a> in his lab for years creating sonic "black holes" that suck in and trap sound waves. (He's a drummer, too.) Physicist <a href="https://www.phas.ubc.ca/users/william-unruh" target="_blank">William Unruh</a> of the University of British Columbia in Vancouver, Canada, first proposed the creation of a sound-wave black-hole replica in 1981 as a safe way of observing the behavior of the stellar version. (After all, creating a real black hole in a lab or anywhere nearby could lead to The End of Life as We Know It.)</p><p>Steinhauer's black-hole replica was "constructed" within a <a href="https://www.livescience.com/54667-bose-einstein-condensate.html" target="_blank">Bose-Einstein condensate (BEC),</a> an extremely strange form of matter in which atoms are cooled to a temperature vanishingly close to absolute zero. At this temperature, there's so little energy available that atoms barely move at all in relation to each other, and thus the entire <a href="https://www.merriam-webster.com/dictionary/superfluid" target="_blank">superfluid</a> begins to behave as one big, unified atom. Within such a frigid condensate, weak quantum fluctuations occur, and these produce pairs of entangled <a href="https://en.wikipedia.org/wiki/Phonon" target="_blank">phonons</a>, compressional waves that can create the air-pressure changes we perceive as sound.</p><p>Working with a cigar-shaped trap just a few millimeters long, Steinhauer cooled some 8,000 iridium atoms into a BEC. Inside it, the speed of sound, the rate at which the condensate flowed, dropped from 343 meters per second to an almost stationary half a millimeter per second. Reducing the density of one area of the BEC to allow atoms to travel at 1 millimeter per second, though he created a supersonic region — at least compared to the lower speed in the rest of the condensate, that is. Its comparatively rapid current overwhelmed and pulled in any high-energy phonons that came near its event horizon, thus trapping them.</p><p>In August, Steinhauer published a paper in <a href="https://www.nature.com/articles/s41586-019-1241-0" target="_blank"><em>Nature</em></a> that documented his observation of phonons emerging from his artificial black hole in line with Hawking's predictions. Steinhauer reports entangled phonon pairs popping into existence together equidistant across the condensate's event horizon and behaving much as Hawking predicted: One pulled over the supersonic waterfall and trapped in the supersonic region, and the other escaping outward, away from it, just as Hawking radiation would do. The symmetry in the number of phonons inside and outside the event horizon further supported their entangled beginnings and eventual separation, as in Hawking's prediction.</p><p>On top of that, the aggregate radiated phonons did indeed produce a thermal spectrum determined by the system's analogue to gravity/mass, which in this model's case was the relationship between the speed of sound and the flow of the BEC, and not individual phonons' sonic wavelengths.</p>
Analogies are usually imperfect<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTYwNjk0NC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY0ODkzNDMyMH0.dt_9tjvChU65e_TuE-idR276Tywb8GnjjxhfqACofj4/img.jpg?width=1245&coordinates=0%2C70%2C0%2C199&height=700" id="5cb83" class="rm-shortcode" data-rm-shortcode-id="c24f5a5debfcf50a12d691f43bb02177" data-rm-shortcode-name="rebelmouse-image" />
Image source: Alex Farias/Shutterstock<p>While the behavior of Steinhauer's phonons in his black hole analogue certainly supports the plausibility of Hawking's hypothesis, it doesn't constitute proof. His experiment deals with sound and phonons instead of light and photons, and obviously operates on an entirely different scale than a real black hole — and scale does matter in quantum physics. Still, it's fascinating.</p><p>Theoretical physicist <a href="http://www.th.u-psud.fr/annuaire2.php3?fiche=renaud.parentani" target="_blank">Renaud Parentani</a> enthuses to <a href="https://www.livescience.com/65683-sonic-black-hole-spews-hawking-radiation.html" target="_blank"><em>Live Science</em></a>, "These experiments are a tour de force. It's a very precise experiment. From the experimental side, Jeff Steinhauer is really, at the moment, the world-leading expert of using cold atoms to probe black hole physics." Other aren't as impressed. Speaking with <a href="https://www.nature.com/news/artificial-black-hole-creates-its-own-version-of-hawking-radiation-1.20430#/hole" target="_blank"><em>Nature</em></a>, physicist <a href="http://ulfleonhardt.weizmann.ac.il" target="_blank">Ulf Leonhardt</a> says that while, "For sure, this is a pioneering paper," he considers it incomplete, however, in part because Steinhauer was only able to correlate phonons of high energy across the event horizon, and didn't find that low-energy phonons also behaved as Hawking predicted. In addition, Leonhardt is concerned that what was inside the trap wasn't a true BEC, and that it could be producing other forms of quantum fluctuation that just <em>look</em> like Hawking radiation.</p>
The end of the world is the main focus of his new book.
- Everybody from Elon Musk to Stephen Hawking has said we should colonize a 'Planet B' due to the threat to our existence. Martin Brees, the UK's Astronomer Royal, has another perspective on it.
- "I think we have to accept that there's no planet B, which can ever be made as comfortable as the Earth," he recently told The Current's Anna Maria Tremonti.
- In a time of ever-worsening climate change that threatens the very existence of human beings, his focus is on maintaining and fixing the planet we now live on, but still with an eye toward the stars.
A Mars Colony?<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTA4MTI4NC9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY0NzA4MjQ5MX0.LdGQubVQ46auy47e1a8Ntd309UNVfn_cPbihvQeIR3A/img.jpg?width=980" id="0930b" class="rm-shortcode" data-rm-shortcode-id="501b2f3b3c78358075ab5051ad9e4f41" data-rm-shortcode-name="rebelmouse-image" alt="Mars Rover Curiosity, Mount Sharp" />Diverse Terrain Types on Mount Sharp, Mars
Photo by NASA/JPL-Caltech/MSSS via Getty Images<p>When you consider that well-known people, such as <a href="https://www.theguardian.com/science/2017/jun/16/life-on-mars-elon-musk-reveals-details-of-his-colonisation-vision" target="_blank">Elon Musk</a> and <a href="https://www.cnbc.com/2017/05/05/stephen-hawking-human-extinction-colonize-planet.html" target="_blank">Stephen Hawking</a>, have talked about the need to begin a colony on Mars because there's a chance Earth won't make it — or at least humans won't — and we'd need a place to start over, it's an interesting prospect. </p><p>When <a href="https://www.cbc.ca/radio/thecurrent/the-current-for-january-7-2019-1.4963706/jan-7-2019-episode-transcript-1.4969087" target="_blank">asked by CBC interviewer</a> Anna Maria Tremonit whether they're wrong about that idea, he responded thusly</p><p style="margin-left: 20px;">"They're only half wrong. I mean I agree with that in the long run, there will be a small community living on Mars and I think they will be important for the future of intelligence. But what I don't agree with is something, which I think both Elon Musk and Stephen Hawking believe, which was there'd be mass emigration. I think we have to accept that there's no Planet B which can ever be made as comfortable as the Earth. We've got to accept that dealing with climate change, though hard, is a doddle compared to terraforming Mars and it's a dangerous delusion I think to believe that there can be mass emigration, a million people or so going to Mars."</p><p>According to Rees, the goal should instead be, </p><blockquote><em>To make the Earth habitable not just now, but for future centuries, that's the top priority.</em></blockquote>
Can we survive sustainably?<img type="lazy-image" data-runner-src="https://assets.rebelmouse.io/eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpbWFnZSI6Imh0dHBzOi8vYXNzZXRzLnJibC5tcy8xOTA4MTI5MS9vcmlnaW4uanBnIiwiZXhwaXJlc19hdCI6MTY1ODk4NzYzMH0.RfSYp96ypHxE9fY0rikdQWrUGXlSgYR7518PwARU4NY/img.jpg?width=980" id="9dd73" class="rm-shortcode" data-rm-shortcode-id="207a4841bffbb85213a9b07898d08661" data-rm-shortcode-name="rebelmouse-image" alt="North Korea nuclear ambitions" />
Empty seats are seen prior to the start of an emergency meeting of the United Nations Security Council concerning North Korea's nuclear ambitions
Drew Angerer/Getty Images<p>How do we ensure Earth's habitability?<br></p><p>In an <a href="http://www.pbs.org/wnet/amanpour-and-company/video/astronomer-royal-lord-martin-rees-climate-change-y6japt/" target="_blank">earlier PBS interview</a>, he talked with Christiane Amanpour about that:</p><p style="margin-left: 20px;">"The Earth's been around for 45 million centuries, but this is the first when one species, namely the human species, has the future of the planet in his hands because what we do in this century will determine whether we leave a depleted planet for future generations or whether we can survive sustainably."</p>