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witnessed 0n the planet Earth in 1054
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 witnessed 0n the planet Earth in 1054apod.nasa.gov |
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Athena |
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Millisecond Pulsars Both numbers might first be multiplied by pi (pi(d)=c), but since pi is the same factor for each it cancels. To get the star speed ratio we divide 811 million by 132, or 6 million. The star is six million times faster than your car piston. Gear ratios translate the engine speed to vehicle velocity, so comparing that “top” speed to a point on the star’s equator might be more appropriate. Let us math together—Bob will check my figures. My top auto speed is 132 mph, which I achieved in my current Subaru Forrester. Before that I had managed 120 in my daughter’s Lexus. I don’t remember if she was driving or me. I managed faster in a European bullet train, and of course faster yet in commercial airliners. But I think most of us have broken 100 at one time or another in a car or motor bike. My son-in-law has topped 160 on his motorcycle. I have a cousin I think has come close in a car, he enjoys lesser known high performance automobiles. Not the fancy things like Lotus, Ferrari, Lamborghini, or even Porsche, which are all over priced brands, but things with pick up and go. I’ll have to quiz him some time on his top speed. Anyway, we’ll use 120 mph as most everyone must have come close to that one time or another. So pi(d)… Oops, the 642 rps pulsar diameter is only 12 to 15 miles, not twenty. I need to redo my math. But taking 12, an equatorial point moves 3.14x12x60x60=135,648 miles per hour. Well, that is a mere thousand times faster than my car. Maybe the comparison isn’t fair, since my car is on the Earth, which at the equator spins through space a thousand miles per hour. |
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Shiva 11:22 That's over 210 kph! You're a danger to the public, not to mention any wombats that might be crossing the highway. (Golly! Hitting a wombat at that speed would push your teeth through the windscreen.) You should be locked up. |
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Speed! On the right open roads out west, a little speeding just to find out is a bit risky, but at least there's no wombats to worry about. I've never done more than 115 myself ('92 Civic), but that was thirty years ago, and only once. Never again. Back in Connecticut/Westchester County, NY, I commuted on an interstate highway where the speed limit was 65, the average speed was 80, reasonably crowded, and there would be jack***es in Porsches and high-end BMWs passing people at what had to be 100 mph top speed. Lots of expensive cars, headed to NYC, driven by idiots, while I was in my used Nissan Altima, also driven by an idiot, but I digress. Never a statie around when one was needed. |
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Sir A* From our perspective, stuff outside the event horizon should be approaching timelessness. Not sure how we ever witness anything cross. I’m also puzzled by black hole mergers. I don’t see how an infinite spacetime barrier might be preserved in a merger. Do BH mergers “onionize?” Or dies the event horizon simply expand? Gemini offers: Black hole spin is measured by analyzing distortions in X-ray light from the accretion disk of hot gas spiraling into the black hole. Methods like X-ray reflection spectroscopy model the warped light, particularly from iron, to determine the spin. Other techniques include gravitational wave analysis during black hole mergers, X-ray continuum fitting, or observing the black hole's shadow. X-ray Reflection Spectroscopy (XRS) This is the most common method for accreting black holes, which have hot material falling into them. How it works: Astronomers examine X-rays emitted from the iron atoms in the inner edge of the accretion disk. Spin effect: The black hole's spin causes extreme gravitational effects that warp the path of the X-ray light and alter the iron's light signature, or spectrum. Analysis: Scientists use X-ray reflection spectroscopy to model these spectral distortions, which directly relates to the black hole's spin rate. End quote So we’re measuring iron orbital velocity. Would a non spinning BH form an accretion disk? Gemini provides: A non-spinning black hole can still form an accretion disk if the infalling matter possesses its own angular momentum. The disk forms due to the conservation of angular momentum as material spirals inward, with the non-rotating black hole providing the central gravitational pull. The black hole's lack of spin doesn't prevent this process; rather, the matter's own motion dictates the formation of the disk. Here's why accretion disks form around any central object, including non-spinning black holes: Conservation of Angular Momentum: When matter falls towards a central object, its initial small amount of angular momentum with respect to the center is amplified as it gets closer. Vortex Formation: This amplified angular momentum causes the matter to swirl into a disk-like structure, much like water forms a vortex around a drain. Stability: An accretion disk is a stable configuration for orbiting matter. Matter that doesn't follow this planar, rotational path will tend to collide with other matter and lose energy, eventually falling into the disk or the black hole. In summary: A non-spinning black hole provides the central gravity. The infalling matter provides the angular momentum. The interaction between the gravity and angular momentum leads to the formation of a disk, not a sphere of matter. End quote. So that was my guess before posing the question. Now, how to tell the difference between a spinning and non spinning BH? Gemini—You can distinguish a spinning black hole from a non-spinning one by observing its black hole shadow and the innermost stable circular orbit (ISCO) of material falling into it. Spinning black holes, also known as Kerr black holes, feature an oblate (flattened) event horizon and a ring-shaped singularity. Non-spinning Schwarzschild black holes have spherical event horizons and point-like singularities. The spin also creates an ergosphere around a Kerr black hole, allowing for energy extraction and causing accretion disks to orbit much closer than around a Schwarzschild black hole. Ok. I always thought the singularity was a point at the center. Is it everything (all the volume) inside the EH? What the hell is a BH “shadow?” As we have imaged only two BHs, have non Kerr BHs been observed? |
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Sgr A* Anyway, non Kerr (non-Kerr) BHs have not (yet) been observed. From Gemini (if you trust this—I’ve no reason to doubt): A non-Kerr black hole has not been conclusively observed. All current observations, such as gravitational waves and black hole shadows, have been consistent with the predictions of the Kerr metric from general relativity. However, observations are ongoing, and a definitive confirmation or denial remains a major goal for physicists. The "no-hair" theorem in general relativity posits that black holes are simple objects defined only by their mass, spin (angular momentum), and electric charge. A non-Kerr black hole would deviate from this theory, potentially indicating new physics or an alternative theory of gravity. Observational challenges Several factors make it difficult to definitively confirm or rule out a non-Kerr black hole: Observational blur: Current instruments like the Event Horizon Telescope and gravitational wave detectors do not yet have the precision to rule out all subtle deviations from the Kerr metric. Blurring effects in black hole images, for example, can make a non-Kerr black hole appear very similar to a Kerr black hole. Strong correlation of parameters: The properties of radiation emitted from the accretion disk around a black hole (used to measure spin) are strongly correlated with any potential deviations from the Kerr solution. This can lead to a scenario where a non-Kerr object with a different spin appears identical to a Kerr black hole with a specific spin. Limited data: Astrophysical black holes are not perfectly isolated, as the Kerr metric assumes. They are often surrounded by accretion disks, part of binary systems, or embedded in a cosmological context, all of which distort their observed properties. |
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Ring A black hole (BH) singularity is a hypothetical point of zero volume and infinite mass density where the known laws of physics and mathematics, including Einstein's theory of general relativity, break down. It represents a breakdown in our physical models rather than a real object, a place where space and time are infinitely curved and any matter that falls into it is thought to be compressed into this point. While general relativity predicts singularities, the emergence of infinities suggests the theory is too simplistic for such extreme conditions, indicating that a more complete "theory of everything" is needed to fully describe what happens at the center of a black hole. Key characteristics of a BH singularity: Zero volume and infinite density: . At a singularity, all the mass of the black hole is condensed into a point with no physical size. End Gemini. So how does a point assume a ring shape? |
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Ringularity End quote. On hearing my thought in singularity confirmed, this naturally followed. My expectation was met. I guess next I want to see the peer reviewed publications, but am satisfied with this. Curiously there is an instability: “Although the Kerr solution predicts an inner horizon and the possibility of a ring singularity, the region inside the inner horizon is thought to be highly unstable in a real black hole.” |
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apatzer 30-Aug-25, 21:56 |
Deleted by apatzer on 30-Aug-25, 21:57.
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Lord Shiva Recent studies provide intriguing evidence that the universe might indeed be rotating, albeit extremely slowly. This idea rests on both theoretical work and observations made with the James Webb Space Telescope (JWST). For instance, astronomers from the University of Hawai'i published a 2025 paper suggesting that if the universe is rotating, it completes one full rotation every 500 billion years—so slowly that such motion is nearly impossible to detect directly. Now here’s the astonishing twist: if we entertain the notion that each black hole creates its own universe and that we are inside Sagittarius A* as such a universe, then while it appears our universe completes one rotation every 500 billion years, an external observer in the parent universe watching Sagittarius A* would see it completing one rotation every 13 minutes. Comparing these rotation periods reveals an immense difference in how time flows between the two universes. To put numbers on it, converting 500 billion years into minutes gives roughly 2.63 × 10^17 minutes. Dividing this by the 13-minute rotation period observed from outside yields a ratio of about 2 × 10^16. This implies that time inside the hypothetical universe contained within Sagittarius A* would flow approximately 20 quadrillion times more slowly compared to time in the parent universe. This dramatic disparity illustrates profound time dilation effects that could arise if a universe were nested inside a rotating black hole when viewed relative to the outer universe’s timeframe. Such an enormous difference in the passage of time highlights how fundamentally different time might behave across these hypothetical cosmic boundaries, reflecting the extreme warping of space and time caused by the intense gravitational and relativistic effects associated with black holes. |
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Silly question time... Question:- Is a non-spinning black hole a real-universe possibility? I would expect that it is only theoretically possible, but in the real universe a BH would inevitably pull in some matter from outside. Such matter would have at least some angular momentum relative to the BH, so wouldn't this angular momentum be transferred into the BH as a dynamic system? OK, so I've exposed my iggerance. Someone who knows, please explain. |
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Cancelled Spin I’m just speculating here… Gemini offers no such scenario, instead delving into non standard physics and exotic matter: A non-Kerr black hole could form in several ways, but they are primarily theoretical scenarios that involve modifying the standard General Relativity (GR) framework, as astrophysical black holes are generally expected to be Kerr black holes according to the no-hair theorem. These theories include: 1. Scalarization in Alternative Gravity Theories Spontaneous Scalarization: In certain modified gravity theories, a black hole can "spontaneously scalarize" if it resides in a specific range of spin and coupling parameters, transitioning from a Kerr black hole to a non-Kerr solution with a scalar field. 2. Deforming the Kerr Metric (Phenomenological Approach) Introducing Deformation Parameters: Researchers can introduce ad hoc deformation parameters into the Kerr metric to explore how deviations from GR would manifest. These parameters can alter the black hole's shape, shadow, and lensing properties compared to a pure Kerr solution. 3. Exotic Matter or Different Matter Models Generic Matter Interactions: The Kerr solution describes a vacuum spacetime; however, different types of matter or different physical conditions could lead to novel black hole solutions. 4. Changes in Horizon Topology Beyond a Critical Spin: Some models suggest that above a critical spin parameter, a non-Kerr black hole's event horizon could transition from a simple 2-sphere to a more complex, topologically non-trivial shape. Why We Expect Kerr Black Holes in the Real Universe No-Hair Theorem: . The no-hair theorem states that black holes are uniquely described by their mass, charge, and spin. In the absence of charge, this means they should be Kerr black holes. Mass and Accretion: . For supermassive black holes, the enormous mass effectively suppresses any deviations from the Kerr metric, making non-Kerr effects negligible in most scenarios. How We Might Observe Non-Kerr Properties Gravitational Waves: . Deviations in gravitational wave signals from merging black holes could indicate a non-Kerr spacetime. Black Hole Shadows: . The precise shape and features of a black hole's shadow, as observed by telescopes, could reveal non-Kerr characteristics. Gravitational Lensing: . Changes in light bending and particle orbits around non-Kerr objects would produce different gravitational lensing patterns than those predicted for Kerr black holes. |
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Another Question Pops Into Mind While no method exists for direct observation of dark matter absorption by a black hole (BH), physicists can determine if it occurs by searching for its gravitational effects on surrounding systems. By looking for "indirect evidence" caused by dark matter's gravitational influence, scientists can potentially find signatures of its presence and absorption. Gravitational wave modifications from black hole mergers When black holes merge, they send gravitational waves through spacetime. If a "dark dress," or spike of dark matter, surrounds the black holes, it can modify the gravitational waves' strength and frequency. This allows scientists to use gravitational wave detectors, like LIGO and LISA, to look for signals that are distinct from those created by black hole mergers in a vacuum. Orbital decay in binary systems A star orbiting a black hole can experience dynamical friction from a surrounding cloud of dark matter, acting like a drag force. This friction causes the star's orbit to decay faster than predicted. In 2023, researchers identified this effect in two binary systems, A0620-00 and XTE J1118+480. The abnormally fast orbital decay provided indirect evidence for a dark matter density spike around the black holes. Accretion disk and proto-jet disruptions A black hole's accretion disk is a bright, swirling disk of superheated material. The gravitational effects of dark matter can subtly influence this disk and the jets it produces. Studying the accretion disks of black holes immersed in dark matter can reveal unusual characteristics, such as extra cusps or double tori. These anomalies could potentially serve as tracers for dark matter, though they can also be mimicked by other cosmic objects. Gravitational lensing by primordial black holes If a portion of dark matter is composed of primordial black holes (PBHs), they could be detected through gravitational microlensing. Microlensing occurs when a compact object passes in front of a distant star, causing its light to be temporarily magnified. The OGLE survey, for example, has looked for these events to place limits on the fraction of dark matter that can be made of PBHs. Supermassive black hole growth in the early universe The existence of supermassive black holes in the early universe, where they shouldn't have had time to form through conventional means, could be linked to decaying dark matter. One theory suggests that decaying dark matter heated the hydrogen gas in the early universe, causing it to collapse into dense clouds that later formed supermassive black holes. This theory also supports the existence of a dark matter candidate that decays into particles like photons. The black hole-dark energy connection Some studies suggest that black holes may be a source of dark energy and that their growth, in part from absorbing matter, contributes to the accelerating expansion of the universe. In this scenario, the density of dark energy would increase with the total mass of black holes in the universe. Observations from the Dark Energy Spectroscopic Instrument (DESI) have shown tantalizing evidence supporting this coupling between supermassive black holes and dark energy. |
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Pulsar clocks |
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Black holes and dark matter |
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Dark Mass Black holes are X-ray sources as in falling atomic matter is shredded, liberating high energy radiation. If DM is axions, do they decompose under strong tidal influence? And into what? Axion decomposition like.y doesn’t liberate energy in the electromagnetic spectrum. Is there a dark mass energy spectrum, possibly dark energy? |
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… How we might detect differences Scientists are looking for observational evidence that could distinguish between a constant dark energy and a dynamic one. Studies are analyzing the universe's evolution and the growth of cosmic structures, which could reveal different behaviors or components of dark energy. In summary, while there is no known spectrum for dark energy in the way there is for light, scientists are actively investigating if dark energy is a single, unchanging entity or a more complex phenomenon with varying forms and properties. |
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a little about dark matter |
