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posted by Fnord666 on Friday June 02 2017, @05:51PM   Printer-friendly
from the abandon-all-hope-ye-who-enter-here dept.

Black holes are perhaps the strangest objects predicted by Einstein's theory of General Relativity, objects so dense that gravity reigns supreme, and not even light can escape beyond a certain distance, known as the event horizon. The actual existence of black hole event horizons has not been proved, but some clever observations made by astronomers at the University of Texas at Austin and Harvard University have tested the alternative hypothesis: instead of an event horizon, there might instead be a solid surface to a black hole that objects colliding against it will hit. They found results that show that this alternative can't be true, and that an event horizon as predicted by GR is more likely. ScienceDaily has an article:

Astronomers at The University of Texas at Austin and Harvard University have put a basic principle of black holes to the test, showing that matter completely vanishes when pulled in. Their results constitute another successful test for Albert Einstein's General Theory of Relativity.

Most scientists agree that black holes, cosmic entities of such great gravity that nothing can escape their grip, are surrounded by a so-called event horizon. Once matter or energy gets close enough to the black hole, it cannot escape — it will be pulled in. Though widely believed, the existence of event horizons has not been proved.

"Our whole point here is to turn this idea of an event horizon into an experimental science, and find out if event horizons really do exist or not," said Pawan Kumar, a professor of astrophysics at The University of Texas at Austin.

Supermassive black holes are thought to lie at the heart of almost all galaxies. But some theorists suggest that there's something else there instead — not a black hole, but an even stranger supermassive object that has somehow managed to avoid gravitational collapse to a singularity surrounded by an event horizon. The idea is based on modified theories of General Relativity, Einstein's theory of gravity.

While a singularity has no surface area, the noncollapsed object would have a hard surface. So material being pulled closer — a star, for instance — would not actually fall into a black hole, but hit this hard surface and be destroyed.

The team figured out what a telescope would see when a star hit the hard surface of a supermassive object at the center of a nearby galaxy: The star's gas would envelope the object, shining for months, perhaps even years.

Once they knew what to look for, the team figured out how often this should be seen in the nearby universe, if the hard-surface theory is true.

[...] "Given the rate of stars falling onto black holes and the number density of black holes in the nearby universe, we calculated how many such transients Pan-STARRS should have detected over a period of operation of 3.5 years. It turns out it should have detected more than 10 of them, if the hard-surface theory is true," Lu said.

They did not find any.

"Our work implies that some, and perhaps all, black holes have event horizons and that material really does disappear from the observable universe when pulled into these exotic objects, as we've expected for decades," Narayan said. "General Relativity has passed another critical test."

The full text of the original paper "Stellar disruption events support the existence of the black hole event horizon" (DOI: 10.1093/mnras/stx542) is available open access from the Monthly Notices of the Royal Astronomical Society.

Further evidence for or against the existence of black hole event horizons will have to wait for the Event Horizon Telescope, which is due to release its first results later this year.


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Event Horizon Telescope Will Soon Take the First Black Hole Photo 21 comments

The Event Horizon Telescope (EHT) is finally ready to take a picture of Sagittarius A*. From April 5th to 14th this year, the virtual telescope that's been in the making for the past two decades will peer into the supermassive black hole in the center of our galaxy. EHT is actually an array of radio telescopes located in different countries around the globe, including the Atacama Large Millimeter/submillimeter Array in Chile.

By using a technique called very-long-baseline interferometry, the EHT team turns all the participating observatories into one humongous telescope that encompasses the whole planet. We need a telescope that big and powerful, because Sagittarius A* is but a tiny pinprick in the sky for us. While scientists believe it has a mass of around four million suns, it also only measures around 20 million km or so across and is located 26,000 light-years away from our planet. The EHT team says it's like looking at a grapefruit or a DVD on the moon from Earth.

To prepare the participating observatories, the team equipped them with atomic clocks for the most precise time stamps and hard-drive modules with enormous storage capacities. Since the scientists are expecting to gather a colossal amount of data, they deployed enough modules to match the capacity of 10,000 laptops. Those hard drives will be flown out to the MIT Haystack Observatory, where imaging algorithms will make sense of EHT's data, once the observation period is done.

Source:

https://www.engadget.com/2017/02/19/event-horizon-telescope-is-ready/


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  • (Score: -1, Troll) by Anonymous Coward on Friday June 02 2017, @06:01PM

    by Anonymous Coward on Friday June 02 2017, @06:01PM (#519480)

    For fat black women.

  • (Score: 2) by MichaelDavidCrawford on Friday June 02 2017, @06:09PM (21 children)

    My understanding is that from the frame of reference of an earthbound astronomer, objects near the event horizon move slower and slower, due to gravitational time dilation. So in a finite time nothing should get to the event horizon.

    From the point of view of an unfortunate astronaut, they fall right in.

    --
    127.0.0.1 www.hosted-pixel.com # I Am Absolutely Serious
    • (Score: 2) by DannyB on Friday June 02 2017, @06:35PM (16 children)

      by DannyB (5839) on Friday June 02 2017, @06:35PM (#519495)

      I understand the object moving slower (and slower) due to gravitational time dilation. Is it an assumption that it would not reach the event horizon in finite time? Or is there some basis for that assertion? (Not that I've read much on the subject. Just asking.) It sounds like the velocity from an earthbound POV approaches zero at the event horizon. Is there a reason it wouldn't do that somewhere beyond the event horizon?

      I remember reading in Hawking's book, years ago, so recollection is vague, but the unfortunate (or fortunate) astronaut who falls in would get to see watch the entire future up to the end of the universe. From his/her POV time would speed up rapidly. But then, spagettification, and would it happen before you got to see very much? And I don't suppose you would see anything through bookshelves.

      Also Hawking radiation, and I could really be botching up the description, but a pair of entangled particles appear near the event horizon, one inside, one outside. The one inside falls in, and the one outside 'radiates' away.

      "Why should we subsidize intellectual curiosity?" -Ronald Reagan

      • (Score: 3, Insightful) by kaszz on Friday June 02 2017, @07:14PM (13 children)

        by kaszz (4211) on Friday June 02 2017, @07:14PM (#519516) Journal

        "Why should we subsidize intellectual curiosity?" -Ronald Reagan

        Please return:
          * Diesel engines
          * Nuclear bombs
          * Nuclear power
          * Computers
          * Rockets
          * Vaccines
          * Anesthesia
          * Cars
          * High voltage transmission equipment
          * Electronics
          * Cryptography
          * Telephones
          * Radio communication
          * Submarines
          * Satellites

        Please return these to your nearest university or nerd. They may be lent back.. for a fee. If we choose to so subsidize.

        • (Score: 1) by khallow on Saturday June 03 2017, @05:18AM (12 children)

          by khallow (3766) Subscriber Badge on Saturday June 03 2017, @05:18AM (#519739) Journal
          There are several observations to make here. First, a fair number of those items happened without significant subsidies (for example, cars, telephones, and anesthesia). Second, almost all of those things would have happened without government subsidy (nuclear power and bombs might not make the list due to liability issues which are a massive sort of government subsidy). Third, where's my subsidy for intellectual curiosity? I don't buy that this money is being allotted in a rational manner.
          • (Score: 2) by kaszz on Saturday June 03 2017, @06:59AM (9 children)

            by kaszz (4211) on Saturday June 03 2017, @06:59AM (#519761) Journal

            Point is that a lot of technology comes from people subsidized at universities. But profits from products enabled by them would most likely finance their "subsidy".

            • (Score: 1) by khallow on Saturday June 03 2017, @12:38PM (8 children)

              by khallow (3766) Subscriber Badge on Saturday June 03 2017, @12:38PM (#519827) Journal

              Point is that a lot of technology comes from people subsidized at universities.

              A lot more comes from people who aren't. Most of that list didn't come from universities even when the technology was heavily subsidized - for example, nuclear anything, computers, rockets, electronics, submarines, satellites, and cryptography. I don't know if there is any context for Reagan's quip any more. But my suspicion is that it was in reply to someone who saw public funding as a dial that you could crank up arbitrarily high to make more science.

              And the question does remain. Why do we need to subsidize (some) intellectual curiosity? Is no one going to develop important things, if we're not throwing public funds at them? Are you going to be more intellectually incurious in the absence of such subsidies? Is the development of highly profitable technologies not adequate compensation for our collective intellectual curiosity?

              • (Score: 3, Interesting) by stormwyrm on Saturday June 03 2017, @05:22PM (7 children)

                by stormwyrm (717) Subscriber Badge on Saturday June 03 2017, @05:22PM (#519917) Journal
                My favourite rebuttal to this is Maxwell's Equations. What would have happened had Queen Victoria's government not seen fit to endow an institution like King's College London with enough funding such that someone like James Clerk Maxwell could make a living doing fundamental physics research? How else could the foundational equations of electromagnetic theory have been discovered except by that sort of subsidy? No one had any idea what those equations would be good for when Maxwell first formulated them, and it was at least fifty years later, some years after Maxwell himself passed away, that its prediction of electromagnetic radiation found application in the form of radio. There was no immediate profit to be had from the equations: that only came much much later. I doubt that private, profit-driven enterprises could have made that kind of discovery because the cycle between discovery and application is far too long, and such enterprises need to soon turn up a profit somehow.
                --
                The right to believe whatever you want does not mean that whatever you want to believe is right.
                • (Score: 1) by khallow on Saturday June 03 2017, @10:17PM (6 children)

                  by khallow (3766) Subscriber Badge on Saturday June 03 2017, @10:17PM (#519997) Journal

                  My favourite rebuttal to this is Maxwell's Equations. What would have happened had Queen Victoria's government not seen fit to endow an institution like King's College London with enough funding such that someone like James Clerk Maxwell could make a living doing fundamental physics research?

                  Someone else would have. It's worth noting here that universities existed at the time in the absence of government subsidy and similarly, people were investigating this important field in the absence of government subsidy as well. Further, Maxwell's equations were well on their way to being discovered due to past work on electric and magnetic field interactions. It was just a matter of putting the pieces together.

                  No one had any idea what those equations would be good for when Maxwell first formulated them, and it was at least fifty years later, some years after Maxwell himself passed away, that its prediction of electromagnetic radiation found application in the form of radio.

                  EM research already had considerable value and considerable money had already been spent on it. And Maxwell found an elegant reformulation of the theory that made all existing EM research more valuable. And radio came out less than 30 years later, not 50 (Maxwell eqns in 1861-62, radio waves discovered in late 1880s). Finally, for the last eight years of Maxwell's life, he was privately funded by a relative of Henry Cavendish.

                  I doubt that private, profit-driven enterprises could have made that kind of discovery because the cycle between discovery and application is far too long, and such enterprises need to soon turn up a profit somehow.

                  There's also private non profit-based research. For example, a fair number of US astronomical observatories have been built with private donations.

                  • (Score: 2) by kaszz on Sunday June 04 2017, @01:41AM (5 children)

                    by kaszz (4211) on Sunday June 04 2017, @01:41AM (#520053) Journal

                    with reliable funding research can be done more efficiently and more and faster results can be had with a another level of quality. Which lets industry exploits this faster (for free..) and with more certainty. And while the delay between discovery and application might been far in the 1900ths. It's way faster these days, usually. Which makes the ROI case even more compelling these days. Then it's the question if important science should be beholden to the private sphere. In the end I think publicly funded research benefits the society in many less than obvious ways.

                    • (Score: 1) by khallow on Sunday June 04 2017, @03:22AM (4 children)

                      by khallow (3766) Subscriber Badge on Sunday June 04 2017, @03:22AM (#520074) Journal

                      with reliable funding research can be done more efficiently and more and faster results can be had with a another level of quality.

                      I disagree. That could happen in theory with public funding, but in practice it doesn't happen that way because there's no incentive to do that.

                      A particularly egregious example (which I might add spurred my skepticism of publicly funded basic science research in the first place) is space science and manned space exploration, which has huge problems with one-off missions (which prioritize dead end technology development over doing space science, exploration, or development), missions decided on the basis of who gets funding rather than what the supposed purpose of the mission is (such as substantially increasing the cost of the International Space Station so that it uses the Space Shuttle and sources Russian space parts), kitchen sink design (throwing in tons of additional features, which have tremendous negative synergy when it comes to the cost and complexity of the mission) and spending staggering sums of money and consuming the lives of some of the best and brightest to little consequence (a space scientist who gets one research mission every 5-10 years could be doing a lot more, even in space science).

                      • (Score: 2) by kaszz on Sunday June 04 2017, @07:46AM (3 children)

                        by kaszz (4211) on Sunday June 04 2017, @07:46AM (#520134) Journal

                        That is a problem with perverted incentives. Guess what people complain about at NASA, administrators! which is the same old again, bureaucrats, HR department, bosses with a few hairs (PHB) that decides with too little clue etc. It's the death-by-MBA in the public funding version. Some universities seems more like a corporation with a big tax exempt and expensive administration than a learning and research institution. I'll suggest the perverted incentives are fixed instead of killing all funding.

                        The problem with a lot of research is that it takes a lot of (uninterrupted) time. It can be as cheap as a person sitting at a desk, or more expensive with a particle accelerator etc. And the outcome may either never happen or show up much later where it never were intended. So stable funding is a necessity.

                        A comparison can be made with research in the 1800-1900 vs 1945-1990.

                        • (Score: 1) by khallow on Sunday June 04 2017, @08:54AM (2 children)

                          by khallow (3766) Subscriber Badge on Sunday June 04 2017, @08:54AM (#520148) Journal

                          That is a problem with perverted incentives.

                          Exactly. A subsidy for "intellectual curiosity" so frequently turns out to be something else, such as a subsidy for "death-by-MBA" because ultimately, that is the perverse incentive of the subsidy - to not only do the minimal behavior required to get the subsidy, but to politically game the system so that the subsidy ends up being about something very different from its expressed purpose. I'm not going to claim here that Reagan was grasping the full nuances of public funding of research or we are grasping the full nuances of Reagan's quote. But a key problem with this kind of thing is that it devolves into being another political tool focused on completely unrelated purposes, such as bureaucratic empire-building or vote garnering, rather than its expressed purpose.

                          There's really only two advantages to public funding. First, it's bigger than almost any other approach. It's the easiest way to rig massive funding and diversion of a society's resources into research. You just need to get the necessary political support. Second, it's relatively nonpartisan in the generic sense which is important for highly disruptive things like nuclear weapons or generating research necessary for regulation creation and enforcement.

                          The key disadvantage is that you can't simply cut funding when things go off the rails. A private NASA with the decades of problems the current one has would have been at least been partially cut off or reformed long ago. Thus, there really isn't a point to having a massive publicly funded system that is grossly inefficient. It actually hurts scientific research more than it helps by diverting resources, such as the efforts of scientists, to unproductive routes (such as spending considerable time and effort running on the bureaucratic wheel merely to obtain more funding) and discouraging private efforts (which tend to be much more effective) from attempting research that is already dominated by publicly funded projects (such as space science or fusion research).

                          • (Score: 2) by kaszz on Sunday June 04 2017, @09:02AM (1 child)

                            by kaszz (4211) on Sunday June 04 2017, @09:02AM (#520150) Journal

                            One idea, let researchers select the management? and of course limit them to max 5% of funding or so. And only active researchers may have a say.
                            Exclude humanities from the process of course ;)

                            • (Score: 1) by khallow on Sunday June 04 2017, @09:54AM

                              by khallow (3766) Subscriber Badge on Sunday June 04 2017, @09:54AM (#520160) Journal

                              One idea, let researchers select the management? and of course limit them to max 5% of funding or so. And only active researchers may have a say.

                              The point is that any such process can be corrupted, even by the researchers themselves (who let us note are collectively rather cheap to corrupt). A public system doesn't have any means of correcting corruption except by convoluted political processes. I gather Reagan's saying, for example, comes from one such attempt.

          • (Score: 0) by Anonymous Coward on Saturday June 03 2017, @05:05PM (1 child)

            by Anonymous Coward on Saturday June 03 2017, @05:05PM (#519908)

            Most of those items to which you refer were developed by companies who used to support basic research. This is no longer the case. Most companies who still have "research" wings focus on short-term payoff applied research. Places like Google and Microsoft are the rare exceptions, and they focus on a very narrow subset of research.

            • (Score: 1) by khallow on Sunday June 04 2017, @09:03AM

              by khallow (3766) Subscriber Badge on Sunday June 04 2017, @09:03AM (#520151) Journal

              Most of those items to which you refer were developed by companies who used to support basic research.

              It's interesting how few people wonder why that is no longer the case. There's always been shortsightedness in business, including scientific research, but it's never been as bad as it is now. We should ask why. The answer is that it is rewarded far more than it's been in the past, for example, by the mechanism of "public risk, private profit" where the risk of business endeavors is pushed onto the public. Publicly funded science is a key way that is done and a fair bit of such effort is merely to pay businesses to do research that they would have done anyway (one can, for example, peruse NASA's list of touted technology "spin offs" [nasa.gov] to find innumerable examples of this practice).

      • (Score: 2) by AthanasiusKircher on Saturday June 03 2017, @05:31AM (1 child)

        by AthanasiusKircher (5291) on Saturday June 03 2017, @05:31AM (#519742) Journal

        I understand the object moving slower (and slower) due to gravitational time dilation. Is it an assumption that it would not reach the event horizon in finite time?

        It really depends on what you mean by "not reach the event horizon in finite time." I assume you're talking about an external observer here. Yes, basically time dilation as viewed from a distant observer basically becomes infinite at the event horizon. But the idea of being able to see an astronaut "frozen in time forever" at the event horizon simply is inaccurate. Why? Because really what time dilation affects is the rate of release of photons that will ultimately reach the distant observer. Since the number of photons emitted from the falling astronaut before crossing the event horizon is finite, there is a finite future time when the "last photon" will be observed.

        But from a more practical standpoint, a distant observer would just see an exponential decay in the number of photons from the source, and this decay will happen quite rapidly. As discussed here [ucr.edu], for a somewhat small black hole, the final approach and "dimming" to basically nothing will likely happen in a matter of seconds or less. For very large black holes, it could be longer, but still not "until the end of universe" kind of scale.

        Is there a reason it wouldn't do that somewhere beyond the event horizon?

        By "beyond the event horizon" I assume you mean at a greater distance outside the black hole? Or do you mean inside the event horizon? Anyhow, the reason all the math breaks down at the event horizon has to do with the speed of light. A common way of discussing this is to say that gravity is so strong at the event horizon that beyond that escape velocity exceeds the speed of light. (That's a little imprecise, but it gets the general idea across.) Light paths inside the event horizon necessarily curve inward. Those immediately outside can curve outward, but it gets less possible the closer you get (and time dilation will cause escaping photons to take ever longer). The event horizon is basically defined as the dividing point between these two zones.

        the unfortunate (or fortunate) astronaut who falls in would get to see watch the entire future up to the end of the universe.

        This, again, is a common misconception. The link above explains it some more. But for most "normal" black holes, the astronaut would likely see some time acceleration upon approach. But the astronaut actually will pass the event horizon at a subjective "normal" rate of speed, and just as the emitted photons are limited, so are those which can arrive to the astronaut from faraway events in the future. For a somewhat more technical explanation, see answers here [stackexchange.com].

        Note there are unusual circumstances with rotating black holes that could theoretically expand this, especially with exotic stuff like wormholes. But the standard scenario for falling into a black hole doesn't allow you to see the entire history of the universe.

        But then, spagettification, and would it happen before you got to see very much?

        For large black holes, one could easily pass the event horizon without being "spaghettified" or possibly harmed at all (depending on what one thinks goes on with the potential "firewall" around the event horizon). Tidal forces for small black holes will rip you apart before you get there, but for a sort of "galactic core" size black hole, the tidal forces might barely be noticeable at the event horizon.

        • (Score: 2) by melikamp on Saturday June 03 2017, @07:05PM

          by melikamp (1886) on Saturday June 03 2017, @07:05PM (#519943) Journal

          Because really what time dilation affects is the rate of release of photons that will ultimately reach the distant observer. Since the number of photons emitted from the falling astronaut before crossing the event horizon is finite, there is a finite future time when the "last photon" will be observed.

          Not to argue, but just to understand... If we think about the EM wave emitted, not photons, there seems to be practically infinite time to detect the wave.

    • (Score: 2) by bob_super on Friday June 02 2017, @06:43PM (2 children)

      by bob_super (1357) on Friday June 02 2017, @06:43PM (#519500)

      I think it's the opposite.
      Time slows for the person going over the event horizon (ignoring how very dead they are).
      Time flows at the faster rate for the distant low-grav observer seeing the object cross the event horizon.

      https://simple.wikipedia.org/wiki/Time_dilation [wikipedia.org]

      • (Score: 0) by Anonymous Coward on Friday June 02 2017, @07:30PM

        by Anonymous Coward on Friday June 02 2017, @07:30PM (#519531)

        Yes, Brian Greene explained it best to me in his book on String Theory (which I still don't understand, but hey, he helped me understand GR).

        Think of gravity as centrifugal force, if you are far away from the center you will feel a stronger pull to the outside (at a given angular speed).

        Note that the further out from the center you are the the further you have to go each rotation, and thus the further light travels with you. Thus, to preserve the speed of light, as you get further out time goes slower.

        Likewise, as you approach a massive object, you get pulled more strongly by that object, and time goes slower for you.

      • (Score: 2) by AthanasiusKircher on Saturday June 03 2017, @05:37AM

        by AthanasiusKircher (5291) on Saturday June 03 2017, @05:37AM (#519743) Journal

        This is incorrect. Your statements are accurate for a 3rd party observer looking at two people, one close to the event horizon and one far away. The one close to the event horizon will appear to have clocks moving slowly; the one far away will appear to have clocks moving fast. The subjective experience of each, however, is a different question. Since the person near the black hole has slow moving clocks, far away stuff appears to move even faster comparatively. But subjective experience of time doesn't "slow down" -- the clock still seems to tick at a "normal" rate for the person near the black hole, and thus they pass through the event horizon relatively quickly (from their perspective of time) compared to what's observed from a distance.

    • (Score: 1, Informative) by Anonymous Coward on Friday June 02 2017, @07:53PM

      by Anonymous Coward on Friday June 02 2017, @07:53PM (#519548)

      No, time is relative. Objects falling into a black hole will always experience the process in finite time. Provided a sufficiently large black hole, you can safely pass the event horizon and even survive for a while. You will never see yourself passing through the black border as that's merely a trick of the light, it will always appear bellow the observer regardless of how close you are to the singularity proper. However, you will actually cross the region of spacetime where the event horizon occurs, and once there you are certainly doomed to be sphagettified and fall into the singularity.

      An outside observer will never see that. To them, the falling object will appear ever more redshifted until their radiation disappears altogether, never seeming to cross the black border.

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