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Black Holes are Everywhere

The views expressed are those of the author and are not necessarily those of Scientific American.

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Holes are everywhere, if you look...

This post is the second in a series that accompanies the upcoming publication of my book ‘Gravity’s Engines: How Bubble-Blowing Black Holes Rule Galaxies, Stars, and Life in the Cosmos’ (Scientific American/FSG).

Black holes, even the really hugely massive ones, are tiny – positively microscopic pinpricks scattered throughout the vastness of spacetime. Even the largest, perhaps ten billion times the mass of our Sun, have event horizons (the surface from within which no light can ever emerge) that reach to only about the orbit of Neptune. That’s a mere 4.5 billion km (or 0.00047 light years), absolutely nothing compared to the scale of galaxies – whose stellar components may reach across more than 100,000 light years. And nothing that massive exists in the Milky Way, where the very largest black hole is only some 4 to 5 million solar masses, lurking close to the galactic center. Its event horizon is only a little larger than the radius of our Sun.

Most of the holes in our galaxy are perhaps 4 or 5 solar masses, and they’re teeny, with horizons of only about 12 km in radius. But there have to be tens of thousands of them, the inevitable remnants of the short lives of huge stars. Rather ironically though, astronomical evidence for the existence of these objects is on less sure footing than the evidence for their supermassive cousins, sitting imperiously at the center of seemingly every galaxy. The most promising astronomical observations of low-mass black holes comes from the study of binary systems, where a visible companion star is being eaten by something rather more obscure. The prototype is the X-ray binary known as Cygnus X-1, discovered back in the 1970s. It consists of a giant blue star in a six day orbit with an indirectly seen object some ten times the mass of the Sun. That body is apparently pulling material from the star and swirling it into a hot disk of matter which glows with X-ray photons. Too massive to be a neutron star (which will collapse to a black hole if more than about 3 solar masses) or white dwarf (limited to about 1.4 solar masses), this companion fits the bill for a black hole.

Artist's impression of Cygnus X-1 (Credit: ESA)

It’s not a done deal though, uncertainties remain in the measurements of this system. The sheer brightness of the blue star making it extremely difficult to pin down the nature of its companion. Other types of binaries, known as soft X-ray transients, may present clearer signposts to stellar-mass black holes. In these systems a more modest-sized star orbits close to an unseen massive companion, but matter streams across to it only occasionally – flaring up in X-ray light for about six months out of every 10 to 50 years. This provides ample opportunity for astronomers to inspect the objects when they’re essentially asleep, disentangling the light of the two bodies. In these cases (and a system called V404 Cygni is the best) it does look like the companions are much too massive to be neutron stars, and likely to be black holes some ten times the mass of the Sun.

There are still people who question whether black holes this size are really what we think they are. Some of this skepticism is based on science that, while unproven, is not entirely implausible. For example, certain field theories for the strong nuclear force allow the confinement of neutrons and protons at lower densities than normally considered, resulting in the formation of objects that are neither neutron stars or black holes (‘Q-stars‘). These could be as massive as 100 suns, yet only 40% larger in radius than the event horizon of an equivalent mass black hole. The distinguishing characteristic for astronomers would be this difference in radius, and of course the presence of an actually observable surface rather than an event horizon.

By contrast, the existence of supermassive black holes – millions to tens of billions of times the mass of the Sun, is on much surer footing, since there really are no plausible alternative theories for the existence of such enormously massive, yet still remarkably compact objects in the universe. They are also extremely potent forces at large across the cosmos, producing colossal amounts of energy at the centers of many galaxies that barrels outwards as great fronts of radiation and particles, and even as ultra-relativistic beams or jets of matter extending for hundreds of thousands of light years. The energy comes from the destruction of matter that is ensnared by their fearsomely steep gravity wells, and swept around the spinning spacetime in their vicinity.

The giant black hole at the center of the Milky Way has been pinned down in an especially spectacular way – by watching what it does to the orbit of nearby stars. The animations here consist of real data taken by Reinhard Genzel’s group at the Max-Planck-Institut für extraterrestrische Physik, and shows the motion of stars at the very galactic center over a period of sixteen years, from 1992 to 2008 (Genzel, together with Andrea Ghez and her group at UCLA recently shared the Crafoord Prize for their pioneering work on locating and characterizing the black hole at the center of our galaxy).

You will need to click on this image to watch the animation. Look closely and you will see the sudden rapid movement of the stars in the middle around something unseen. That something has a mass of more than 4 million suns.




You can also watch the motions here, in slightly more detail that zooms in and plots the real data on the stellar orbits – that fast closest approach of the nearest star happens at about 7,500 miles a second, almost 400 times faster than the Earth orbits the Sun, revealing the colossal scale of the unseen mass at the center.

Orbits of stars within 1 arcsecond of the Galactic center followed over 15 years (Keck/UCLA/A. Ghez)

And here’s a chart of stellar trajectories from the past 15 years of observations by the Ghez group, showing the highly elliptical orbits around an unseen central mass.

There is plenty of other evidence too, from radio wavelength observations of the Galactic center, to X-ray data that reveal almost daily ‘flare’ events from this region – a possible signature of asteroid-sized chunks of matter getting shredded immediately outside the event horizon.

Some of today’s most important astrophysical questions are how black holes like this originate, and how they relate to the specific galactic environment around them – the same kind of environment that we are a part of. This raises a strange-sounding, but fascinating possibility; is it conceivable that there is a connection between the nature of these extraordinary places and the conditions that give rise to life in the universe?

….to be continued.

Caleb A. Scharf About the Author: Caleb Scharf is the director of Columbia University's multidisciplinary Astrobiology Center. He has worked in the fields of observational cosmology, X-ray astronomy, and more recently exoplanetary science. His books include Gravity's Engines (2012) and The Copernicus Complex (2014) (both from Scientific American / Farrar, Straus and Giroux.) Follow on Twitter @caleb_scharf.

The views expressed are those of the author and are not necessarily those of Scientific American.

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  1. 1. promytius 1:46 pm 06/11/2012

    Clear and clearly fascinating; thanks.

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  2. 2. JamesDavis 3:56 pm 06/11/2012

    I didn’t see anything disappear in either of the scenes, so could you be misnaming Black Holes and they are actually black or purple stars. How large would a star have to be to collapse and leave a black hole as large as the one at the center of the universe, and how small would a star have to be to be called a star, and would a star actually have to produce heat? And if it is a black star, could that explain dark matter in the universe?

    Since the stars are more condense at the center of the universe than they would be at the edge, couldn’t those other stars be orbiting that huge black star like our planets are in our galaxy, and it could be the gravity of that black star at the center that is holding everything in place and not allowing the universe expand too rapidly? Could that be a possibility?

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  3. 3. jtdwyer 6:58 pm 06/11/2012

    Nice article, although I’m not convinced that “Black Holes are Everywhere”. Wouldn’t the most likely locations of stellar mass black holes be near stellar nurseries where most short-lived massive stars are born?

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  4. 4. caleb_scharf 7:31 pm 06/11/2012

    Well, you have to give me some poetic license! I agree one might expect most in these places – however many stellar clusters dissipate due to dynamical instabilities and galactic tides and it also seems likely that there are various situations in which a black hole may be flung away from its point of origin (eg. black hole-black hole merger). Given time the low mass black hole population may get smeared out around a galaxy.

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  5. 5. jtdwyer 8:58 pm 06/11/2012

    OK – I’ll give you the poetic license & a plausible scenario for eventual redistribution – thanks!

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  6. 6. frankboase 10:55 pm 06/15/2012

    For the likes of us stupid people out here it would have been nice to see a spot representing our sun against, that which is a billion x larger. Difficult to get my mind around a billion.

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  7. 7. frankboase 11:02 pm 06/15/2012

    Fascinating stuff; “This raises a strange-sounding, but fascinating possibility; is it conceivable that there is a connection between the nature of these extraordinary places and the conditions that give rise to life in the universe?”
    Wonder if there is a connection between all this ‘stuff’ and consciousness?

    Link to this
  8. 8. anselm 8:10 am 06/16/2012

    Ref.Dr caleb_scharf 7:31 pm 06/11/2012, Thanks and Appreciate this your write-up,-it was a Critical important Physical Mapping,required to Extrapolate, the Base- from where String Theory originates, to have a proper understanding of the Hierarchy of below the Planck scales & inverse Cascading to Cosmological Scale’s -the Time Scale instant can be Deciphered from this Geometrical Reflective Mirror image, by translating it into Higher Dimensions 9D,10D,11D, in simultaneous Parrallel’s under Tandem Time Lock.

    The Unision of the study by,” The Ghez group”, showing the highly elliptical orbits around an unseen central mass ,There is plenty of other evidence too, from radio wavelength observations of the Galactic center, to X-ray data that reveal almost daily ‘flare’ events from this region – a possible signature of asteroid-sized chunks of matter getting shredded immediately outside the event horizon.” this research focuses on the depth of locating the path to a Keyway- that will direct the Focus to the simplicity of Nature’s secretive working’s.

    the Entire Article is ,Mesmerize with the hidden dice , down the Alley and missed behind , is the fact that the Einstien’s Gravitational Equation is still incomplete and the Right Hand Side the important “””TORQUE “””of Angular Momentum of all CELESTIAL BODIES has not been Mathematically solved,by any body else, its the missing Link –which must be found to make a explicitly clarity painted breakthrough to unify the Quantum World and Gravitation, and locate the physical HIGGS FIELD,
    The Graviton, Monopole.
    The path of the Trace tracked by the Majestic Moon’s BEADED ORBIT & ROTATION,the Moons EXTREME deep CURVE, always Zig-Zagg and Bouncing with Saw tooth precision, coupling the earth and sun ,in a TUG TORSION,is an integral component to interlink & Couple the two Worlds– Macro (GRAVITATION) and Micro(Quantum).

    “Blackhole_ appear CENTERING within our Solar System”,whenever the “DYNAMIC Stability” of our Planetary Systems GEOMETRIZED ORBITALS & ROTATIONS,-TENDS to dangerous levels of Obscure difficulties ,that threatens the BALANCE and stability-the POWERFUL INFINITE ENERGY TORQUE BLIP_BLIP_BLACKHOLE CONE SYNCHRONISED, Pulls back on CORRECTED TRACTION.

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  9. 9. Melkholy 1:05 am 06/19/2012

    Dear Friends;
    Of course; we do not argue that your scientists in the West, has most knowledge for most fields of science more than ours in Arab countries.
    But some times we believe that our philosophy or our religion vision may offer easy understanding for some items which still complicated in physics theories.
    The following samples confirm that the basic assumptions of physics were wrong;
    1 – Einstein was devoted the last 30 years of his life to an unsuccessful search for a “unified field theory”.
    2 – Steven Weinberg said; “a unified theory of all forces will probably require radically new ideas” (Scientific American: A Unified Physics by 2050? Dec. 1999).
    3 – Caleb said; “since there really are no plausible alternative theories”.
    Based on our understanding that physics or any science never reaches its end, we researched the majority of physics theories (1963 – 2005) till we reached (our) Unified Physics Theory which offered new basic assumptions of physics.
    Thru those new rules we discovered the Antimatter and the Gravity Element which we named it “Misrfaoum” with symbol “Mf”.
    According to our findings, the main properties of gravity element are;
    1. Gravity element is the last element (no; 118).
    2. Gravity element is metalloid element
    3. Gravity element is the heaviest element in the earth and the universe.
    4. The density of gravity element is (about) 14 gm/cm3 (or more).
    5. The gravity element stays continuously (in a gaseous state) inside the earth inner core (and inside the inner cores of all planets, stars, suns, moons, steroids and meteors or comets).
    Because the variation between the density of gravity of planets not due to its size only, but according to the quantities of gravity element in its inner cores.
    Then, it is quite clear that Black Holes are gaseous planets (Like all gaseous planets), but it contain huge quantities of gravity element.
    Therefore, due to the huge gravity of Black Holes attract every thing were near of it and attract the photons and energy too, then it become unseen for us. Regards from Egypt,

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  10. 10. angellbill 6:52 am 06/25/2012

    Not being a physicist, I cannot understand why black holes are really black. Sure I’ve read that gravity is so intense that even light cannot escape. In other readings, however, I find that photons are massless and if they are massless, why does the pull of gravity from the black hole affect them and not allow them to escape and thus light not escape a black hole? I’ve also read that space itself is moving into the black hole at speeds equal to the speed of light, thus light going the other way (away from the black hole), is basically standing still and not moving in an outward direction away from the black hole. But even if space itself is moving into the black hole, (which i find very hard to believe and/or understand), why does this inward movement of space have any impact to photons ?

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  11. 11. angellbill 7:28 am 06/25/2012

    Atom Smashers (LHC) Why do they tell us anything at all.

    Smash anything and what do you get ? Usually a lot of junk. A lot of smashed bits and pieces from whatever was smashed. Why then, when we smash protons together at intense energies, do we determine that what comes out of the smashing is actually something useful and a “core” component of the protons that were smashed. Even with billions and billions of smashes, each smash is probably slightly different from the smash before it and after it. Such things as velocity, angle of smashing, gravity fluctuations, etc will cause the smashes to be slightly different. Why then should we have any consistency in the resulting particles from the smashes and why should the detection and analysis of the resulting particles tell us anything about general physics of the items being smashed instead of the particle results from that particular smash. Sure, over time, we would likely see more of some type of particle and less of other types of particles, but isn’t this simply the result of the specific smashes rather than any clue as to the internal makeup of the protons that we are smashing. Would the ‘particle zoo’ just be a bunch of different results from different smashes? If we smash anything at high enough energies, we will get pieces of the pre-smashed matter. But do these pieces mean anything? With so much data being generated, isn’t there a possibility of “finding” whatever someone is looking for, even to a 5 sigma “certainty”? Are the results that we capture and analyse, simply the results that will be obtained from the methods being used? In other words, if we could ‘examine’ a proton without smashing it, would we get similar results? Most of the particle results we have from the last 50 years or so, come from the same types of experiments, albeit more and more powerful experiments, but still smashes.

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  12. 12. Andrew Planet 1:03 pm 08/17/2012

    I do hope the day will come when serious scientists stop teaching that nothing can escape the gravitational pull of a black hole. I have not read this anywhere else but bipolar black hole high energy jets travel well beyond the gravitational pull of the black hole they came from, having been gravitationally been drawn in from an accretion disc in the first place. Its self evident from the information already available on black holes

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  13. 13. Caleb A. Scharf in reply to Caleb A. Scharf 5:09 pm 08/20/2012

    The fact is that nothing can escape if it originates *at* the event horizon (or within). Jets and everything else that we see coming from black holes all originate outside the horizon, and probably a few Schwarzschild radii (event horizon radii for a non-spinning hole) out from the hole.

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