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Reflections on Messier 87’s Black Hole

Messier 87, a massive elliptical galaxy in the Virgo cluster, is some 55 million light years from Earth, and even though the black hole at its center has a mass 6.5 billion times that of the Sun, it’s a relatively small object, about the size of our Solar System. Resolving an image of that black hole is, says the University of Arizona’s Dimitrios Psaltis, like “taking a picture of a doughnut placed on the surface of the moon.” But the M87 black hole is one of the largest we could see from Earth, making it a natural target for observations, in this case using radio telescopes working at a frequency of 230 GHz, corresponding to a wavelength of 1.3mm.

A decade ago, working with Avery Broderick, Harvard’s Avi Loeb highlighted the advantages of M87 as an observational target, finding it in many ways preferable to the black hole at the heart of our own Milky Way:

M87 provides a promising second target for the emerging millimeter and submillimeter VLBI capability. Its presence in the Northern sky simplifies its observation and results in better baseline coverage than available for Sgr A*. In addition, its large black hole mass, and correspondingly long dynamical timescale, makes possible the use of Earth aperture synthesis, even during periods of substantial variability.

That paper, “Imaging the Black Hole Silhouette of M87: Implications for Jet Formation and Black Hole Spin,” is worth revisiting (abstract), for those intrigued with how these observations get made and the kinds of things we can learn from them.

I was reminded, when I first saw the now famous image, of the nature of M87 itself. Elliptical galaxies, unlike our barred spiral Milky Way, show slow rates of star formation, their primary population being older stars, and as you would imagine, they contain little gas and dust, while also housing a large number of globular clusters. Back in 2012, I ran across a paper by Falguni Suthar and Christopher McKay (NASA Ames) assessing habitability in such galaxies. What an environment to set a science fiction story! Consider the image below before we cut to the black hole image that is now center stage in the news, because here’s the context:

Image: A composite of visible (or optical), radio, and X-ray data of the giant elliptical galaxy, M87. M87 lies at a distance of 55 million light years and is the largest galaxy in the Virgo cluster of galaxies. Bright jets moving at close to the speed of light are seen at all wavelengths coming from the massive black hole at the center of the galaxy. It has also been identified with the strong radio source, Virgo A, and is a powerful source of X-rays as it resides near the center of a hot, X-ray emitting cloud that extends over much of the Virgo cluster. The extended radio emission consists of plumes of fast-moving gas from the jets rising into the X-ray emitting cluster medium. Credit: X-ray: NASA/CXC/CfA/W. Forman et al.; Radio: NRAO/AUI/NSF/W. Cotton; Optical: NASA/ESA/Hubble Heritage Team (STScI/AURA), and R. Gendler.

Could life survive in environments like this? I bring this up again as background, but also because yesterday we looked at the question of hardy microorganisms and their ability to withstand high levels of X-ray and UV radiation. Here’s what McKay and Suthar said in 2012:

Complex life forms are sensitive to ionizing radiation and changes in atmospheric chemistry that might result. However, microbial life forms, e.g. Deinococcus radiodurans, can withstand high doses of radiation and are more flexible in terms of atmospheric composition. Furthermore, microbial life in subsurface environments would be effectively shielded from space radiation. Thus, while a high level of radiation from nearby supernovae may be inimical to complex life, it would not extinguish microbial life.

It’s fascinating to me that we’ve begun studying such questions on a galactic scale. Fascinating too that we’re now peering into the heart of an active galaxy to reveal its powerhouse black hole. By now the image is familiar, but let’s see it again because it’s just extraordinary.

Image: Scientists have obtained the first image of a black hole, using Event Horizon Telescope observations of the center of the galaxy M87. The image shows a bright ring formed as light bends in the intense gravity around a black hole that is 6.5 billion times more massive than the Sun. Credit: Event Horizon Telescope Collaboration.

One thing I saw little attention given to in the coverage was that the Event Horizon Telescope, which produced the image, was supplemented by work from spacecraft. Remember that the EHT is comprised of telescopes located around the surface of our planet, to produce a planet-scale interferometer capable of making such an observation. But the Chandra X-ray spacecraft was also involved, as was the Nuclear Spectroscopic Telescope Array (NuSTAR), and the Neil Gehrels Swift Observatory. All of these, working at X-ray wavelengths, observed the M87 black hole at the same time it was under study by the EHT in April of 2017.

I point to this because while the space assets could not image the black hole, data from them were used to measure the brightness of the M87 jet, particles driven by an enormous energy boost from the black hole itself and surging away from it at nearly the speed of light. The hope here is that X-rays can help us measure particle events near the event horizon to coordinate with the black hole images. Also involved in space was the Neutron star Interior Composition Explorer (NICER), a NASA experiment on the International Space Station that looked at the center of the Milky Way and the black hole known as Sgr A*. Part of the EHT’s mandate is to study the origin of jets like this one, so these extraordinary interactions now become visible.

As to the ground-based observatories of the EHT themselves, what an accomplishment! The international team involved totalled over 200 astronomers, whose work is presented in a special issue of Astrophysical Journal Letters. In the black hole work, the EHT used an array of eight radio telescopes with worldwide coverage, from the Antarctic to Spain, Chile and Hawaii, all located in high-altitude settings where conditions are ideal for observation.

Jonathan Weintroub (CfA) coordinates the EHT’s Instrument Development Group:

“The resolution of the EHT depends on the separation between the telescopes, termed the baseline, as well as the short millimeter radio wavelengths observed. The finest resolution in the EHT comes from the longest baseline, which for M87 stretches from Hawai’i to Spain. To optimize the long baseline sensitivity, making detections possible, we developed a specialized system which adds together the signals from all available SMA dishes on Maunakea. In this mode, the SMA acts as a single EHT station.”

Spectacular. The very long baseline interferometry creates a virtual dish that is planet-sized, able to resolve an object to 20 micro-arcseconds. Working with a conjunction of four nights that would produce clear seeing for all eight observatories, the telescopes took in massive amounts of data — 5,000 trillion bytes of data in all — saved on 1,000 storage disks. Transmitting all that information for subsequent processing was ruled out, for air transport from FedEx could take the hard disks onto which the data had been recorded to a single location much faster. These are signals that needed to be aligned within trillionths of a second to achieve a valid result.

The resulting imagery is the payoff. The central dark region is surrounded by a ring of light, as Einstein’s equations led scientists to expect. We can’t, of course, see the black hole itself, but plasma emitted from its accretion disk, where matter piles up as material falls into the black hole, is heated to billions of degrees and accelerated almost to lightspeed. We get an image of the black hole’s shadow’ that is about 2.5 times larger than the event horizon. M87’s event horizon is thought to be some 25 billion miles across, making it 3 times the size of Pluto’s orbit.

“Once we were sure we had imaged the shadow, we could compare our observations to extensive computer models that include the physics of warped space, superheated matter and strong magnetic fields. Many of the features of the observed image match our theoretical understanding surprisingly well,“ said Luciano Rezzolla, professor for theoretical astrophysics at Goethe University and a researcher on the EHT. “This makes us confident about the interpretation of our observations, including our estimation of the black hole’s mass.“

Image: This artist’s impression depicts the paths of photons in the vicinity of a black hole. The gravitational bending and capture of light by the event horizon is the cause of the shadow captured by the Event Horizon Telescope. Credit: Nicolle R. Fuller/NSF.

This is a black hole massive enough that a planet orbiting it could move around it within a week while traveling, says MIT’s Geoffrey Crew, close to the speed of light. Crew’s colleague Vincent Fish, also at MIT’s Haystack Observatory, amplifies on the point:

“People tend to view the sky as something static, that things don’t change in the heavens, or if they do, it’s on timescales that are longer than a human lifetime. But what we find for M87 is, at the very fine detail we have, objects change on the timescale of days. In the future, we can perhaps produce movies of these sources. Today we’re seeing the starting frames.”

Now that’s something worth waiting for, movies of the accretion disk caught in the tortured spacetime of a galaxy’s central black hole. M87 anchors a jet stretching tens of thousands of light years, so we’re talking about seeing the dynamics of the jet’s interactions with the black hole. Fine-tuning EHT methods and expanding its sites points in the direction of further breakthrough imagery.

But what an accomplishment we’ve already achieved via instruments all over the world — ALMA and APEX in Chile, the IRAM 30 meter telescope in Spain, the James Clerk Maxwell telescope and the Submillimeter Array (both in Hawaii), the Large Millimeter Telescope (LMT) in Mexico, the Submillimeter Telescope (SMT) in Arizona and the South Pole Telescope (SPT) in Antarctica.

The papers are The Event Horizon Telescope Collaboration et al., “First M87 Event Horizon Telescope Results. I. The Shadow of the Supermassive Black Hole,” Astrophysical Journal Letters Vol. 875, No. 1 (10 April 2019) (abstract); and from the same issue: “First M87 Event Horizon Telescope Results. II. Array and Instrumentation” (abstract); “First M87 Event Horizon Telescope Results. III. Data Processing and Calibration” (abstract); “First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole” (abstract); “First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring” (abstract); and “First M87 Event Horizon Telescope Results. VI. The Shadow and Mass of the Central Black Hole” (abstract). The paper on M87 and galactic habitability is Suthar & McKay, “The Galactic Habitable Zone in Elliptical Galaxies,” International Journal of Astrobiology, published online 16 February 2012 (abstract).


Comments on this entry are closed.

  • Harry R Ray April 11, 2019, 9:41

    I, like everyone else am just overwhelmed tith the totality of this finding, so on waxing philosophical on that. lets get into the nitpicking little details. Black holes and their event horizons are PERFECTLY SPHERICAL by nature, so I was shocked to see that the black hole’s shadow APPEARS to be ELIPTICAL with a ratio of 4/3! I ask Paul, or any other Centauri Dreams reader who knows the answer)WHY? Is it because of the warping of spacetime in a particular direction, or is it just an artifact of the imaging system?

    • Ron S. April 11, 2019, 12:51

      Only a non-rotating BH is spherical. Every BH that results from gravitational collapse will have angular momentum and will therefore not be spherical. And it gets more complex than that.


      Also, the shape depends on the rotation axis orientation from our perspective. I don’t know if they discuss this aspect of the measurement, but I suspect they must know something about it since the image resolution should show which parts of the accretion disk are moving away and towards us.

  • Al Jackson April 11, 2019, 9:42

    One thing I have a bee in my bonnet about. Yesterday several news articles repeated the story that Einstein did not think black holes could exist, as if Einstein bore some fault! Karl Schwarzschild not only sent Einstein the ‘exterior’ solution of the gravitational equations for a sphere but later the ‘interior’ solution, for a sphere of incompressible fluid. At the time no one had any idea that stellar matter might get ‘strange’. It was 20 years before Chandrasekhar showed there was an upper limit to White Dwarf mass. Then another 7 years for Tolman ,Oppenheimer and Volkoff to push that limit to Neutron stars. Even then it took years before the Chandrasekhar limit was accepted due to some wrong headedness on the part of Eddington. Einstein was not the only one who thought the ‘black hole’ solution to a gravitating sphere was a mathematical artifact. Einstein had perfectly reasonable feelings about physical models of high mass spheres, Einstein is not a fault for not liking Black holes. I am not sure what he thought of the Chandrasekhar – Oppenheimer modeling, I have never seen a history of his thinking. It took nearly 25 more years, until the early 1960s, for John Wheeler and co-workers* to show that the best equation of state (which relied on modern particle physics) led to the strange situation of what Oppenheimer called ‘continued collapse’+. Even then it took part of the 60s and into 70s for the concept of a Black Hole to gain acceptance (and there still are some who still don’t believe it). So Einstein has no fault here he was just following the reasonable conclusion.
    * Gravitation Theory and Gravitational Collapse, B.Kent Harrison; Kip S.Thorne; Masami Wakano; John Archibald Wheeler, 1965.
    + Factoring in current Equations of State still support ‘continued collapse’.

  • Michael Spencer April 11, 2019, 10:15

    No doubt there is a link someplace answering my question, but I’ve not found it:

    How is an optical image derived from radar data? Is this done by 1:1 mapping? (SHF1—> Color1, SHF2—>Color2), or am I over-simplifying the process?


    • Antonio April 11, 2019, 11:31

      From what I understood from a quick reading of the papers: more energy received in that pixel -> more yellow, less energy -> more red.

  • ljk April 11, 2019, 10:19

    National Science Foundation/EHT Press Conference Revealing First Image of Black Hole:


    TED Talk: How to take a picture of a black hole | Katie Bouman –


    • wsguerin April 11, 2019, 10:56

      LJK or anyone,

      Is it really a photograph if it was generated by radio telescope interferometry?


      • Ron S. April 11, 2019, 12:52

        What would you prefer it be called? Photograph works for me.

        • Harry R Ray April 12, 2019, 9:28

          The “photograph” is NOT real. It is just a reconstruction of an IMAGE produced by a combination of DATA from various radio wavelengths. Any infra-red “photograph” is an image derived in the same way. It’s the image that’s important, NOT the photograph.

          • Ron S. April 13, 2019, 10:48

            Every photograph is an image, but is every image a photograph? Do we reserve the term “photograph” for a lens generated raster of pixels? Does it matter whether the post-processing of data is all in our brains or with a software intermediary? Must ado about little, IMO.

          • Adam Warnock April 13, 2019, 11:41

            Technically, photograph is correct. Radio is part of the EM spectrum, so it would have photons associated with it. They would be lower energy photons than you would have with visible light, but photons nonetheless. Seeing as photon and photograph share the same root, I would say that it’s accurate to call it a photograph.

            • wsguerin April 16, 2019, 9:40

              Ron, Harry, Adam, and all,

              I continue to vacillatingly differ, although yes, it’s a tempest in a radio dish.

              Check this link out for details of the techniques used

              I suggest that the methodology might be called “algorithmic photography” as data from multiple scopes has been correlated, algorithmically processed, and then test fit to match prior assumptions about how the image should look based on machine learning. Four different teams independently used their own processing strategies and came up with similar images.

              I think it’s mostly about informing/refining/correcting the public’s perception that a _photograph_ is something taken through a glass lens on their phone or by more conventional means like the Hubble Space Telescope. The Pōwehi image was created by over 200 people, using the most exquisite technologies spread across the planet, and is in no way, despite the photons, a photograph.

              Analogously, the LIGO teams recorded gravitational waves that the public then mistakingly believed were “heard” due to the coincidence of the BNS’s final orbital periods aligning to the audio wavelengths we sense.

              On the other hand, I recognize that aperture synthesis creates a means to transform wavelengths we can’t directly sense into images we can understand and perhaps collapsing (pun intended) all the effort into the convenient term “photograph” is just the way it goes.

              A retro-imaginaed headline might have read “Scientists create the first image of a black hole using cutting edge Algorithmic Photography techniques.”


  • Jim Baird April 11, 2019, 11:20

    Paul, Thank you for this. Well written and organized in a manner that even this lo-IQ fellow thinks he understands the magnitude of the planning and work of great minds that went into it. And speaking of magnitudes: “a black hole that is 6.5 billion times more massive than the Sun.” WOW!

    • Paul Gilster April 11, 2019, 12:25

      My friend, you are anything but ‘lo-IQ’!

  • Antonio April 11, 2019, 11:41

    “It’s fascinating to me that we’ve begun studying such questions on a galactic scale.”

    What fascinates me is the amount of people that equate “life” to “terrestrial life”. When I first saw the pic of the black hole and the videos, what first came to my mind were the cheela. After that, I reread some articles about alternatives to blackholes, like gravastars, black stars, etc. and wondered whether they could be visited by them.

  • Thomas R Mazanec April 11, 2019, 12:05

    What is the prospect for using this “telescope” to resolve Sag A*? It is something like 0.0005 the size of M87’s BH, but it is something like 0.0005 as far.

    • Antonio April 11, 2019, 15:59

      I heard in a presentation that we will have an image of Sgr A* maybe at the end of this year.

      The diameter of the shadow is 47-50 μas for M87* and 19-38 μas for Sgr A*.

      • Antonio April 11, 2019, 16:04

        Sorry, I switched the numbers… It’s 47-50 μas for Sgr A* and 19-38 μas for M87*.

  • Ron S. April 11, 2019, 12:58

    One aspect of the photograph I haven’t seen commonly discussed is that the “hole” isn’t really a black area in the image. There is EM emitting matter in front of the BH. However there is less of it than off to the sides because the depth of emitting material is shorter. They chose a color map that shows the kind of detail that they wanted to highlight. Think of it as similar to sun spots: they aren’t really dark, just a little cooler than the surrounding photosphere. It’s a matter of contrast.

  • Thomas R Mazanec April 11, 2019, 14:01
  • Gary Wilson April 11, 2019, 14:55

    Pardon my ignorance but are the bright arcs around the bottom half of the black hole due to rapid acceleration and heating of particles in an accretion disc? If so why do they not extend completely around the black hole? Is there a layman’s explanation I would be able to understand?

    • Antonio April 11, 2019, 17:09

      The bottom part is rotating towards us and the upper part is rotating away from us. This causes the bottom part to look brighter due to relativistic effects. Indeed, the asymmetry in the brightness is the first evidence we have that the BH is rotating.

      • Gary Wilson April 12, 2019, 14:02

        Thanks Antonio, that’s a big help. Will they be able to calculate a rotation rate? It’s hard to imagine that the black hole is the size of our solar system. Amazing what we are able to detect now. Einstein would be thrilled I would think, although I realize he disliked the idea of discontinuities in our universe. I think of it as a tear in the fabric of spacetime, but leading where?

  • Gary Wilson April 11, 2019, 15:13

    I’ve also been reading with great interest about the Israeli lunar lander Beresheet. It is due to land on the moon today. It was mainly produced by an Israeli non profit space venture firm called SpaceIL and Israeli defence contractor Israel Aerospace Industries. But the bulk of the money was provided by the U.S. (100 million) and the lander was launched on a Falcon 9 from Cape Canaveral. Kudos to everyone involved.

    • ljk April 11, 2019, 17:14

      I am very sorry to report that the lander crashed:



      I wonder if these items that were placed onboard the lander were able to survive (from Wikipedia):

      The spacecraft carried a digital “time capsule” containing over 30 million pages of data, including a full copy of the English-language Wikipedia, the Wearable Rosetta disc, the PanLex database, the Torah, children’s drawings, a children’s book inspired by the space launch, memoirs of a Holocaust survivor, Israel’s national anthem (Hatikvah), the Israeli flag, and a copy of the Israeli Declaration of Independence.

      • ljk April 12, 2019, 14:04

        According to the Planetary Society blog news item linked above:

        The first sign of trouble came at about 19:21 UTC, when flight controllers reported one of Beresheet’s inertial measuring units had reset, temporarily shutting off the flow of telemetry. It was unclear if this was related to the engine problem that ultimately doomed the spacecraft.

        Roughly a minute later, a telemetry indicator for Beresheet’s velocity turned red, indicating what may have been a higher-than-expected 74.9 meters per second vertical approach speed. Shortly thereafter, indicator lights for Beresheet’s engines blinked off, and an official in mission control announced there was a problem with the spacecraft’s main engine.

        The main engine came back online, but at that point, the spacecraft’s altitude showed just 149 meters, while its vertical speed was still 134 meters per second, and its horizontal speed was 947 meters per second. At that point, all telemetry from the spacecraft stopped, and ground observers reported a loss of signal at 19:23.

        One of the cultural items aboard the lander:


      • Gary Wilson April 12, 2019, 14:05

        Yes, I saw that too ljk. What a shame. This is difficult stuff and we now have another example of how difficult. Mars is a graveyard for failed probes as well I think.

        • Wojciech J April 14, 2019, 6:16

          They will be launching another one, as they have funds for that.

          • ljk April 15, 2019, 9:25

            News on the building of the Beresheet 2 lunar lander:


            To quote:

            Israel will keep shooting for the moon.

            The team behind the nation’s Beresheet probe, which crashed during its historic lunar-landing attempt Thursday (April 11), will take another crack at Earth’s nearest neighbor.

            “We’re going to actually build a new halalit — a new spacecraft,” billionaire businessman and philanthropist Morris Kahn said in a video statement posted on Twitter by the nonprofit group SpaceIL. “We’re going to put it on the moon, and we’re going to complete the mission.”

            Related: Israel’s 1st Moon Lander Beresheet in Pictures

            The work on Beresheet 2.0 will begin immediately, he added: the team is meeting this weekend to start planning the new project.

            Kahn is president of SpaceIL, which built and operated Beresheet along with the company Israel Aerospace Industries. He also funded the mission to a large degree, covering about 40% of its total $100 million price tag.

            X Prize officials announced shortly after Thursday’s crash that the Beresheet team will still get a special $1 million award.

            “I think they managed to touch the surface of the moon, and that’s what we were looking for for our Moonshot Award,” said X Prize CEO Anousheh Ansari.

            Beresheet’s main goals were to advance Israel’s space program and to generate excitement about science, technology, engineering and math among young people. And the mission succeeded in both of these aims, even though it didn’t nail the landing, Beresheet team members have said.

            Indeed, Kahn cited Beresheet’s substantial global reach as a reason to try again.

            He decided to build Beresheet 2.0 “in light of all the support that I’ve got from all over the world, and the wonderful messages of support and encouragement and excitement,” Kahn said in the video.

        • ljk April 15, 2019, 9:19

          The Lunar Orbiter Laser Altimeter (LOLA) may have survived the lander’s impact and could still be usable:


          Also LRO is going to image the impact site.

      • ljk April 17, 2019, 10:50

        If at first you don’t succeed…

        Israel hoped to become the fourth country to soft-land a spacecraft on the surface of the Moon last week, but its Beresheet lander crashed after suffering technical problems. Jeff Foust reports on the landing attempt and SpaceIL’s future plans.

        Monday, April 15, 2019


        To quote:

        SpaceIL was intended to be a one-time effort, although IAI said it’s seeking commercial opportunities for landers based on Beresheet. Future versions of the lander, IAI executives have said, could carry 30 to 60 kilograms of scientific payloads and incorporate improvements like precision landing technologies.

        SpaceIL, though, may get a second shot of its own. On Saturday, Morris Kahn, the billionaire chairman of SpaceIL who contributed more than $40 million to the $100 million project, announced a “Beresheet 2” lunar lander. “We’re going to put it on the Moon and we’re going to complete the mission,” he said in a brief video. Details about how that lander will be developed, and funded, have not been disclosed.

        Some of the funding, though, could come directly from the Israeli government. Netanyahu suggested that might happen in remarks after the failed landing. “If at first you don’t succeed, you try again,” he said.

  • Michael April 11, 2019, 15:50

    Interesting is that the ‘density’ of the BH is less than that of water. Further any object falling in will eventually have practically all of its energy given up as gravity waves trapped inside the BH. Could these GW’s be preventing the singularity from forming?

    • Ron S. April 11, 2019, 17:29

      I’ll address your first sentence. The Schwarzchild radius is in linear proportion to the mass. Double the mass and the radius doubles. Volume grows with the cube of the radius. That’s why the density is so low. It’s not telling us anything of interest. The interior of the BH (within the horizon) is almost entirely empty space, except for the unknown thingamajig in the vicinity of the center.

      • Michael April 11, 2019, 17:56

        I will address the last part of your paragraph, how do you know it’s empty space and has a unknown thingamajig at its centre, it could be filled with gravity wave radiation for all we know.

        • Ron S. April 11, 2019, 21:45

          What is generating those gravitational waves and where are they going? That’s for you to explain. I believe my description is more in line with our current state of knowledge: not much. Also, I said “vicinity of the center” not “center”. I have no theoretical basis to pin anything down to a precise location. Do you?

          • Michael April 12, 2019, 13:41

            In brief we know as much about the BH’s innards as the greatest scientific minds, between zero and naff all.

  • Gary Wilson April 11, 2019, 16:32

    I have seen John Rennie state that the density of a black hole would be equal to that of liquid water i.e. 1 g/cubic cm. I frankly don’t understand this. And that is an average density apparently. At the center the density would be infinite, hence the formation of a singularity. Do all black holes have singularities at their center? I believe the consensus is they do.

    • Michael April 13, 2019, 5:17

      As a star collapses to form a BH huge gravity waves are emitted outwards and importantly inwards, it’s these waves that may prevent the singularity from forming when they become trapped inside the event horizon threshold. In the event of a supermassive BH any object falling in emits GW’s and as it goes over the EH so all GW’s are trapped inside the BH.

    • Bruce D. Mayfield April 13, 2019, 10:37

      Yes, when statements about low density black holes are made it is indeed calculated by dividing the mass by the entire volume inside its Schwarzschild surface. But that “surface” is merely a mathematical construct, a boundary where escape velocity equals c. Theoretically, there is an infinite density zero volume singularity at the center.

      A Neutron Star’s density just before it collapses into a black hole is informative on this issue: “Neutron stars have overall densities of 3.7×10^17 to 5.9×10^17 kg/m^3 (2.6×10^14 to 4.1×10^14 times the density of the Sun),[b] which is comparable to the approximate density of an atomic nucleus of 3×10^14 kg/m^3 [28] The neutron star’s density varies from about 1×10^9 kg/m^3 in the crust—increasing with depth—to about 6×10^17 or 8×10^17 kg/m^3 denser than an atomic nucleus) deeper inside.[27]”

      Saying that something that is made from even further collapsed neutron star material is low density just doesn’t make sense.

  • Bill April 11, 2019, 17:02

    Another link! This one to a very good presentation of exactly what we’re looking at in the photo. It’s in layman’s terms and even I could grasp the information.


    • Antonio April 11, 2019, 18:23

      Very good video! Thanks!

      • Adam Byrne April 13, 2019, 3:19

        Great video thanks.

  • Michael April 11, 2019, 18:03

    This is not the largest BH either ! TON 618 measures in at 66 Billion solar masses? You would find it hard to even know you fell in !

    • Michael April 11, 2019, 18:04

      Google image it, mind blowing.

    • Robert April 12, 2019, 12:23

      Why? Is that because if it’s so large the tidal forces crossing the event horizon would be unnoticeable?

      • Michael April 12, 2019, 17:50

        Yip, it could be detected with instruments though as there would be a very slight shear force.

  • Harold Shaw April 11, 2019, 21:06

    Imagine what could be seen if we had radio telescopes on the moon and combined them with an array on Earth. Would that be possible using the same approach to interferometery used here? Could the same approach be used for optical interferometery?

  • Michael C. Fidler April 12, 2019, 9:02

    I find the circus a true and cruel joke even down to the maiden’s great algorithm. Halton Arp would be turning in his grave at the BS the Astro community is putting out, I think you know what I mean, since the jet is suppose to be almost pointing directly towards us in M87 to explain the “A Powerful Energy Beam in Space Seems to Exceed the Speed of Light” ! You do any of you remember Halton Arp?


    And now for the great finally!!! “Jet from Milky Way’s central black hole may be facing Earth.” “But now, using the Atacama Large Millimeter/submillimeter Array in concert with other radio telescopes around the world, researchers have seen signs of what may be a jet coincidentally aimed almost directly at Earth.”

    Jet from Milky Way’s central black hole may be facing Earth.


    • Michael C. Fidler April 13, 2019, 10:13

      3 Huge Questions the Black Hole Image Didn’t Answer.

      1. How do black holes produce their enormous jets of hot, fast matter?

      2. How do general relativity and quantum mechanics fit together?

      3. Were Stephen Hawking’s theories as correct as Einstein’s?


    • Patient Observer April 14, 2019, 12:01

      Science reporters (who often appear to have no science background whatsoever) need clicks on their articles. In addition to the Sky is Falling trick, anthropomorphizing astronomical objects is a used to induce clicks; “Cuddly Comet Decked Out Green to Breeze by Earth”, “Giant Amazon Women May Live on Venus”, or “Your Friendly Neighborhood Gas Giant Protects Earth But Was Caught Napping When the Dinosaurs Were Killed!” . OK, I made those up but it was not a big exaggeration from what I have seen.

  • ljk April 12, 2019, 10:18

    Peering down the cliff of infinity: The first image of the event horizon of a black hole

    Phil Plait

    April 10, 2019


    To quote:

    To be clear, you are not actually seeing the black hole itself. That circular hole in the center of the ring is not the black hole, but really an effect of its gravity. It’s being called the “shadow” of the black hole, but I think of it more as its cloaking device: The gravity is bending the light from the material around it, sending it toward us, leaving a gap where the black hole itself is. Perhaps the best way to describe it is as the silhouette of the black hole’s gravity.

    • ljk April 12, 2019, 10:21

      From the above article, which I highly recommend for those who want explanations in layman’s terms:

      *Note: The Event Horizon Telescope did look at the black hole in the center of our galaxy as well, but it’s much more difficult to create an image of it due to how variable it is, changing its brightness on a scale of hours and days. The M87 black hole is more stable, so easier to image. By a quirk of geometry, it’s about 1,600 times bigger than “our” black hole, but about 2,000 times farther away, so it appears roughly the same size as ours from Earth.

  • xcalibur April 12, 2019, 18:28

    This is a major step forward. The image may seem vague, but this is a direct observation of a phenomenon that we’ve only inferred until now.

    Black holes are strange beasts, and I find myself wondering about them. Is their center/singularity a puncture in space-time, or is it an extremely dense point that’s ‘off the charts’ but still theoretically quantifiable? To explain, let’s say you represented gravitational fields with a 2d plane in a 3d space — the stronger an object’s gravity, the further down it ‘sinks’ into the plane, and the greater its ‘indentation’ or concave basin. In this model, an ‘extremely dense’ black hole would sink very far down without breaking the plane; while a ‘puncture’ black hole would break the plane at the bottom, leaving an opening. In other words, ‘extremely dense’ would be a very high value but not infinite, while the ‘puncture’ would register as infinite. Let’s not forget, a number that is vast enough may appear infinite when it really isn’t, due to limitations of measurement.

    Pardon me for any misunderstandings, as I’m only a layman.

    • Patient Observer April 13, 2019, 19:31

      Scientific American magazine had several articles postulating that BHs may not have singularities but, believe me, the alternative theories were even weirder. Some theories suggested quantum entanglements and pairs of BHs having similar connectedness. This mesh of entanglements/BH connections somehow form the fabric of space-time. All I can do is be amazed.

  • Adam April 12, 2019, 18:53

    Hi Paul
    Since the EHT’s avowedly next target is the SMBH in the Milky Way’s Center, it’s worth knowing just how far away that SMBH (aka Sagittarius A*) happens to be…
    A geometric distance measurement to the Galactic Center black hole with 0.3% uncertainty
    The team reporting this measurement were the same one who measured the effects of relativity on the orbit of one of the stars close to Sagittarius A* last year. In that report they measured the distance to be 8,122 parsecs, plus/minus 31 parsecs. Their new distance to Sag A* is 8,178 parsecs, plus or minus 35. The two figures are withing 2 sigma of each other, which is considered to be agreement in measurements as challenging as these.
    So quietly, we’ve entered a new era of high precision in measuring our own Galaxy. Combined with GAIA’s results, there will be very interesting science ahead for all Milky Way fans.

    • Paul Gilster April 12, 2019, 19:53

      Yes, remarkable times for those of us fascinated with galactic center!

  • Mark April 12, 2019, 23:10

    Shouldn’t the black hole actually be white, due to Hawking radiation?

    • Ron S. April 13, 2019, 10:55

      The temperature of a stellar mass BH is so close to absolute zero that the difference is indistinguishable. In fact since the cosmic background temperature is a relatively balmy 2.7 K those low energy photons are adding to the BH mass. The universe will have to grow exceedingly cold before a stellar mass BH can begin to evaporate, and then it will take a very, very long time. They’re really, really cold.

      • Patient Observer April 13, 2019, 19:22

        BH’s are among the coldest objects yet they generate in their accretion disks some of the highest temperatures in the universe. Amazing stuff.

  • Michael April 13, 2019, 5:22

    Imagine using this as a gravity focus telescope, we could see to the beginning and end of time, the very first GW’s would faintly seen.

  • Patient Observer April 13, 2019, 9:32

    Beyond my comprehension how doubling the mass of a black hole doubles its diameter (resulting in a reduction of its bulk density to 25% or the original value). Per wikipedai, a solar mass BH has a diameter of about 4 miles. A trillion solar mass BH would have a diameter of about 4 trillion miles or about 1 light year (roughly the mass of the Milky Way galaxy).

    Per Wikipedia, the mass of the visible universe is (dark and regular matter) about 25 billion times our galaxy. A BH with the mass of the visible universe would have a diameter of 25 billion light years. The diameter of the universe is estimated at 45 billion light years.

    So, when the universe was little younger, it had sufficient mass to form a black hole (actually, all way back to the big bang).

    So, how could the universe expand if it qualified in terms of density and volume as a BH? Not trying to advance any speculation, just curious:)

    • Patient Observer April 13, 2019, 10:41

      To be sure, there are a lot of other factors such as space itself is expanding which may somehow prevent formation of a BH universe. Also, the visible universe is apparently a tiny part of the entire universe (whch may be infinite in spacial extend they say). My curiosity has been sucked into a BH:)

    • Ron S. April 13, 2019, 11:07

      Cosmology can be even stranger than black holes. No, the universe isn’t a BH since there is no outside: if there were an outside it, too, is part of the universe. However there can be a observation horizon. As the universe ages our observational horizon increases as photons from a greater distance reach us. It is possible that areas of the universe are so distant that their photons can never reach us, no matter how long we wait. That is, the recession velocity is greater than c. This is not a contradiction of theory since c is a local measurement, without respect to spacetime curvature along the photon’s path. You can see that there is a similarity to BH in this regard.

      • Patient Observer April 13, 2019, 19:20

        That helps but still, a subset of the universe, especially during its earlier history could have exceeded the BH density. IIRC, there is a theory about primordial BHs that may have formed in in the earliest moments of the Big Bang so I wonder what was going on there. On the other hand, this stuff way beyond my pay grade.

    • Michael April 14, 2019, 4:54

      @PO There is the possibility of our universe been smeared over the surface of a larger sphere of space time. If you imagine a sphere like a beach ball where the mass of our universe is pushing down on space time denting it would then appear flat.

  • Frank Smith April 15, 2019, 7:40

    Now that we’ve actually seen a black hole, the wave front has been officially collapsed, so black holes are now really real :)

    Truly amazin’ technological achievement by the astronomers resolving an object 43 micro-arc seconds across.

  • Alex April 17, 2019, 13:58

    The Secret of Dark Elements Finally Revealed:


  • ljk April 17, 2019, 14:25

    The Black Hole `Photo’: Seeing More Clearly

    Posted on April 16, 2019 | 15 Comments

    Ok, after yesterday’s post, in which I told you what I still didn’t understand about the Event Horizon Telescope (EHT) black hole image (see also the pre-photo blog post in which I explained pedagogically what the image was likely to show and why), today I can tell you that quite a few of the gaps in my understanding are filling in (thanks mainly to conversations with Harvard postdoc Alex Lupsasca and science journalist Davide Castelvecchi, and to direct answers from professor Heino Falcke, who leads the Event Horizon Telescope Science Council and co-wrote a founding paper in this subject). And I can give you an update to yesterday’s very tentative figure.


  • ljk April 29, 2019, 8:28


    2019 April 27

    The Galaxy, the Jet, and the Black Hole

    Image Credit: NASA, JPL-Caltech, Event Horizon Telescope Collaboration

    Explanation: Bright elliptical galaxy Messier 87 (M87) is home to the supermassive black hole captured by planet Earth’s Event Horizon Telescope in the first ever image of a black hole. Giant of the Virgo galaxy cluster about 55 million light-years away, M87 is the large galaxy rendered in blue hues in this infrared image from the Spitzer Space telescope. Though M87 appears mostly featureless and cloud-like, the Spitzer image does record details of relativistic jets blasting from the galaxy’s central region.

    Shown in the inset at top right, the jets themselves span thousands of light-years. The brighter jet seen on the right is approaching and close to our line of sight. Opposite, the shock created by the otherwise unseen receding jet lights up a fainter arc of material. Inset at bottom right, the historic black hole image is shown in context, at the center of giant galaxy and relativistic jets.

    Completely unresolved in the Spitzer image, the supermassive black hole surrounded by infalling material is the source of the enormous energy driving the relativistic jets from the center of active galaxy M87.