What does the black hole look like "photographed" from the back?
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'What does the black hole look like "photographed" from the back?'
Black holes are spheres*, so the question is: 'What is "inside" a black hole?'
The answer is that no one knows, because whatever falls into a black hole cannot get out. For example, a spacecraft that traveled into a black hole could not send radio messages back out.
For an entertaining look at what would happen if someone fell into a black hole, see the "Black Hole Apocalypse" DVD hosted by astrophysicist and novelist Janna Levin.
* Strictly speaking, the black hole's event horizon is a sphere. See the Wikipedia article titled "Event horizon".
I watched some of the question-and-answer portion of the black hole image presentation. I saw a reporter basically ask, "This image is blurry. Can you people make it sharper?" I had to leave before the melee I presume then occurred. Question: How much injury can a hundred enraged astrophysicists inflict upon a single journalist? (Any?)
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'I saw a reporter basically ask, "This image is blurry. Can you people make it sharper?"'
If you are referring to the NSF press conference, it is online, and the answer was "Yes"*:
1. Add more telescopes and increase the frequency (Doeleman).
2. Adjust the imaging process to make certain features less blurry (Marrone).
* On YouTube starting at 40:40: "National Science Foundation/EHT Press Conference Revealing First Image of Black Hole" (Streamed live on Apr 10, 2019)
mr overbye is a genius at taking something that most of us know nothing about except, 'my god it's unimaginable' to making it less so.
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I believe the official report says what was captured was not an image of a black hole but an image of the shadow of a black hole.
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Thank you, Dennis, for this further information about the incredible image we saw, and what it represents. I have lived almost my whole life with the idea of the theory of black holes; now I have seen the evidence. (I think the first reference to a black hole I encountered was in an episode of Star Trek the original series in the late 1960s. The Enterprise "ran into" a black hole and it threw them back in time. They then use the black hole to slingshot them back to their time. Pretty incredible when you think about how little was known about black holes back then. And the series was sophisticated enough to postulate that a spaceship could travel faster than the speed of light by creating a warp field around it that nullified the laws of physics, and that the energy to power it was caused by a controlled reaction of matter and antimatter.)
But I digress. These are good times for those of us who grew up during the space program and whose imaginations were captured by the incredible feats of landing on the moon, orbiting the first space station (Skylab), and all the unmanned missions that have shown us all the planets in our solar system (and yes I'm counting New Horizons' flyby of Pluto, which I will always consider a planet).
I am filled with awe at the wonders of the universe which the human race has developed the technology to explore (which is also pretty awesome).
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My immediate thoughts about Black holes are 1. products of a Big Bang and/or beginning points of preparation for the next Big Bang.
@JW: They aren't products of a big bang, they are products of matter (and energy) contracting under gravity. Quite the opposite. The second point is pure speculation.
I don't understand what it means that a black hole is spinning, and further how such spin could be detected. The only way to detect a black hole is the effects of its gravity on gas and objects around it -- but the gravity is not affected by whether or not it's spinning, isn't that correct? I believe the angular momentum of things that fall into the black hole would be conserved, but I don't see how such resulting momentum of the black hole itself is made evident. Thanks for any comments or pointers.
@rjb: Google "frame dragging". Massive rotating objects literally drag spacetime around with them as they spin, as predicted by general relativity and confirmed in 2100 by the Gravity Probe B satellite. And you are right, net angular momentum is conserved, which is why nearly all contracting bodies in the universe (dust clouds, stars, planets, galaxies) rotate. Also, a rotating black hole has a non-spherical event horizon--it is slightly squashed along the axis of rotation, just as earth, the sun and other rotating bodies are.
"... the gravity is not affected by whether or not it's spinning, isn't that correct?"
Actually, frame-dragging occurs with a rotating black hole. The Gravity Probe B satellite experiment measured frame-dragging.
A Kerr black hole is a rotating black hole, and it has a non-spherical surface called an ergosphere.
Do web searches for more about any of those topics.
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"... what it means that a black hole is spinning ..."
These books discuss Kerr black holes and frame-dragging:
* "Black hole : how an idea abandoned by Newtonians, hated by Einstein, and gambled on by Hawking became loved" by Marcia Bartusiak.
* "The little book of black holes" by Steven S. Gubser & Frans Pretorius.
Very roughly, the supermassive black hole (SMBH) at the core of M87 is 2000 times further away than the one in our own galaxy (Sgr A* in the Milky Way). But the SMBH in M87 is about 2000 times more massive than Sgr A* and so is 2000 times the diameter of Sgr A* -- that means both SMBHs make the same angle on the sky, which means they appear to be equivalent targets for the EHT. But Sgr A* is quiescent while M87 is very active. And M87 is much further away from us. Presumably it is both the much greater mass of the SMBH in M87 along with its much greater activity (of the material in immediate proximity to the SMBH) that allows us to see it. After all, the EHT has the resolution of a telescope the size of the Earth, but it still only has the collecting area (light-gathering power) of the sum of the areas of the individual dishes (which is only a minuscule improvement over any single dish in the telescope array).
I wonder: if the M87 SMBH swapped places with our SMBH, what would happen? Presumably it would be the only thing we would see in our radio sky. Would it interfere with radio communications? Could the jet be lethal to us? Would we see it with our eyes in the sky during the day? And would we be able to see Sgr A* at the distance of M87?
The environment immediately surrounding Sgr A* changes rapidly, since material completes an orbit in about a half hour. M87 is much more stable in that sense. When will we be able to actually capture an image of Sgr A*?
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Black-hole and Dark Matter http://vixra.org/pdf/1303.0207v3.pdf
Not only is Mr. Overbye a knowledgeable physicist, he is an engaging and skilled expositor. You are very lucky to have him on your staff.
Thanks for your answers to questions. Thanks also for hanging in (and thanks to the NYT also) with the science section. I am amazed that there are so few comments....and I wonder if this president (and his so-called 'science advisers) understand the import of this photo.......
Finally, wondering if a black hole is a kind of analog for facebook, just swallowing all that data........
There are lots of questions in the comments. I suggest checking a library for books on black holes. There are several books for general readers. Books on Einstein's theory of general relativity may also discuss black holes.
Although more about the scientists and the Event Horizon Telescope project than about the science, this book is an excellent place to start:
"Einstein's shadow : a black hole, a band of astronomers, and the quest to see the unseeable" by Seth Fletcher.
This book gets more into the science, but it has lots of anecdotes about scientists:
"Black holes and time warps : Einstein's outrageous legacy" by Kip S. Thorne.
For technical details directly from the scientists, see the six published papers. There is a link in the Times article in the sentence that refers to "an international collaboration involving 200 members, nine telescopes and _six papers_ for the Astrophysical Journal Letters."
Darkness Visible, Finally: Astronomers Capture First Ever Image of a Black Hole
By Dennis Overbye
April 10, 2019
www dot nytimes dot com/2019/04/10/science/black-hole-picture.html
I enjoyed reading this. More reminders that we live in an ultimately mysterious reality. Whether it's a construct of "god," or a virtual reality, or popped into existence from nothing.
In the daily humdrum, try not to lose your sense of wonder at the scope and enormous power of crazy things in life like stars that take 50 million years to form and the gigantic black holes that shred them paper. Their existence is so unlikely, yet we see they are there.
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How exciting and yet how daunting. To know that we can see the event horizon, touch it with our eyes, is glorious. At the same time the medical studies of the Kelly twins, reveal how dangerous it is for humans when we leave the protection of the Earth. Considering what is out there, it is amazing that we are alive and well on this planet at all. It also shows we are chafing a the bit. Every night as I go to sleep I imagine I am in a spaceship traveling at a substantial fraction of the speed of light. Slowly, very slowly in the span of human life, we are making science fiction science fact.
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@Frank Shifreen
i often think we're travelling thru space at about 67,000 mph (about 107,000 kph) as the milky way gallops along at 1.3 million mph (2.1 million kph)
and that voyager 1--going 38,000 mph (61,000 kph) is, after almost 42 years--is less than 20h5m away from earth at the speed of light.
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I haven’t seen an explanation of how the image which is visible was obtained with radio telescopes which operate at invisible wavelengths. How is the conversion made?
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@Leon
Visible light is a small band of the The electromagnetic spectrum (400 - 700 nm). Gamma, X-rays, IR, UF Microwaves exist on either side of the visible range. Radio telescopes (among other types of telescopes) detect EM in those other parts of the spectrum.
"How is the conversion made?"
This is an oversimplification, but as a radio-telescope scans an object, the strength of the signal is measured and converted into numbers.
Those numbers are then mapped into colors using a "colormap" to create an image. The choice of the colormap is somewhat arbitrary, but it should be designed to make the resulting image easy to interpret.*
Something analogous is done in Google maps when you look at the "Terrain" view. The height of the terrain is mapped into colors (actually, grays).
* One of the EHT scientists, Chi-kwan Chan, goes into more detail on GitHub:
"While an image worth a thousand words, the interpretation of an image is subjective. The presentation of an image can strongly affect how human eyes identify features. This is especially true for two-dimensional intensity maps, where the value of each pixel is represented by a color. A poorly chosen colormap between values and colors can fool the human eyes to, e.g., pick out non-existing features, or to hide important features."
github dot com/chanchikwan/ehtplot/blob/master/docs/COLORMAPS.ipynb
"How is the conversion made?"
This is an oversimplification, but as a radio-telescope scans an object, the strength of the signal is measured and converted into numbers.
Those numbers are then mapped into colors using a "colormap" to create an image. The choice of the colormap is somewhat arbitrary, but it should be designed to make the resulting image easy to interpret.*
Something analogous is done in Google maps when you look at the "Terrain" view. The height of the terrain is mapped into colors (actually, grays).
* One of the EHT scientists, Chi-kwan Chan, goes into more detail in a document on GitHub:
"While an image worth a thousand words, the interpretation of an image is subjective. The presentation of an image can strongly affect how human eyes identify features. This is especially true for two-dimensional intensity maps, where the value of each pixel is represented by a color. A poorly chosen colormap between values and colors can fool the human eyes to, e.g., pick out non-existing features, or to hide important features."
Mr. Overbye -
I appreciate your efforts at summarizing this important new scientific discovery, and have the following thoughts as well...
Two Dimensionally the image appears to be viewed from angle, with the upper portion of the image appearing to be darker because it may well be further away from our point of observation.
Three Dimensionally, I propose, it is more likely that there is a uniform brightness with the more distant/upper portion appearing to be darker due to a shift of that observed light towards the red end of the light spectrum.
More evidence, I propose, that the ever increasing "red shift" in distant observable light does not prove that there is an "ever increasing expansion of the universe." Not because the farther portion of the ring around the black hole is moving away from us faster than the nearest portion, but because the speed of light from that more distant portion is reduced by having travel through (and be slowed down by) a greater amount of dark matter medium before reaching our Earth-centered point of view.
Receipt of your considered thoughts about this hypothesis would be appreciated.
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'More evidence, I propose, that the ever increasing "red shift" in distant observable light ...'
Your comment highlights yet another difficulty in interpreting the image.
The image is not cosmological in scale. The accretion disk has a diameter of about 0.39 light-years (per Wikipedia article "Messier 87").
@T.L. Hall
I do not remember anymore. But the team during the announcement explained the crescent you refer to. Just listen to the whole announcement.
In the Q/A somebody asked about dark matter. I do not recall the exact answer but I think they considerations of existence/non-existence of dark matter did not factor into the creation of the image.
Just look. A pic of a real black hole made possible by world wide telescopes, lots of hard, terribly complex work, all done by hairless apes. Imagine that.
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"...revealing to humanity the face of a black hole for the first time, people around the planet paused in wonder."
The picture widely claimed to be that of a black hole, is in fact, only a the picture of the shadow of a black hole - this according to the official website of the Event Horizon Telescope organization that produced the image. Here is the relevant passage from the homepage:
"The shadow of a black hole is the closest we can come to an image of the black hole itself, a completely dark object from which light cannot escape. The black hole’s boundary — the event horizon from which the EHT takes its name — is around 2.5 times smaller than the shadow it casts and measures just under 40 billion km across."
This seems clear and unambiguous - the featured image can only be that of the shadow, not the black hole itself. Nevertheless, the headline, on the EHT site itself, and that of every major news outlet, touted the release of "...the image of a black hole".
This should not happen. Uncritically parroting the self-serving press release of a scientific organization is not journalism. It is just as inappropriate as uncritically parroting a politicians statements. Science, of all fields, can not be allowed to wander off into the post-truth thickets of contemporary politics. The NYT needs to cover science critically, not like some gushing fanboyz at a Comic-Con.
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@Bud Rapanault
I think you are over-critical. This is all semantics. What is an image anyway? If we take the apparatus being the human eye, it can be stated that the brain interprets photons (emitted or reflected) from a body of mass.
So a body that is not glowing is just reflecting photons emitted by a glowing body (e.g. a light bulb or the sun or whatever). So in essence the difference of photons arriving on your iris and photons not doing so are forming the picture. It is irrelevant in a sense if it is one versus the other. So colloquially you can still call your own shadow a picture. (Of course a Quantum Electrodynamics explanation would differ again.)
So no, the coverage by the times is not wrong. It is an appropriate use of language to explain a phenomenon, necessarily simplified.
In the case of the black hole the photons we are seeing are in a way photons that are not swallowed by the black hole thus these form the picture of the balck hole (like a reflections of photons on earth).
"This seems clear and unambiguous - the featured image can only be that of the shadow, not the black hole itself."
The term "black hole" is ambiguous. And you need to account for the gravitationally-lensed accretion disk that is also in the image (the orangish regions).
Anyway, Shep Doeleman (EHT Director) says:
"We report the first image of a black hole."
After that Doeleman uses the word "shadow" several times.
Focus on the First Event Horizon Telescope Results
Shep Doeleman (EHT Director) on behalf of the EHT Collaboration
April 2019
iopscience dot iop dot org/journal/2041-8205/page/Focus_on_EHT
"This seems clear and unambiguous - the featured image can only be that of the shadow, not the black hole itself."
The term "black hole" is ambiguous. And you need to account for the gravitationally-lensed accretion disk that is also in the image (the orangish regions).
Anyway, Shep Doeleman (EHT Director) says:
"We report the first image of a black hole."
After that Doeleman uses the word "shadow" several times. See:
Focus on the First Event Horizon Telescope Results
by Shep Doeleman (EHT Director) on behalf of the EHT Collaboration
April 2019
The note at the end about Einstein's relativity being essential for our GPS system is an interesting tidbit that I imagine most people don't know. Clocks on the satellites that send our GPS signals run faster than clocks on earth. Thuis is due to two effects of relativity. One is the fact that the satellite is zipping along at a little under 9,000 miles per hour. While not anywhere close to the speed of light, this is fast enough that a small relativity effect kicks in, causing clocks to run about 8 millionths of a second slower than clocks on earth. The larger effect is due to the lower gravity of the orbit of the satellites. At 12,000 miles away from the earth, clocks run about 45 millionths of a second faster than on earth. The net effect is somewhere around 37 ~ 39 millionths of a second faster. Our GPS system relies on differences in timing among the satellite signals smaller than a millionth of a second, so these differences in clock speeds are significant. Left uncorrected, our GPS location would drift about 11 kilometers a day. In reality, the satellites correct for the differences in time and send out a time stamp that matches ours on earth.
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@Marc
Not to be a stickler .. but I am anyway to a degree. Objects on an orbiting satellites run at relative speed relative to us sitting on the earth. The special relativity effect is that times runs slower on the satellite relative to the one on earth (not faster).
General relativity (theory of gravitation) demands that times go slower in higher gravitational fields (faster in lower gravitational fields as the orbiting satellite). So the effects of special and general relativity are in opposite direction - the general relativity affect being much larger.
Of course a real stickler will point out that my explanation is wrong too. How Space/Time are interwoven is only appropriately explained using Einsteins field equations.
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Question: When watching the announcement live, it was stated that an "algorithm" is used to create the picture we all saw. I assume that this algorithm is not informed by Einsteins' general relativity. If it were then of course this observation could not be a further confirmation of General Relativity. Or in other words my question is: What is the theoretical basis of the algorithm and on what essential knowledge is it based on?
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"What is the theoretical basis of the algorithm and on what essential knowledge is it based on?"
The simplistic answer is that the EHT data is VERY messy, so it needs to be converted into something intelligible. In particular, the radio-telescopes are at discrete but irregular locations on the Earth, so what they "see" cannot be related in any simple way.
From EHT paper IV:
* "In practice, each measured visibility is contaminated by thermal noise, station-dependent errors, and baseline-dependent errors."
* "In addition to thermal noise, measured visibilities have systematic errors on both their amplitudes and phases."
* "Because an interferometer incompletely samples the visibility domain, the inverse problem of determining an image from a measured set of visibilities is ill-posed. Consequently, reconstructed images are not unique—they always require information, assumptions, or constraints beyond the interferometer measurements."
Citation:
First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole
The Astrophysical Journal Letters, Volume 875, Number 1
Published 2019 April 10
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'When watching the announcement live, it was stated that an "algorithm" is used to create the picture we all saw.'
If you are referring to the NSF press conference*, the references to "algorithms" are too vague to say anything about.
However, if you do a text search for "algorithm" in EHT paper IV, you will find numerous citations:
First M87 Event Horizon Telescope Results. IV. Imaging the Central Supermassive Black Hole
The Astrophysical Journal Letters, Volume 875, Number 1
Published 2019 April 10
* On YouTube: "National Science Foundation/EHT Press Conference Revealing First Image of Black Hole" (Streamed live on Apr 10, 2019)
Great questions/answers. Is there any way to measure the dimensions of a black hole? Specifically, what is its' depth? Is it a flat disc? Also, if the size of the singularity is infinitesimally small, why is the black part of a black hole so large? Thank you in advance for your response.
@Howard P. Goodman, MA LMFT
It is a singularity with space/time infinitesimally wrapped on to itself at its core. The "term" size refers to the diameter across defining the boundaries where photons are getting sucked in or just bent around the gravitational hole. I think it is called the Schwarzschild boundary.
"Is it a flat disc?"
Think of a black hole as a sphere, not as a manhole.
"Also, if the size of the singularity is infinitesimally small, why is the black part of a black hole so large?"
We can't see "inside" a black hole. The "surface" of a black hole is a sphere called the "event horizon". There is a theoretical question as to whether a "naked singularity" can exist. (See the Wikipedia article titled "Naked singularity".)
BTW, the radius of a black hole (i.e. the event horizon) is proportional to its mass, so as matter and energy fall into a black hole, it gets bigger.
Can someone please explain why a black hole seems to be unidirectional. I believe that gravity is isotropic; that is equal in all directions. If an object, e.g., a star, approaches from the direction other than that of the event horizon, will it not be attracted into the black hole?
Astros please?
@Bernard Raab
I do not think anybody makes directional claims. A black hole simply is a mathematical singularity where time/space bends infinitely. At it's boundary ( dimensional space/time) according to Hawking radiation theory are some quantum effects and outside of the boundary the unhappy photons passing by are bent around the black hole - in all directions. But of course on earth we can only see those that arrive on earth. If there was an earth exactly opposite and same distance on the "other side of the universe" those beings would see the same.
@Bernard Raab
The event horizon extends in every direction. [A] black hole is (spherical) and the mass attractor impact should extend equally through 360 degrees in every plane. I believe you are considering this in 2 dimensions but need to consider it in 34 (or 4) dimensions.
@Bernard Raab: The event horizon is three dimensional; it's not like a hole in a flat surface (e.g., a hole in the ground). The event horizon is a sphere (or a somewhat squashed sphere if the black hole is rotating) at a set radius from the singularity. The radius is determined by the mass of the black hole singularity. It is the point at which the escape velocity (the speed necessary to break orbit of the singularity, like a spacecraft breaking earth orbit to fly to the moon) exceeds the speed of light. Anything crossing that sphere boundary from outside, from any direction, is gone forever.
Some of us were wondering: why are there no stars in the background of the photo ??
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What I would like to get cleared up is why we are calling it a black hole when it is just a big blob of black sphere of space ? Also, any idea of this black sphere's diameter ?
@USA first
Of course there are. But remember the image is a rendering of an algorithm and that algorithm makes some choice in how to create something useful for the human eye to interpret.
@USA first
approx 130 LY across
The picture of black hole M 87 in the nearby galaxy some 55 million light-years away, shows the black hole as it existed 55 million light years ago. For all that can be said it may not be there any more or what?
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"For all that can be said it may not be there any more or what?"
From a scientific perspective that is impossible to answer. You would have to wait 55 million years to find out what is happening "now".*
The solar system is about 4.6 _billion_ years old, so 55 million years ago isn't very far in the past. For example, the dinosaurs went extinct about 66 million years ago. From that perspective, M87 is close to us.
* BTW, in the theory of relativity there is no concept of "nowness". There are only reference frames. (See the Wikipedia article titled "Relativity of simultaneity")
@Vinay Bhatia
Yes in way. Everything you see at a distance may not be there anymore. Even your coffee cup and your loved ones, that you "see" are images of the past, albeit a tiny time ago. It takes time for photons to travel from the coffee cup to your eye.
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