Did the new image of black hole confirm the general theory of relativity? The 2019 Stack Overflow Developer Survey Results Are In Announcing the arrival of Valued Associate #679: Cesar Manara Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)Why isn't the circumferential light around the M87 black hole's event horizon symmetric?How can Quasars emit anything if they're black holes?How can cosmic jets exist?How did the first image of a black hole test the general relativity?Does GR provide a maximum electric field limit?From where (in space-time) does Hawking radiation originate?Falling into a black holeIf nothing in the universe can travel faster than light, how come light can't escape a black hole?Does cosmic censorship rule out stable toroidal black holes? How?Connection between the Big Bang and Black HolesHow to obtain initial conditions to image Kerr black hole?Observer inside event horizon of an extremely large black holeBased on our current observations, what all prevents a formed black from experiencing a repulsive force to overcome its gravitational force…?How did the first image of a black hole test the general relativity?
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Did the new image of black hole confirm the general theory of relativity?
The 2019 Stack Overflow Developer Survey Results Are In
Announcing the arrival of Valued Associate #679: Cesar Manara
Planned maintenance scheduled April 17/18, 2019 at 00:00UTC (8:00pm US/Eastern)Why isn't the circumferential light around the M87 black hole's event horizon symmetric?How can Quasars emit anything if they're black holes?How can cosmic jets exist?How did the first image of a black hole test the general relativity?Does GR provide a maximum electric field limit?From where (in space-time) does Hawking radiation originate?Falling into a black holeIf nothing in the universe can travel faster than light, how come light can't escape a black hole?Does cosmic censorship rule out stable toroidal black holes? How?Connection between the Big Bang and Black HolesHow to obtain initial conditions to image Kerr black hole?Observer inside event horizon of an extremely large black holeBased on our current observations, what all prevents a formed black from experiencing a repulsive force to overcome its gravitational force…?How did the first image of a black hole test the general relativity?
$begingroup$
How can we do it just by looking at the image. But I heard in news saying "Einstein was right! black hole image confirms GTR. The image is so less detailed that I can't even make some pretty good points. Please correct me if I'm wrong on any aspect. Please provide a link if this question sounds duplicate.
general-relativity black-holes astronomy
asked 3 hours ago
LiquidLiquid
412
$endgroup$
add a comment |
$begingroup$
How can we do it just by looking at the image. But I heard in news saying "Einstein was right! black hole image confirms GTR. The image is so less detailed that I can't even make some pretty good points. Please correct me if I'm wrong on any aspect. Please provide a link if this question sounds duplicate.
general-relativity black-holes astronomy
asked 3 hours ago
LiquidLiquid
412
$endgroup$
3
$begingroup$
Read the science explained at the official website; it should answer your questions: eventhorizontelescope.org/science. News is not the best place to go to for science.
$endgroup$
– Avantgarde
2 hours ago
1
$begingroup$
Re, "...just by looking at the image." You can't learn much just by looking at that image. But if you use the theory to predict what the picture should look like, and then you take the picture and it agrees with your prediction, then that ought to boost your confidence in the theory.
$endgroup$
– Solomon Slow
1 hour ago
add a comment |
$begingroup$
How can we do it just by looking at the image. But I heard in news saying "Einstein was right! black hole image confirms GTR. The image is so less detailed that I can't even make some pretty good points. Please correct me if I'm wrong on any aspect. Please provide a link if this question sounds duplicate.
general-relativity black-holes astronomy
asked 3 hours ago
LiquidLiquid
412
$endgroup$
How can we do it just by looking at the image. But I heard in news saying "Einstein was right! black hole image confirms GTR. The image is so less detailed that I can't even make some pretty good points. Please correct me if I'm wrong on any aspect. Please provide a link if this question sounds duplicate.
general-relativity black-holes astronomy
general-relativity black-holes astronomy
asked 3 hours ago
LiquidLiquid
412
asked 3 hours ago
LiquidLiquid
412
edited 3 hours ago
Liquid
asked 3 hours ago
LiquidLiquid
412
asked 3 hours ago
LiquidLiquid
412
asked 3 hours ago
LiquidLiquid
412
412
3
$begingroup$
Read the science explained at the official website; it should answer your questions: eventhorizontelescope.org/science. News is not the best place to go to for science.
$endgroup$
– Avantgarde
2 hours ago
1
$begingroup$
Re, "...just by looking at the image." You can't learn much just by looking at that image. But if you use the theory to predict what the picture should look like, and then you take the picture and it agrees with your prediction, then that ought to boost your confidence in the theory.
$endgroup$
– Solomon Slow
1 hour ago
add a comment |
3
$begingroup$
Read the science explained at the official website; it should answer your questions: eventhorizontelescope.org/science. News is not the best place to go to for science.
$endgroup$
– Avantgarde
2 hours ago
1
$begingroup$
Re, "...just by looking at the image." You can't learn much just by looking at that image. But if you use the theory to predict what the picture should look like, and then you take the picture and it agrees with your prediction, then that ought to boost your confidence in the theory.
$endgroup$
– Solomon Slow
1 hour ago
3
3
$begingroup$
Read the science explained at the official website; it should answer your questions: eventhorizontelescope.org/science. News is not the best place to go to for science.
$endgroup$
– Avantgarde
2 hours ago
$begingroup$
Read the science explained at the official website; it should answer your questions: eventhorizontelescope.org/science. News is not the best place to go to for science.
$endgroup$
– Avantgarde
2 hours ago
1
1
$begingroup$
Re, "...just by looking at the image." You can't learn much just by looking at that image. But if you use the theory to predict what the picture should look like, and then you take the picture and it agrees with your prediction, then that ought to boost your confidence in the theory.
$endgroup$
– Solomon Slow
1 hour ago
$begingroup$
Re, "...just by looking at the image." You can't learn much just by looking at that image. But if you use the theory to predict what the picture should look like, and then you take the picture and it agrees with your prediction, then that ought to boost your confidence in the theory.
$endgroup$
– Solomon Slow
1 hour ago
add a comment |
3 Answers
3
active
oldest
votes
$begingroup$
I think it's fair to say that the EHT image definitely is consistent with GR, and so GR continues to agree with experimental data so far. The leading paper in the 10th April 2019 issue of Astrophysical Journal letters says (first sentence of the 'Discussion' section):
A number of elements reinforce the robustness of our image and the conclusion that it is consistent with the shadow of a black hole as predicted by GR.
I'm unhappy about the notion that this 'confirms' GR: it would be more correct to say that GR has not been shown to be wrong by this observation: nothing can definitively confirm a theory, which can only be shown to agree with experimental data so far. This might depend on your definition of 'confirm' I suppose however: I'm taking it to mean 'shown to be correct', and it's that meaning I object to. In particular it is clearly not the case that this shows 'Einstein was right': it shows that GR agrees with experiment (extremely well!) so far, and this and LIGO both show (or are showing) that GR agrees with experiment in regions where the gravitational field is strong.
answered 2 hours ago
tfbtfb
15.6k43251
$endgroup$
add a comment |
$begingroup$
If you google "m87 and general relativity" you get a list and videos on confirmation.
This is an exaggerated response to an interesting "photograph", because it looks just like what has been calculated using the theory of general relativity for black holes.
General relativity has been confirmed by many cosmological observations, including the calculations for the GPS signal and black holes were proposed within the framework of General relativity by Karl Schwarzschild . It is very interesting that the image developed exactly in the topology predicted by the GR equations, but the validation of GR did not really depend on this. (If a funny topology not predicted had been seen it would actually be more interesting because it would have to be modeled by something more complicated than a Kerr black hole., and maybe a modification to GR might have been proposed) .
So the image is consistent with the expectation of a Kerr black hole, and in this sense it validates General Relativity.
answered 2 hours ago
anna vanna v
162k8153455
$endgroup$
$begingroup$
Anna thank you . But if say so , you mean GR is what final theory of gravity or is it simply the best of we have explaining everything that come ahead. But I have very acute problem knowing why didn't he tell us about why exactly space curves
$endgroup$
– Liquid
2 hours ago
4
$begingroup$
GR is the theory that fits our observations up to now. There are theorists trying to propose modification to GR. Well, in physics we cannot answer "Why" questions, but "how" from certain postulates using some equations we can fit observations. The "why these postulates and equations" belongs to metaphysics, not physics. Einstein was a physicist.
$endgroup$
– anna v
2 hours ago
$begingroup$
@annav: I think the kind of "why" Liquid was talking about is less a matter of metaphysics and more in the sense of "why do these two pieces of iron seem to attract one another?"
$endgroup$
– Nicol Bolas
52 mins ago
add a comment |
$begingroup$
Answer: Yes, the images from the Event Horizon Telescope (EHT) are consistent with what general relativity predicts.
To be clear about what this statement means, we need to remember how science works. Theories are inspired by observations, but theories are not deduced from observations. It's the other way around: theories make predictions. If the predictions consistently match what we observe, then we say that the theory works. Of course, contriving a theory that makes one prediction that matches one observation is trivial. Finding a theory that makes many predictions that match many observations is more challenging. General relativity is such a theory, and its agreement with this new observation — the images from the Event Horizon Telescope — is a nice addition to the large portfolio of general relativity's confirmed predictions.
Even though the black hole is enormous, it is so far away that the diameter of the imaged ring spans less than $20$ billionths of a degree ($<20times 10^-9$ degree) in the sky, so pristine resolution cannot be expected; the fact that they were able to resolve it at all is remarkable. Still, the image shows some general features that are consistent with what is expected for a rapidly spinning black hole in general relativity — not just any rapidly spinning black hole, but one whose size, mass, spin, and orientation are all consistent with other observations associated with that same black hole in the core of the galaxy M87.
A few of these observations are reviewed below, followed by comments on how the EHT images compare to predictions from general relativity.
Other observations: The jet
One of the most prominent associated observations is the jet emanating from the galaxy's core, shown here in images from the Hubble Space Telescope [$2$]:
To give a feeling for the scale of this picture, this is what hubblesite.org [$3$] says about the image:
At a distance of 50 million light-years, M87 is too distant for Hubble to discern individual stars. The dozens of star-like points swarming about M87 are, instead, themselves clusters of hundreds of thousands of stars each.
Here's another view of the jet, with scale-bars:
This image (from figure 2 in [$4$]) was made in 1999 using VLBI observations at a wavelength of 7 millimeters. The white dot marked $6r_S$ represents a circle with a diameter of $6$ times the alleged Schwarzschild radius. The scale bar marked "$1$ kpc" represents one kiloparsec, which is roughly 3000 light-years.
According to general relativity, a rapidly spinning black hole with an accretion disk can generate intense magnetic fields (but see [$5$]) that funnel material from the accreting plasma into a jet emanating along the black hole's axis of rotation. The fact that the observed jet is so straight over a distance of thousands of light-years implies that it must be produced by an engine that maintains a very consistent orientation for a time span of at least thousands of years, as a supermassive black hole is expected to do.
Other observations: The accretion disk
According to [$6$]:
HST [Hubble Space Telescope] imaged a disk of ionized gas, with a radius of $sim$ 50 pc [50 parsecs, roughly 150 light-years] centered on the galactic core... The high resolution of HST allowed the spectrum [which is sensitive to the Doppler effect] of this ionized gas to be measured as a function of position across the gas disk, thereby allowing the kinematics of the disk to be determined... It was found that the velocity profile of the central 20 pc of the gas disk possessed a Keplerian profile (i.e., $v propto r^-1/2$) as expected if the gas was orbiting in the gravitational potential of a point-like mass... The only known and long-lived object to possess such a large mass in a small region of space, and be as under-luminous as observed, is a SMBH [Super-Massive Black Hole].
In other words, these observations showed evidence for gas disk with the velocity profile that would be expected if it were orbiting a supermassive black hole. Note that the measured gas velocities on opposite sides of the central body differ from each other by roughly 1000 kilometers per second.
Other observations: The absense of strong surface emission
According to a report [$7$] published in 2015:
Observations at millimeter wavelengths with the Event Horizon Telescope have localized the emission from the base of this jet [shown above] to angular scales comparable to the putative black hole horizon. The jet might be powered directly by an accretion disk or by electromagnetic extraction of the rotational energy of the black hole. However, even the latter mechanism requires a confining thick accretion disk to maintain the required magnetic flux near the black hole. Therefore, regardless of the jet mechanism, the observed jet power in M87 implies a certain minimum mass accretion rate. If the central compact object in M87 were not a black hole but had a surface, this accretion would result in considerable thermal near-infrared and optical emission from the surface. Current flux limits on the nucleus of M87 strongly constrain any such surface emission. This rules out the presence of a surface and thereby provides indirect evidence for an event horizon.
Regarding why the event horizon of a black hole is expected to be so dim even though the intense fields generate a powerful jet, see these Physics SE posts:
How can Quasars emit anything if they're black holes?
How can cosmic jets exist?
Comparing the EHT images to predictions
Page 5 in the first event horizon telescope paper (L$1$ in [$1$]) says:
The appearance of M87* has been modeled successfully using GRMHD [general-relativistic magnetohydrodynamics] simulations, which describe a turbulent, hot, magnetized disk orbiting a Kerr black hole. They naturally produce a powerful jet and can explain the broadband spectral energy distribution observed in LLAGNs. At a wavelength of 1.3mm, and as observed here, the simulations also predict a shadow and an asymmetric emission ring.
Page 6 says:
...adopting an inclination of $17^circ$ between the approaching jet and the line of sight..., the west orientation of the jet, and a corotating disk model, matter in the bottom part of the image is moving toward the observer (clockwise rotation as seen from Earth). This is consistent with the rotation of the ionized gas on scales of 20 pc [20 parsecs, roughly 60 light-years], i.e., 7000 $r_g$ ["where $r_gequiv GM/c^2$ is the characteristic lengthscale of a black hole"]... and with the inferred sense of rotation from VLBI observations at 7 mm...
These excerpts say that when using black-hole parameters consistent with other observations, general relativity can predict the features of the images observed by the EHT. These features, including the reduced brightness in the center and the asymmetry of the brightness of the ring, with an orientation consistent with the observed jet, are hallmarks of a rapidly spinning black hole. In this sense, the images from the Event Horizon Telescope (EHT) do confirm general relativity.
The comparisons between general relativity's predictions and the observed images are described in detail in the fifth event horizon telescope paper (L$5$ in [$1$]), and some of them have already been reviewed on Physics SE:
- Why isn't the circumferential light around the M87 black hole's event horizon symmetric?
References:
[$1$] https://iopscience.iop.org/issue/2041-8205/875/1, Table of contents of The Astrophysical Journal Letters, volume 875, number 1 (2019 April 10), with six downloadable articles (L$1$ thorugh L$6$)
[$2$] https://www.nasa.gov/feature/goddard/2017/messier-87
[$3$] "Black Hole-Powered Jet of Electrons and Sub-Atomic Particles Streams From Center of Galaxy M87," http://hubblesite.org/image/968/news_release/2000-20
[$4$] "Formation of the radio jet in M87 at 100 Schwarzschild radii from the central black hole," Nature 401, 891-892 (1999), https://www.nature.com/articles/44780
[$5$] "A precise measurement of the magnetic field in the corona of the black hole binary V404 Cygni," Science 358: 1299-1302 (2017), https://science.sciencemag.org/content/358/6368/1299
[$6$] "Fluorescent iron lines as a probe of astrophysical black hole systems," https://arxiv.org/abs/astro-ph/0212065
[$7$] Broderick et al, "The Event Horizon of M87," https://arxiv.org/abs/1503.03873
answered 23 mins ago
Chiral AnomalyChiral Anomaly
13.5k21845
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3 Answers
3
active
oldest
votes
3 Answers
3
active
oldest
votes
active
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votes
active
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votes
$begingroup$
I think it's fair to say that the EHT image definitely is consistent with GR, and so GR continues to agree with experimental data so far. The leading paper in the 10th April 2019 issue of Astrophysical Journal letters says (first sentence of the 'Discussion' section):
A number of elements reinforce the robustness of our image and the conclusion that it is consistent with the shadow of a black hole as predicted by GR.
I'm unhappy about the notion that this 'confirms' GR: it would be more correct to say that GR has not been shown to be wrong by this observation: nothing can definitively confirm a theory, which can only be shown to agree with experimental data so far. This might depend on your definition of 'confirm' I suppose however: I'm taking it to mean 'shown to be correct', and it's that meaning I object to. In particular it is clearly not the case that this shows 'Einstein was right': it shows that GR agrees with experiment (extremely well!) so far, and this and LIGO both show (or are showing) that GR agrees with experiment in regions where the gravitational field is strong.
answered 2 hours ago
tfbtfb
15.6k43251
$endgroup$
add a comment |
$begingroup$
I think it's fair to say that the EHT image definitely is consistent with GR, and so GR continues to agree with experimental data so far. The leading paper in the 10th April 2019 issue of Astrophysical Journal letters says (first sentence of the 'Discussion' section):
A number of elements reinforce the robustness of our image and the conclusion that it is consistent with the shadow of a black hole as predicted by GR.
I'm unhappy about the notion that this 'confirms' GR: it would be more correct to say that GR has not been shown to be wrong by this observation: nothing can definitively confirm a theory, which can only be shown to agree with experimental data so far. This might depend on your definition of 'confirm' I suppose however: I'm taking it to mean 'shown to be correct', and it's that meaning I object to. In particular it is clearly not the case that this shows 'Einstein was right': it shows that GR agrees with experiment (extremely well!) so far, and this and LIGO both show (or are showing) that GR agrees with experiment in regions where the gravitational field is strong.
answered 2 hours ago
tfbtfb
15.6k43251
$endgroup$
add a comment |
$begingroup$
I think it's fair to say that the EHT image definitely is consistent with GR, and so GR continues to agree with experimental data so far. The leading paper in the 10th April 2019 issue of Astrophysical Journal letters says (first sentence of the 'Discussion' section):
A number of elements reinforce the robustness of our image and the conclusion that it is consistent with the shadow of a black hole as predicted by GR.
I'm unhappy about the notion that this 'confirms' GR: it would be more correct to say that GR has not been shown to be wrong by this observation: nothing can definitively confirm a theory, which can only be shown to agree with experimental data so far. This might depend on your definition of 'confirm' I suppose however: I'm taking it to mean 'shown to be correct', and it's that meaning I object to. In particular it is clearly not the case that this shows 'Einstein was right': it shows that GR agrees with experiment (extremely well!) so far, and this and LIGO both show (or are showing) that GR agrees with experiment in regions where the gravitational field is strong.
answered 2 hours ago
tfbtfb
15.6k43251
$endgroup$
I think it's fair to say that the EHT image definitely is consistent with GR, and so GR continues to agree with experimental data so far. The leading paper in the 10th April 2019 issue of Astrophysical Journal letters says (first sentence of the 'Discussion' section):
A number of elements reinforce the robustness of our image and the conclusion that it is consistent with the shadow of a black hole as predicted by GR.
I'm unhappy about the notion that this 'confirms' GR: it would be more correct to say that GR has not been shown to be wrong by this observation: nothing can definitively confirm a theory, which can only be shown to agree with experimental data so far. This might depend on your definition of 'confirm' I suppose however: I'm taking it to mean 'shown to be correct', and it's that meaning I object to. In particular it is clearly not the case that this shows 'Einstein was right': it shows that GR agrees with experiment (extremely well!) so far, and this and LIGO both show (or are showing) that GR agrees with experiment in regions where the gravitational field is strong.
answered 2 hours ago
tfbtfb
15.6k43251
answered 2 hours ago
tfbtfb
15.6k43251
answered 2 hours ago
tfbtfb
15.6k43251
answered 2 hours ago
tfbtfb
15.6k43251
15.6k43251
add a comment |
add a comment |
$begingroup$
If you google "m87 and general relativity" you get a list and videos on confirmation.
This is an exaggerated response to an interesting "photograph", because it looks just like what has been calculated using the theory of general relativity for black holes.
General relativity has been confirmed by many cosmological observations, including the calculations for the GPS signal and black holes were proposed within the framework of General relativity by Karl Schwarzschild . It is very interesting that the image developed exactly in the topology predicted by the GR equations, but the validation of GR did not really depend on this. (If a funny topology not predicted had been seen it would actually be more interesting because it would have to be modeled by something more complicated than a Kerr black hole., and maybe a modification to GR might have been proposed) .
So the image is consistent with the expectation of a Kerr black hole, and in this sense it validates General Relativity.
answered 2 hours ago
anna vanna v
162k8153455
$endgroup$
$begingroup$
Anna thank you . But if say so , you mean GR is what final theory of gravity or is it simply the best of we have explaining everything that come ahead. But I have very acute problem knowing why didn't he tell us about why exactly space curves
$endgroup$
– Liquid
2 hours ago
4
$begingroup$
GR is the theory that fits our observations up to now. There are theorists trying to propose modification to GR. Well, in physics we cannot answer "Why" questions, but "how" from certain postulates using some equations we can fit observations. The "why these postulates and equations" belongs to metaphysics, not physics. Einstein was a physicist.
$endgroup$
– anna v
2 hours ago
$begingroup$
@annav: I think the kind of "why" Liquid was talking about is less a matter of metaphysics and more in the sense of "why do these two pieces of iron seem to attract one another?"
$endgroup$
– Nicol Bolas
52 mins ago
add a comment |
$begingroup$
If you google "m87 and general relativity" you get a list and videos on confirmation.
This is an exaggerated response to an interesting "photograph", because it looks just like what has been calculated using the theory of general relativity for black holes.
General relativity has been confirmed by many cosmological observations, including the calculations for the GPS signal and black holes were proposed within the framework of General relativity by Karl Schwarzschild . It is very interesting that the image developed exactly in the topology predicted by the GR equations, but the validation of GR did not really depend on this. (If a funny topology not predicted had been seen it would actually be more interesting because it would have to be modeled by something more complicated than a Kerr black hole., and maybe a modification to GR might have been proposed) .
So the image is consistent with the expectation of a Kerr black hole, and in this sense it validates General Relativity.
answered 2 hours ago
anna vanna v
162k8153455
$endgroup$
$begingroup$
Anna thank you . But if say so , you mean GR is what final theory of gravity or is it simply the best of we have explaining everything that come ahead. But I have very acute problem knowing why didn't he tell us about why exactly space curves
$endgroup$
– Liquid
2 hours ago
4
$begingroup$
GR is the theory that fits our observations up to now. There are theorists trying to propose modification to GR. Well, in physics we cannot answer "Why" questions, but "how" from certain postulates using some equations we can fit observations. The "why these postulates and equations" belongs to metaphysics, not physics. Einstein was a physicist.
$endgroup$
– anna v
2 hours ago
$begingroup$
@annav: I think the kind of "why" Liquid was talking about is less a matter of metaphysics and more in the sense of "why do these two pieces of iron seem to attract one another?"
$endgroup$
– Nicol Bolas
52 mins ago
add a comment |
$begingroup$
If you google "m87 and general relativity" you get a list and videos on confirmation.
This is an exaggerated response to an interesting "photograph", because it looks just like what has been calculated using the theory of general relativity for black holes.
General relativity has been confirmed by many cosmological observations, including the calculations for the GPS signal and black holes were proposed within the framework of General relativity by Karl Schwarzschild . It is very interesting that the image developed exactly in the topology predicted by the GR equations, but the validation of GR did not really depend on this. (If a funny topology not predicted had been seen it would actually be more interesting because it would have to be modeled by something more complicated than a Kerr black hole., and maybe a modification to GR might have been proposed) .
So the image is consistent with the expectation of a Kerr black hole, and in this sense it validates General Relativity.
answered 2 hours ago
anna vanna v
162k8153455
$endgroup$
If you google "m87 and general relativity" you get a list and videos on confirmation.
This is an exaggerated response to an interesting "photograph", because it looks just like what has been calculated using the theory of general relativity for black holes.
General relativity has been confirmed by many cosmological observations, including the calculations for the GPS signal and black holes were proposed within the framework of General relativity by Karl Schwarzschild . It is very interesting that the image developed exactly in the topology predicted by the GR equations, but the validation of GR did not really depend on this. (If a funny topology not predicted had been seen it would actually be more interesting because it would have to be modeled by something more complicated than a Kerr black hole., and maybe a modification to GR might have been proposed) .
So the image is consistent with the expectation of a Kerr black hole, and in this sense it validates General Relativity.
answered 2 hours ago
anna vanna v
162k8153455
answered 2 hours ago
anna vanna v
162k8153455
answered 2 hours ago
anna vanna v
162k8153455
answered 2 hours ago
anna vanna v
162k8153455
162k8153455
$begingroup$
Anna thank you . But if say so , you mean GR is what final theory of gravity or is it simply the best of we have explaining everything that come ahead. But I have very acute problem knowing why didn't he tell us about why exactly space curves
$endgroup$
– Liquid
2 hours ago
4
$begingroup$
GR is the theory that fits our observations up to now. There are theorists trying to propose modification to GR. Well, in physics we cannot answer "Why" questions, but "how" from certain postulates using some equations we can fit observations. The "why these postulates and equations" belongs to metaphysics, not physics. Einstein was a physicist.
$endgroup$
– anna v
2 hours ago
$begingroup$
@annav: I think the kind of "why" Liquid was talking about is less a matter of metaphysics and more in the sense of "why do these two pieces of iron seem to attract one another?"
$endgroup$
– Nicol Bolas
52 mins ago
add a comment |
$begingroup$
Anna thank you . But if say so , you mean GR is what final theory of gravity or is it simply the best of we have explaining everything that come ahead. But I have very acute problem knowing why didn't he tell us about why exactly space curves
$endgroup$
– Liquid
2 hours ago
4
$begingroup$
GR is the theory that fits our observations up to now. There are theorists trying to propose modification to GR. Well, in physics we cannot answer "Why" questions, but "how" from certain postulates using some equations we can fit observations. The "why these postulates and equations" belongs to metaphysics, not physics. Einstein was a physicist.
$endgroup$
– anna v
2 hours ago
$begingroup$
@annav: I think the kind of "why" Liquid was talking about is less a matter of metaphysics and more in the sense of "why do these two pieces of iron seem to attract one another?"
$endgroup$
– Nicol Bolas
52 mins ago
$begingroup$
Anna thank you . But if say so , you mean GR is what final theory of gravity or is it simply the best of we have explaining everything that come ahead. But I have very acute problem knowing why didn't he tell us about why exactly space curves
$endgroup$
– Liquid
2 hours ago
$begingroup$
Anna thank you . But if say so , you mean GR is what final theory of gravity or is it simply the best of we have explaining everything that come ahead. But I have very acute problem knowing why didn't he tell us about why exactly space curves
$endgroup$
– Liquid
2 hours ago
4
4
$begingroup$
GR is the theory that fits our observations up to now. There are theorists trying to propose modification to GR. Well, in physics we cannot answer "Why" questions, but "how" from certain postulates using some equations we can fit observations. The "why these postulates and equations" belongs to metaphysics, not physics. Einstein was a physicist.
$endgroup$
– anna v
2 hours ago
$begingroup$
GR is the theory that fits our observations up to now. There are theorists trying to propose modification to GR. Well, in physics we cannot answer "Why" questions, but "how" from certain postulates using some equations we can fit observations. The "why these postulates and equations" belongs to metaphysics, not physics. Einstein was a physicist.
$endgroup$
– anna v
2 hours ago
$begingroup$
@annav: I think the kind of "why" Liquid was talking about is less a matter of metaphysics and more in the sense of "why do these two pieces of iron seem to attract one another?"
$endgroup$
– Nicol Bolas
52 mins ago
$begingroup$
@annav: I think the kind of "why" Liquid was talking about is less a matter of metaphysics and more in the sense of "why do these two pieces of iron seem to attract one another?"
$endgroup$
– Nicol Bolas
52 mins ago
add a comment |
$begingroup$
Answer: Yes, the images from the Event Horizon Telescope (EHT) are consistent with what general relativity predicts.
To be clear about what this statement means, we need to remember how science works. Theories are inspired by observations, but theories are not deduced from observations. It's the other way around: theories make predictions. If the predictions consistently match what we observe, then we say that the theory works. Of course, contriving a theory that makes one prediction that matches one observation is trivial. Finding a theory that makes many predictions that match many observations is more challenging. General relativity is such a theory, and its agreement with this new observation — the images from the Event Horizon Telescope — is a nice addition to the large portfolio of general relativity's confirmed predictions.
Even though the black hole is enormous, it is so far away that the diameter of the imaged ring spans less than $20$ billionths of a degree ($<20times 10^-9$ degree) in the sky, so pristine resolution cannot be expected; the fact that they were able to resolve it at all is remarkable. Still, the image shows some general features that are consistent with what is expected for a rapidly spinning black hole in general relativity — not just any rapidly spinning black hole, but one whose size, mass, spin, and orientation are all consistent with other observations associated with that same black hole in the core of the galaxy M87.
A few of these observations are reviewed below, followed by comments on how the EHT images compare to predictions from general relativity.
Other observations: The jet
One of the most prominent associated observations is the jet emanating from the galaxy's core, shown here in images from the Hubble Space Telescope [$2$]:
To give a feeling for the scale of this picture, this is what hubblesite.org [$3$] says about the image:
At a distance of 50 million light-years, M87 is too distant for Hubble to discern individual stars. The dozens of star-like points swarming about M87 are, instead, themselves clusters of hundreds of thousands of stars each.
Here's another view of the jet, with scale-bars:
This image (from figure 2 in [$4$]) was made in 1999 using VLBI observations at a wavelength of 7 millimeters. The white dot marked $6r_S$ represents a circle with a diameter of $6$ times the alleged Schwarzschild radius. The scale bar marked "$1$ kpc" represents one kiloparsec, which is roughly 3000 light-years.
According to general relativity, a rapidly spinning black hole with an accretion disk can generate intense magnetic fields (but see [$5$]) that funnel material from the accreting plasma into a jet emanating along the black hole's axis of rotation. The fact that the observed jet is so straight over a distance of thousands of light-years implies that it must be produced by an engine that maintains a very consistent orientation for a time span of at least thousands of years, as a supermassive black hole is expected to do.
Other observations: The accretion disk
According to [$6$]:
HST [Hubble Space Telescope] imaged a disk of ionized gas, with a radius of $sim$ 50 pc [50 parsecs, roughly 150 light-years] centered on the galactic core... The high resolution of HST allowed the spectrum [which is sensitive to the Doppler effect] of this ionized gas to be measured as a function of position across the gas disk, thereby allowing the kinematics of the disk to be determined... It was found that the velocity profile of the central 20 pc of the gas disk possessed a Keplerian profile (i.e., $v propto r^-1/2$) as expected if the gas was orbiting in the gravitational potential of a point-like mass... The only known and long-lived object to possess such a large mass in a small region of space, and be as under-luminous as observed, is a SMBH [Super-Massive Black Hole].
In other words, these observations showed evidence for gas disk with the velocity profile that would be expected if it were orbiting a supermassive black hole. Note that the measured gas velocities on opposite sides of the central body differ from each other by roughly 1000 kilometers per second.
Other observations: The absense of strong surface emission
According to a report [$7$] published in 2015:
Observations at millimeter wavelengths with the Event Horizon Telescope have localized the emission from the base of this jet [shown above] to angular scales comparable to the putative black hole horizon. The jet might be powered directly by an accretion disk or by electromagnetic extraction of the rotational energy of the black hole. However, even the latter mechanism requires a confining thick accretion disk to maintain the required magnetic flux near the black hole. Therefore, regardless of the jet mechanism, the observed jet power in M87 implies a certain minimum mass accretion rate. If the central compact object in M87 were not a black hole but had a surface, this accretion would result in considerable thermal near-infrared and optical emission from the surface. Current flux limits on the nucleus of M87 strongly constrain any such surface emission. This rules out the presence of a surface and thereby provides indirect evidence for an event horizon.
Regarding why the event horizon of a black hole is expected to be so dim even though the intense fields generate a powerful jet, see these Physics SE posts:
How can Quasars emit anything if they're black holes?
How can cosmic jets exist?
Comparing the EHT images to predictions
Page 5 in the first event horizon telescope paper (L$1$ in [$1$]) says:
The appearance of M87* has been modeled successfully using GRMHD [general-relativistic magnetohydrodynamics] simulations, which describe a turbulent, hot, magnetized disk orbiting a Kerr black hole. They naturally produce a powerful jet and can explain the broadband spectral energy distribution observed in LLAGNs. At a wavelength of 1.3mm, and as observed here, the simulations also predict a shadow and an asymmetric emission ring.
Page 6 says:
...adopting an inclination of $17^circ$ between the approaching jet and the line of sight..., the west orientation of the jet, and a corotating disk model, matter in the bottom part of the image is moving toward the observer (clockwise rotation as seen from Earth). This is consistent with the rotation of the ionized gas on scales of 20 pc [20 parsecs, roughly 60 light-years], i.e., 7000 $r_g$ ["where $r_gequiv GM/c^2$ is the characteristic lengthscale of a black hole"]... and with the inferred sense of rotation from VLBI observations at 7 mm...
These excerpts say that when using black-hole parameters consistent with other observations, general relativity can predict the features of the images observed by the EHT. These features, including the reduced brightness in the center and the asymmetry of the brightness of the ring, with an orientation consistent with the observed jet, are hallmarks of a rapidly spinning black hole. In this sense, the images from the Event Horizon Telescope (EHT) do confirm general relativity.
The comparisons between general relativity's predictions and the observed images are described in detail in the fifth event horizon telescope paper (L$5$ in [$1$]), and some of them have already been reviewed on Physics SE:
- Why isn't the circumferential light around the M87 black hole's event horizon symmetric?
References:
[$1$] https://iopscience.iop.org/issue/2041-8205/875/1, Table of contents of The Astrophysical Journal Letters, volume 875, number 1 (2019 April 10), with six downloadable articles (L$1$ thorugh L$6$)
[$2$] https://www.nasa.gov/feature/goddard/2017/messier-87
[$3$] "Black Hole-Powered Jet of Electrons and Sub-Atomic Particles Streams From Center of Galaxy M87," http://hubblesite.org/image/968/news_release/2000-20
[$4$] "Formation of the radio jet in M87 at 100 Schwarzschild radii from the central black hole," Nature 401, 891-892 (1999), https://www.nature.com/articles/44780
[$5$] "A precise measurement of the magnetic field in the corona of the black hole binary V404 Cygni," Science 358: 1299-1302 (2017), https://science.sciencemag.org/content/358/6368/1299
[$6$] "Fluorescent iron lines as a probe of astrophysical black hole systems," https://arxiv.org/abs/astro-ph/0212065
[$7$] Broderick et al, "The Event Horizon of M87," https://arxiv.org/abs/1503.03873
answered 23 mins ago
Chiral AnomalyChiral Anomaly
13.5k21845
$endgroup$
add a comment |
$begingroup$
Answer: Yes, the images from the Event Horizon Telescope (EHT) are consistent with what general relativity predicts.
To be clear about what this statement means, we need to remember how science works. Theories are inspired by observations, but theories are not deduced from observations. It's the other way around: theories make predictions. If the predictions consistently match what we observe, then we say that the theory works. Of course, contriving a theory that makes one prediction that matches one observation is trivial. Finding a theory that makes many predictions that match many observations is more challenging. General relativity is such a theory, and its agreement with this new observation — the images from the Event Horizon Telescope — is a nice addition to the large portfolio of general relativity's confirmed predictions.
Even though the black hole is enormous, it is so far away that the diameter of the imaged ring spans less than $20$ billionths of a degree ($<20times 10^-9$ degree) in the sky, so pristine resolution cannot be expected; the fact that they were able to resolve it at all is remarkable. Still, the image shows some general features that are consistent with what is expected for a rapidly spinning black hole in general relativity — not just any rapidly spinning black hole, but one whose size, mass, spin, and orientation are all consistent with other observations associated with that same black hole in the core of the galaxy M87.
A few of these observations are reviewed below, followed by comments on how the EHT images compare to predictions from general relativity.
Other observations: The jet
One of the most prominent associated observations is the jet emanating from the galaxy's core, shown here in images from the Hubble Space Telescope [$2$]:
To give a feeling for the scale of this picture, this is what hubblesite.org [$3$] says about the image:
At a distance of 50 million light-years, M87 is too distant for Hubble to discern individual stars. The dozens of star-like points swarming about M87 are, instead, themselves clusters of hundreds of thousands of stars each.
Here's another view of the jet, with scale-bars:
This image (from figure 2 in [$4$]) was made in 1999 using VLBI observations at a wavelength of 7 millimeters. The white dot marked $6r_S$ represents a circle with a diameter of $6$ times the alleged Schwarzschild radius. The scale bar marked "$1$ kpc" represents one kiloparsec, which is roughly 3000 light-years.
According to general relativity, a rapidly spinning black hole with an accretion disk can generate intense magnetic fields (but see [$5$]) that funnel material from the accreting plasma into a jet emanating along the black hole's axis of rotation. The fact that the observed jet is so straight over a distance of thousands of light-years implies that it must be produced by an engine that maintains a very consistent orientation for a time span of at least thousands of years, as a supermassive black hole is expected to do.
Other observations: The accretion disk
According to [$6$]:
HST [Hubble Space Telescope] imaged a disk of ionized gas, with a radius of $sim$ 50 pc [50 parsecs, roughly 150 light-years] centered on the galactic core... The high resolution of HST allowed the spectrum [which is sensitive to the Doppler effect] of this ionized gas to be measured as a function of position across the gas disk, thereby allowing the kinematics of the disk to be determined... It was found that the velocity profile of the central 20 pc of the gas disk possessed a Keplerian profile (i.e., $v propto r^-1/2$) as expected if the gas was orbiting in the gravitational potential of a point-like mass... The only known and long-lived object to possess such a large mass in a small region of space, and be as under-luminous as observed, is a SMBH [Super-Massive Black Hole].
In other words, these observations showed evidence for gas disk with the velocity profile that would be expected if it were orbiting a supermassive black hole. Note that the measured gas velocities on opposite sides of the central body differ from each other by roughly 1000 kilometers per second.
Other observations: The absense of strong surface emission
According to a report [$7$] published in 2015:
Observations at millimeter wavelengths with the Event Horizon Telescope have localized the emission from the base of this jet [shown above] to angular scales comparable to the putative black hole horizon. The jet might be powered directly by an accretion disk or by electromagnetic extraction of the rotational energy of the black hole. However, even the latter mechanism requires a confining thick accretion disk to maintain the required magnetic flux near the black hole. Therefore, regardless of the jet mechanism, the observed jet power in M87 implies a certain minimum mass accretion rate. If the central compact object in M87 were not a black hole but had a surface, this accretion would result in considerable thermal near-infrared and optical emission from the surface. Current flux limits on the nucleus of M87 strongly constrain any such surface emission. This rules out the presence of a surface and thereby provides indirect evidence for an event horizon.
Regarding why the event horizon of a black hole is expected to be so dim even though the intense fields generate a powerful jet, see these Physics SE posts:
How can Quasars emit anything if they're black holes?
How can cosmic jets exist?
Comparing the EHT images to predictions
Page 5 in the first event horizon telescope paper (L$1$ in [$1$]) says:
The appearance of M87* has been modeled successfully using GRMHD [general-relativistic magnetohydrodynamics] simulations, which describe a turbulent, hot, magnetized disk orbiting a Kerr black hole. They naturally produce a powerful jet and can explain the broadband spectral energy distribution observed in LLAGNs. At a wavelength of 1.3mm, and as observed here, the simulations also predict a shadow and an asymmetric emission ring.
Page 6 says:
...adopting an inclination of $17^circ$ between the approaching jet and the line of sight..., the west orientation of the jet, and a corotating disk model, matter in the bottom part of the image is moving toward the observer (clockwise rotation as seen from Earth). This is consistent with the rotation of the ionized gas on scales of 20 pc [20 parsecs, roughly 60 light-years], i.e., 7000 $r_g$ ["where $r_gequiv GM/c^2$ is the characteristic lengthscale of a black hole"]... and with the inferred sense of rotation from VLBI observations at 7 mm...
These excerpts say that when using black-hole parameters consistent with other observations, general relativity can predict the features of the images observed by the EHT. These features, including the reduced brightness in the center and the asymmetry of the brightness of the ring, with an orientation consistent with the observed jet, are hallmarks of a rapidly spinning black hole. In this sense, the images from the Event Horizon Telescope (EHT) do confirm general relativity.
The comparisons between general relativity's predictions and the observed images are described in detail in the fifth event horizon telescope paper (L$5$ in [$1$]), and some of them have already been reviewed on Physics SE:
- Why isn't the circumferential light around the M87 black hole's event horizon symmetric?
References:
[$1$] https://iopscience.iop.org/issue/2041-8205/875/1, Table of contents of The Astrophysical Journal Letters, volume 875, number 1 (2019 April 10), with six downloadable articles (L$1$ thorugh L$6$)
[$2$] https://www.nasa.gov/feature/goddard/2017/messier-87
[$3$] "Black Hole-Powered Jet of Electrons and Sub-Atomic Particles Streams From Center of Galaxy M87," http://hubblesite.org/image/968/news_release/2000-20
[$4$] "Formation of the radio jet in M87 at 100 Schwarzschild radii from the central black hole," Nature 401, 891-892 (1999), https://www.nature.com/articles/44780
[$5$] "A precise measurement of the magnetic field in the corona of the black hole binary V404 Cygni," Science 358: 1299-1302 (2017), https://science.sciencemag.org/content/358/6368/1299
[$6$] "Fluorescent iron lines as a probe of astrophysical black hole systems," https://arxiv.org/abs/astro-ph/0212065
[$7$] Broderick et al, "The Event Horizon of M87," https://arxiv.org/abs/1503.03873
answered 23 mins ago
Chiral AnomalyChiral Anomaly
13.5k21845
$endgroup$
add a comment |
$begingroup$
Answer: Yes, the images from the Event Horizon Telescope (EHT) are consistent with what general relativity predicts.
To be clear about what this statement means, we need to remember how science works. Theories are inspired by observations, but theories are not deduced from observations. It's the other way around: theories make predictions. If the predictions consistently match what we observe, then we say that the theory works. Of course, contriving a theory that makes one prediction that matches one observation is trivial. Finding a theory that makes many predictions that match many observations is more challenging. General relativity is such a theory, and its agreement with this new observation — the images from the Event Horizon Telescope — is a nice addition to the large portfolio of general relativity's confirmed predictions.
Even though the black hole is enormous, it is so far away that the diameter of the imaged ring spans less than $20$ billionths of a degree ($<20times 10^-9$ degree) in the sky, so pristine resolution cannot be expected; the fact that they were able to resolve it at all is remarkable. Still, the image shows some general features that are consistent with what is expected for a rapidly spinning black hole in general relativity — not just any rapidly spinning black hole, but one whose size, mass, spin, and orientation are all consistent with other observations associated with that same black hole in the core of the galaxy M87.
A few of these observations are reviewed below, followed by comments on how the EHT images compare to predictions from general relativity.
Other observations: The jet
One of the most prominent associated observations is the jet emanating from the galaxy's core, shown here in images from the Hubble Space Telescope [$2$]:
To give a feeling for the scale of this picture, this is what hubblesite.org [$3$] says about the image:
At a distance of 50 million light-years, M87 is too distant for Hubble to discern individual stars. The dozens of star-like points swarming about M87 are, instead, themselves clusters of hundreds of thousands of stars each.
Here's another view of the jet, with scale-bars:
This image (from figure 2 in [$4$]) was made in 1999 using VLBI observations at a wavelength of 7 millimeters. The white dot marked $6r_S$ represents a circle with a diameter of $6$ times the alleged Schwarzschild radius. The scale bar marked "$1$ kpc" represents one kiloparsec, which is roughly 3000 light-years.
According to general relativity, a rapidly spinning black hole with an accretion disk can generate intense magnetic fields (but see [$5$]) that funnel material from the accreting plasma into a jet emanating along the black hole's axis of rotation. The fact that the observed jet is so straight over a distance of thousands of light-years implies that it must be produced by an engine that maintains a very consistent orientation for a time span of at least thousands of years, as a supermassive black hole is expected to do.
Other observations: The accretion disk
According to [$6$]:
HST [Hubble Space Telescope] imaged a disk of ionized gas, with a radius of $sim$ 50 pc [50 parsecs, roughly 150 light-years] centered on the galactic core... The high resolution of HST allowed the spectrum [which is sensitive to the Doppler effect] of this ionized gas to be measured as a function of position across the gas disk, thereby allowing the kinematics of the disk to be determined... It was found that the velocity profile of the central 20 pc of the gas disk possessed a Keplerian profile (i.e., $v propto r^-1/2$) as expected if the gas was orbiting in the gravitational potential of a point-like mass... The only known and long-lived object to possess such a large mass in a small region of space, and be as under-luminous as observed, is a SMBH [Super-Massive Black Hole].
In other words, these observations showed evidence for gas disk with the velocity profile that would be expected if it were orbiting a supermassive black hole. Note that the measured gas velocities on opposite sides of the central body differ from each other by roughly 1000 kilometers per second.
Other observations: The absense of strong surface emission
According to a report [$7$] published in 2015:
Observations at millimeter wavelengths with the Event Horizon Telescope have localized the emission from the base of this jet [shown above] to angular scales comparable to the putative black hole horizon. The jet might be powered directly by an accretion disk or by electromagnetic extraction of the rotational energy of the black hole. However, even the latter mechanism requires a confining thick accretion disk to maintain the required magnetic flux near the black hole. Therefore, regardless of the jet mechanism, the observed jet power in M87 implies a certain minimum mass accretion rate. If the central compact object in M87 were not a black hole but had a surface, this accretion would result in considerable thermal near-infrared and optical emission from the surface. Current flux limits on the nucleus of M87 strongly constrain any such surface emission. This rules out the presence of a surface and thereby provides indirect evidence for an event horizon.
Regarding why the event horizon of a black hole is expected to be so dim even though the intense fields generate a powerful jet, see these Physics SE posts:
How can Quasars emit anything if they're black holes?
How can cosmic jets exist?
Comparing the EHT images to predictions
Page 5 in the first event horizon telescope paper (L$1$ in [$1$]) says:
The appearance of M87* has been modeled successfully using GRMHD [general-relativistic magnetohydrodynamics] simulations, which describe a turbulent, hot, magnetized disk orbiting a Kerr black hole. They naturally produce a powerful jet and can explain the broadband spectral energy distribution observed in LLAGNs. At a wavelength of 1.3mm, and as observed here, the simulations also predict a shadow and an asymmetric emission ring.
Page 6 says:
...adopting an inclination of $17^circ$ between the approaching jet and the line of sight..., the west orientation of the jet, and a corotating disk model, matter in the bottom part of the image is moving toward the observer (clockwise rotation as seen from Earth). This is consistent with the rotation of the ionized gas on scales of 20 pc [20 parsecs, roughly 60 light-years], i.e., 7000 $r_g$ ["where $r_gequiv GM/c^2$ is the characteristic lengthscale of a black hole"]... and with the inferred sense of rotation from VLBI observations at 7 mm...
These excerpts say that when using black-hole parameters consistent with other observations, general relativity can predict the features of the images observed by the EHT. These features, including the reduced brightness in the center and the asymmetry of the brightness of the ring, with an orientation consistent with the observed jet, are hallmarks of a rapidly spinning black hole. In this sense, the images from the Event Horizon Telescope (EHT) do confirm general relativity.
The comparisons between general relativity's predictions and the observed images are described in detail in the fifth event horizon telescope paper (L$5$ in [$1$]), and some of them have already been reviewed on Physics SE:
- Why isn't the circumferential light around the M87 black hole's event horizon symmetric?
References:
[$1$] https://iopscience.iop.org/issue/2041-8205/875/1, Table of contents of The Astrophysical Journal Letters, volume 875, number 1 (2019 April 10), with six downloadable articles (L$1$ thorugh L$6$)
[$2$] https://www.nasa.gov/feature/goddard/2017/messier-87
[$3$] "Black Hole-Powered Jet of Electrons and Sub-Atomic Particles Streams From Center of Galaxy M87," http://hubblesite.org/image/968/news_release/2000-20
[$4$] "Formation of the radio jet in M87 at 100 Schwarzschild radii from the central black hole," Nature 401, 891-892 (1999), https://www.nature.com/articles/44780
[$5$] "A precise measurement of the magnetic field in the corona of the black hole binary V404 Cygni," Science 358: 1299-1302 (2017), https://science.sciencemag.org/content/358/6368/1299
[$6$] "Fluorescent iron lines as a probe of astrophysical black hole systems," https://arxiv.org/abs/astro-ph/0212065
[$7$] Broderick et al, "The Event Horizon of M87," https://arxiv.org/abs/1503.03873
answered 23 mins ago
Chiral AnomalyChiral Anomaly
13.5k21845
$endgroup$
Answer: Yes, the images from the Event Horizon Telescope (EHT) are consistent with what general relativity predicts.
To be clear about what this statement means, we need to remember how science works. Theories are inspired by observations, but theories are not deduced from observations. It's the other way around: theories make predictions. If the predictions consistently match what we observe, then we say that the theory works. Of course, contriving a theory that makes one prediction that matches one observation is trivial. Finding a theory that makes many predictions that match many observations is more challenging. General relativity is such a theory, and its agreement with this new observation — the images from the Event Horizon Telescope — is a nice addition to the large portfolio of general relativity's confirmed predictions.
Even though the black hole is enormous, it is so far away that the diameter of the imaged ring spans less than $20$ billionths of a degree ($<20times 10^-9$ degree) in the sky, so pristine resolution cannot be expected; the fact that they were able to resolve it at all is remarkable. Still, the image shows some general features that are consistent with what is expected for a rapidly spinning black hole in general relativity — not just any rapidly spinning black hole, but one whose size, mass, spin, and orientation are all consistent with other observations associated with that same black hole in the core of the galaxy M87.
A few of these observations are reviewed below, followed by comments on how the EHT images compare to predictions from general relativity.
Other observations: The jet
One of the most prominent associated observations is the jet emanating from the galaxy's core, shown here in images from the Hubble Space Telescope [$2$]:
To give a feeling for the scale of this picture, this is what hubblesite.org [$3$] says about the image:
At a distance of 50 million light-years, M87 is too distant for Hubble to discern individual stars. The dozens of star-like points swarming about M87 are, instead, themselves clusters of hundreds of thousands of stars each.
Here's another view of the jet, with scale-bars:
This image (from figure 2 in [$4$]) was made in 1999 using VLBI observations at a wavelength of 7 millimeters. The white dot marked $6r_S$ represents a circle with a diameter of $6$ times the alleged Schwarzschild radius. The scale bar marked "$1$ kpc" represents one kiloparsec, which is roughly 3000 light-years.
According to general relativity, a rapidly spinning black hole with an accretion disk can generate intense magnetic fields (but see [$5$]) that funnel material from the accreting plasma into a jet emanating along the black hole's axis of rotation. The fact that the observed jet is so straight over a distance of thousands of light-years implies that it must be produced by an engine that maintains a very consistent orientation for a time span of at least thousands of years, as a supermassive black hole is expected to do.
Other observations: The accretion disk
According to [$6$]:
HST [Hubble Space Telescope] imaged a disk of ionized gas, with a radius of $sim$ 50 pc [50 parsecs, roughly 150 light-years] centered on the galactic core... The high resolution of HST allowed the spectrum [which is sensitive to the Doppler effect] of this ionized gas to be measured as a function of position across the gas disk, thereby allowing the kinematics of the disk to be determined... It was found that the velocity profile of the central 20 pc of the gas disk possessed a Keplerian profile (i.e., $v propto r^-1/2$) as expected if the gas was orbiting in the gravitational potential of a point-like mass... The only known and long-lived object to possess such a large mass in a small region of space, and be as under-luminous as observed, is a SMBH [Super-Massive Black Hole].
In other words, these observations showed evidence for gas disk with the velocity profile that would be expected if it were orbiting a supermassive black hole. Note that the measured gas velocities on opposite sides of the central body differ from each other by roughly 1000 kilometers per second.
Other observations: The absense of strong surface emission
According to a report [$7$] published in 2015:
Observations at millimeter wavelengths with the Event Horizon Telescope have localized the emission from the base of this jet [shown above] to angular scales comparable to the putative black hole horizon. The jet might be powered directly by an accretion disk or by electromagnetic extraction of the rotational energy of the black hole. However, even the latter mechanism requires a confining thick accretion disk to maintain the required magnetic flux near the black hole. Therefore, regardless of the jet mechanism, the observed jet power in M87 implies a certain minimum mass accretion rate. If the central compact object in M87 were not a black hole but had a surface, this accretion would result in considerable thermal near-infrared and optical emission from the surface. Current flux limits on the nucleus of M87 strongly constrain any such surface emission. This rules out the presence of a surface and thereby provides indirect evidence for an event horizon.
Regarding why the event horizon of a black hole is expected to be so dim even though the intense fields generate a powerful jet, see these Physics SE posts:
How can Quasars emit anything if they're black holes?
How can cosmic jets exist?
Comparing the EHT images to predictions
Page 5 in the first event horizon telescope paper (L$1$ in [$1$]) says:
The appearance of M87* has been modeled successfully using GRMHD [general-relativistic magnetohydrodynamics] simulations, which describe a turbulent, hot, magnetized disk orbiting a Kerr black hole. They naturally produce a powerful jet and can explain the broadband spectral energy distribution observed in LLAGNs. At a wavelength of 1.3mm, and as observed here, the simulations also predict a shadow and an asymmetric emission ring.
Page 6 says:
...adopting an inclination of $17^circ$ between the approaching jet and the line of sight..., the west orientation of the jet, and a corotating disk model, matter in the bottom part of the image is moving toward the observer (clockwise rotation as seen from Earth). This is consistent with the rotation of the ionized gas on scales of 20 pc [20 parsecs, roughly 60 light-years], i.e., 7000 $r_g$ ["where $r_gequiv GM/c^2$ is the characteristic lengthscale of a black hole"]... and with the inferred sense of rotation from VLBI observations at 7 mm...
These excerpts say that when using black-hole parameters consistent with other observations, general relativity can predict the features of the images observed by the EHT. These features, including the reduced brightness in the center and the asymmetry of the brightness of the ring, with an orientation consistent with the observed jet, are hallmarks of a rapidly spinning black hole. In this sense, the images from the Event Horizon Telescope (EHT) do confirm general relativity.
The comparisons between general relativity's predictions and the observed images are described in detail in the fifth event horizon telescope paper (L$5$ in [$1$]), and some of them have already been reviewed on Physics SE:
- Why isn't the circumferential light around the M87 black hole's event horizon symmetric?
References:
[$1$] https://iopscience.iop.org/issue/2041-8205/875/1, Table of contents of The Astrophysical Journal Letters, volume 875, number 1 (2019 April 10), with six downloadable articles (L$1$ thorugh L$6$)
[$2$] https://www.nasa.gov/feature/goddard/2017/messier-87
[$3$] "Black Hole-Powered Jet of Electrons and Sub-Atomic Particles Streams From Center of Galaxy M87," http://hubblesite.org/image/968/news_release/2000-20
[$4$] "Formation of the radio jet in M87 at 100 Schwarzschild radii from the central black hole," Nature 401, 891-892 (1999), https://www.nature.com/articles/44780
[$5$] "A precise measurement of the magnetic field in the corona of the black hole binary V404 Cygni," Science 358: 1299-1302 (2017), https://science.sciencemag.org/content/358/6368/1299
[$6$] "Fluorescent iron lines as a probe of astrophysical black hole systems," https://arxiv.org/abs/astro-ph/0212065
[$7$] Broderick et al, "The Event Horizon of M87," https://arxiv.org/abs/1503.03873
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$begingroup$
Read the science explained at the official website; it should answer your questions: eventhorizontelescope.org/science. News is not the best place to go to for science.
$endgroup$
– Avantgarde
2 hours ago
1
$begingroup$
Re, "...just by looking at the image." You can't learn much just by looking at that image. But if you use the theory to predict what the picture should look like, and then you take the picture and it agrees with your prediction, then that ought to boost your confidence in the theory.
$endgroup$
– Solomon Slow
1 hour ago