<p>There are roughly three methods to &quot;discover&quot; black holes:</p>
<ol>
<li>Find the x-ray signature of their accretion disk.</li>
<li>Discover the gravitational wave signature of black hole mergers.</li>
<li>Be clever and find something new, such as the radial velocity measurements that discovered the &quot;unicorn&quot;.</li>
</ol>
<p>The processing of gravitational waves is almost entirely automatic.  The measurements of stress that are made by Ligo and Virgo are automatically processed to look for evidence of a &quot;chirp&quot;, and candidates are automatically flagged for further investigation. GW discoveries currently don't exactly locate the black hole, but does discover their existence and give information on mass and distance.</p>
<p>X-ray sources are automatically located by X-ray nova searches, with space telescopes. The telescope scans a region of the sky, looking for changes, and flags possible sources for further investigation. The hard work is in showing that a particular X-ray source is a black hole and not a neutron star or something else. This tends to involve gathering a combination of evidence rather than a single &quot;discovery&quot;.</p>
<p>Other methods, such as the radial velocity can also be processed automatically (by automatic systems looking for exoplanets).  These can discover candidates, but gathering the evidence that the signal is due to a black hole is a human task.</p>
<p>Many &quot;black holes&quot; are in reality &quot;black hole candidates&quot;. There is evidence of something, and that is consistent with a black hole, and so rather than a &quot;discovery&quot;, there is a process whereby other hypotheses are eliminated by further observations, until only the black hole hypothesis remains.</p>

CC BY-SA 4.0
2021-08-25T12:47:25.510Z
Thank you very much! This answer my question. Would you suggest any source to explore those techniques more in depth?
nicolopinci
CC BY-SA 4.0
2021-08-25T13:44:56.433Z
IMHO, I would not call the method of gravitational waves capturing (in this case particular those which signal's match Einstein's mass predictions towards black hole(s) being the source of such gravitational waves) be termed as "discovery" (in the astronomical sense of this word) since this method doesn't has the capability to figure out the location of such black holes and their distance to the Earth.
Alex
CC BY-SA 4.0
2021-08-25T14:38:19.210Z
@Alex You are mistaken. Look at any LIGO/Virgo paper about reported compact coalescing events and you'll see they measure the distance to the source from Earth and they constrain the region on the Earth's sky to locate the direction the signal came from.
Daddy Kropotkin
CC BY-SA 4.0
2021-08-25T14:57:45.617Z
@Daddy Kropotkin This distance estimation and constraint of the region with regards to black hole location are too vague to call this to be an "astronomical discovery".  Besides, this method is not based on a direct astronomical observation but rather on the indirect inference from the Einstein's theory.
Alex
CC BY-SA 4.0
2021-08-26T00:09:06.827Z
This doesn’t cover various methods used to measure supermassive black holes, which is what the OP’s reference to “one of Andrea Ghez’s talks” is about.
Peter Erwin
CC BY-SA 4.0
2021-08-26T14:31:26.693Z
@Alex  The discovery of the gravitational wave signal is at 5$\sigma$, but the source of the signal is inferred. But that is no different than how it works in electromagnetic astronomy, where luminosity, radial velocity, spectroscopy etc... of an object are measured and the object's type, mass, spin, etc... are inferred with models of stellar and galactic evolution which are far more theoretically uncertain than is pure general relativity. https://physics.stackexchange.com/questions/238782/meaning-of-5-1-sigma-significance-with-regards-to-gw150914
Daddy Kropotkin
CC BY-SA 4.0
2021-08-26T15:01:45.487Z
@Daddy Kropotkin Quoting from your last comment (capitalizing is mine): "...luminosity, radial velocity, spectroscopy etc... of an OBJECT are MEASURED..."         
                                                   In above case there exists already DISCOVERED ASTRONOMICAL OBJECT with some of it parameters being directly measured.  My point is: one can't call the astronomical object, which existance is based only on inference as being DISCOVERED.
Alex
CC BY-SA 4.0
2021-08-26T23:21:08.660Z
@Alex You're making a semantic argument that has no physical content. Is a dark matter halo not an astronomical object?
Daddy Kropotkin
CC BY-SA 4.0
2021-08-27T01:50:43.847Z
@Daddy Kropotkin One might say that "dark matter" as well as "dark energy" at this point of knowledge are just  two hypothetical concepts introduced to make the theories be in agreement with otherwise unexplainable observational facts...
Alex
CC BY-SA 4.0
2021-08-27T09:53:54.167Z
Ok, this has gone on long enough and has drifted far from the answer.  I've changed "located" to ""discovered"".  A GW observation discovers the existence, mass and distance of a black hole, but not its location.
James K
CC BY-SA 4.0
2021-08-27T11:41:16.207Z
GW observation allows to "INFER" (NOT "discover") the existence, mass and distance of a black hole.
Alex
CC BY-SA 4.0
2021-08-27T11:52:38.117Z
see https://astronomy.stackexchange.com/questions/14019/discovery-in-astronomy-vs-one-in-physics-do-they-differ-in-required-burden-of
James K
CC BY-SA 4.0
2021-08-27T12:47:51.937Z
Thank you for this discussion, I am learning something new. @DaddyKropotkin has made a good point I think, since it looks like those methods are not valid for any black hole, so I will clarify this in the question.
nicolopinci
CC BY-SA 4.0
2021-08-27T13:00:06.513Z
@nicolopinci (I was motivated by Peter Erwin's comment above)
Daddy Kropotkin
CC BY-SA 4.0
2021-09-03T11:58:30.233Z
http://www.sci-news.com/astronomy/chandra-gravitationally-lensed-dual-active-galactic-nucleus-10023.html
Alex
CC BY-SA 4.0
2021-09-08T14:52:05.327Z
https://spaceaustralia.com/news/new-gravitational-wave-detector-records-rare-events
Alex
CC BY-SA 4.0
2022-02-02T15:43:34.073Z
@Peter Erwin Will be the gravitational wave caused by below described event detected?https://www.science.org/content/article/crash-titans-imminent-merger-giant-black-holes-predicted
Alex
CC BY-SA 4.0
2022-02-02T16:14:56.817Z
@Alex “The only certain signal is gravitational waves, but the ponderous colliding masses would emit them at too low a frequency to be picked up by detectors such as the Laser Interferometer Gravitational-Wave Observatory, which is tuned to smaller mergers.”
Peter Erwin
CC BY-SA 4.0
2022-02-02T19:54:33.577Z
@Peter Erwin The article thow suggests that PTA might detect the gravitational memory signal related to projected event - do you agree with that?
Alex
CC BY-SA 4.0
2022-02-16T15:03:02.440Z
@Peter Erwin                                      
 Now, with the help of NASA's Hubble Space Telescope, scientists have discovered an isolated stellar-mass black hole about 5,150 light-years away from Earth, in the direction of the bulge in the center of the Milky Way.

"We now know that isolated black holes exist," Sahu said. "And they have masses similar to the black holes found in binaries. And there must be lots of them out there."
Alex
CC BY-SA 4.0
2022-02-16T17:03:30.100Z
@alex: that would come under method 3 "Be clever"
James K
CC BY-SA 4.0
2022-06-27T13:25:09.407Z
Neutron stars, the extremely dense cores of massive dead stars, spiraling toward each other or into a black hole can raise tidal waves in the oceans of heavy charged particles surrounding the neutron stars. Those tidal waves reveal themselves through regular flashes of electromagnetic radiation, which can serve as an early warning system for impending mergers, the researchers found. 
Such electromagnetic flares could become very early warning signs of NSBH (∼ 1 yr before merger) and BNS (∼ 10 yr before merger) mergers and tools to study neutron star oceans. 
arxiv.org/abs/2205.13541
Alex
CC BY-SA 4.0
2021-08-25T12:44:15.363Z
2021-08-27T09:54:32.437Z
2021-08-27T09:54:32.437Z
James K
<p>Black holes have been discovered using several techniques, as outlined by <a href="https://astronomy.stackexchange.com/questions/24/how-are-black-holes-found">How are black holes found?</a>. Are there automatic methods for locating them (e.g., artificial intelligence or image analysis techniques), or does the discovery still rely on actual people analyzing, e.g., the movement of stars in a certain portion of the space?</p>

CC BY-SA 4.0
2021-08-25T12:15:15.073Z
I would be specifically interested to find out whether the process of black holes discovery in the Milky Way (and perhaps in neighboring Milky Way galaxies) via optical lensing could be automated...
Alex
CC BY-SA 4.0
2021-08-25T12:42:36.097Z
@Alex I think this is also interesting. My idea was to analyze image series taken at different times and to say, only based on the evolution showed there, if there is a black hole or not, for example because there are bodies orbiting around something that is invisible in the pictures at certain speeds and so on, but without necessarily writing full detailed equations that describe the motion laws hypothesized in case there is a black hole.
nicolopinci
CC BY-SA 4.0
2021-08-26T14:33:41.640Z
Hi, you might want to un-accept the answer below, since you were asking about supermassive black holes, but the answer below is discussing methods for detecting stellar mass black holes, which are not necessarily the same methods.
Daddy Kropotkin
CC BY-SA 4.0
2021-08-27T11:23:16.613Z
@DaddyKropotkin my question was quite generic in fact, and since I am not a physicist, it looked complete to me. But what you are saying is that it does not cover all the possible types of black holes, am I right? So, for some black holes (the supermassive ones) there are still no automatic methods? Or they exist but they are just different?
nicolopinci
CC BY-SA 4.0
2021-08-27T12:38:32.873Z
INdeed, methods for supermassive black holes exist and they are generally different, but with some overlap. Editing your question to make this clear might help to attract a more accurate answer. Your current question references Andrea Ghez, who works on supermassive black holes, but the answer you accepted is about general methods for detecting stellar mass black holes. The methods can be different generally because stellar mass and supermassive black holes tend to exist in different astrophysical circumstances/environments
Daddy Kropotkin
CC BY-SA 4.0
2021-08-30T14:32:32.387Z
FYI - These 3 merging galaxies  (see below link), which were observed and it was confirmed that each of them have the central massive black hole, are currently in the initial stage of merging. They can produce detectable gravitational waves when their black holes come closer and start orbiting each other 
 https://www.aanda.org/articles/aa/full_html/2021/07/aa41210-21/aa41210-21.html
Alex
CC BY-SA 4.0
2021-08-31T00:05:11.537Z
This (the link below) article mentions the possibility of using in the future (instead or in addition of interferometers) the instrumentation based on measuring effects of interaction between gravitational waves and electromagnetic field. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5390036/
Alex
CC BY-SA 4.0
2021-09-08T14:32:13.290Z
The bulk acoustic wave (BAW) resonator experiment uses a high-frequency gravitational wave detector that is based on the principles of the resonant mass detector. 
In the first 153 days of BAW two events were detected that could, in principle, be high-frequency gravitational waves. 
One possible explanation for the signals is that they were created by primordial black holes. Merging low mass primordial black holes would not be able to be detected by LIGO or Virgo.
Another explanation is that the signals were caused by high-mass dark matter candidate particles.
Alex
CC BY-SA 4.0
2022-06-11T18:04:06.260Z
NASA has announced that it has isolated the mass and location of what could be a “wandering” black hole using the Hubble Space Telescope. This is the first time in the space agency’s history it has been able to achieve this, despite there being over 100 million black holes populating our galaxy. 
 https://petapixel.com/2022/06/10/hubble-records-mass-and-location-of-a-black-hole-for-the-first-time-ever/                         https://www.nasa.gov/feature/goddard/2022/hubble-determines-mass-of-isolated-black-hole-roaming-our-milky-way-galaxy
Alex
CC BY-SA 4.0
2022-06-16T15:57:19.767Z
https://www.sciencealert.com/for-the-first-time-a-lone-black-hole-has-been-found-wandering-the-milky-way  https://www.sciencealert.com/we-really-may-have-found-a-rogue-dark-black-hole-wandering-the-milky-way
Alex
<black-hole><orbit><image-processing>
Are there automatic methods to locate (stellar and supermassive) black holes?
nicolopinci
# Are there automatic methods to locate (stellar and supermassive) black holes?

(Asked by: username_0 on 2021-08-24)

Black holes have been discovered using several techniques, as outlined by [How are black holes found?](https://astronomy.stackexchange.com/questions/24/how-are-black-holes-found). Are there automatic methods for locating them (e.g., artificial intelligence or image analysis techniques), or does the discovery still rely on actual people analyzing, e.g., the movement of stars in a certain portion of the space?

**Tags:** black-hole, orbit, image-processing
> **Comments:**
> **username_1**: I would be specifically interested to find out whether the process of black holes discovery in the Milky Way (and perhaps in neighboring Milky Way galaxies) via optical lensing could be automated...  
> **username_0**: @Alex I think this is also interesting. My idea was to analyze image series taken at different times and to say, only based on the evolution showed there, if there is a black hole or not, for example because there are bodies orbiting around something that is invisible in the pictures at certain speeds and so on, but without necessarily writing full detailed equations that describe the motion laws hypothesized in case there is a black hole.  
> **username_2**: Hi, you might want to un-accept the answer below, since you were asking about supermassive black holes, but the answer below is discussing methods for detecting stellar mass black holes, which are not necessarily the same methods.  
> **username_0**: @DaddyKropotkin my question was quite generic in fact, and since I am not a physicist, it looked complete to me. But what you are saying is that it does not cover all the possible types of black holes, am I right? So, for some black holes (the supermassive ones) there are still no automatic methods? Or they exist but they are just different?  
> **username_2**: INdeed, methods for supermassive black holes exist and they are generally different, but with some overlap. Editing your question to make this clear might help to attract a more accurate answer. Your current question references Andrea Ghez, who works on supermassive black holes, but the answer you accepted is about general methods for detecting stellar mass black holes. The methods can be different generally because stellar mass and supermassive black holes tend to exist in different astrophysical circumstances/environments  
> **username_1**: FYI - These 3 merging galaxies  (see below link), which were observed and it was confirmed that each of them have the central massive black hole, are currently in the initial stage of merging. They can produce detectable gravitational waves when their black holes come closer and start orbiting each other   https://www.aanda.org/articles/aa/full_html/2021/07/aa41210-21/aa41210-21.html  
> **username_1**: This (the link below) article mentions the possibility of using in the future (instead or in addition of interferometers) the instrumentation based on measuring effects of interaction between gravitational waves and electromagnetic field. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5390036/  
> **username_1**: The bulk acoustic wave (BAW) resonator experiment uses a high-frequency gravitational wave detector that is based on the principles of the resonant mass detector.  In the first 153 days of BAW two events were detected that could, in principle, be high-frequency gravitational waves.  One possible explanation for the signals is that they were created by primordial black holes. Merging low mass primordial black holes would not be able to be detected by LIGO or Virgo. Another explanation is that the signals were caused by high-mass dark matter candidate particles.  
> **username_1**: NASA has announced that it has isolated the mass and location of what could be a “wandering” black hole using the Hubble Space Telescope. This is the first time in the space agency’s history it has been able to achieve this, despite there being over 100 million black holes populating our galaxy.   https://petapixel.com/2022/06/10/hubble-records-mass-and-location-of-a-black-hole-for-the-first-time-ever/                         https://www.nasa.gov/feature/goddard/2022/hubble-determines-mass-of-isolated-black-hole-roaming-our-milky-way-galaxy  
> **username_1**: https://www.sciencealert.com/for-the-first-time-a-lone-black-hole-has-been-found-wandering-the-milky-way  https://www.sciencealert.com/we-really-may-have-found-a-rogue-dark-black-hole-wandering-the-milky-way  

---

## 1 answers

### Answer by username_3 on 2021-08-25. Score: 2

There are roughly three methods to "discover" black holes:

1. Find the x-ray signature of their accretion disk.
2. Discover the gravitational wave signature of black hole mergers.
3. Be clever and find something new, such as the radial velocity measurements that discovered the "unicorn".

The processing of gravitational waves is almost entirely automatic. The measurements of stress that are made by Ligo and Virgo are automatically processed to look for evidence of a "chirp", and candidates are automatically flagged for further investigation. GW discoveries currently don't exactly locate the black hole, but does discover their existence and give information on mass and distance.

X-ray sources are automatically located by X-ray nova searches, with space telescopes. The telescope scans a region of the sky, looking for changes, and flags possible sources for further investigation. The hard work is in showing that a particular X-ray source is a black hole and not a neutron star or something else. This tends to involve gathering a combination of evidence rather than a single "discovery".

Other methods, such as the radial velocity can also be processed automatically (by automatic systems looking for exoplanets). These can discover candidates, but gathering the evidence that the signal is due to a black hole is a human task.

Many "black holes" are in reality "black hole candidates". There is evidence of something, and that is consistent with a black hole, and so rather than a "discovery", there is a process whereby other hypotheses are eliminated by further observations, until only the black hole hypothesis remains.

> **Comments:**
> **username_0**: Thank you very much! This answer my question. Would you suggest any source to explore those techniques more in depth?  
> **username_1**: IMHO, I would not call the method of gravitational waves capturing (in this case particular those which signal's match Einstein's mass predictions towards black hole(s) being the source of such gravitational waves) be termed as "discovery" (in the astronomical sense of this word) since this method doesn't has the capability to figure out the location of such black holes and their distance to the Earth.  
> **username_2**: @Alex You are mistaken. Look at any LIGO/Virgo paper about reported compact coalescing events and you'll see they measure the distance to the source from Earth and they constrain the region on the Earth's sky to locate the direction the signal came from.  
> **username_1**: @Daddy Kropotkin This distance estimation and constraint of the region with regards to black hole location are too vague to call this to be an "astronomical discovery".  Besides, this method is not based on a direct astronomical observation but rather on the indirect inference from the Einstein's theory.  
> **username_4**: This doesn’t cover various methods used to measure supermassive black holes, which is what the OP’s reference to “one of Andrea Ghez’s talks” is about.  
> **username_2**: @Alex  The discovery of the gravitational wave signal is at 5$\sigma$, but the source of the signal is inferred. But that is no different than how it works in electromagnetic astronomy, where luminosity, radial velocity, spectroscopy etc... of an object are measured and the object's type, mass, spin, etc... are inferred with models of stellar and galactic evolution which are far more theoretically uncertain than is pure general relativity. https://physics.stackexchange.com/questions/238782/meaning-of-5-1-sigma-significance-with-regards-to-gw150914  
> **username_1**: @Daddy Kropotkin Quoting from your last comment (capitalizing is mine): "...luminosity, radial velocity, spectroscopy etc... of an OBJECT are MEASURED..."                                                             In above case there exists already DISCOVERED ASTRONOMICAL OBJECT with some of it parameters being directly measured.  My point is: one can't call the astronomical object, which existance is based only on inference as being DISCOVERED.  
> **username_2**: @Alex You're making a semantic argument that has no physical content. Is a dark matter halo not an astronomical object?  
> **username_1**: @Daddy Kropotkin One might say that "dark matter" as well as "dark energy" at this point of knowledge are just  two hypothetical concepts introduced to make the theories be in agreement with otherwise unexplainable observational facts...  
> **username_3**: Ok, this has gone on long enough and has drifted far from the answer.  I've changed "located" to ""discovered"".  A GW observation discovers the existence, mass and distance of a black hole, but not its location.  
> **username_1**: GW observation allows to "INFER" (NOT "discover") the existence, mass and distance of a black hole.  
> **username_3**: see https://astronomy.stackexchange.com/questions/14019/discovery-in-astronomy-vs-one-in-physics-do-they-differ-in-required-burden-of  
> **username_0**: Thank you for this discussion, I am learning something new. @DaddyKropotkin has made a good point I think, since it looks like those methods are not valid for any black hole, so I will clarify this in the question.  
> **username_2**: @nicolopinci (I was motivated by Peter Erwin's comment above)  
> **username_1**: http://www.sci-news.com/astronomy/chandra-gravitationally-lensed-dual-active-galactic-nucleus-10023.html  
> **username_1**: https://spaceaustralia.com/news/new-gravitational-wave-detector-records-rare-events  
> **username_1**: @Peter Erwin Will be the gravitational wave caused by below described event detected?https://www.science.org/content/article/crash-titans-imminent-merger-giant-black-holes-predicted  
> **username_4**: @Alex “The only certain signal is gravitational waves, but the ponderous colliding masses would emit them at too low a frequency to be picked up by detectors such as the Laser Interferometer Gravitational-Wave Observatory, which is tuned to smaller mergers.”  
> **username_1**: @Peter Erwin The article thow suggests that PTA might detect the gravitational memory signal related to projected event - do you agree with that?  
> **username_1**: @Peter Erwin                                        Now, with the help of NASA's Hubble Space Telescope, scientists have discovered an isolated stellar-mass black hole about 5,150 light-years away from Earth, in the direction of the bulge in the center of the Milky Way.  "We now know that isolated black holes exist," Sahu said. "And they have masses similar to the black holes found in binaries. And there must be lots of them out there."  
> **username_3**: @alex: that would come under method 3 "Be clever"  
> **username_1**: Neutron stars, the extremely dense cores of massive dead stars, spiraling toward each other or into a black hole can raise tidal waves in the oceans of heavy charged particles surrounding the neutron stars. Those tidal waves reveal themselves through regular flashes of electromagnetic radiation, which can serve as an early warning system for impending mergers, the researchers found.  Such electromagnetic flares could become very early warning signs of NSBH (∼ 1 yr before merger) and BNS (∼ 10 yr before merger) mergers and tools to study neutron star oceans.  arxiv.org/abs/2205.13541  

---

