Missing pulsar problem (MPP)

[Dandav]

Any idea why Theoretical predictions have indicated that there should be more than 10^3 active radio pulsars within the distance of 10 pc of the Milky Way galaxy center (GC)?

https://link.springer.com/article/10.1140/epjc/s10052-024-12486-2

"An astronomical puzzle called the missing pulsar problem (MPP) refers to the failed expectation to observe a large number of pulsars within the distance of 10 pc of the Milky Way galaxy center (GC). Theoretical predictions have indicated that there should be more than 103 active radio pulsars in that region [1,2,3], but these numbers have not been observed."

[alexander]

If you follow those pesky [1,2,3] in the section of the paper that you are quoting, those things that tend to indicate that there is a citation being provided for the things that were stated before it, you will come across this paper:
https://iopscience.iop.org/article/10.1086/423975/fulltext/

Section 2 goes over the prediction.

[Dandav]

Thanks

Do appreciate your reply.

In this article it is stated:

https://iopscience.iop.org/article/10.1086/423975/fulltext/

"Evidence from the near-infrared spectrum of S0-2 (Ghez et al. 2003a) and the integrated spectrum within 05 of Sgr A* (Genzel et al. 1997; Eckart et al. 1999; Figer et al. 2000; Gezari et al. 2002) suggest that the observed Sgr A* stellar cluster is largely composed of luminous (104 L), early-type (O9 to B0) stars. If these stars are near the main sequence, their masses are 1020 M. How these stars came to reside so near the supermassive BH remains a puzzle; "

"Stars of mass 10 - 20 M⊙ have nuclear lifetimes of 10^7 yr and leave neutron star (NS) remnants. Therefore, we expect a significant number of NSs to be bound to Sgr A* in orbits similar to those of the observed cluster stars, as well as in more compact orbits. Source confusion has so far inhibited the discovery of stars with orbital periods of 10 yr about Sgr A* (Genzel et al. 2003; Ghez et al. 2003b), although we anticipate that massive stars and NSs populate this region. The most exciting possibility is that some of the NSs orbiting Sgr A* may be detectable radio pulsars, an idea first considered in the prescient article by Paczyski & Trimble (1979). In § 2, we estimate the total number of normal radio pulsars (i.e., those with surface magnetic field strengths of 10111013 G) that may currently orbit the central BH with periods of 100 yr."

Now the issue is clear.

1. Due to S0-2 orbital motion around Sgr A* Their mass should be at about 10 - 20 M⊙.

2. Based on the current understanding, Stars of mass 10 - 20 M have nuclear lifetimes of 107 yr and leave neutron star (NS) remnants.

3. The most exciting possibility is that some of the NSs orbiting Sgr A* may be detectable radio pulsars,

Now it is clear why Theoretical predictions have indicated that there should be more than 10^3 active radio pulsars within the distance of 10 pc of the Milky Way galaxy center (GC). 

However, as we don't observe even one of those theoretical 10^3 active radio pulsars, could it be that there is an error in our theoretical understanding?

Out of the above three main points it is clear that 1 and 3 should be correct.

Therefore, let me focus on 2.

"Stars of mass 10 - 20 M⊙ have nuclear lifetimes of 10^7 yr and leave neutron star (NS) remnants."

The nuclear lifetimes of 10^7 yr isn't an issue in our discussion.

Hence, let's focus on the following: "leave neutron star (NS) remnants"

Why do we believe that Stars of mass 10 - 20 M⊙ must leave neutron star (NS) remnants?

Why those kinds of stars can't be formed near the GC itself?

 

https://www.aanda.org/articles/aa/full_html/2012/04/aa17181-11/aa17181-11.html

Interstellar gas within  ~10 pc of Sagittarius A∗

Sgr A∗ sits in the heart of a dense cluster of young, massive and luminous stars, which are concentrated within the central parsec and are distributed in two relatively thick disks that are highly inclined toward each other and rotate in opposite directions

The old cluster dominates the stellar mass by far, with  ~ 10^6   M⊙ inside the central 1 pc (Schödel et al. 2009), as opposed to  ≲ 1.5 × 10^4   M⊙ in the young cluster 

So, Sgr A∗ sits in the heart of two dense gas clusters that that are highly inclined toward each other and rotate in opposite directions.

One with stellar gas mass of  ~ 10^6   M⊙ and the other one with  ≲ 1.5 × 10^4   M⊙. and their Maximal distance from Sgr A∗ is 1Pc.

It is also stated that we observe young, massive and luminous stars in those massive gas clusters.

In the first article it was stated:

https://link.springer.com/article/10.1140/epjc/s10052-024-12486-2

"Theoretical predictions have indicated that there should be more than 10^3 active radio pulsars in that region [1,2,3], but these numbers have not been observed. This paradox has been magnified by the observation of magnetar SGR J1745-29 [4] by the NuSTAR and Swift satellites. This observation revealed that the failures to detect ordinary pulsars at low frequencies could not be simply due to strong interstellar scattering but to an intrinsic deficit produced by other causes." 

Hence:

Could it be that the failures to detect ordinary pulsars is due to the simple understanding that S0-2 are young, massive and luminous stars that had been formed in one of those massive gas clusters (and therefore there is no need for pulsars)?

Edited October 25 by Dandav

[OceanBreeze]

9 hours ago, alexander said:

If you follow those pesky [1,2,3] in the section of the paper that you are quoting, those things that tend to indicate that there is a citation being provided for the things that were stated before it, you will come across this paper:
https://iopscience.iop.org/article/10.1086/423975/fulltext/

Section 2 goes over the prediction.

Welcome back! The average IQ of this forum has been raised considerably with your return.

[OceanBreeze]

2 hours ago, Dandav said:

Thanks

Do appreciate your reply.

In this article it is stated:

https://iopscience.iop.org/article/10.1086/423975/fulltext/

"Evidence from the near-infrared spectrum of S0-2 (Ghez et al. 2003a) and the integrated spectrum within 05 of Sgr A* (Genzel et al. 1997; Eckart et al. 1999; Figer et al. 2000; Gezari et al. 2002) suggest that the observed Sgr A* stellar cluster is largely composed of luminous (104 L), early-type (O9 to B0) stars. If these stars are near the main sequence, their masses are 1020 M. How these stars came to reside so near the supermassive BH remains a puzzle; "

"Stars of mass 10 - 20 M⊙ have nuclear lifetimes of 10^7 yr and leave neutron star (NS) remnants. Therefore, we expect a significant number of NSs to be bound to Sgr A* in orbits similar to those of the observed cluster stars, as well as in more compact orbits. Source confusion has so far inhibited the discovery of stars with orbital periods of 10 yr about Sgr A* (Genzel et al. 2003; Ghez et al. 2003b), although we anticipate that massive stars and NSs populate this region. The most exciting possibility is that some of the NSs orbiting Sgr A* may be detectable radio pulsars, an idea first considered in the prescient article by Paczyski & Trimble (1979). In § 2, we estimate the total number of normal radio pulsars (i.e., those with surface magnetic field strengths of 10111013 G) that may currently orbit the central BH with periods of 100 yr."

Now the issue is clear.

1. Due to S0-2 orbital motion around Sgr A* Their mass should be at about 10 - 20 M⊙.

2. Based on the current understanding, Stars of mass 10 - 20 M have nuclear lifetimes of 107 yr and leave neutron star (NS) remnants.

3. The most exciting possibility is that some of the NSs orbiting Sgr A* may be detectable radio pulsars,

Now it is clear why Theoretical predictions have indicated that there should be more than 10^3 active radio pulsars within the distance of 10 pc of the Milky Way galaxy center (GC). 

However, as we don't observe even one of those theoretical 10^3 active radio pulsars, could it be that there is an error in our theoretical understanding?

(clip a lot of false reasoning)

 

Could it be that the failures to detect ordinary pulsars is due to the simple understanding that S0-2 are young, massive and luminous stars that had been formed in one of those massive gas clusters (and therefore there is no need for pulsars)?

From reading the paper referred to by alexander, the low number of pulsar detections is a fairly simple matter of the signal detection capability of current radiotelescopes.

Example: For the 100 m Robert C. Byrd Green Bank Telescope operating at ν ≳ 10 GHz, sensitivities of Smin ≃ 10 μJy may be possible. (one microJansky = 10^–29W/m²/Hz)

From section 3 of the reference:

A crude estimate of  the fraction of pulsars near Sgr A with flux densities greater than Smin is made “by restricting to the range α = 0–1 and assuming a flat distribution, p(α < 1) = 0.1. After evaluating a simple integral, we find that ∼1% of the active pulsars near Sgr A*, or as many as 1–10 (see § 2), may be detectable with current technology.”

“The planned Square Kilometer Array4 (SKA) will easily achieve sensitivities of ≲1 μJy and could perhaps ultimately find ≳100 orbiting pulsars.”

[Dandav]

11 hours ago, OceanBreeze said:

From reading the paper referred to by alexander, the low number of pulsar detections is a fairly simple matter of the signal detection capability of current radiotelescopes.

Correct.

However, that paper referred to by alexander had been set in 2003/2004.

https://iopscience.iop.org/article/10.1086/423975/fulltext/

Received 2003 September 27; accepted 2004 July 3

Don't you agree that in the last 20 years we have improved our technology for better signal detection capability?

The article which I have offered with regards the Interstellar gas within  ~10 pc of Sagittarius A had been published online on   23 March 2012

 

14 hours ago, Dandav said:

https://www.aanda.org/articles/aa/full_html/2012/04/aa17181-11/aa17181-11.html

Interstellar gas within  ~10 pc of Sagittarius A∗

Sgr A∗ sits in the heart of a dense cluster of young, massive and luminous stars, which are concentrated within the central parsec and are distributed in two relatively thick disks that are highly inclined toward each other and rotate in opposite directions

The old cluster dominates the stellar mass by far, with  ~ 10^6   M⊙ inside the central 1 pc (Schödel et al. 2009), as opposed to  ≲ 1.5 × 10^4   M⊙ in the young cluster 

So, Sgr A∗ sits in the heart of two dense gas clusters that that are highly inclined toward each other and rotate in opposite directions.

One with stellar gas mass of  ~ 10^6   M⊙ and the other one with  ≲ 1.5 × 10^4   M⊙. and their Maximal distance from Sgr A∗ is 1Pc.

It is also stated that we observe young, massive and luminous stars in those massive gas clusters.

Hence, in 2012 we already have the technology to overcome the dense gas cluster distraction and detect young, massive and luminous stars that are located inside that cluster at a maximal distance of only 1PC from the Sagittarius A∗

The emitted Energy of Pulsar should be much more powerful than a star. As an example:

https://phys.org/news/2017-02-brightest-furthest-pulsar-universe.html

"This X-ray source is the most luminous of its type detected to date: it is 10 times brighter than the previous record holder. In one second it emits the same amount of energy released by our sun in 3.5 years."

Therefore, if we have the technology already in 2012 to detect stars in the core of dense gas cluster, why that technology can't help us to detect pulsar with higer emitted energy than any star?

Please also be aware that from 1PC to 10PC (from the Sagittarius A∗) there is no dense gas cluster, therefore there should not be any distraction to our signal detection capability.

Even so, we don't detect any pulsar in that range.

Not in 2012 and not even today while our signal detection capability had been clearly improved.

How long do we need to wait before understanding that as we don't detect any pulsar, there is a possibility that there are no pulsars there?

In that article it is also stated:

""Only a neutron star is compact enough to keep itself together while rotating so fast," adds Gian Luca."

""The discovery of this very unusual object, by far the most extreme ever discovered in terms of distance, luminosity and rate of increase of its rotation frequency, sets a new record for XMM-Newton, and is changing our ideas of how such objects really 'work'," says Norbert Schartel, ESA's XMM-Newton project scientist

So, as the observation "is changing our ideas of how such objects (pulsars) really work", why the missing observation of pulsars isn't changing our ideas how 10 - 20 M⊙ star really work?

Why do we refuse to accept the observation (and especially - the missing observation) as is?

Could it be that the Missing Pulsar Problem (MPP) is just in our imagination?

Edited October 26 by Dandav

[OceanBreeze]

3 hours ago, Dandav said:

Don't you agree that in the last 20 years we have improved our technology for better signal detection capability?

 

Only the Square Kilometer Array, which I mentioned in my previous post, will have the necessary signal sensitivity of ≲1 μJy to detect about 10% (≳100) of the orbiting pulsars near Sgr A. This array is still being built in Australia and South Africa and will not come on line (see first light) until 2027.

[alexander]

On 10/25/2024 at 12:15 PM, OceanBreeze said:

Welcome back! The average IQ of this forum has been raised considerably with your return.

Oh, I highly doubt that, I'm just a newbie 🙂. I was looking though some old posts for something and I wondered if my account is still active, turned out it was, so a quick password reset later I was looking if there were any on-going discussions of atomic clocks, recent(ish) Special Relativity affirming experiments, where we see that special relativity holds to mm scale, or gravimetry, or LIGO or something (basically any place where a highly precise clock and/or clock sync is needed, because, as always, squirrel).

Going back to the original post and questions being posed, I am not even an amateur in astronomy, so I leave it to Ocean who is well more competent at answering specifics, this, however is more my style of question:

On 10/25/2024 at 9:24 AM, Dandav said:

However, as we don't observe even one of those theoretical 10^3 active radio pulsars, could it be that there is an error in our theoretical understanding?

There are, well, three possibilities to consider, as far as I can see:

1.  Our current theoretical understanding of galactic and star system formation is wrong
2.  Our current theoretical understanding is correct but we lack practical way of detecting these pulsars for one reason or another
3.  Our current theoretical understanding is correct but there is some other reason why we are not observing pulsars close to the galactic center

Ocean covered 2 option pretty well, I think:

On 10/25/2024 at 12:20 PM, OceanBreeze said:

From section 3 of the reference:

A crude estimate of  the fraction of pulsars near Sgr A with flux densities greater than Smin is made “by restricting to the range α = 0–1 and assuming a flat distribution, p(α < 1) = 0.1. After evaluating a simple integral, we find that ∼1% of the active pulsars near Sgr A*, or as many as 1–10 (see § 2), may be detectable with current technology.”

 

Option 3 is an unknown unknowns problem. Given we understand the physics and given the amount of actual pulsars matches our predicted amount, and that we have the capability of detecting them, it's an unknown unknown as to why the amount detected doesn't match the amount predicted, and this frequently means new science. We take the evidence and measurements, input that into theoretical physicists, and eventually something interesting may come out of it, and I am waaaay not smart enough to understand those papers, I stare at them like Newton would stare at a modern Mathematics journal, I am not comparing myself to Sir Isaac, just stating a fact about modern math, lol, but yes, hence unknown unknowns, no idea where this leads, maybe instruments have fundamental mistakes, maybe model makes some assumption that at some extreme results in some wonky physics that doesn't match observations, maybe we have a fundamental issue with mass, however with LIGO, gravity tests with neutrons and recent SR-affirming studies, where we first measure red shift due to SR within at 450m scale and confirm it to 10^-5 sort of precision, and then that we see gravitational red shift down to mm scale (see https://www.scienceopen.com/document?vid=45d9ca18-b55c-44aa-a64b-b6903d2b64b6 and https://www.nature.com/articles/s41566-020-0619-8). So, with those in mind, it will likely have to be something other than our understanding of mass, but it could be mass-related.

 

And we slowly get to option 1, where we consider that our understanding of star, star system, and galactic formation is wrong. Here, while the models are not perfect, but then again, it's a model, it's not going to be perfect by definition, we have to remember, galactic formation is tied to early universe, as we need to understand where and how gas clouds formed during the early expansion of the universe, and here we match our understanding to CMB, and find that, while CMB was first measured in 1964, it was predicted in 1948, and not only do all of the observations match the prediction exactly, both of the almost perfect black body spectrum and its detailed prediction of the anisotropies in the cosmic microwave background, our simulations show that the overall pattern of the CMB roughly matches what we have measured, which tell us 2 things, really, we have a pretty good understanding about early universe formation, and that the universe is pretty flat overall.

We understand gravity, we understand early universe formation and rough distribution of masses across the universe. Then we take our protogalactic clouds and we apply a monolithic collapse model to get giant masses of gas collapsing into galaxies, we can then look at a bit of a smaller scale to take care of stars, knowing the mass distribution within the collapsing galactic disk, and assuming GR model of gravity, of course. That gets us the kinds of masses we are likely to observe at various distances from the GC, we can use maybe slightly simpler Kepler laws to track galactic movement, so that we can predict galactic collision, and apply multiple merger models to get overall distribution of not only galaxies, but also objects within galaxies to look kind of like the real world. And, once we get to the first sets of stars dying or being destroyed by yet another merger, creating gravitational instability, we can probably track the formation of the black hole as well as the formation and reformation of luminous and later pulsating stars in various sections of the Galaxy. Large and difficult models, lots of compute time, but we usually find that we can get this pretty close to what we observe, obviously questions remain, we have to correct for dark energy at least for the time being, but the model works pretty well and creates usable predictions. 

Given that the model mostly works, gives useful predictions, actually there is one more step. In this model, given out understanding of the evolution of the stars, which comes from how they form, QM, GR and probably a few fields I am missing, although i don't think something crazy like QCD is on the table here, anyways, given our current understanding of gravity, current understanding of how stars work, we can predict how stars evolve over time, given the prediction, we then confirm, which we have, that our understanding of star evolution matches our prediction, for example, if we say that we predict that some amount of early stars of a certain size are going to become neutron stars and some will be white dwarfs, and we know the probability of those outcomes, we can confirm that with observations, and I believe we find that we are generally pretty close.

So, with all that in mind, given that with sufficient amount of processing, we can inflate a nearly singularity to the modern universe, we can see distribution of galaxies similar to what we see today, we can see the interaction of those galaxies and evolution of them over time, and come up with galaxies not dissimilar to the ones observed today, given that we understand the evolution of stars, from gas clouds to star systems to what happens in those systems over time and how stars generally evolve, and confirm that theory with observations. I think it is highly unlikely that our theoretical understanding is so far off, that we predict 3 orders of magnitude more of a certain type of an object within some distance of GC, and then basically fail to find any of those objects there.

Note: I believe that everything I have stated is relatively well known and accepted and probably pretty basic for you guys, that said, because I just don't have the time at the moment to go back this up with research, I concede points that may not be factually correct ahead of time, appreciate if you have something for me to read on my misunderstanding, and apologize for misstating whatever I may have. If I have to address my overall point, I will do so as needed.  

[Dandav]

On 10/26/2024 at 11:29 AM, OceanBreeze said:

Only the Square Kilometer Array, which I mentioned in my previous post, will have the necessary signal sensitivity of ≲1 μJy to detect about 10% (≳100) of the orbiting pulsars near Sgr A. 

I still don't understand the logic.

It is very clear that an average pulsar emits much more energy than a star:

On 10/26/2024 at 7:59 AM, Dandav said:

The emitted Energy of Pulsar should be much more powerful than a star. As an example:

https://phys.org/news/2017-02-brightest-furthest-pulsar-universe.html

"This X-ray source is the most luminous of its type detected to date: it is 10 times brighter than the previous record holder. In one second it emits the same amount of energy released by our sun in 3.5 years."

In 2012 we already had the technology to detect stars in the massive gas cloud:

On 10/25/2024 at 5:24 PM, Dandav said:

of young, massive and luminous stars, which are concentrated within the central parsec

This massive gas cloud is located at a distance of only 1 pc from the SMBH.

On 10/25/2024 at 5:24 PM, Dandav said:

The old cluster dominates the stellar mass by far, with  ~ 10^6   M⊙ inside the central 1 pc

I assume that It is very difficult to detect those stars due to the gas distortion.

On the other hand, based on the current understanding, 1000 pulsars should be in the range of up to 10 pc.

In this aria there is no gas cloud and no distortion.

So, how could it be that in 2012 the signal sensitivity that we had was good enough to detect stars in the massive gas cloud distortion, but even after 12 years (while we constantly improve our signal sensitivity) we still can't detect even one pulsar (which should emit much more energy than any star) outside the gas could distortion?

On 10/27/2024 at 10:29 PM, alexander said:

There are, well, three possibilities to consider, as far as I can see:

1.  Our current theoretical understanding of galactic and star system formation is wrong
2.  Our current theoretical understanding is correct but we lack practical way of detecting these pulsars for one reason or another
3.  Our current theoretical understanding is correct but there is some other reason why we are not observing pulsars close to the galactic center

Thanks for considering those possibilities.

On 10/27/2024 at 10:29 PM, alexander said:

given that we understand the evolution of stars, from gas clouds to star systems

We do understand the evolution of stars from gas clouds and we clearly see the young, massive and luminous stars in the massive gas cloud that is located at up to 1 pc from the SMBH. 

Therefore, why do we refuse to understand that S0-2 stars have been formed in this massive gas cloud/cluster but drifted outwards to their current location?

Why do we insist for 1000 pulsars?

On 10/26/2024 at 11:29 AM, OceanBreeze said:

This array is still being built in Australia and South Africa and will not come on line (see first light) until 2027.

We can wait till 2027 for this new array.

However, what would we do or understand if even this better array won't detect any pulsar?

Is there any possibility that we would accept the idea that MPP is not realistic or we should continue to wait till 2045 or 2100?

Edited October 29 by Dandav

[Dandav]

On 10/27/2024 at 10:29 PM, alexander said:

here we match our understanding to CMB, and find that, while CMB was first measured in 1964, it was predicted in 1948, and not only do all of the observations match the prediction exactly, both of the almost perfect black body spectrum and its detailed prediction of the anisotropies in the cosmic microwave background, our simulations show that the overall pattern of the CMB roughly matches what we have measured, which tell us 2 things, really, we have a pretty good understanding about early universe formation, and that the universe is pretty flat overall.

As you mention the CMB and just to make it clear:

We think that the CMB is an indication about early universe formation, and that the universe is pretty flat overall.

However, why we do not consider it as an indication about the universe itself?

In the following article it is stated:

https://en.wikipedia.org/wiki/Cosmic_microwave_background

"The cosmic microwave background radiation is an emission of uniform black body thermal energy coming from all directions. Intensity of the CMB is expressed in kelvin (K), the SI unit of temperature. The CMB has a thermal black body spectrum at a temperature of 2.72548±0.00057 K.

The CMB is not completely smooth and uniform, showing a faint anisotropy that can be mapped by sensitive detectors. "

If the CMB is about early universe, then how can we explain that it isn't completely smooth and uniform?

On the other hand, if we would consider the CMB as a radiation from the matter (stars, galaxies...) in the Universe, then do you agree that the difference in the matter densities in each direction can explain why it isn't completely smooth and uniform?

In any case, I assume that the CMB can't help us to understand the following:

1. The puzzle of how S0-2 stars came to reside so near the supermassive BH (Missing Pulsar Problem)?

On 10/25/2024 at 5:24 PM, Dandav said:

How these stars came to reside so near the supermassive BH remains a puzzle; "

2. How a Pulsar could emit in just one second the same amount of energy released by our sun in 3.5 years.

On 10/26/2024 at 7:59 AM, Dandav said:

In one second it emits the same amount of energy released by our sun in 3.5 years."

Therefore, somehow we need to find solutions for those problems.