I Is there a plan for a search for nearby black holes?

[nikkkom]

It looks obvious to me: small BHs usually do not radiate to a detectable extent - they can only radiate if they have an accretion disk.

The other way to detect them in multiple star systems is to detect other star's movements (easy-ish) and prove that another body is heavy, but does not radiate anything (relatively hard). Maybe it's just the case that no one yet embarked on a systematic combing through binary star catalogs for these cases.

 

[Chronos]

GAIA is in the hunt for things like transient luminosity changes due to microlensing caused by a black hole [or other massive body] passing in front of a background star GAIA is particularly well suited for this task since it will catalog the entire sky down to a limiting magnitude of 20.5 - which is sufficient to cover a very large number of stars. The first such events have, in fact, already been detected, as noted here; http://sci.esa.int/gaia/58546-gaia-spies-two-temporarily-magnified-stars/.If the MW really is 'teeming' with black holes', as suggested by some, these are just a hint of what can be expected over the life of the mission - considering objects like planets and black holes tend to have relatively high proper motions. As usual, the real challenge is in making sense out of all the data. Fortunately, there is a large pool of slave labor [grad students] available to draw upon.

 

[snorkack]

In case of a microlens, you also have to search for nature of the microlensing body.

Does microlensing event disclose anything about the distance to lens?

 

[Buzz Bloom]

Hi @Chronos:

Thank you for your link to the ESA GAIA site. From there I found

http://gsaweb.ast.cam.ac.uk/alerts/alertsindex .​

I am hoping you can explain a detail to me. What is the class "CV"?
On page 3, items 7 and 10 have class CV. Below are the details for item 7.

Name Gaia18alh
TNS: AT2018tl
Observed: 2018-02-12 17:56:06
RA (deg.): 100.63864
Dec. (deg.): 40.04256
Mag.: 16.31
Historic mag.: N/A
Historic scatter: N/A
Class: CV
Published: 2018-02-18 15:17:37
Comment: Confirmed CV also reported as ASASSN-18ci and 18cn (see vsnet-alert 21883)​

At

https://en.wikipedia.org/wiki/List_of_astronomy_acronyms#C​

I found

• CV – (celestial object) Cataclysmic Variable, a type of variable binary star system that contains a white dwarf and a companion star that changes

Is this what the index "CV" means?

Regards,
Buzz

 

[Chronos]

I agree with your conclusion and source for the meaning of CV, Astrophysicists are notoriously fond of acronyms, so a handy reference guide is generally helpful. Some of acronyms are rather obscure, so, It is considered good practice and polite to first spell out the whole thing, followed by its acronym [in brackets], or even provide an index to avoid alienating the audience. The IAU ia the authority for all things astronomical, and even has a system for recognizing additions to its official list - re:http://cdsarc.u-strasbg.fr/viz-bin/DicForm

 

[Chronos]

You need to know something about the distance to the lensee [background object] and lens to estimate the lens mass as noted here; https://oneminuteastronomer.com/9237/gravitational-lens/,

"Astronomers can do more than take pretty pictures of gravitational lenses. Using the ideas developed by Einstein and others, if the distance to the foreground and background objects can be determined using http://oneminuteastronomer.com/5478/edwin-hubble/, and if the degree of deflection by the “lens” is measured, then astronomers can calculate the mass of the foreground object. This is, of course, simply amazing. That we can determine the mass of, for example, a cluster of hundreds of galaxies billions of light years away by measuring some light with a telescope and applying some inspired mathematics. And yet science enables such things."

Obfiously, the background star is the easy part since it can be seen and its distance is probably known. The lens - not so much. Being all black and such this gets pretty tricky. One way would be to time the duration of the lensing event. A good measurement would provide its apparent size and probable distance. Not saying this is easy, and still leaves some uncertainty.

 

[glappkaeft]

LIGO has been collecting data since 2002 and did not get their first hit until 2015 and has only managed to record a couple more hits to date. That is not the kind of success that inspires confidence our quaint little backwater hosts 100+ million black holes after 20+ years of scanning the observable universe for BH events.

First that is misrepresenting events more than just a little. The original LIGO equipment was much less sensitive than the Advanced LIGO that started gathering data for the first run September 12, 2015 and found the first confirmed merger two days later. Before the first run was ended January, 2016 it discovered one candidate and one more confirmed merger.

The second even more sensitive run started November 30, 2016 but was was suspended between May 8 and June 8 for maintenance, Virgo joined the two LIGOs on August 1 and the run was shut down August 25. This run discovered four mergers, two of them in August alone.

Secondly they detect mergers not black holes. I don't know the estimated percentage of black holes in close binary systems but it must be tiny.

 

[Chronos]

Understood, My point is, massive stars are not renowned as hermits as discussed here;https://www.e-education.psu.edu/astro801/content/l5_p7.html , by John Dutton of PSU. Furthermore; https://arxiv.org/abs/1306.1811, The Multiplicity of High-Mass Stars, states

"Preliminary results suggest that the multiplicity rate drops from 80% for the highest masses to 20% for stars of 3 solar masses. Our analysis indicates that the binary systems often contain close pairs with components of similar mass. This coincidence cannot originate from a random tidal capture in a dense cluster but is likely due to a particular formation process for high-mass stars."

Assuming black hole originate from high mass stars and high mass stars prefer company, expecting a high proportion of black holes to reside in binary systems does not seem unreasonable.

Yes, the sensitivity of LIGO has much improved since it first came on line, but, so has that of telescopes, The number of planets found in the solar system did not appreciably increase in the years following deployment of the telescope. I do not find it rash to infer this tends to oppose any claim the solar system may be 'teeming' with faint planets.

 

[Monsterboy]

What is the minimum feasible mass of a black hole which will allow it to exist without losing mass due to hawking radiation ? Given that, the only source of energy for the black hole is the CMB i.e energy lost due to hawking radiation = energy gained by absorbing the CMB radiation.

 

[Chronos]

The smallest known black holes tip the scales at around 5 solar masses. A few may even be as small as ~3 solar masses, but this is difficult to confirm. In any event, that is not nearly small enough to emit a detectable amount of Hawking radiation. For that, you need a subsolar mass black hole. Aside from PBH [primordial black holes], there is no known way [even in theory] for such tiny black holes to form.

 

[JMz]

I would appreciate seeing your thoughts about my probe idea. Re (1) Are you saying that even a probe visiting the neighborhood of a black hole would be unable to detect the Hawking radiation?

As for sending a probe to the BH's neighborhood: How long are you willing to wait for it to get there? (You are obviously willing to wait ~ 100 years for it to send back data on whatever it finds when it gets there, so I imagine you are the patient sort.) For reference, the Voyagers and Pioneers travel at ~ 1 LY per 10,000 years.

 

[Buzz Bloom]

As for sending a probe to the BH's neighborhood: How long are you willing to wait for it to get there? (You are obviously willing to wait ~ 100 years for it to send back data on whatever it finds when it gets there, so I imagine you are the patient sort.) For reference, the Voyagers and Pioneers travel at ~ 1 LY per 10,000 years.

Hi JMz:

My suggestion was intended as a thought experiment perhaps involving somewhat more advanced technology for the spaceship engines than what is available today. At the time I wrote that I had an idea for a design for a telescope which would orbit the black hole, with a shield to prevent any CMB radiation for entering the telescope from all directions except that facing the BH. My thought was that the BH itself would block CMB from that direction. However, after exploring the possibilities of the design in some detail, I realized that it would not work.
See
https://www.physicsforums.com/threa...velength-em-gets-through-a-small-hole.943357/

I continued that discussion as a "INBOX Conversation" with @vsv, and I learned that my telescope design would have to be much larger than the size of the BH in order for a significant amount of the Hawking radiation to enter the telescope. Therefore the CMB coming from the direction of the BH would overwhelm the Hawking radiation entering the telescope.

My personal conclusion for all of this investigation was that I should not give any serious credence to the existence of Hawking radiation since it appears that actually ever detecting it is at the very least close to impossible.

Regards,
Buzz

 

[JMz]

My personal conclusion for all of this investigation was that I should not give any serious credence to the existence of Hawking radiation since it appears that actually ever detecting it is at the very least close to impossible.

There is, however, the interest in watching for very-low-mass primordial BHs to evaporate. But no BHs smaller than a few solar masses have ever been detected, AFAIK. And I don't know what the estimated abundance is, so the expectation value for the distance to the closest one could be much larger than 100 LY.

 

[Buzz Bloom]

There is, however, the interest in watching for very-low-mass primordial BHs to evaporate.

Hi JMz:

I read somewhere (sorry, I don't remember where) that any primordial BHs would have already evaporated a long time ago.

Regards,
Buzz

 

[glappkaeft]

Hi JMz:

I read somewhere (sorry, I don't remember where) that any primordial BHs would have already evaporated a long time ago.

Only if they are small enough. The range of sizes speculated about then it comes to primordial black holes is vast (micrograms to 1000s solar masses) and lifetimes vary even more.

Putting 13.7 Gyr lifetime into the calculator at http://xaonon.dyndns.org/hawking/ (looks resonable but I don't know enough to tell for sure) gives a mass of 1.72*10¹¹ kg which is similar to a sub 1 km stony asteroid.

 

[Buzz Bloom]

Putting 13.7 Gyr lifetime into the calculator at http://xaonon.dyndns.org/hawking/ (looks resonable but I don't know enough to tell for sure) gives a mass of 1.72*1011 kg which is similar to a sub 1 km stony asteroid.

Hi glappkaeft:

Thanks for your post. It caused me to remember that the original source I read was about primordial BHs (PBHs) as an unsatisfactory candidate to be a form of dark matter, rather than PBHs in general. I have not seen any analysis regarding models for the formation of PBHs. Do you know of any? There is also an plausible issue about small PBHs merging with other stuff (including other PBHs) into large ones, perhaps then becoming the seeds for galaxy formation.

Regards,
Buzz

 

[glappkaeft]

When it comes to most areas of physics I'm a happy self though amateur (the only pure physics course required was electromagnetism in the computer science master I studied at university). However just googling "formation of PBH" and looking at the research papers from creditable sources will give you material for months to come if you want to self-study.

 

[JMz]

Only if they are small enough. The range of sizes speculated about then it comes to primordial black holes is vast (micrograms to 1000s solar masses)

Yes. For any target date (like, 13.8 GYr), there is a batch of PBH's that are evaporating just then. But how common that size is, is unknown -- as are any issues about the distribution compared to, say, baryonic matter.

 

[glappkaeft]

Yes. For any target date (like, 13.8 GYr), there is a batch of PBH's that are evaporating just then. But how common that size is, is unknown -- as are any issues about the distribution compared to, say, baryonic matter.

Well, everything about PBH is unknown since it is unknown if they exist at all...

 

[JMz]

Quite right! :-)

 

[Monsterboy]

Hi JMz:

I read somewhere (sorry, I don't remember where) that any primordial BHs would have already evaporated a long time ago.

That's why I asked the question of the "minimum feasible mass" of a black hole which will allow it to not evaporate due to hawking radiation, given the current intensity of CMB.

What is the minimum feasible mass of a black hole which will allow it to exist without losing mass due to hawking radiation ? Given that, the only source of energy for the black hole is the CMB i.e energy lost due to hawking radiation = energy gained by absorbing the CMB radiation.

If this mass less than one solar mass( most probably much much less), then the probability of finding a black hole of this mass will be very very low. But if we ever find such a black hole (or make one ?) or a less massive one, it might answer two questions.
1. Is Hawking Radiation real ? If it isn't then will never find a black hole that small or close to that.
2. Are PBHs responsible for dark matter ? If we find one such black hole, there might be billions of others spread out throughout the galaxy

 

[Chronos]

The mass fraction of dark matter that could consist of PBH's is constrained to about 10% as discussed here; https://arxiv.org/abs/1705.05567, Primordial black hole constraints for extended mass functions. This is actually tighter than the usual constraints based on monochromatic mass distributions.

 

[glappkaeft]

That's why I asked the question of the "minimum feasible mass" of a black hole which will allow it to not evaporate due to hawking radiation, given the current intensity of CMB.

https://www.physicsforums.com/threads/black-holes-and-hawking-radiation.860484/#post-5403327

 

[T Y Thomas Jr]

The GAIA mission is the biggest project currently underway. The first data release milestone was achieved in 2016 with; https://arxiv.org/abs/1609.04303,Gaia Data Release 1: Astrometry - one billion positions, two million proper motions and parallaxes This monumental endeavor will catalog over a billion stars in the MW, along with a number of extragalactic sources - including over 500,000 quasars. Its limiting magnitude is 20.5 and will reach stars in the MW core. The odds of it revealing hitherto undiscovered black holes in the solar neighborhood are considered very favorable. IRAC ans SWIFT have, and will continue to contribute to the observational databese as well. Our knowledge of compact stars will be significantly expanded by these missions over the next decade as researchers sift through this mountain of new data pouring in. Given current knowledge of the abundance of high mass [8+ solar] stars in the solar neighborhood, the odds of finding 125 black hole candidates within 100 light years do not appear promising.

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Paper identifier '1609.04303,Gaia' not recognized

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But I tried to see it. Thanks anyway. T Y Thomas Jr

 

[Monsterboy]

Well, everything about PBH is unknown since it is unknown if they exist at all...

How would we even know whether we are looking at a primordial black hole or a regular one caused by star collapse ? If a PBH has survived till today there is a good chance that it would also be surrounded by other stuff which make an accretion disk or something. It might look just like any other black hole right ?

 

[JMz]

How would we even know whether we are looking at a primordial black hole or a regular one caused by star collapse ? If a PBH has survived till today there is a good chance that it would also be surrounded by other stuff which make an accretion disk or something. It might look just like any other black hole right ?

That's about right. The one noticeable difference is that star-collapse BH's will generally have at least ~ 1 Solar mass or somewhat more. PBH's may have formed with a much larger range of masses, including ones that are small enough to be evaporating right now.