Page 1 of 2 12 LastLast
Results 1 to 30 of 35

Thread: The center of the Milky Way is teeming with black holes

  1. #1
    Join Date
    Sep 2015
    Posts
    534

    The center of the Milky Way is teeming with black holes

    The center of the Milky Way is teeming with black holes
    http://www.cbs17.com/news/check-this...s-1/1101784006

    "Astronomers poring over old x-ray observations have found signs of a dozen black holes in the inner circle of the Milky Way. And since most black holes can't even be spotted that way, they calculate that there are likely thousands of them there. They estimate it could be about 10,000, maybe more, according to a study in Wednesday's journal Nature .

    "There's lots of action going on there," said study lead author Chuck Hailey, a Columbia University astrophysicist. "The galactic center is a strange place. That's why people like to study it."

    The stellar black holes are in addition to — and essentially circling — the already known suppermassive black hole, called Sagittarius A , that's parked at the center of the Milky Way.

    In the rest of the massive Milky Way, scientists have only spotted about five dozen black holes so far, Hailey said."
    "The newly discovered black holes are within about 19.2 trillion miles (30.9 trillion kilometers) of the supermassive black hole at the center. "

    Few questions:
    1. How could it be that in the center, near Sagittarius A, there are 10,000 Black holes, while in the rest of the Milky way we have only spotted five dozen BH?
    2. What is the meaning of "essentially circling"? Does it mean rotation velocity? If so, what is the estimated maximal rotation velocity?
    3. If I understand it correctly - (30.9 trillion kilometers) is is about 3 LY.
    So, what is the closest BH radius & orbital velocity around the Sagittarius A? Can we get better estimation for Sagittarius A mass based on this data (comparing to S0 stars)?
    4. Why we are sure that all of them are black holes? Why not gas stellar/clouds?
    5. What is the source for all of this huge mass?
    6. Our scientists have always claimed that the Sagittarius A eats the nearby mass.
    So, how could it be that around Sagittarius A, the mass dense is so high (10,000 Black holes..)? Why it doesn't eat them all? Why it has lost its appetite?
    Last edited by Dave Lee; 2018-Jun-14 at 07:41 PM.

  2. #2
    Join Date
    Mar 2007
    Location
    Falls Church, VA (near Washington, DC)
    Posts
    8,262
    The supermassive black hole at the center only eats stuff that blunders into the radius of no escape, which is only a few million miles in this case. A star or remnant thereof that is orbiting a lightyear or so away is in no danger unless a close encounter with something else deflects it into a collision course.

  3. #3
    Join Date
    Jan 2008
    Posts
    654
    Quote Originally Posted by Dave Lee View Post
    1. How could it be that in the center, near Sagittarius A, there are 10,000 Black holes, while in the rest of the Milky way we have only spotted five dozen BH?
    You are not comparing like with like. The study found 12 black holes but they estimate 10,000. Estimates of the number if black holes in the Milky way is in the range ten million to a billion.

    2. What is the meaning of "essentially circling"? Does it mean rotation velocity? If so, what is the estimated maximal rotation velocity?
    3. If I understand it correctly - (30.9 trillion kilometers) is is about 3 LY.
    So, what is the closest BH radius & orbital velocity around the Sagittarius A? Can we get better estimation for Sagittarius A mass based on this data (comparing to S0 stars)?
    4. Why we are sure that all of them are black holes? Why not gas stellar/clouds?
    The above is probably defined and/or discussed in the study but I don't have a subscription to Nature.

    5. What is the source for all of this huge mass?
    Like all other black holes dead stars, dust and gas.

    6. Our scientists have always claimed that the Sagittarius A eats the nearby mass.
    No, that is bad pop-sci.

  4. #4
    Join Date
    Jun 2006
    Posts
    1,032
    Wouldn't these blackholes affect the orbits of the stars that have been detected in orbit around the central blackhole. When the G2 cloud made a close pass it didn't seem to be affected by unseen masses within 3 light year, they must be very close and very uniform in distribution.

  5. #5
    Join Date
    Mar 2007
    Location
    Falls Church, VA (near Washington, DC)
    Posts
    8,262
    Quote Originally Posted by transreality View Post
    Wouldn't these blackholes affect the orbits of the stars that have been detected in orbit around the central blackhole. When the G2 cloud made a close pass it didn't seem to be affected by unseen masses within 3 light year, they must be very close and very uniform in distribution.
    Yes, there will be mutual perturbations, just as our planets perturb each other as they orbit the Sun. The supermassive black hole is overwhelmingly dominant in that region, so those perturbations will be slight except in rare cases of extremely close encounters. An analogy in our solar system was the extremely close encounter of Comet Shoemaker-Levy 9 and Jupiter.

  6. #6
    Join Date
    Sep 2015
    Posts
    534
    Thanks

    Quote Originally Posted by glappkaeft View Post
    You are not comparing like with like. The study found 12 black holes but they estimate 10,000. Estimates of the number if black holes in the Milky way is in the range ten million to a billion.
    If our scientists estimate that there are 10,000 BH, don't you think that they have found that the current mass density at a 3LY should support this huge mass requirement?
    Even if we only focus in the real evidences;
    In a radius of only 3LY we have found 12 BH, while in whole galaxy (over than 50,000 LY) we have only found about 60 BH.
    In other words, don't you think that it proves that the mass density in this relativity short radius is maximal comparing to the whole galaxy (even by elimination the total mass of the SMBH).

    With regards to the source of that mass density:

    Quote Originally Posted by glappkaeft View Post
    Like all other black holes dead stars, dust and gas.
    So, from where those dead stars are coming?
    Is it from outside or from inside?
    If it comes from outside;
    Does it mean that the whole mass of the galaxy is drifting inwards to be eaten by the SMBH?
    If so, can we assume that the Sun is currently drifting inwards and it will be converted to a dust in the mouth of the SMBH?
    Do we know if the Sun is drifting inwards?

    Quote Originally Posted by Hornblower View Post
    The suppermassive black hole at the center only eats stuff that blunders into the radius of no escape, which is only a few million miles in this case. A star or remnant thereof that is orbiting a light-year or so away is in no danger unless a close encounter with something else deflects it into a collision course.
    If the SMBH is so big, don't you think that it must eat enough to justify its current size?
    As it is bigger, don't you think that it must eat more and more?
    So, what is the estimated mass consumption of the SMBH in last year or in the last billion years?
    Last edited by Dave Lee; 2018-Jun-15 at 08:31 AM.

  7. #7
    Join Date
    Jul 2005
    Location
    Massachusetts, USA
    Posts
    21,785
    As noted above stellar mass black holes are rarely in a situation in which you can find them with today's equipment. Ways that you can find them include:
    1. The black hole is in a black-widow relationship with another star (ie it is very close, and pulling material from the other star, and that material gets very hot in an accretion disk and gives off x-rays (all 12 of the ones in this study were found that way).
    2. By lucky chance the black hole passes in front of a more distant star from our point of view, and happens to be in an area being studied by something like OGLE or MACHO, and we see its lensing effect (I think one black hole has been seen this way).
    3. Two black holes merge, and get detected by ALIGO (zero black holes in our galaxy have been found this way)

    As you note, with more lengthy and careful study of the S stars, you'd expect to see some perturbation of their orbits, but so far as I know, we haven't been able to observe them precisely enough for long enough yet to make unambiguous claims about specific black hole being found that way yet.

    You asked how they got there... and it is clear that in the Milky Way and most other large spirals, massive (O & B) stars are created near the center. The specifics of how are a topic of debate in current papers, but broadly, gas migrates to the center and stars form there.

    If the SMBH is so big, don't you think that it must eat enough to justify its current size?
    As it is bigger, don't you think that it must eat more and more?
    So, what is the estimated mass consumption of the SMBH in last year or in the last billion years?
    justify? Not sure what you mean. It is probably the case that Sgr A* was more than 90% of its current mass 10 billion years ago, and most of its increase since than happened during mergers with smaller galaxies. Currently, it is not radiating a lot of energy, so it isn't growing noticeably. The two Gamma Ray bubbles indicate that there was a minor growth event perhaps 7 million years ago.
    Forming opinions as we speak

  8. #8
    Join Date
    Mar 2007
    Location
    Falls Church, VA (near Washington, DC)
    Posts
    8,262
    A word to the wise for Dave Lee and everyone else: Make sure you do not let bad popular media writing about black holes mislead you into thinking they are ravenous beasts that suck in and eat everything that merely comes somewhere near them, as compared with being on a collision course. Most of the stuff that a large black hole consumes is gas and dust spiraling in from an accretion disk. This is when the gas is dense enough to behave as a fluid rather than a swarm of independent particles. The fluid dynamics are such that the gas loses energy and spirals in.

  9. #9
    Join Date
    Jul 2006
    Posts
    12,232
    I was asked just yesterday as to why spiral accretion disks form, instead of the material just flowing straight into the event horizon.

    I mumbled something about conservation of angular momentum but basically muffed the answer.

    I feel I let the board down.
    Time wasted having fun is not time wasted - Lennon
    (John, not the other one.)

  10. #10
    Join Date
    Sep 2015
    Posts
    534
    Quote Originally Posted by antoniseb View Post
    As noted above stellar mass black holes are rarely in a situation in which you can find them with today's equipment. Ways that you can find them include:
    1. The black hole is in a black-widow relationship with another star (ie it is very close, and pulling material from the other star, and that material gets very hot in an accretion disk and gives off x-rays (all 12 of the ones in this study were found that way).
    2. By lucky chance the black hole passes in front of a more distant star from our point of view, and happens to be in an area being studied by something like OGLE or MACHO, and we see its lensing effect (I think one black hole has been seen this way).
    3. Two black holes merge, and get detected by ALIGO (zero black holes in our galaxy have been found this way)

    As you note, with more lengthy and careful study of the S stars, you'd expect to see some perturbation of their orbits, but so far as I know, we haven't been able to observe them precisely enough for long enough yet to make unambiguous claims about specific black hole being found that way yet.
    Thanks


    Quote Originally Posted by Hornblower View Post
    A word to the wise for Dave Lee and everyone else: Make sure you do not let bad popular media writing about black holes mislead you into thinking they are ravenous beasts that suck in and eat everything that merely comes somewhere near them, as compared with being on a collision course. Most of the stuff that a large black hole consumes is gas and dust spiraling in from an accretion disk. This is when the gas is dense enough to behave as a fluid rather than a swarm of independent particles. The fluid dynamics are such that the gas loses energy and spirals in.
    Thanks for your advice.
    However, I read the answers and I read the articles, but it seems to me that we are missing some key element with that SMBH.

    So, let's try to understand it as follow:

    The SMBH is stable for the last 7 to 10 Billion years:
    Quote Originally Posted by antoniseb View Post
    It is probably the case that Sgr A* was more than 90% of its current mass 10 billion years ago, and most of its increase since than happened during mergers with smaller galaxies. Currently, it is not radiating a lot of energy, so it isn't growing noticeably. The two Gamma Ray bubbles indicate that there was a minor growth event perhaps 7 million years ago.
    Technically in the last 10 Billion years it might consume about 10% of his size. As its current estimated mass is 4*10^6 Sun mass, than we can assume that it consumes about 4*10^5 Sun mass - Let's call it Mass consumption in the last 10 billion years.

    So, what is the source for this Mass consumption?
    Could it be that our SMBH catch a near by dwarf galaxy for a dinner?
    I assume that the answer is No!
    So, if I understand it correctly, that mass consumption must come from the galaxy itself.
    In other words, it must come from the near 3LY around the SMBH.

    But, we have already found that this area is full with mass.
    Actually, it is the MOST dense aria in the whole Milky way galaxy.
    This is not the end. This aria is also the birth place for massive (O & B) stars.

    Quote Originally Posted by antoniseb View Post
    You asked how they got there... and it is clear that in the Milky Way and most other large spirals, massive (O & B) stars are created near the center. The specifics of how are a topic of debate in current papers, but broadly, gas migrates to the center and stars form there.
    So, now I'm quite confused.
    What is the source for the matter in the accretion disk?
    How could it be that the 3LY in the center, delivers about 4 * 10^5 Sun mass (in the last 10 Billion years) to be eaten by the SMBH, delivers all the requested mass to create the massive (O & B) stars and still be full of mass (actually it has the highest mass density in the whole galaxy)?
    This is real enigma for me.
    Don't you agree that (at least for the last 10 Billion years) this mass must come from somewhere inside the galaxy?
    Last edited by Dave Lee; 2018-Jun-15 at 06:47 PM.

  11. #11
    Join Date
    Jul 2005
    Location
    Massachusetts, USA
    Posts
    21,785
    Quote Originally Posted by Dave Lee View Post
    ... Don't you agree that (at least for the last 10 Billion years) this mass must come from somewhere inside the galaxy?
    No. Maybe it does, but I don't agree that it must. Also, I said more than 90%... It could have been 99%, there's a lot of doubt about the precise history of its growth.
    Side note: whole small galaxies have masses 100 to 10,000 times the mass of Sgr A*. Obviously it didn't consume ANY of them, but it can be fed by clouds, and perhaps other black holes, including larger central ones.

    Extragalactic gas clouds have been observed, including some that are on their way to falling into the Milky Way. When one of them interacts with the gas orbiting in the plane of the galaxy, there can (depending on direction of the fall) be a event that takes away angular momentum from both, resulting in a fall roughly toward the center of the galaxy. The denser dark matter that the Cuspy Dark Matter models suggest for the galaxy may also have an impact on the path of this falling gas, and the stars that form from it.
    Forming opinions as we speak

  12. #12
    Join Date
    May 2003
    Posts
    5,934
    I'm not sure I see the issue. Sure, any matter that enters the central black hole of the galaxy will generally come from the area right near the black hole. But there's material further away that will (on average, over time) move in to that space, giving an equilibrium situation where the density remains more or less constant. When water goes down the drain in the bathtub, all the water that goes down the drain comes from the area right near the drain, but that doesn't make the area right near the drain become devoid of water. Water just fills in from the areas further out. Stars orbiting the center of the galaxy don't have the kind of friction water has, to cause them to slowly spiral inward, but gas does, and as it moves inward it will be compressed, triggering new star formation.

    From here, I see that the density of stars near the center is about 10 million stars per cubic parsec. Further down on the page, there's a calculation that shows that if the black hole has been growing at a steady rate over its lifetime (and if we assume that its lifetime is about the same as the Milky Way itself), that works out to about one solar mass of material every 5,000 years. It's possible that over a very long time period, you could end up with the area right near the black hole becoming mostly depleted of matter (when everything that has a trajectory that might take it too close has already been absorbed, and any galactic collisions that might change trajectories so that they come too close become rarer than they are today), but I think that this would take longer than the current age of the universe.
    Conserve energy. Commute with the Hamiltonian.

  13. #13
    Join Date
    Sep 2015
    Posts
    534
    Thanks

    It is clear to me that we do not want to deal with that key tough question:

    What is the source for the high mass/gas density in that 3LY radius.

    We claim that: "It could have been 99%, there's a lot of doubt about the precise history of its growth"
    If I will say that even 1% means 4 * 10^4 Sun mass, then the answer might be that: "It could have been 99.9..99%.
    Just remember that if we look around us, there is not even one star in a radius of 3LY.
    However, at the center of our universe, at the same radius of 3LY our scientists claim that: "The center of the Milky Way is teeming with black holes" (with estimated 10,000 BH).

    But, we don't see any issue with that:
    Quote Originally Posted by Grey View Post
    I'm not sure I see the issue. Sure, any matter that enters the central black hole of the galaxy will generally come from the area right near the black hole. But there's material further away that will (on average, over time) move in to that space, giving an equilibrium situation where the density remains more or less constant. When water goes down the drain in the bathtub, all the water that goes down the drain comes from the area right near the drain, but that doesn't make the area right near the drain become devoid of water. Water just fills in from the areas further out. Stars orbiting the center of the galaxy don't have the kind of friction water has, to cause them to slowly spiral inward, but gas does, and as it moves inward it will be compressed, triggering new star formation.
    You agree that the nearby matter is drifting in (as the water example), but why don't we develop the outcome of this drifting?
    So, let me use this water example as follow:
    When water goes down the drain in the bathtub, then don't you agree that at some point of time we should see less water at the bath?
    We can claim that new water is coming from dwarf galaxy and therefore, we still see water in the bath although the water goes down the drain.
    If so, we actually claim - by definition - that there is a migration of water to the drain.

    However, from your point of view, stars can't migrate inwards, only gas can do it.

    So what is the source for this gas?
    If it migrates inwards, then it must come from somewhere.
    Do we see even one real gas cloud near our aria?
    Why all of those gas clouds are mainly concentrated at the center of the galaxy and drifting inwards?

    I also don't understand the following idea:
    "and as it moves inward it will be compressed, triggering new star formation."
    Why the galaxy drifts the gas inwards, set new stars just to be eaten by the SMBH?

  14. #14
    Join Date
    Mar 2007
    Location
    Falls Church, VA (near Washington, DC)
    Posts
    8,262
    Quote Originally Posted by Dave Lee View Post
    Thanks

    It is clear to me that we do not want to deal with that key tough question:

    What is the source for the high mass/gas density in that 3LY radius.

    We claim that: "It could have been 99%, there's a lot of doubt about the precise history of its growth"
    If I will say that even 1% means 4 * 10^4 Sun mass, then the answer might be that: "It could have been 99.9..99%.
    Just remember that if we look around us, there is not even one star in a radius of 3LY.
    However, at the center of our universe, at the same radius of 3LY our scientists claim that: "The center of the Milky Way is teeming with black holes" (with estimated 10,000 BH).

    But, we don't see any issue with that:


    You agree that the nearby matter is drifting in (as the water example), but why don't we develop the outcome of this drifting?
    So, let me use this water example as follow:
    When water goes down the drain in the bathtub, then don't you agree that at some point of time we should see less water at the bath?
    We can claim that new water is coming from dwarf galaxy and therefore, we still see water in the bath although the water goes down the drain.
    If so, we actually claim - by definition - that there is a migration of water to the drain.

    However, from your point of view, stars can't migrate inwards, only gas can do it.

    So what is the source for this gas?
    If it migrates inwards, then it must come from somewhere.
    Do we see even one real gas cloud near our aria?
    Why all of those gas clouds are mainly concentrated at the center of the galaxy and drifting inwards?

    I also don't understand the following idea:
    "and as it moves inward it will be compressed, triggering new star formation."
    Why the galaxy drifts the gas inwards, set new stars just to be eaten by the SMBH?
    My bold. Yes, lots of them, including such things as the Orion nebula. It and other such nebulae are dense concentrations, with more rarefied gas everywhere. The total mass of interstellar gas is over 1,000 times that of the central black hole, so there is plenty left to trickle in toward the center.

  15. #15
    Join Date
    Sep 2015
    Posts
    534
    Quote Originally Posted by Hornblower View Post
    The total mass of interstellar gas is over 1,000 times that of the central black hole, so there is plenty left to trickle in toward the center.
    Thanks

    But what about the volume?
    The center is very compact.
    I assume that the volume outside the center is at least several Millions (or Billions) bigger than the center.
    So, even if there are 1,000 times more interstellar of gas, the concentration in the center must be higher.

    In any case, with regards to your answer:

    Quote Originally Posted by Hornblower View Post
    My bold. Yes, lots of them, including such things as the Orion nebula. It and other such nebulae are dense concentrations, with more rarefied gas everywhere.
    So Orion Nebula is considered as a gas cloud.
    However, how many nebulas /gas clouds there are in Orion?
    Based on its name, I assume that there is only one Nebula in the whole Orion arm.
    What is the length of Orion? Is it 10,000 light years or 15,000 light years?
    So, there is one gas cloud in a length of 10,000 light years.
    However, what is the gas cloud density in the center of the galaxy?
    Don't you think that their concentration there is overwhelming comparing to the entire galaxy?

    Why is it?
    What is the source for so high gas clouds concentration in the center?
    Last edited by Dave Lee; 2018-Jun-16 at 07:20 AM.

  16. #16
    Join Date
    Aug 2002
    Posts
    9,097
    Quote Originally Posted by Dave Lee View Post
    So Orion Nebula is considered as a gas cloud.
    However, how many nebulas /gas clouds there are in Orion?
    Based on its name, I assume that there is only one Nebula in the whole Orion arm.

    I am sorry, but you are on an astronomy board, so you can be expected to know at least a little about astronomy.
    The Orion nebula (wiki) (Messier 42) is called so because it is in the constellation Orion (near the belt), and not because it is "the only nebula in the Orion arm".
    So, before you come up with comments and questions, it might be good if you actuallyinform yourself a little on the topic, by reading actual astronomy lecture books.
    All comments made in red are moderator comments. Please, read the rules of the forum here and read the additional rules for ATM, and for conspiracy theories. If you think a post is inappropriate, don't comment on it in thread but report it using the /!\ button in the lower left corner of each message. But most of all, have fun!

    Catch me on twitter: @tusenfem
    Catch Rosetta Plasma Consortium on twitter: @Rosetta_RPC

  17. #17
    Join Date
    Sep 2015
    Posts
    534
    Thanks and sorry for my misunderstanding.
    So, how many gas clouds there are in the Orion arm?

  18. #18
    Join Date
    Mar 2007
    Location
    Falls Church, VA (near Washington, DC)
    Posts
    8,262
    Quote Originally Posted by Dave Lee View Post
    Thanks and sorry for my misunderstanding.
    So, how many gas clouds there are in the Orion arm?
    If by gas clouds you mean the dense clumps which are visible if illuminated by embedded or nearby stars, I have no easy means of finding out how many there are in a given region of the galaxy. Online searches typically turn up a lot of junk for every reliable source, if any. I have seen from various sources that the total mass of gas in the galaxy is some 10 to 15 per cent of the total mass of stars, or upwards of 10 billion solar masses. That would be upwards of 2,500 times the mass of the central black hole. At the present time there is relatively little remaining right at the center, as indicated by the relatively low level of accretion disk activity compared to that of quasars and Seyfert galaxies. In the early formative stages of the galaxy there is believed to have been a lot more, which would have made Sagittarius A* a much stronger radio source than it is now. The best theory now indicates that a lot of gas that does not fall into the black hole is eventually blown away by the strong radiation. It appears that the fluid dynamic action under the present conditions is doing little to replenish the gas right at the center.

    It is my understanding that the mechanism behind the initial formation of supermassive black holes is still a mystery.

  19. #19
    Join Date
    Aug 2003
    Location
    The Wild West
    Posts
    9,357
    Quote Originally Posted by Dave Lee View Post
    ....they calculate that there are likely thousands of them there. They estimate it could be about 10,000, maybe more, according to a study in Wednesday's journal Nature.
    This claim is based on the estimate:

    But binary black hole systems are likely only 5 percent of all black holes, so that means there are really thousands of them, Hailey said.
    Five percent? That doesn't seem likely, since google tells me:

    Stellar surveys found that more than half of all Sun-like stars were part of multiple systems. For more massive stars, like O- and B-type stars, the number was estimated to be as high as 80 percent.
    I see now there is some dispute on the percentage of binaries or multiple systems. It apparently holds true, though, that more massive stars are more likely to reside in multiple systems.

    Nevertheless, if binary systems make up 50% of all stars (say, stars more massive than red dwarfs) instead of just 5%, then the quoted article's estimate of black holes near the galactic center must be reduced by 10 times.
    Everyone is entitled to his own opinion, but not his own facts.

  20. #20
    Join Date
    Jun 2007
    Posts
    5,641
    Quote Originally Posted by Cougar View Post
    This claim is based on the estimate:



    Five percent? That doesn't seem likely, since google tells me:



    I see now there is some dispute on the percentage of binaries or multiple systems. It apparently holds true, though, that more massive stars are more likely to reside in multiple systems.

    Nevertheless, if binary systems make up 50% of all stars (say, stars more massive than red dwarfs) instead of just 5%, then the quoted article's estimate of black holes near the galactic center must be reduced by 10 times.
    You are assuming black hole binaries are as common as star binaries. Stellar black holes only form from direct collapse as hypernovas, which are likely to eject the resulting black hole from a multi-star system.

    edit: "only" is too strong, I suppose, they could form from a neutron star consuming its companion, but that would also account for the lack of a companion.
    Last edited by cjameshuff; 2018-Jun-16 at 01:59 PM.

  21. #21
    Join Date
    Sep 2015
    Posts
    534
    Quote Originally Posted by Hornblower View Post
    If by gas clouds you mean the dense clumps which are visible if illuminated by embedded or nearby stars, I have no easy means of finding out how many there are in a given region of the galaxy. Online searches typically turn up a lot of junk for every reliable source, if any. I have seen from various sources that the total mass of gas in the galaxy is some 10 to 15 per cent of the total mass of stars, or upwards of 10 billion solar masses. That would be upwards of 2,500 times the mass of the central black hole. At the present time there is relatively little remaining right at the center, as indicated by the relatively low level of accretion disk activity compared to that of quasars and Seyfert galaxies. In the early formative stages of the galaxy there is believed to have been a lot more, which would have made Sagittarius A* a much stronger radio source than it is now. The best theory now indicates that a lot of gas that does not fall into the black hole is eventually blown away by the strong radiation. It appears that the fluid dynamic action under the present conditions is doing little to replenish the gas right at the center.

    It is my understanding that the mechanism behind the initial formation of supermassive black holes is still a mystery.
    Thanks

    With regards to the following:

    Quote Originally Posted by Hornblower View Post
    The best theory now indicates that a lot of gas that does not fall into the black hole is eventually blown away by the strong radiation
    Why do we estimate that some of the gas blown away from the SMBH?
    Do we have/see any evidence for that?
    Why don't we just assume that all the gas falls into the SMBH?

    This is also very interesting message:
    Quote Originally Posted by Hornblower View Post
    It appears that the fluid dynamic action under the present conditions is doing little to replenish the gas right at the center.
    Is it based on some kind of observation? Or is it just a wishful thinking/theory?
    Last edited by Dave Lee; 2018-Jun-16 at 03:55 PM.

  22. #22
    Join Date
    May 2003
    Posts
    5,934
    Quote Originally Posted by Dave Lee View Post
    Thanks

    It is clear to me that we do not want to deal with that key tough question:

    What is the source for the high mass/gas density in that 3LY radius.

    We claim that: "It could have been 99%, there's a lot of doubt about the precise history of its growth"
    If I will say that even 1% means 4 * 10^4 Sun mass, then the answer might be that: "It could have been 99.9..99%.
    Just remember that if we look around us, there is not even one star in a radius of 3LY.
    However, at the center of our universe, at the same radius of 3LY our scientists claim that: "The center of the Milky Way is teeming with black holes" (with estimated 10,000 BH).

    But, we don't see any issue with that:
    It's not that we don't want to deal with a "tough question". It's really that there is no mysterious problem here that needs to be resolved. Of course the density of gas and stars in the Milky Way (and other galaxies) is much higher in the center than it is further out. That's exactly what we see from even a cursory examination, and it's also exactly what you'd expect from a collection of stars, gas, and dust that are gravitationally bound. That's the way gravity works. Se we don't see an issue because we see things behaving just as they should.

    Quote Originally Posted by Dave Lee View Post
    You agree that the nearby matter is drifting in (as the water example), but why don't we develop the outcome of this drifting?
    So, let me use this water example as follow:
    When water goes down the drain in the bathtub, then don't you agree that at some point of time we should see less water at the bath?
    We can claim that new water is coming from dwarf galaxy and therefore, we still see water in the bath although the water goes down the drain.
    If so, we actually claim - by definition - that there is a migration of water to the drain.
    Sure, and that's why we think that a typical SMBH will grow over time. But again, remember that the mass of the black hole is a small fraction of the total mass of the galaxy (in the case of the Milky Way, it's on the order of a millionth of the total mass). So, if 0.2 microliters have drained out of a 200 liter bathtub, will you notice that the water level has changed significantly?

    Quote Originally Posted by Dave Lee View Post
    However, from your point of view, stars can't migrate inwards, only gas can do it.
    It's not that they can't, it's just that it's less likely. Stars largely interact with each other only through gravity, and that means that orbital energy is conserved, so only if circumstances are just right will a star get sent toward the center and then have the right kind of interaction to stay there. For gas, it's easier to have collisions between the individual atoms or molecules that result in losses of energy due to radiation. This cooling makes it easier for clouds of gas to contract under gravity than stars.

    Quote Originally Posted by Dave Lee View Post
    So what is the source for this gas?
    If it migrates inwards, then it must come from somewhere.
    Do we see even one real gas cloud near our aria?
    Why all of those gas clouds are mainly concentrated at the center of the galaxy and drifting inwards?
    Initial formation of the galaxy, plus more added every time the Milky Way absorbs a smaller galaxy. Although much of the initial gas has already become stars, typical estimates still place the estimated mass of gas in the Milky Way at about 10% to 15% of the mass of the stars. There's no shortage.

    Quote Originally Posted by Dave Lee View Post
    I also don't understand the following idea:
    "and as it moves inward it will be compressed, triggering new star formation."
    Why the galaxy drifts the gas inwards, set new stars just to be eaten by the SMBH?
    I'm not quite sure what you're asking here. If gas gets pulled toward the center, that squeezes the same mass into a smaller volume. That increases the density (hence why we'd expect the density near the center to be higher), and compressing interstellar gas to a higher density tends to trigger star formation. We see this frequently during galactic collisions.
    Conserve energy. Commute with the Hamiltonian.

  23. #23
    Join Date
    Sep 2015
    Posts
    534
    Thanks

    If I understand it correctly:

    Gas clouds and maybe some other mass is drifting inwards to the accretion disc and spin at almost the speed of light.
    The SMBH eats some of this mass/plasma in the accretion disc, but sometimes it rejects it outside from the disc.

    However:
    How do we know that:
    1. The gas clouds/mass is really approaching the SMBH and get in to the accretion disc?
    2. The plasma in the accretion disc spin at almost the speed of light?
    2. The SMBH eats some of the mass/Atom/Plasma from the accretion disc?
    3. Sometimes, the SMBH rejects that mass/Atom/Plasma outside from the accretion disc?

    Do we have real evidences for all of that or is it just a theory?
    Last edited by Dave Lee; 2018-Jun-17 at 07:20 PM.

  24. #24
    Join Date
    Jul 2005
    Location
    Massachusetts, USA
    Posts
    21,785
    Quote Originally Posted by Dave Lee View Post
    ... Do we have real evidences for all of that or is it just a theory?
    Yes there is lots of real evidence, and you sound dismissive when you use the phrase "just a theory".
    Without getting into specifics, when you look at the identifiers for objects in space, these are catalog numbers, and there are billions of objects in our galaxy which are catalogued, and have measurements connected to them. Some of your writing here suggests that you think that these models are someone just waving their hands for no reason, as opposed to the models being built to give context for the billions of observations that lead to them. I suggest that you go to this website: https://arxiv.org/list/astro-ph/new and read a few papers. It will give you more of a sense of what we do and do not know, and how we come to the conclusions we come to. It will be fun.
    Forming opinions as we speak

  25. #25
    Join Date
    Mar 2003
    Posts
    2,985
    Quote Originally Posted by antoniseb View Post
    Yes there is lots of real evidence, and you sound dismissive when you use the phrase "just a theory".
    Without getting into specifics, when you look at the identifiers for objects in space, these are catalog numbers, and there are billions of objects in our galaxy which are catalogued, and have measurements connected to them. Some of your writing here suggests that you think that these models are someone just waving their hands for no reason, as opposed to the models being built to give context for the billions of observations that lead to them. I suggest that you go to this website: https://arxiv.org/list/astro-ph/new and read a few papers. It will give you more of a sense of what we do and do not know, and how we come to the conclusions we come to. It will be fun.

    My daughter (bless her cotton socks) bought me a T-shirt that says "When you say 'It's just a theory', what I hear is 'I don't understand science'."

    I did my post-grad on this topic a disturbing number of years ago (hence the handle - it was looking at mechanisms that could transport "feeding" material into the nuclear region of sustained AGNs). so I can tell you from personal experience that there were many thousands of papers on the topic back then - with the subsequent advent of vastly superior observatories in all wavelengths and computing power that was unimaginable (to me, at least!) at the time, I shudder to think how deeply researched this topic must be by now.

  26. #26
    Join Date
    Sep 2015
    Posts
    534
    Quote Originally Posted by antoniseb View Post
    Yes there is lots of real evidence, and you sound dismissive when you use the phrase "just a theory".
    Without getting into specifics, when you look at the identifiers for objects in space, these are catalog numbers, and there are billions of objects in our galaxy which are catalogued, and have measurements connected to them. Some of your writing here suggests that you think that these models are someone just waving their hands for no reason, as opposed to the models being built to give context for the billions of observations that lead to them. I suggest that you go to this website: https://arxiv.org/list/astro-ph/new and read a few papers. It will give you more of a sense of what we do and do not know, and how we come to the conclusions we come to. It will be fun.
    Thanks

    The article is very interesting.

    Just as an example -
    Merging stellar-mass binary black holes

    https://arxiv.org/pdf/1806.05820.pdf

    It is stated:

    "The LIGO and Virgo detectors have recently directly observed gravitational waves from several mergers of pairs of stellar-mass black holes, as well as from one merging pair of neutron stars. These observations raise the hope that compact object mergers could be used as a probe of stellar and binary evolution, and perhaps of stellar dynamics.
    This colloquium-style article summarizes the existing observations, describes theoretical predictions for formation channels of merging stellar-mass black-hole binaries along with their rates and observable properties, and presents some of the prospects for gravitational-wave astronomy."

    "Merging binary black holes are rare outcomes indeed! [Merging binary neutron stars are similarly rare: while stars with initial masses sufficient to form a neutron star, between roughly 8 and 20 solar masses, are more common than the heavier stars necessary to form black holes, neutron star natal kicks and mass loss during supernovae are more likely to disrupt binaries; the expected yields for binary neutron star mergers are within an order of magnitude of those for binary black holes.]"

    So, they try to observe gravitational waves in order to get better understanding on merging process.
    However, I wonder why our scientists are so sure that they only see merging activity?
    Could it be that at least with some gravitational waves observations, they actually see a divorcing process instead of merging?
    Why they don't even think about a possibility for divorcing?
    How do they distinguish between merging and divorcing process?

    So, sometimes I got the fealling that if our scientists have an idea, they look at the observation though the filter of that idea.
    I would consider it as a mistake.
    They have to look at any observation without any pre ideas and try to find what could be the outcome of what they see.

    Therefore, I want to know on which observation they have based their ideas for the activity process in accretion disc.

  27. #27
    Join Date
    Mar 2010
    Location
    United Kingdom
    Posts
    6,965
    Quote Originally Posted by Dave Lee View Post
    However, I wonder why our scientists are so sure that they only see merging activity?
    Because they modelled what a merger should look like, based on the theory that has been extensively tested in less extreme conditions, and then found the predicted signature in the data.

    Quote Originally Posted by Dave Lee View Post
    Could it be that at least with some gravitational waves observations, they actually see a divorcing process instead of merging?
    No.

    Quote Originally Posted by Dave Lee View Post
    Why they don't even think about a possibility for divorcing?
    Because it is physically impossible without some external impetus.

    Quote Originally Posted by Dave Lee View Post
    How do they distinguish between merging and divorcing process?
    The inspiral chirp is positive, an outspiral one would be negative. We saw positive.

    Quote Originally Posted by Dave Lee View Post
    So, sometimes I got the fealling that if our scientists have an idea, they look at the observation though the filter of that idea.
    I would consider it as a mistake.
    They have to look at any observation without any pre ideas and try to find what could be the outcome of what they see.
    Testing a model by making observations is core scientific method. If observations don't fit the model new models are made. Looking at every observation and just making up random things it could be is too time consuming to be a useful approach to the exobytes of data there are out there. After all - when you hear a knock at the door do you:
    a) Answer it based on your model that it is likely someone who wants to talk to you
    b) Sit there and ask if it could be
    ..i) Aliens talking
    .ii) Five gerbils in a plastic ball bumping into your skirting board
    iii) Two clowns banging a plank against a baseball bat
    iv) A mid air collision involving swallows carrying coconuts
    .v) Two wooden puppets who have come to life having a duel in your front garden
    vi) A wooden tank made by bees firing wooden shells at your door
    vii) A clog wearing ninja landing on your roof
    etc etc etc

  28. #28
    Join Date
    Sep 2015
    Posts
    534
    Thanks

    I like your example...

    In any case;

    Based our current theory, gas clouds are drifting inwards to the accretion disc.
    So, did we really see any gas cloud moving in?
    If yes, would you please direct me to the relevant article?
    Last edited by Dave Lee; 2018-Jun-18 at 03:26 PM.

  29. #29
    Join Date
    May 2003
    Posts
    5,934
    Quote Originally Posted by Dave Lee View Post
    So, they try to observe gravitational waves in order to get better understanding on merging process.
    However, I wonder why our scientists are so sure that they only see merging activity?
    Could it be that at least with some gravitational waves observations, they actually see a divorcing process instead of merging?
    Why they don't even think about a possibility for divorcing?
    How do they distinguish between merging and divorcing process?

    So, sometimes I got the fealling that if our scientists have an idea, they look at the observation though the filter of that idea.
    I would consider it as a mistake.
    They have to look at any observation without any pre ideas and try to find what could be the outcome of what they see.

    Therefore, I want to know on which observation they have based their ideas for the activity process in accretion disc.
    I think Shaula addressed the substance of these questions. But I want to address the underlying assumption. You seem to always be assuming that scientists are blinded by their assumptions, and don't even ask simple questions before leaping to a conclusion. Instead, wouldn't it make sense to assume that someone who is so intrigued by the notion of studying gravitational waves that they have dedicated their entire career to it is at least as intelligent as you and I, and that they've questioned the things they observed and worked hard to come up with the best possible explanation for them. As Shaula notes, the gravitational wave signatures of separating binaries would be completely different from a merger. But even if they were very similar, wouldn't it make sense to assume that someone studying them would have thought of that and tried to find a way to address the issue, rather than just ignoring it?

    Similarly, AGN Fuel points out that, on the question of how material might be transported toward the central black hole of a galaxy, there has been a huge amount of research. Many scientists have written thousands of papers, bouncing ideas off of each other trying to determine what mechanisms might work and what might not. But wouldn't it make sense to assume that people have been trying to figure it out (or at least ask the question), rather than assuming that nobody has ever considered the issue?

    I'm not saying you should never ask questions, and I'm not saying that scientists are never wrong. But on the whole, they're pretty smart people who have a genuine desire to understand how the universe works. It might make sense to assume that questions that you can think up based on a cursory understanding of galactic dynamics are questions that have already occurred to someone whose career is studying that, rather than assuming that these questions don't ever occur to anybody but you.
    Conserve energy. Commute with the Hamiltonian.

  30. #30
    Join Date
    Oct 2009
    Location
    a long way away
    Posts
    10,374
    Quote Originally Posted by Dave Lee View Post
    So, did we really see any gas cloud moving in?
    If yes, would you please direct me to the relevant article?
    Here is one: https://www.nature.com/news/why-gala...a-flop-1.15591

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •