Is M85 Missing a Black Hole?

Article written: 16 Oct , 2011
Updated: 24 Dec , 2015
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The conventional wisdom of galaxies is that they should have a central massive black hole (CMBH). The presence of such objects has been confirmed in our own galaxy as well as numerous other galaxies, including the Andromeda galaxy (M31) and even some dwarf galaxies. The mass of these objects, several million times the mass of the Sun, has been found to be related to many properties of galaxies as a whole, indicating that their presence may be critical in the formation and evolution of galaxies as a whole. As such, finding a massive galaxy without a central black hole would be quite surprising. Yet a recent study by astronomers from the University of Michigan Ann Arbor seems to have found an exception: The well known M85.

To determine the mass of the CMBH, the team used the spectrograph on board the Hubble Space Telescope to examine the pull the central object had on stars in the nearby vicinity. The higher this mass is, the more quickly the stars should orbit. This orbital velocity is detected as a shift in the color of the light, blue as the stars move towards us, red as they move away. The amount the light is shifted is dependent on just how fast they move.

Doppler shift of gas and dust caused by M84's supermassive black hole. Image Credit: Gary Bower, Richard Green (NOAO), the STIS Instrument Definition Team, and NASA

Doppler shift of gas and dust caused by M84's supermassive black hole. Image Credit: Gary Bower, Richard Green (NOAO), the STIS Instrument Definition Team, and NASA

This technique has been used previously in other galaxies, including another large elliptical of similar brightness in the Messier catalog, M84. This galaxy had its CMBH probed by Hubble in 1997 and was determined to have a mass of 300 million solar masses.

When this method was applied to M85 the team did not discover a shift that would be indicative of a black hole with a mass expected for a galaxy of such size. Using another, indirect method of determining the CMBH mass by looking at the the amount of overall light from the galaxy, which is generally correlated with black hole mass, would indicate that M85 should contain a black hole of 300 million to 2 billion solar masses. Yet this study indicates that, if M85 contains a central black hole at all, the upper limit for the black hole would be around 65 million solar masses.

This study is not the first to report a non-detection for the galaxy, a 2009 study led by Alessandro Capetti from Osservatorio Astronoimco di Torino in Italy, searched M85 for signs of radio emission from the black hole region. Their study was unable to detect any significant radio waves from the core which, if M85 had a significant black hole, should be present, even with a small amount of gas feeding into the core.

Overall, these studies demonstrate a significant shortcoming in secondary methods of black hole mass estimation. Such indirect methods have been previously used with confidence and have even been the basis for studies drawing the connection between galaxy evolution and black hole mass. If cases like M85 are more common that previously thought, it may prompt astronomers to rethink just how connected black holes and a galaxies properties really are.

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17 Responses

  1. Torbjörn Larsson says

    But isn’t galaxy mergers supposed to be able to kick one or perhaps even both CMBH’s out? Maybe it is a recent galaxy zombie. “Army of lightsources.”

    • Anonymous says

      I’m also wondering if maybe *both* models of galactic formation might be correct? Maybe galaxies sometimes formed from an extension of the accretion disk of a large black hole, and sometimes they formed directly from collapsing gas clouds.

      Maybe M85 is simply an example of the latter type of galactic formation (though your idea seems a bit more likely to me;)).

  2. Jonathan May says

    If the CMBHs were kicked out, wouldn’t they have enough gravity to drag matter/stars/etc away from the parent galaxy with them?

    • Anonymous says

      Well, actually, even though it is super massive, the gravity of such objects doesn’t go THAT far, as one might think. It only affects the very inner region. Probably of the order of 10 parsecs. On its way out it would certainly drag some stars with it, but only those which lay in the path of the SMBH.
      The galaxy itself wouldn’t care that much. The SMBH is not the dominating gravity source in a galaxy. The Dark Matter is.
      I think, there are some ideas concerning “lonely” SMBHs with some companion stars around them in intergalactic space. But those should be fairly hard to detect, naturally.

  3. Anonymous says

    I don’t know the complete details of this technique, but wouldn’t an unfortunately aligned large dust cloud be able to block our view of the central most part, as seen by Hubble?

    • Anonymous says

      There are a number of tests for dust along the line of sight. For example, one can take the ratio of the Hydrogen Alpha and Beta emission lines to get the so-called ‘Balmer decrement’, which is related to the amount of extinction caused by dust along the light path. There are others too that they no doubt would have used to rule out a major dust cloud…

  4. Anonymous says

    As I understand it our own galaxy’s black hole is a bit of a light weight when it comes to CMBHs, coming in at 10 million solar masses.

    A black hole with a mass M defines a gravitational potential ? = -GM/r and the Schwarzschild radius of the black hole is R_s = 2GM/c^2 where R_s/r = -2?/c^2. The force of gravity on a mass m is F = -m?? which has the magnitude |F| = m?/r = mR_sc^2/r^2, or the acceleration of gravity a = R_sc^2/r^2. We can then easily calculate the distance r at which the gravitational acceleration of a body equals the acceleration of 10m/sec^2 for a given R_s. For a SMBH with R_s = 10^7km (about that of our galactic BH) the distance out is

    r = sqrt{R_s*c^2/a} = sqrt{[10^9m*10^{16}m^2/s^2]/10m/s^2} = 10^{12}m

    or 10^{10}km.

    One can estimate the gravitational effective length of a black hole, or the region where its gravity can influence another star. We consider the gravitational force F = mR_sc^2/r^2 for a distribution of matter in a volume V so that m = ?V. For the gravity to influence a region the density of matter with some pressure P must have a pressure gradient less than the gravitaitonal force. Hence

    dP/dr < -?R_sc^2/r^2

    The pressure is P = F/A, A = area = 4?r^2, so dP/dr = -F/2?r The force is the work required to reverse the motion of a particle F = dE/dr, where E = mv^2/2, so F = mv(dv/dr) ~ mv(1/?t) for ?t the time it takes a particle to cross the volume with radius r so ?t ~ r/v. So setting this to equality and solving for r we get as an approximation

    ?v^2/r ~ ?R_sc^2/r^2

    and so

    r ~ R_s/(v^2/c^2) = R_s/?^3

    Most stars in a galaxy move at around 300km/sec for a ? ~ 10^{-3} which means the radius of influence by a CMBH is about 10^6R_s. For our 10 million solar mass BH this is then about 10^{13}km or around one light year. So Dr Flimmer’s estimate is more or less right. Now this refers not to just material that is nudged by the CMBH, but demarks a zone where material moving at this average velocity is going to more or less be gravitationally bound by the BH. For a billion solar mass BH the zone extends to about 1000 light years.

    LC

    • Roger Overcash says

      M 85 is a lenticular galaxy comparable in size ( size being a matter of definition) to the Milky Way, a spiral.
      A lenticular appears to be a transition point between a spiral and an elliptical the latter having a one to seven billion solar mass SMBH not being unusual. Our Milky Way’s SMBH has been estimated at 4.1 through 4.7 million solar masses depending on technique of measurement (I believe this estimate is way too small for reasons too lengthy to give here). Now, with this, I would expect m 85 to have an adequate mass SMBH to show a discernable Doppler shift indicating it’s presence. However, being a lenticular, this galaxy would also have a disk structure and if angled face on, would not show any discernable difference in red and blue shift. The image of m 85 with this article is under magnified and over exposed but still vaguely indicates only a small tilt from face on which would also give a small contrast in red and blue shift . The correct tilt should be known. ( please don’t discipline me for not researching this). An edge on tilt would show the full red/blue Doppler shift. The researchers however should know this and have compensated.
      Question; has anyone seen the spectra of m 85 in this article? I see m 84. This is starting to look like OPERA already.

      • Roger Overcash says

        An addition to my post addressing this time, the lack or the near lack of radio radiation detected in the direction of the core of m 85.
        M 85 contain predominately old yellow stars, a relative “clean” galaxy not having sufficient material (gas and dust) to create new stars. Being “clean”, it is not surprising that an accretion disk is small or not available to create radio radiation ( the mechanism here is rather complex but not unlike the earth’s magnetic field being stretched back by a solar storm, snaps and recombines nearer the earth releasing radio radiation (energy) in the process). Without an accretion disk, jets cannot form.
        The lack of or the presence of an accretion disk due to stars within the roach limit of the SMBH is not surprising either way as this is not an on going continual process for a stable mature galaxy. Under these conditions, the lack of detecting radio radiation in the core of this galaxy is not suitable evidence to dismiss the presence of a SMBH.

      • Anonymous says

        I will confess that I am not heavily educated in the structure of galaxies. If I understand what you are saying the galaxy with a small CMBH that is in a quiet state would not give much signature of such a BH at a distance. I would imagine that an observer 100 million light years away at some other galaxy and 100 million years in the future would have difficulty finding the CMBH in our galaxy. The CMBH in the Milky Way is rather small, and it does not have the huge tell tale jets and activity we see in other galaxies with CMBHs that are 10 or 100 times the mass. Of course there may be episodes of increased activity and if M85 has a small CMBH it might have similar episodes. We may just be seeing M85 in a period of relative dormancy at its center.

        LC

      • Roger Overcash says

        I agree with you in that we may just be seeing M85 in a period of relative dormancy at its center and this may explain the lack or near lack of observed radio radiation.
        There are many ways to indirectly observe a black hole of any size and “roughly” determine its mass. Radio radiation, X-rays, ultraviolet radiation, synchronous radiation, etc. These however require interacting matter. A “lone” black hole of any size could go undetected except for any gravitational lensing it might exhibit. In a binary system, the visible star will show a tale tail wobble and the BH is almost always accompanied by an accretion disk. Another way is to resolve stars near the SMBH. On months end observation, orbits and speeds can be determined for stars near the SMBH and thus the mass of the SMBH. This requires high magnification and resolution to be achieved. The Andromeda and a few ellipticals in the Virgo cluster has been examined in this manner. Note: M85 is on the inner edge of the Virgo cluster.
        Gravitational lensing is another way (already mentioned).

        Now, the next technique, one used by the astronomers conducting the study of M85s “CMBH”, is a spectrum of the galaxy. You as a physicist already know that a blue Doppler shift indicates movement towards you and a red shift is receding movement. A spectrum of an edge on or nearly edge on spiral should show both red and blue shifts as the stars on one side of the galaxy is revolving towards you and the other side away from you. A strong marked difference in the red and blue shift shows a higher speed towards and away from you and thus indicates a more massive CMBH. Now, lets imagine a spiral or disk faced on. From our vantage point we neither see the stars recede or approach, they are essentially going around in circles. A Doppler shift will not be indicated here. The angle of tilt of a galaxy will influence the red/blue Doppler shift giving a misleading value if not considered in the analysis.

        *The picture of M85 in this article is unclear but vaguely indicates a small tilt from face on. This would naturally show only a small red/blue shift ( the results obtained) regardless of the mass of the CMBH. Also, I have not seen a Doppler spectrum of M85 in this article but it shows one of M84. This galaxy, visually, should contain a much larger CMBH. I wonder if the researching astronomers here are graduate students.
        I value very much your opinion. What do you think.

      • Anonymous says

        As I calculated above a 10^7M_sol BH would only have serious influence on stars out to about a light year. Stars moving at about galactic orbital velocities would be bound to this BH within that radius. That is not an enormous distance when compared to galactic scales. It would be very hard to image something to that small an angular resolution. The JWST might be able to do this with sufficiently nearby galaxies.

        These large black holes are actually a rather small part of the gravitational make up of a galaxy. This is even for the giant SMBH that come in at a billion solar masses.

        LC

  5. Anonymous says

    I have a question about black hole forming.
    I know that a black hole means too much mass in a too tiny volume.

    Is the black hole formed in a star the cause of the explosion? The outer shell explodes and compresses the matter during the explosion?
    Or is the black hole formed because there is too much mass after the star exploded and it cooled so much that it shrinks beyond the event horizon.

    Is there a lower limit in mass where black holes can naturally form?
    I know that in the case of the LHC black holes can form but could this also occur naturally on gas clouds? E.g. I doubt that Jupiter could collapse into a black hole if it cools down to 0 Kelvin. Unless you create a shell around it and detonates it like a nuclear bomb?

    • Anonymous says

      Well, these are kind of fundamental questions, and need probably a longer answer. But let’s see.

      A star (building stellar sized black holes – for the SMBHs at galactic centers there must be a different mechanism….) is stable, because the radiation pressure balances its gravity.
      A planet is (interestingly) stabilised by degeneration pressure of the electrons in atoms (the reason why atoms are stable). Even if you would cool them down to 0K they would still be stable.

      But back to the stars. How a star’s life ends depends on its mass. A star with a similar mass to the sun ends rather quietly. The hydrogen burning ends (probably goes on up to carbon, but that’s not so important here). That means that the heat pressure from below is going down causing the stars interior (close to the core) to shrink. Thus it will reheat. However it is not enough to cause a new fusion process. The core keeps shrinking until a similar process begins that also keeps planets stable: The electrons degenerate. That is a strong pressure countering gravity, keeping the core stable. Due to the heat, the outer layers of the star expand and flow away leaving behind the hot core. A white dwarf is born.

      If a star is more massive than about 8 solar masses, things are different. The fusion process happens faster and it goes all the way up to iron. After that you would lose energy through fusion instead of gaining it. So the fusion process comes to a hold, eventually. In fact, the last few fusion steps from, say, oxygen to iron happen on the order of days. So, we can safely assume, that almost instantaneously a massive iron core is build, which cannot stabilise itself at that moment. The core has a mass which is greater than 1.4 solar masses, the Chandrasekhar limit. Beyond that mass electron degeneracy is not able to stabalise the core. The electrons get sort of pushed into the nuclei unleashing a burst of neutrinos while the electrons and protons combine to neutrons. The outburst of neutrinos slams into the outer layers of the former star, causing a sudden movement outward – that is to say; an explosion. A supernova.
      Neutrons can also degenerate. This means, if the core is less than about 3 solar masses it can be stabalised by the neutron degeneracy. Everything more massive than 3 solar masses cannot counter gravity and will become a black hole.

      I hope, this made it somehow clear, how it works. Degeneracy, as a short explanation, the effect that two individual fermions (like electrons or neutrons) cannot be in the same state. I.e., they cannot be in the same place at the same time with the same parameters. At least one thing has to be different. So, they kind of push each other around causing a lot of pressure!

      Concernung your question, if there is a lower limit to black holes: Well, in principle: No. Anything that shrinks below its event horizon becomes a black hole. But usually it is quite hard to compress something so much that it becomes a black hole. As we have seen, you need a fairly massive star to build one at all. The core must be more massive than 3 solar masses. The rest of the star is not counted in that and is probably a lot more massive.
      The LHC black holes are no threat, if they exist at all. The reason for that is: Nature has far better accelerators than we can possibly build. The earth is hit by lots of particles orders of magnitudes more energetic than the particles of the LHC every day. And yet, here we are! So, don’t worry, we are safe from the LHC. 😉

    • Anonymous says

      Well, these are kind of fundamental questions, and need probably a longer answer. But let’s see.

      A star (building stellar sized black holes – for the SMBHs at galactic centers there must be a different mechanism….) is stable, because the radiation pressure balances its gravity.
      A planet is (interestingly) stabilised by degeneration pressure of the electrons in atoms (the reason why atoms are stable). Even if you would cool them down to 0K they would still be stable.

      But back to the stars. How a star’s life ends depends on its mass. A star with a similar mass to the sun ends rather quietly. The hydrogen burning ends (probably goes on up to carbon, but that’s not so important here). That means that the heat pressure from below is going down causing the stars interior (close to the core) to shrink. Thus it will reheat. However it is not enough to cause a new fusion process. The core keeps shrinking until a similar process begins that also keeps planets stable: The electrons degenerate. That is a strong pressure countering gravity, keeping the core stable. Due to the heat, the outer layers of the star expand and flow away leaving behind the hot core. A white dwarf is born.

      If a star is more massive than about 8 solar masses, things are different. The fusion process happens faster and it goes all the way up to iron. After that you would lose energy through fusion instead of gaining it. So the fusion process comes to a hold, eventually. In fact, the last few fusion steps from, say, oxygen to iron happen on the order of days. So, we can safely assume, that almost instantaneously a massive iron core is build, which cannot stabilise itself at that moment. The core has a mass which is greater than 1.4 solar masses, the Chandrasekhar limit. Beyond that mass electron degeneracy is not able to stabalise the core. The electrons get sort of pushed into the nuclei unleashing a burst of neutrinos while the electrons and protons combine to neutrons. The outburst of neutrinos slams into the outer layers of the former star, causing a sudden movement outward – that is to say; an explosion. A supernova.
      Neutrons can also degenerate. This means, if the core is less than about 3 solar masses it can be stabalised by the neutron degeneracy. Everything more massive than 3 solar masses cannot counter gravity and will become a black hole.

      I hope, this made it somehow clear, how it works. Degeneracy, as a short explanation, the effect that two individual fermions (like electrons or neutrons) cannot be in the same state. I.e., they cannot be in the same place at the same time with the same parameters. At least one thing has to be different. So, they kind of push each other around causing a lot of pressure!

      Concernung your question, if there is a lower limit to black holes: Well, in principle: No. Anything that shrinks below its event horizon becomes a black hole. But usually it is quite hard to compress something so much that it becomes a black hole. As we have seen, you need a fairly massive star to build one at all. The core must be more massive than 3 solar masses. The rest of the star is not counted in that and is probably a lot more massive.
      The LHC black holes are no threat, if they exist at all. The reason for that is: Nature has far better accelerators than we can possibly build. The earth is hit by lots of particles orders of magnitudes more energetic than the particles of the LHC every day. And yet, here we are! So, don’t worry, we are safe from the LHC. 😉

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