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Survey of Super Massive Black Holes Completed

Posted by ryuzaki0 on from the now-we-know-where-not-to-go dept.

eldavojohn writes "NASA has announced the completion of a survey of nearby supermassive black holes. Every galaxy that revolves around a supermassive black hole within 400 light-years of our own galaxy has been cataloged. From the article: 'Called active galactic nuclei, or AGN, these black holes have masses of up to billions of Suns compressed into a region about the size of our solar system. The all-sky census, performed using NASA's Swift satellite over a nine-month period, detected more than 200 nearby AGN.' I'm starting to feel very lucky to have grown up in the Milky Way Galaxy."

9 of 169 comments (clear)

  1. 400 light years isn't that far... by mhotchin · · Score: 5, Informative

    400 lightyears? Didn't the submitter read the article?

    It's 400 *million* light years.

    1. Re:400 light years isn't that far... by CodeBuster · · Score: 3, Informative

      Indeed, the nearest major galaxy in the local group is actually the Andromeda Galaxy at ~2.5 million light years distance, give or take a few thousand since the distance can only be measured relatively indirectly via Cepheid variable stars. The Andromeda galaxy is also thought to be on a collision course with the Milky Way (although it is impossible to know for sure if they will actually collide because the tangential velocity of the Andromeda Galaxy with respect to the Milky Way is not known). So, assuming that some other disaster does not befall humanity in the meantime, which would certainly be miraculous given our recorded history and more recent events, we will know the answer in ~3 billion years or so (predicted time to impact or convergence rather since both galaxies are mostly empty space).

  2. 400 light years?!?! by philgross · · Score: 3, Informative

    That would be 400 million light years. 400 light years wouldn't get you out of our local arm of the Milky Way.

  3. We Live in a (semi-)Active Galaxy by idsfa · · Score: 3, Informative

    Hate to break it to you, but there's a >million solar mass black hole at the center of our galaxy. We're not considered an "Active Galaxy" only because it is on a diet.

  4. Re:Is this survey to be trusted? by Harmonious+Botch · · Score: 4, Informative

    Considering our space boffins have a problem seeing large asteroids really close up -- not even one light second away...why should we believe that they have seen all the black holes many light years away?"

    Because black holes - or, to be precise, the region in space right next to them - emit a lot more radiation. A LOT MORE.

  5. Density of black holes by Harmonious+Botch · · Score: 4, Informative

    The average density of a supermassive black hole can be very low, and may actually be lower than the density of water.

    That sounds suspicious, especially coming from wikipedia. Something with a density that low could not likely bend light enough to keep it from escaping, even if very large.

    The singularity that bends light does not have that low density. It has an incredibly high density. But the AVERAGE density is the mass of the singularity divided by all that space inside the event horizon.

    1. Re:Density of black holes by GeffDE · · Score: 4, Informative

      No, the actual physical object is the volume inside the event horizon. Why is it called a black hole? Because anything that entered the event horizon does not escape. So a black hole is the volume enclosed by the event horizon. The singularity is the extraordinarily dense pit of gravity at the center of a black hole. They are two different things. Defining the size of a black hole by its event horizon is...how it should be done, if you think about it. The "object" in the middle is was causes all the action to happen, but that doesn't make it the only part of a black hole.

      --
      It has been a nervous year, with people beginning to feel like Christian Scientists with appendicitis.
  6. Re:relativity by ajs · · Score: 4, Informative
    That sounds suspicious, especially coming from wikipedia.

    It would sound more reasonable coming from Slashdot? What source of information on the Web do you think is more reliable? I've certainly fixed my share of errors on Wikipedia, but that's becuase I hunt them down, as do many others. That kind of fact-checking is almost non-existant on most of the Web, so if I'm going to trust any one source (and I don't) for such information, it would be Wikipedia.

    And, as others have noted, you were mis-understanding the definition of "average density". There's a fairly well-known calculation that states that a spherical volume of material with the density of water, and a diameter less than that of Jupiter's orbit would form an event horizon, effectively constituting a black hole. It's a nice visualization of a complex phenomenon. R. Huber has done the math for us (pdf) if you want to check for yourself.

  7. Re:relativity by Ckwop · · Score: 3, Informative
    That sounds suspicious, especially coming from wikipedia. Something with a density that low could not likely bend light enough to keep it from escaping, even if very large.

    It's nice to see a skeptic; It's a virtue to be a skeptic and not a sin. However, in this case your skepticism is misplaced.

    The simplest black hole solution to the equations that govern General Relativity is Schwarzschild's solution. In this he shows that the radius of a black hole is directly proportional to its mass. Elementary geometry tells us that the volume of a sphere is proportional to the cube of the radius. Therefore, the density, which is just mass over volume, that is required to create a blackhole decreases the more mass you have.

    I find the figure fairly reasonable for the amount of mass these super-massive black-holes contain.

    Simon