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Survey of Super Massive Black Holes Completed
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."
400 lightyears? Didn't the submitter read the article?
It's 400 *million* light years.
I'm starting to feel very lucky to have grown up in the Milky Way Galaxy.
Yes. Living near one of those super-massive black holes would certainly suck. Being one with everything around you sounds nice and radiant - but it leaves you all strung out over time, and it seems to take forever! The light at the end of the tunnel is you.
Ryan Fenton
They are black and holey
Oh great, did you have to bring race *and* religion into this?
Table-ized A.I.
The article says that it is every super massive black hole within 400 million light years. Also, as for being "lucky" to be in the Milky Way, our Galaxy has a super massive black hole at the center of it. Actually, we are a very typical galaxy. We are slightly larger than the average and we are a spiral galaxy (there are more elliptical galaxies and irregular galaxies than spiral). We are very typical. Also, as for being lucky about not being closer to the center of the galaxy (someone above mentioned that as well) if we were closer to the black hole at the center, it would not mean much. We are in an orbit around it and thus we won't be falling into it any time soon, even if we were closer to it. We do, though, have a great location in the galaxy. We are far enough out that we can look across the plane of our galaxy (only at some wavelengths because dust obscures a lot) and get a good view of it. We also can look out pretty well too. And to make things even cooler, our solar system actually bobs up and down through the main plane of the galaxy. It take about 30 million years to complete a complete cycle, but in 5 or so million years we will have a pretty cool view from above of the Milky Way. I don't remember exactly what the angle is that we would be viewing the galaxy from, not huge, but enough to be useful. The point of all this is that the advantage of this survey is to have a complete list of super massive black holes so as we are testing out theories we can apply these theories (and how they measure up) across not only a wide data set, but also a very complete set. There is so much left to be learned about black holes and this catalogue will certainly help.
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.
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.
First, the diameter of a "black hole" is proportional to its mass. The sun, for example, must be compressed to a diameter of about 3km to become a black hole. A black hole with the mass of billion suns would have a dameter=3 billion km or 1000 times our solar system. The density of this black hole would be "low" as in much thinner than air. (Do the math yourself. Mass of sun is 2x10E30kg)
Anyway, as a region of space gets denser, time slows down, and as the density approaches the density required to become black hole, time just freezes.
What you will see when looking at a "black hole" is just a region of space with the eventual event horizon of the hole just frozen in time, and as you move outside, time goes through the "molasses" stage, and as you get further away, gets normal.
The black hole will not form in any finite time since time there just stopped!
For the observer falling towards the "hole", time in the rest of the universe just speeds up. In a matter of minutes the universe will age billions of years, and the observer will first hand know the ultimate fate of the universe in a distant future.
don't cut it off www.mgmbill.org
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.