Survey of Super Massive Black Holes Completed 169
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 light years isn't that far... (Score:5, Informative)
It's 400 *million* light years.
400 light years?!?! (Score:4, Informative)
We Live in a (semi-)Active Galaxy (Score:3, Informative)
Re:Is this survey to be trusted? (Score:5, Informative)
Because black holes - or, to be precise, the region in space right next to them - emit a lot more radiation. A LOT MORE.
Density of black holes (Score:5, 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.
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.
Re:400 light years isn't that far... (Score:4, Informative)
Re:relativity (Score:5, Informative)
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 [chestnutcafe.com] (pdf) if you want to check for yourself.
Re:relativity (Score:3, Informative)
57600 light-seconds
10713600000 miles
The sun is 800,000 miles across. So, width-wise, the solar system is
13392 suns wide
Volume is the cube of the linear width, so the solar system could fit
2,401,797,132,288 sunc
in its volume.
Although the density of the core of the sun is very high, I'm thinking it's not so high that "billions" of suns would make such a volume be denser than water when that volume could hold two and a half trillion suns just to be as dense as one sun.
It may be more on the order of as dense as a helium baloon, or even lighter.
Re:Density of black holes (Score:4, Informative)
Re:relativity (Score:4, Informative)
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
...but 78 billion light years is TOO far (Score:3, Informative)
In actual fact the WMAP probe is the furthest we have seen, NOT the Hubble deep field since that looks at the Universe ~300k years after the Big Bang before there were any stars, let alone galaxies.
That said it was a nice video but it would have been nicer if they got their facts correct when trying to sound impressive!