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Largest Black Hole Measured
porkpickle tips us to a BBC article on the quasar OJ287, a binary object containing largest black hole yet discovered, weighing in at 18 billion times the mass of Sol. Researchers were able to estimate its mass due to the presence of a smaller black hole in orbit around it. When the smaller companion's orbit intersects OJ287's accretion disk, once every 12 years, it triggers a burst of radiation that was detected by the Spitzer Space Telescope. More detail and a diagram are available on the Turku University site.
My googling says its even more impressive (http://curious.astro.cornell.edu/question.php?number=31) 100 billion stars in the Milky Way and most are smaller than the sun, so 18 billion makes it very greedy indeed!
A black hole has an event horizon. This horizon has a very well-defined size.
The event horizon is often considered the size of a black hole since nothing could ever leave that space.
I think astronomers are reluctant to guess at a size limit now as they don't want another discovery to make them look like asses.
There is no "I disagree" mod for a reason. Flamebait, Troll, and Overrated are not substitutes.
Using this illustration and my trusty piece of paper straight edge, I estimate the long axis of the orbit to be 21000 AU and the minor axis to be 16000 AU. Using Ramunjan's Approximation for the circumference of the elliptical orbit and converting to light years, I guesstimate the circumference of the orbit to be ~1.99 (call it 2) light years.
For a 12 year orbital period this means that the orbiting black hole is AVERAGING 1/6c (~49965km/sec, call it 50k km/sec)... meaning at periquaserion it's really booking! Much faster than The Dash!
Tom.
Actually it's way more complicated than that. Only non-rotating black holes could ever truly be point masses. Any angular momentum creates complicated tidal effects near the center, resulting in a non-point-mass. Carried further, the "singularity" expands until the point where it would effectively reach the event horizon itself, resulting in a naked singularity, which some calculations have shown can have actual size. Adding further rotation will (to a point), actually change the size of the "singularity". Of course, this is all moot, since that's not at all what the article was talking about, but that's my .02$.
Other people have answered your question (radiation cannot escape from inside the horizon, but it can still generate a static external field), but here is a FAQ with more detail, including the quantum picture.
Furthermore, as the Earth-Sun barycenter is well outside the Sun's Schwarzschild radius, it would be outside the event horizon of a solar-mass black hole, too. Not that the location of the barycenter even matters to the stability of the orbit.
There are exoplanets — the first discovered, actually — known to orbit neutron stars, which are only 10-20 km in radius. There's no reason why planets couldn't orbit black holes too.
That's misleading, and I'm guessing you don't really understand what you're describing. A rotating black hole (aka every black hole, to some extent), is still a singularity (no need for quotation marks, it still has zero volume) despite not being a point. It's a ring with zero cross-sectional area, sort of like an infinitely thin thread arranged in a circle.
Furthermore, this thread is based on quibbling over semantics without really understanding what the author quite validly meant. The "black hole" aspect of a singularity is a description of the effects of its event horizon, which of course scales with mass. A more massive black hole is by definition larger then a less massive black hole. Someone mod this up so this misunderstanding can be cleared up for more people.