View Full Version : Most massive body known?

02-27-2004, 09:16 AM
What is the most massive celestial body currently known? I'm guessing maybe a quasar somewhere.

Please don't say Marlon Brando.

02-27-2004, 09:24 AM
Well, it would be that guy from the Guinness Book of World Records who died a few years ago, who weighed over 1,000 pounds! ;)

Seriously, the most massive star whose mass is in fact known is half of a double system in Cepheus -- I don't recall which Greek-letter designation the system is. There may well be more massive single stars, but the calculation of stellar masses is educated guesswork except in doubles. Probably S Doradus might qualify.

Nobody is certain what the quasars in fact are. If they are single, unary bodies radiating at the rate they appear to, and in fact as distant as their red-shift suggests that they are, then they would indeed be more massive by far than any known star. But all this depends on hypotheses as to their distance and hence their absolute radiative output based on their observed output and speculative distance, their actual composition (star? closely-packed group of stars heterodyning? sequence of supernovae setting each other off in order? something else entirely?), etc.

02-27-2004, 09:29 AM
What is the most massive celestial body currently known? I'm guessing maybe a quasar somewhere.

Please don't say Marlon Brando.

I donlt know that a Quasar counts as they sort of aren;t an object unto themselves. I think Quasars are a 'result' of the presence of a supermassive black hole at the center of a distant galaxy. As such I'd say the most massive celestial body know would be a supermassive black hole. The ones that cause quasars I think are near a billion solar masses so biggest or not they are quite massive.

I also assume by 'massive' you mean the actual mass of the object in question and not the volume of space it fills.

02-27-2004, 01:09 PM
Yeah, you'd have to define "body", and even then there'd be a lot of "definitional threshold" problems. Is the local group of galaxies a "body"? No, you say, because it is way too thinly dispersed and full of vast areas that are essentially a vacuum. And you say the same thing about an individual galaxy. But many stars are themselves pretty tenuous, and defining where they quit -- where the boundaries are -- isn't always a straightforward matter. Consider this thing (http://www.starlore.net/epsaur.htm), which might be a candidate. At times the entire system has been described as a star, at other times as a huge cloud containing a star, or as a huge attenuated star containing stars of its own wit hin itself.

02-27-2004, 03:17 PM
I think if you're talking about something that isn't a cloud or a cluster of stars, then it would have to be one of the supermassive black holes that reside near the centers of galaxies. Some of these monsters are billions of solar masses and have event horizons larger than the diameter of the solar system. These things are so heavy that if their mass were spread out evenly within the event horizon, they would have about the same density as water. Saturn, for reference, is less dense than water. So imagine something with the slightly more than the density of Saturn, only big enough to swallow the entire solar system in one bite.

The masses of these objects can only be inferred from the velocities of stars and gas that orbit them. Hence there's a fair amount of error plus or minus. I've not seen a reference to the "biggest" of the supermassive black holes discovered so far, and perhaps none have been given that distinction because the error in weighing the things might be great enough to make such a designation unreliable. But there's no question the things are hugely massive, beyond all comprehension.

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