Difference between a neutron star and black hole

Quote: Wizard

I have heard the expression agujero negro for a black hole. That would seem to go against the idea that agujero is a small hole, like the kind caused by a pin prick. Then again, maybe the source was not clear on the distinction between hoyo y agujero.

Actually, a black hole is extremely small and incredibly massive (a teaspoon full weighs millions of tons), so a Spanish-speaking astronomer might be inclined to use his word for "small hole" to emphasize the size of the black hole relative to the expanse of stellar matter surrounding it.

Quote: NowTheSerpent

Actually, a black hole is extremely small and incredibly massive (a teaspoon full weighs millions of tons), so a Spanish-speaking astronomer might be inclined to use his word for "small hole" to emphasize the size of the black hole relative to the expanse of stellar matter surrounding it.

I think you may be confusing a black hole with a neutron star, which does have that kind of density. At the risk of hijacking the thread, and being wrong, nobody is sure how big black holes are in terms of size, since they can't be directly seen.

In a thread a while back I postulated that "infinity" is just an abstract concept, and there in the universe we live in nothing is infinite. Somebody challenged me saying a black hole has infinite density, but when I pressed for evidence I was denied.

I think I can fairly say that everyone agrees that hoyos negros are extremely massive and extremely small, but nobody is sure in what form that mass exists. Perhaps it spills over into other dimensions.

Quote: Wizard

I think you may be confusing a black hole with a neutron star, which does have that kind of density.

A black hole would have an even greater density, as it has an even greater gravitational gradient that can trap light. Neutron stars not only not trap light, they emit it in various frequencies, including radio waves.

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At the risk of hijacking the thread, and being wrong, nobody is sure how big black holes are in terms of size, since they can't be directly seen.

True. But you can see the event horizon and you can measure it's size. We can also measure a black hole's mass. Divide mass by volume and you have the density.

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I think I can fairly say that everyone agrees that hoyos negros are extremely massive and extremely small, but nobody is sure in what form that mass exists. Perhaps it spills over into other dimensions.

Well, we know they emit Hawking radiation, or something like that. What I can say with almost absolute certainty is: everything is always far more complicated than it originally appears to be. So far we can't see the "singularity" that si the actual black hole, jus the event horizon around it. So long story short: we don't know much about the dimensions of black holes, save what we can infer from what's around them.

Quote: Nareed

True. But you can see the event horizon and you can measure it's size. We can also measure a black hole's mass. Divide mass by volume and you have the density.

I thought the event horizon was the point at which the gravity of the black hole was strong enough to pull light in. This would obviously be much larger than the black hole itself. So, I can see how we could get the mass of the black hole from the event horizon, but not the size.

Getting back to Spanish, I bought a lot of kids' books in Spanish at a bookstore in the Mexico City airport, including the whole series of "Diary of a Wimpy Kid" books. I knew we had the English versions at home, which my son likes. Anyway, the Spanish version translated "wimpy kid" to renacuajo, which translates back to English as "tadpole." Any comment from the more experienced readers on other usages of the word renacuajo?

Quote: Wizard

I thought the event horizon was the point at which the gravity of the black hole was strong enough to pull light in.

At this point you should ask an astronomer, or a science writer.

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Any comment from the more experienced readers on other usages of the word renacuajo?

I've never seen nor heard it used as anything other than a tadpole.

Quote: Wizard

I think you may be confusing a black hole with a neutron star, which does have that kind of density. At the risk of hijacking the thread, and being wrong, nobody is sure how big black holes are in terms of size, since they can't be directly seen.

Possibly. I know that both neutron stars and black holes are products of supernovae explosions and have incredible gravity. A neutron star will result from the gravitational contraction of the supernova remains, but if the contraction is rapid and massive enough (ten solar masses or more), it will continue to collapse the matter in on itself, thus forming the black hole, which will of necessity be extremely small, the event horizon itself being no more than (maybe) 20 miles across - hence the appropriate use of the word agujero, "puncture", "pin hole" - compared to the expansive accretion disk of thousands of miles surrounding it. Incidentally, Cygnus X-1 has been nearly confirmed to contain a black hole; Circinus X-1 may contain just a neutron star.

Quote: Wizard

I thought the event horizon was the point at which the gravity of the black hole was strong enough to pull light in. This would obviously be much larger than the black hole itself. So, I can see how we could get the mass of the black hole from the event horizon, but not the size.

There is actually a formula for the radius of a black hole (if you know the mass):

Surprisingly, if it were possible to actually reach the massive black holes at center of galaxy's, they would only be about 20 times the density of air. The more massive the black hole, the less dense it would be. Read the "[w]hole" article here

I am curious what "Wizard's Dad" would have to say. New observation platforms have been launched since the article referenced above was written in the mid-nineties.

Quote: Ayecarumba

Surprisingly, if it were possible to actually reach the massive black holes at center of galaxy's, they would only be about 20 times the density of air.

Oh come on, that can't be right... can it?

One interesting thing that has occurred to me is that prior to accumulating enough mass so that light cannot escape, the light that would be transmitted out would be traveling at the speed of light, no experiment in space would show the speed as different. Then when it turns into a black hole, nothing. It would be like turning off the radiation with a switch!

It also occurs to me that within the black hole, nothing much would have seemed to have happened. If it were possible to conduct experiments, again light would be observed to have that same speed. [I'm less sure about within the black hole]

I was watching more Discovery ("through the Wormhole" maybe?) and the subject was neutron stars. They explained how they came to be and what they are, and went on to say that the gravity on the surface of said star was one million billion times that of the surface of Earth. I found that quite incomprehensible, so I'm glad they gave an example - If your house was on the surface of the star, and you climbed onto your kitchen counter and jumped off to the floor, by the time you reached the floor you would be traveling at Four Million Miles Per Hour.

The universe is amazing =) This random fact brought to you by Morgan Freeman.