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Three Largest Stars Identified
mOoZik writes "BBC News is reporting that astronomers have identified the three biggest stars known to science, having diameters of more than 1.5 billion km. If they were located in the same place as our own Sun - at the centre of the Solar System - the stars would stretch out further than the orbit of Jupiter!"
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Why wouldn't these huge starts turn into black holes?
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The mass of these stars must be outrageous. Could it be possible that they are already black holes that we are able to see only because we are already within the event horizon of the stars' gravitational pulls?
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Is that at least one giant goes supernova in my lifetime. I don't think that's too much to ask
:wq
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Anyone heard ahything that way?
I've heard anything from tomorrow afternoon to 2 milion years. I've heard it's been getting increasingly variable since 1940.
If it goes supernova (and it's WAY big enough) what would be the results here? Genetic disorders? Extinction? Has anyone done the math on this?
RS
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It would be interesting to find the largest non-red giant stars. As once our own sun turns into a red giant, it's radius is supposed to extend out past Jupiter as well.
This puppy would actually eclipse Saturn, whose mean orbit is about 1.43 billion km.
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Don't worry about it. These giants are big, but not necessarily massive enough to go supernova at the end of their lives.
Besides, hypothetically, even if it were to explode like a supernova, it won't affect us much. Here is the number:
d = distance to the closest giant (5200light-yr)
E = total energy arising from supernova (1e51erg or something like that)
The energy receied at the Earth is
E / (4 *pi *d*d).
Now compare this number with the energy we receive every second from the Sun:
E_sun / (4 * pi * r*r)
where r is the distance between the Earth and the Sun (1.5e13 cm). You do the math, then the ratio of these two quantities comes out to be:
[E/(4*pi*d*d)] / [E_sun/(4*pi*r*r)] ~ 2.4
So all we get from this supernova is about 2 seconds worth of energy received from the Sun. And I'll tell you that the actual energy received from the supernova is much, much smaller.
... and the astronomers name it the Beowulf Cluster.
Correct me if I'm wrong, but isn't red giants dencity pretty low? So when a star transforms into a red giant, it's bound to get much larger. So wouldn't it be cooler to find actually non-dying star of this magnitude?
(Well definetly not cooler)
Shows what little they know. If they were located in the same place as our own Sun, Jupiter would burn up and not have an orbit!
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Several other posts have danced around the question a little bit, without answering it directly. It's a good question.
While these stars are big, filling a large volume of space, the article doesn't mention their mass. This is the ultimate determinant of what becomes a black hole and what doesn't.
Stars have gravity trying to pull everything into the center off it's mass. In physics pressure is basically equal to temapture, so as all the mass is squezed together, it heats up and begins nuclear fission. This creates a lot of heat, and the star's mass tries to expand. Gravity and pressure find a happy meidum and that is how the star ends up a particular size.
As the star burns it's fuel, it has to get hotter or it will stop 'burning', due to the way nuclear fusion works. Eventually it will burn up its fuel and prssure will not balance gravity, and the whole star will collapse. If it is really heavy, say several times the mass of the sun, it will probably collapse into a black hole. If it is slightly heavier than our sun, it might end up as a very dense neutron star. Otherwise, it will end up as a white dwarf, a small star that is somewhat like a ember left over after a campfire. If a star is really massive it can also explode in a supernova to lose some weight and avoid becomming a black whole.
As I mentioned, the article doesn't say what the mass of the star is, but it's probably a safe bet that is above the black hole limit. When it finishes burining its fuel, it will likely go supernova and/or become a black hole.
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"1.5 billion km across" means nothing to me. How many Libraries of Congress could the star hold?
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If they were located in the same place as our own Sun - at the centre of the Solar System...
So that's where I left it!
I'm sure that someone who keeps up on the latest astronomical findings could give a better answer than I, but: No.
I doubt that there's much of a correlation between larger stars and larger planets orbiting them. The tricky thing about extrasolar astronomy is that we simply can't detect "normal" (i.e. non-gas-giant, although their prevalence might say that gas giants are actually normal, and rocky planets like the earth are maybe unusual) planets around other stars right now.
As far as I know, extrasolar planets are really only detected (or detectable, right now) in two ways: 1) find a star's wobble which can't be explained by visible objects. From the wobble and the mass of the star (extrapolated from its color, generally), calculate that there must be a planet of some size orbiting it. But to wobble a typical star takes a pretty big planet: an uber-Jupiter, especially if you want this wobble detectable from earth; 2) find that once in a while, several pixels on a CCD's image of the star get occluded by something transiting the star. Again, this takes something of considerable size.
There is a wikipedia article (at http://en.wikipedia.org/wiki/Extrasolar_planet with many more details, and disproving my guess that there are only two currently-used methods which have produced reasonably-confirmed planet detections -- pulsar timing methods have also seemed to work) which is relatively concise and nice.
Red supergiants may be large, but their density have been described by e.g. Larry Niven as "red-hot vacuum." At least their outer layers are very tenuous at best. Given that the masses are typically only a few orders of magnitude more than the Sun, at most, but that their volumes are enormously much bigger, there can't be that
This means (surface) gravity is low and they can get by with less hydrostatic pressure to maintain their bulk.
The *core* is typically very dense, much denser than the Sun. Higher pressures are needed to support fusion of higher-order elements. Makes the surface layers even less dense, since a lot of the mass is still in the core.
The right unit is: (pick one)
1/Furlongs
2/Light-Fortnight