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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!"
Large dosen't mean heavy. LARGE RED stars are going to be very thin, not much density. All of their material will be spread out over quite a large area. A LARGE BLUE star on the other hand, would be quite dense (and short lived...they burn their fuel much faster and die in billiant novas, or if they are TOO heavy, as blackholes.)
There are lies, damned lies, and statistics.
Why wouldn't these huge starts turn into black holes? This URL may help you
According to the web site: A star of 15 solar masses exhausts its hydrogen in about one-thousandth the lifetime of our sun. It proceeds through the red giant phase, but when it reaches the triple-alpha process of nuclear fusion , it continues to burn for a time and expands to an even larger volume. The much brighter, but still reddened star is called a red supergiant. Betelgeuse , at the shoulder of Orion, is the best-known example. Absolute luminosities may reach -10 magnitude compared to +5 for our sun.
Some of these supergiants are unstable and form the very important Cepheid variables. In their final stages, supergiants may explode into supernovae . The collapse of these massive stars may produce a neutron star or a black hole .
Some call me Howie Feltersnatch
And for some more black-hole info:
:). The last time I watched it, I was surprised how dark it was (no pun intended) for a "Disney Movie". May also have explained why I liked it so much as a kid...
Black Hole FAQ
And on a side note, it's been a long time since I've watched my DVD of "The Black Hole", so I may have to do that now
N.
"Nothing strengthens authority so much as silence." - Charles de Gaulle
YES, they can be that thin.
m
If I may be lazy and just give you a URL:
http://www.astronomynotes.com/evolutn/s5.ht
There are lies, damned lies, and statistics.
Actually, it will engulf the first three planets, but not extend to Jupiter.
A blog like any other.
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.
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.
HA! I just wasted some of your bandwidth with a frivolous sig!
You might want to check university pages, not just some guy's geocities page.
Stars collapse once the core has exhausted its available fuel. This is only a minute fraction of the star's total mass, but it's critical. When the core goes dark the rest of the star falls on it.
According to an article in Discover magazine a few years ago, parts of the star will fall towards the center with a speed as high as a third of the speed of light! This causes enormous pressure, during the "big crunch" the density of the star may be 5-6 higher than the density of a neutron star. IIRC the massive neutrino flux is produced at this time. BTW this "core" is substantially far larger than the core mentioned earlier.
Matter can't be compressed this hard for long and the core "bounces" back. That is what flings the outer layers of the star into space. But force goes both ways - what throws stellar masses into space also increases the pressure on the remaining core. If the density gets too high a black hole is created and it quickly consumes the core, but the outer layers have already been ejected. Otherwise the core eventually bounces back entirely and you have a neutron star. A neutron star is a core of degenerate matter covered by a layer of normal matter.
You do not get cycles of explosions.
(I seem to recall hearing about flares on neutron stars after enough normal mass has fallen to trigger fusion, but those flares are fall smaller than supernovas.)
For every complex problem there is an answer that is clear, simple, and wrong. -- H L Mencken