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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.
It seems they were able to measure temperature and luminance, thus making them red [super]giants.
A blog like any other.
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
KW johnholmesitarii (9,800 light-years away), V354 ronjeremycephei (9,000 light-years away), and KY lexingtonsteelcygni (5,200 light-years away).
we're ripping up the neighborhood!
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
Light pressure and the heat of fusion.
Stars don't become black holes until they burn up their fuel, collapsing (and perhaps exploding, perhaps even multiple times) in on themselves until they are much more dense than any visible stars. Then, assuming they they haven't blown off so much of their mass that they no longer have enough mass and will instead become a dwarf or a neutron star, they can collapse to become a black hole.
Link: HOW BLACK HOLES ARE FORMED
"It is our blasphemy which has made us great, and will sustain us, and which the gods secretly admire in us." - Zelazny
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.
Already happened, back in March of 1987 in the Large Magellanic Cloud in the Southern Hemisphere. Sure, it was 100K light years away, but it's still pretty substantial.
Please stand clear of the doors, por favor mantenganse alejado de las puertas
This puppy would actually eclipse Saturn, whose mean orbit is about 1.43 billion km.
In Soviet Russia, all our base are belong to you!
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.
Well, that may not be true, either, according to the article I read about a decade ago:
/. What have I done?
ApJ article (1993): Our Sun III
Oh gosh, I referenced ApJ in
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!
Question is a bit weird.
but I'll try to answer it in the most intelligent way I can.
Gravity is supposed to travel at the speed of light. So if we can observe the light from these large stars, they are still fusion powered light sources as far as we are concerned. So, no - not black holes (yet).
As measured by the astronomers, the distance between us and these stars makes any gravitational influence they may have on us irrelevent. Unless these measurements are wrong...but you would need good reason to doubt either the observable data or the theoretical physics behind our interpretation. The inverse square law is fairly simple, with just high school algebra you can even work it out yourself if you know what the variables are.
Again, if you trust the physics our scientist have learned over the last century: No, we can't be inside the event horizon of a black hole. Black holes and the region around them are not euclidian. Which is another way of saying normal geometry (and Newtonian physics) do not work. Consider the following (but please get a second opinion from a "real" physicist as I'm just pulling it off the top of my head): Relativity tells us there is no such thing as an absolute frame of reference. Within an event horizon, however, you can not avoid the presence of the singularity.
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.
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
> certainly more massive
:) You also lose points for not mentioning the Eddington limit, which is just so damn cool it should be mentioned in any discussion of stellar dynamics, even if it's not actually explained. (Eta Carinae, you're the one...)
Correct.
> probably just as dense (if not denser
Incorrect, both in the sense of mean density and in the sense of the density of most of the star.
> they are much, much hotter
Incorrect.
> the bigger a star is, the hotter it must be to
> equilibriate
The more massive a star is. Not bigger. The discussion is big in terms in volume. And it's only hotter while it's on the main sequence/during the hydrogen burning phase.
> contrary to what you might expect, the bigger a
> star is, the shorter its lifetime is, since it
> has to consume its fuel so much faster.
True for values of bigger==more massive.
See e.g. Carrol and Ostlie, chapters 10 and 13.
> So to answer your question, the reason these
> stars don't become black holes is the same as
> the reason that any supermassive stars don't.
There is no "reason these stars don't become black holes." They likely are becoming black holes. The reason they aren't black holes is because they haven't gotten there yet. In the global sense, the black hole is a much, much lower energy state than a cloud of hydrogen, so it takes a long time to blow off all that energy.
> The only difference with these is that they burn
> their fuel much faster than other stars,
> and correspondingly, can be expected to snuff it
> much sooner.
Correct.
> I might be wrong about some of this, but I'm
> pretty sure most of what I said is true, at
> least to a first approximation.
Um, better luck next time?
Qualification: I'm a PhD candidate in astronomy. So, although astrophysics isn't my field, I at least know my stuff well enough to pass my comps.