This is worth a look;

http://www.cnn.com/2002/TECH/space/0...ter/index.html

Yeah, saw the story at;

http://spaceflightnow.com/news/n0204/11newmatter/

Now that is cool!

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Bailey’s second law; There is no relationship between the three virtues of intelligence, education, and wisdom.

Supposing it is really a "quark star", I wonder what could deter the final collapse into BH, once we know that quarks "merge" to form ordinary particles like protons. I'm charmed and feeling strange.[img]/phpBB/images/smiles/icon_smile.gif[/img]

I suppose I'll have something to talk to my astronomy prof. next week. As for the one billion tons per teaspoon, I had been instructed that was one hundred million tons per tsp. Am I wrong? The site? Both?


-Adam

Another take from the Washington Post

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<font size=-1>[ This Message was edited by: ToSeek on 2002-04-11 09:51 ]</font>

Here's an article with more details from the Washington Post(!):
http://www.washingtonpost.com/wp-dyn...2002Apr10.html

This actually makes sense, and you start to wonder why it wasn't predicted.

Neutron stars are formed when the temperature (energy) and pressure are high enough to prevent the continued existence of atoms and to allow (force?) the protons and neutrons to merge. Similar conditions existed in the early Universe.

And, before there were atoms, before there were hadrons, there were quarks. So, if the interior of a star can mimic the appropriate stage in the development of the Universe, then quark stars are possible... if not required. All that is needed is for the right energy level to exist for quarks to be "freed" from their hadrons and for there to be enough outward pressure to avoid the continuing collapse of the star.

"Those who are not shocked when they first come across quantum theory cannot possibly have understood it."
Niels Bohr

"I suppose I'll have something to talk to my astronomy prof. next week. As for the one billion tons per teaspoon, I had been instructed that was one hundred million tons per tsp. Am I wrong? The site? Both?" [Firefox]]

It depends if you're using the Martha Stewart or Betty Crocker Astronomy Cookbook.
The higher weight, one billion tons is probably a tablespoon. Since a teaspoon is 1/2 that amount, that would make a teaspoon 500 million tons. However, since the lower figure is 100 million tons, that would have to be a "pinch" in the classic astronomical cooking sense.

(:raig




<font size=-1>[ This Message was edited by: Mespo_Man on 2002-04-11 10:15 ]</font>

Looks like we have some bad Home Ec here. A teaspoon is 1/3 of a tablespoon. Just had to point that out. :P


-Adam

"Looks like we have some bad Home Ec here. A teaspoon is 1/3 of a tablespoon. Just had to point that out. [img]/phpBB/images/smiles/icon_razz.gif[/img]" [Firefox]

DAMN! No wonder my star recipies don't work out. They go supernova way too fast. It's Hell on the oven lining, also.

(:raig

The whole thing seems to raise a paradox, at least to my tortured brain. There would have to be an incredibly fine-tuned energy level to keep the quarks in such "suspension" mode, since the environment in the quark (i.e. quantum) level is unstable by definition. A little more mass and they collapse into a BH. A little less and the quarks decay into the run-of-the-mill matter. The task is to find the mysterious force (or effect) which can prevent the matter from ultimately collapsing into a Black Hole, after going beyond the Exclusion Principle.

<font size=-1>[ This Message was edited by: Argos on 2002-04-11 13:41 ]</font>

Um, it was predicted. Theorists have been writing papers about "strange stars" and "quark stars" for years. No one has really been able to work out a believable equation of state, though, as far as I understand it, and until now, there hasn't been any observational evidence to motivate people to really take it seriously beyond an interesting idea.

I don't know who came up with the idea first, but it wouldn't surprise me if it were decades ago. Neutron stars were first suggested in 1934, right after the discovery of the neutron, but they weren't discovered until 1967! So, I don't know when Strange Stars were first hypothesized, but I know I've seen papers published on the subject for years.

Don

Well, I haven't read the papers yet (I mean the Astrophysical Journal, not the New York Times!), so I can't be sure, but I would presume that it is indeed another kind of degeneracy pressure, just like electron degeneracy pressure holds up white dwarfs and neutron degeneracy pressure holds up neutron stars. Quarks are fermions, too, so presumably they would have their own degeneracy pressure. I'm not a theorist, so I'm not totally sure about that, but that's what I'd imagine it would be. I'm not sure what role the strong force would play in this. At those densities, wouldn't it be attractive? I'll have to read the papers and get back to this.

See ya,

Don

Right you are, Sir!

Weizmann Institute Astrophysicist Hot on the Tracks of a New "Strange" Star

January 12, 1998 - A new "strange" star is suspected to be lurking in our galaxy - and a Weizmann Institute astrophysicist is hot on its tracks.

In research published in the January 12 issue of Physical Review Letters, Prof. Vladimir Usov of the Institute's Condensed Matter Physics Department outlines the last of three characteristics that may enable astronomers to finally identify examples of strange stars, whose existence was predicted nearly 15 years ago.

The existence of such matter was posited in 1984 by Prof. Edward Witten of the Institute for Advanced Study in Princeton...

However, the theoretical strange stars would represent an even further stage in stellar evolution: according to Usov, when the core of a neutron star is sufficiently dense, neutron matter can be converted into quark matter.

Both neutron and strange stars are not only extremely stable but also improbably dense: one cubic centimeter of strange quark matter would weigh about 1 billion tons.

Although neutron and strange stars are similar in size and density, Usov used theoretical calculations to search for unique behaviors that would set a quark star apart from its neutron "cousin."

These three unique behaviors are as follows:

First, the energy of X-rays emitted by a strange star is about 10 to 100 times greater than that of X-rays emitted by a neutron star.

Secondly, the X-rays emitted by strange stars are fired in pulses, each lasting around 1 millisecond.

Finally, the strange star, while comprising mostly quarks, also contains a small quantity of electrons. As negatively-charged electrons try to escape from the star, a very strong electric field is created over its surface. This electric field causes spontaneous creation of pairs consisting of electrons and their positively charged counterparts, called positrons. The electrons and positrons can annihilate each other when they meet, leading to the release of high-energy gamma radiation. This so-called annihilation gamma-ray emission can be detected by astronomers.

http://wis-wander.weizmann.ac.il/wei...1.200.4.1.html

Does that mean that you could have a star so hot and/or dense that it was comprised entirely of super-strings?

<font size=-1>[ This Message was edited by: 4-Lom on 2002-04-12 03:47 ]</font>

You're probably right, Don. As Jim pointed out, there is at least one model which predicts quarks in state of degeneracy in the prime times universe. But we know that the degeneracy pressure keeping white dwarfs stable stems from well defined electromagnectic interactions and neutron stars from the Exclusion Principle. I dont know if my questioning is coherent, but what about quarks?

One problem with detecting a quark star is that its outwardly-apparent properties are expected to be much like those of a neutron star -- similar range of masses, radii, etc.

Here is why the two putative quark stars have been identified as such:

RXJ1856 (400 lyr, Corona Australis) is identified as one because it is something like half the size that a neutron star is expected to be, judging from its temperature and luminosity.

3C58 (10,000 lyr, Cassiopeia, observed as supernova in August 1181 in China and Japan) is identified as one because it has cooled off faster than expected for a neutron star; its surface temperature is too small by a factor of 2.

However, there are various theoretical difficulties; RXJ1856 may have a "hot spot" that causes trouble with the estimate, and the cooling rate of a neutron star is rather difficult to calculate precisely.

Degeneracy pressure is what produces the shape of every object not hot enough for thermal pressure to do so. Here is how it happens:

Particles with half-odd spins like electrons (spin 1/2) follow Fermi-Dirac statistics, meaning that only one can occupy a quantum state at a time. Those with integer spins follow Bose-Einstein statistics, meaning that any number can occupy a quantum state at a time.

If one puts electrons into an electron-impermeable box and keeps them cold, the first one will enter the lowest possible state, the ground state. The second one also enters the ground state, but with opposite spin. The next one enters at the next state up, and the next one at that state, but with opposite spin. Etc.; the electrons gradually pile up and get into higher and higher states, thus shorter wavelengths and greater momenta.

Familiar physical objects get their shape and properties as a result of degeneracy effects and electrostatic interactions among electrons and nuclei; as one adds electrons to nuclei, they fill sets of quantum states or shells; something can be seen from the Periodic Table of Elements.

Most atoms' electrons are localized in the atoms; some outer ones may be shared with neighboring atoms, producing a chemical bond, and some outer ones may not be localized and instead wander around, producing a metal.

If one crushes a familiar material enough, outside pressure will compete with electrostatic effects, and at a high-enough pressure, its outer electrons will become less constrained by the nuclei, and the material will become metallic, something observed for hydrogen.

And with sufficient pressure, the nuclei can become overwhelmed, thus producing a kind of degenerate electron gas. White dwarfs are composed of this.

Crushing even further will force the electrons to react with protons, forming neutronium, something like an atomic nucleus with mostly neutrons. These are spin-1/2, like electrons, meaning that they produce degeneracy pressure. But these particles rather strongly resist being squeezed below a certain size; exactly how much is difficult to determine, causing serious uncertainties in neutron-star structure estimates.

Protons and neutrons (nucleons) contain three quarks that interact with gluons; however, this interaction is very strong, making calculations difficult.

Protons are up-up-down, neutrons are up-down-down.

And now for what a quark star is supposed to be. If compressed enough, nucleons may lose their separate identities and become one big quark/gluon soup. Also, some down quarks may change to strange ones, producing a "strange star". Quarks are also spin-1/2, and they also produce degeneracy pressure. But they interact very strongly with gluons, complicating the calculations.

So what's a neutron star and what's a quark star will continue to be a difficult question.

...with answers like that, it should be a difficult question.

There was a news article recently about a theory concerning an odd physical state that could prevent an object from collapsing to a singularity...what have we got there? Uncollapsium?

Complete amateur here...

I notice that predictions concerning a quark star weren't made until quarks had been hypothesized. Makes sense. When the building blocks of quarks are discerned, then won't we have to allow for the possibility of stars constructed from *these* building blocks? The last poster asked about super-string stars...

From all my reading of popular books and textbooks, there doesn't seem to be a consensus on the divisibility of matter. *Is* there a fundamental building block of nature? If the universe is infinitely large, is it also infinitely small?

If I understand correctly, pysicists don't concern themselves with objects smaller than the Planck length for a variety of reasons.

And yet I suspect that Quarks are composed of *something*. Historically, nearly every generation has assumed they have found the ultimate building blocks of matter, only to be proven wrong. And superstrings? Are they also composed of smaller packets?

Which leads to the next thought... Maybe there is no such thing as a singularity? Maybe, in fact, there are untold varieties of black holes consisting of matter that has been crushed to a variety of smaller and smaller states of energy? Maybe black holes could be, in fact, superstring stars?

Just an off-the-cuff thought...

~Patrick

So why doesn't a quark star become a supranova?
http://www.academicpress.com/inscigh...002/grapha.htm

Reading that article, I didn't notice anything concerning these "quark" stars, let alone why they don't go supernova. Something I missed, perhaps?


-Adam

If a star is made of nothing but quarks does that mean it's really a big subatomic particle?

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Life is like a box of chocolates. All of your choices are bad for you.

I haven't had time to read all the articles linked, but I seem to remember that neither neutron stars nor the hypothetical quark stars are pure--both have crusts of (relatively) normal matter and there was a possiblity offered that a predominately neutron star might have a core of quark matter. Very hard, though, to ascertain the detailed structure of such objects except through theoretical calcs.

Imagine logging onto the web and looking at pictures taken by a robotic spacecraft of the surface of a neutron star instead of pictures of Mars...*sigh*

--Don Stahl

The school newspaper picked this story off the AP. The headline was:

I got a kick out of that. Ok, carry on.

Ben

You telling me that you can get stars with big ears? (quark from star trek ds9) [img]/phpBB/images/smiles/icon_biggrin.gif[/img]

__________________
<marquee> the guy that has come from mars, for no reason (no reason, or you think for no reason......) </Marquee>

...now, you all have to read Robert Forward's "Dragon's Egg". There will be a test.

The idea of a spacecraft landing on a neutron star is certainly interesting to think about. However, there is the problem of surviving the NS's gravity, which is very strong at its surface.

An object can survive if its gravity-generated internal pressure is less than its material's yield pressure.

The gravity pressure P ~ rho*g*h (density, acceleration of gravity = GM/R^2, height)

The yield pressure of an object is approximately P ~ rho*a^2 (density, sound velocity). Sound with this pressure amplitude will create a size amplitude comparable to the wavelength.

The density cancels out, and for survival, we get

g*h < a^2

For reasonably-rigid solid objects, a is a few km/s, and for a size of 1 m on Earth (10 m/s^2), we find that 10 (m/s)^2 < 10^7 (m/s)^2 This equation means that one could build a tower about 1000 km in height before its base gets seriously compressed.

However, for a neutron star, g ~ 10 m/s (1.4*m_sun/m_earth)/(r_earth/10 km)^2 or something like 10^12 m/s^2. For an object 1 meter tall, we find that 10^13 m/s^2 > 10^7 (m/s). So the only sort of spacecraft that could survive there would have to be smaller than a bacterium!

Getting there faces the serious problem of tides; an object will be stretched in one direction and squeezed in another -- and the stretching fights the object's tensile strength, which is generally less than its compressional strength. For tides, the differential gravity is ~ (GM/R^3)*h One interesting relationship is that w^2 = GM/R^3 where w is the angular frequency of a circular orbit at radius R; w = 2*pi*f, (f is the "true" frequency).

Repeating the previous calculations, we must compare w^2*h^2 and a^2 at various distances. At a neutron star's surface, w ~ 10^4 s^-1 (period ~ 1 ms). Doing the calculation for a 1-meter object yields

10^8 > 10^7

The object thus falls apart something like 50 km above it. However, a bacterium-sized spacecraft can easily make it through.

It might be interesting to redo these calculations with more realistic numbers for material strengths; I suspect that real spacecraft would be more fragile than what I've assumed here (being mostly solid blocks of metal).

An additional problem comes from the NS's luminosity and possibly that of a companion star. It is somewhat difficult for me to grab a hold of precise luminosity figures, but here are some approximate numbers:

Isolated pulsar: ~ 1 solar luminosity (Joanna Rankin's pages)

High-mass X-ray binary: ~ 100 - 10^4 L_sun with a companion with luminosity 10^5 L_sun

Low-mass X-ray binary: 1 - 100 L_sun and maybe more; companion insignificant


If one assumes that one's spacecraft may safely be heated to 1000 K, or at least its pulsar-facing side, then we find that it would be 0.1 AU away from the Sun. This is using the Stefan-Boltzmann and inverse-square laws, sigma*T^4 ~ L/R^2

So one may approach to about 15 million km of an isolated pulasar, which is about 10^6 its radius! The pulsars with companions are worse; with LMXB, one gets 0.1 to 1 AU or more, while with HMXB, one gets 30 AU.

So it would be very difficult to safely approach a neutron star, unless it was a dead isolated pulsar -- and dead isolated pulsars are rather hard to find.

What a great exposition! Forward gives us the isolated neutron star. He goes to the trouble of providing the astronauts with a believable tidal compensator made of degenerate matter...well, all right; sort of believable. And the explorers never land, but they are visited by inhabitants of the neutron star...who are about the size of paramecia. Without my copy here, I can't recall how the explorers were protected from radiation, nor how close to the surface they came. I would think the magnetic field would be a very serious concern as well, not to mention what happens to the radiation near the neutron star when it happens to sweep up things such as comets or asteroids.

Well, going from memory here, the Cheela were not quite that small; being about the size of a sesame seed and barely visible to the naked eye.

The orbiter was placed in (neutro?)-stationary orbit above the "west" pole, so it orbited the star 5 times per second. I don't think radiation was specifically addressed in the book. However, they had acceleration pods built into the orbiter that protected them from the g-forces going in, and they were shown to be proof from radiation in the sequel, Starquake.
Perhaps their position above the magnetic pole shielded them from some of the effects. I also remember they strung up a bunch of cable around the star to create a giant energy-producing dynamo.

Excellent book, and highly recommended simply for the mind-opening idea of life in the strangest of all places. And it's about as scientifically accurate as the author could make it. Read it if you can folks!

__________________
...And that, my liege, is how we know the Earth to be banana-shaped. --Sir Bedevere