Physicists Identify New Kind of Star

Apr 01, 2010

(PhysOrg.com) -- Stars don't exactly ease into retirement, and for some stellar objects, the twilight years just got more complicated.

How a star spends its final days depends on its mass. After burning through their supply of nuclear fuel, smaller stars collapse into extremely dense . Scientists believe more massive stars implode into —regions of space where the force of gravity created by the collapsing star is so strong that not even light can escape its pull.

But a group of physicists say there may be another stage in the life of before being snuffed out by total collapse into black hole.

Stars could burn for millions of years as electroweak stars, according to Glenn Starkman, a professor of physics at Case Western Reserve University. Starkman, together with former graduate and post-doctoral students, describe the electroweak star in a paper submitted to .

Starkman and his team theorize that at the extreme temperatures and densities reached during stellar collapse could give rise to the electroweak phase of a star's life. Ordinary stars are powered by the fusion of light nuclei into heavier ones—such as hydrogen into helium in the center of our sun. Electroweak stars would be powered by the total conversion of quarks—particles that make up the building blocks of those nuclei—into much lighter particles called leptons.

The energy created by the conversion could halt the implosion of the dying star, granting it something of a celestial reprieve before total collapse into a black hole. In fact, if the electroweak burning is efficient, it could consume enough mass to prevent what's left from ever becoming a black hole.

Most of the energy eventually emitted from electroweak stars is in the form of , which are nearly without mass and hard to detect. A small fraction comes out as light, which is where the electroweak star's signature will likely be found, says Starkman. "But to understand that small fraction, we have to understand the star better than we do," he says.

And until scientists know more, it's hard to tell electroweak stars from other stars. Generations of scientists have plenty of time to learn though. Starkman's group calculates that this phase of a star's life can last more than 10 million years—a long time for us, but just an instant in the life of a star.

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Dr_Mabuse
1 / 5 (1) Apr 02, 2010
Electroweak stars would be powered by the total conversion of quarks—particles that make up the building blocks of those nuclei—into much lighter particles called leptons...
What's about conservation of baryon number ?
Is this an april joke ?
kraisar
not rated yet Apr 02, 2010
Baryon conservation is actually only an approximate conservation. There is a type of anomaly (called Chiral anomaly), which produces something called a Sphaleron in the electroweak potential. The difference of Baryon and Lepton number is conserved by this process however. The reason this would be brought up at all is because at relatively low temperatures it would be uncommon but if the star is hot enough they could become more likely and hence allow the process to occur with a higher probability.
Dr_Mabuse
1 / 5 (1) Apr 02, 2010
Baryon conservation is actually only an approximate conservation ?

Please tell me only one experimental result that confirms a violation of that.
Is there any evidence for the creation of a sphaleron ?
On Wikipedia German i found that temperatures T > 100 GeV will be necessary to show up any effect of sphalerons.
The new LHC should create such temperatures. Let's see,
Skeptic_Heretic
not rated yet Apr 02, 2010
Baryon conservation isn't involved. Lepton expulsion accounts for the loss of matter energy.
kraisar
not rated yet Apr 02, 2010
Baryon conservation is actually only an approximate conservation ?

Please tell me only one experimental result that confirms a violation of that.
Is there any evidence for the creation of a sphaleron ?
On Wikipedia German i found that temperatures T > 100 GeV will be necessary to show up any effect of sphalerons.
The new LHC should create such temperatures. Let's see,

Quite right, I didn't mean to imply that this effect has been observed just giving the theoretical basis for why these theoretical stars could be present. Obviously if we don't see stuff like this happen then we can say stars like this can't exist.

Baryon conservation isn't involved. Lepton expulsion accounts for the loss of matter energy.

No, it is involved because the leptons are being generated by the conversion of quarks into leptons (and these quarks are the ones inside baryons).
Skeptic_Heretic
not rated yet Apr 02, 2010
No, it is involved because the leptons are being generated by the conversion of quarks into leptons (and these quarks are the ones inside baryons).
Not sure why you're completely ignoring the potential for anti-lepton creation due to hadron decay, but if you want to go that way, you can.

Dealing with degenerate matter at ultra-high temperatures yields potentials previously unexpected within stellar interaction. We very well could be talking about neutron decay or even something more phenominal such as pentaquark organization.

You can no longer stand firm on the standard model and conservational laws when we've already shown that these are more akin to normal matter behavior under ordinary conditions.
Salander
5 / 5 (7) Apr 02, 2010
"Physicists Identify New Kind of Star"?
Nooo... Physicists *theorize* new kind of star.
kraisar
not rated yet Apr 03, 2010
Not sure why you're completely ignoring the potential for anti-lepton creation due to hadron decay, but if you want to go that way, you can.

Hadrons can indeed decay into leptons-anti-leptons but as far as I am aware it is generally mesons that do this because they have 0 baryon number to start with (made of a quark and anti-quark). Mesons don't really make up most of a star, instead it is baryonic matter (3 quarks). Also the article states
Electroweak stars would be powered by the total conversion of quarks—particles that make up the building blocks of those nuclei—into much lighter particles called leptons.

The fact that they call it electroweak and not weak indicates it takes place at high temperatures and couple this with the fact the article says 'total conversion of quarks into leptons' and it seems to not be just mesons but also baryonic states.
Also their paper at http://arxiv.org/...20v1.pdf seems to indicate this as well.
kraisar
not rated yet Apr 03, 2010
Not sure why you're completely ignoring the potential for anti-lepton creation due to hadron decay, but if you want to go that way, you can.

Hadrons can indeed decay into leptons-anti-leptons but as far as I am aware it is generally mesons that do this because they have 0 baryon number to start with (made of a quark and anti-quark). Mesons don't really make up most of a star, instead it is baryonic matter (3 quarks). Also the article states
"Electroweak stars would be powered by the total conversion of quarks particles that make up the building blocks of those nuclei—into much lighter particles called leptons."
The fact that they call it electroweak and not weak indicates it takes place at high temperatures and couple this with the fact the article says 'total conversion of quarks into leptons' and it seems to not be just mesons but also baryonic states.
Also their paper at http://arxiv.org/...20v1.pdf seems to indicate this as well.
kraisar
not rated yet Apr 03, 2010
Not sure why you're completely ignoring the potential for anti-lepton creation due to hadron decay, but if you want to go that way, you can.

Hadrons can indeed decay into leptons-anti-leptons but as far as I am aware it is generally mesons that do this because they have 0 baryon number to start with (made of a quark and anti-quark). Mesons don't really make up most of a star, instead it is baryonic matter (3 quarks). Also the article states
"Electroweak stars would be powered by the total conversion of quarks particles that make up the building blocks of those nuclei—into much lighter particles called leptons."
The fact that they call it electroweak and not weak indicates it takes place at high temperatures.
kraisar
not rated yet Apr 03, 2010
Sorry for the triple post...I was getting some sort of error (not well-formed character) when attempting to post so I thought it didn't go through but I guess it did (and won't let me edit anything apparently even during the 3 minute window bah).
Skeptic_Heretic
5 / 5 (1) Apr 03, 2010
kraisar,

Yes, hadrons decay would be abnormal under most circumstances, but by many theories the internal components of stars are incredibly high in hadron count, making this potentially a far greater possibility. Especially with that much fusion going on, the rampant creation of hadrons at high temperatures would allow for more abundant lepton/anti-lepton creation. This would allow for the star to actually shine as opposed to simply exploding, and if I'm not reading incorrectly, this is the mechanism by which the researches propose the star remains stable for that relatively short period of time.
kraisar
not rated yet Apr 03, 2010
I'm not disputing that hadrons can decay into leptons. But one needs to distinguish between baryons and mesons. Even with high numbers of baryons at low temperatures (low being compared to the electroweak scale) baryon to lepton processes are either forbidden or highly suppressed (B and L number are conserved..meaning it doesn't appear at tree level or even perhaps one-loop levels). In fusion there generally is not really an abundance of mesons produced. I will grant that eventually you may get some but this is still just a weak interaction. Electroweak interactions happen at much higher temperatures and can allow baryon -> lepton channels by the actual conversion of quarks into leptons by the electroweak force (which is what their paper talks about). After this then you have lepton-antilepton annihilation and even pressure from neutrinos as they say the densities are very very high at this point. B and L are not constant but B-L is still conserved in the scope of the theories.
Skeptic_Heretic
5 / 5 (1) Apr 04, 2010
Ok, so neutrons are baryons, they're being created in massive amount by these processes, in the meantime there are leptons being freed from their electromagnetic prisions due to fusion.

Is that more clear? The continual bleeding of electrons from their orbits around prior neutrons would also be the source for expulsion, and my original point.
rjhuntington
1 / 5 (2) Apr 04, 2010
If stars are powered by nuclear fusion in their cores, why is the Sun's corona hotter than its photosphere? Wouldn't temperature decrease with distance from the core?
Skeptic_Heretic
5 / 5 (1) Apr 04, 2010
If stars are powered by nuclear fusion in their cores, why is the Sun's corona hotter than its photosphere? Wouldn't temperature decrease with distance from the core?

Greater density allows for more efficient conduction and convection. Or at least that's the mechanic I've been lead to believe.
seneca
1 / 5 (1) Apr 04, 2010
I presume, it's rather something like neutrino star. Neutrinos are most lightweight particles of matter, so they could form stars, too.. And they can interact via electroweak interaction only..
kraisar
not rated yet Apr 04, 2010
Ok, so neutrons are baryons, they're being created in massive amount by these processes, in the meantime there are leptons being freed from their electromagnetic prisions due to fusion...

What do you mean? Yes neutrons are baryons but they don't contain electrons or anything like that. The neutrons in a star will probably become bound into nuclei but even if you get a free neutron decaying or spontaneous fission the process is still weak force interactions in which a quark changes into another type of quark by a W boson which then decays into a lepton/neutrino type product. B and L are conserved. They are talking about a much higher energy process (still theoretical) in which some quarks interact with an electroweak boson and changes into some leptons. (specifically they mention a configuration of 9 quarks transforming into 3 anti-neutrinos). It is the much increased interaction cross-section that causes pressure.