Forget Neutron Stars, Quark Stars Might be the Densest Bodies in the Universe

Article written: 30 Jun , 2008
Updated: 24 Dec , 2015
by

So neutron stars may not be the densest exotic objects in the cosmos after all. Recent observations of ultra-luminous supernovae suggest that these explosions may create an even more exotic remnant. Neutron stars can form after a star ends its life; measuring only 16 km across, these small but massive objects (one and a half times the mass of the Sun) may become too big for the structure of neutrons to hold it together. What happens if the structures of the neutrons inside a neutron star collapse? Quark stars (a.k.a. “Strange” stars) may be the result, smaller and denser than neutron stars, possibly explaining some abnormally bright supernovae observed recently…

Three very luminous supernovae have been observed and Canadian researchers are hot on the trail as to what may have caused them. These huge explosions occur at the point when a massive star dies, leaving a neutron star or black hole in their wake. Neutron stars are composed of neutron-degenerate matter and will often be observed as rapidly spinning pulsars emitting radio waves and X-rays. If the star was massive enough, a black hole might be formed after the detonation, but is there a phase between the mass of a neutron star and a black hole?

It appears there might be a smaller, more massive star on the block, a star composed not of hadrons (i.e. neutrons), but of the stuff that makes up hadrons: quarks. They are thought to be one step up the star-mass ladder, the point at which the mass of the supernova remnant is slightly too big to be a neutron star, but too small to form a black hole. They are composed of ultra-dense quark matter, and as neutrons break down it is thought some of their “up” and “down” quarks are converted into “strange” quarks, forming a state known as “strange matter.” It is for this reason that these compact objects are also known as strange stars.

Quark stars may be hypothetical objects, but the evidence is stacking up for their existence. For example, supernovae SN2005gj, SN2006gy and SN2005ap are all approximately 100 times brighter than the “standard model” for supernova explosions, leading the Canadian team to model what would happen if a heavy neutron star were to become unstable, crushing the neutrons into a soup of strange matter. Although these supernovae may have formed neutron stars, they became unstable and collapsed again, releasing vast amounts of energy from the hadron bonds creating a “Quark-Nova”, converting the oversized neutron star into a quark star.

If quark stars are behind these ultra-luminous supernovae, they may be viewed as super-sized hadrons, not held together by the nuclear strong force, but by gravity. Now there’s a thought!

Source: NSF


24 Responses

  1. meaenlabocadeotro says

    the universe is evolving too

  2. Bill says

    There has never been a quark detected in isolation; their existence can only be theorized and, in experiments, inferred. Is there a particle physicist who will step forward and say that quarks can form matter other than as constituents of other particles, like protons and electrons? I think not.

    A thought on: “quarks held together by gravity”. The electromagnetic “EM” force is ten to the 39th power stronger than the gravitational force. Quarks are held together more strongly than the strong nuclear force that binds nuclear particles, which in turn is stronger than the EM force. How then can this quoted statement possibly be true?

  3. Astrofiend says

    Bill Says:
    June 30th, 2008 at 3:05 pm

    “A thought on: “quarks held together by gravity”. The electromagnetic “EM” force is ten to the 39th power stronger than the gravitational force. Quarks are held together more strongly than the strong nuclear force that binds nuclear particles, which in turn is stronger than the EM force. How then can this quoted statement possibly be true?”

    In Quantum Chromodynamics, a process called quark deconfinement is supposed to take place, leading to what’s called a quark-gluon plasma. Wikipedia says:

    “A quark-gluon plasma (QGP) is a phase of quantum chromodynamics (QCD) which exists at extremely high temperature and/or density. This phase consists of (almost) free quarks and gluons, which are the basic building blocks of matter. Experiments at CERN’s Super Proton Synchrotron (SPS) first tried to create the QGP in the 1980s and 1990s: the results led CERN to announce the discovery of a “new state of matter”[1] in 2000. Currently, experiments at Brookhaven National Laboratory’s Relativistic Heavy Ion Collider (RHIC) are continuing this effort[2]. Three new experiments running on CERN’s Large Hadron Collider (LHC), ALICE[3], ATLAS and CMS, will continue studying properties of QGP.”

    Apparently the colour-charge of the quarks is screened just as electric charge is screened in a ‘normal’ plasma. This is a bit beyond me, but there you go. I guess the only charge that the quarks effectively carry that is universally attractive is the ‘charge’ of mass, and so that is how you get the quarks held together by the gravitational force. This can all be found on wikipedia under “Quark-gluon plasma”.

  4. Astrofiend says

    Sorry – should read “I guess the only charge that the quarks then effectively carry (in the QGP state) that is universally attractive is the ‘charge’ of mass”…

  5. Chris says

    Astrofiend, please don’t quote Wikipedia! Try another source that can actually be sourced reliably. Wikipedia is NOT the gospel truth, especially when it comes to complex problems of physics.

  6. Chris says

    Actually, what I really meant to say is that the Wikipedia quote didn’t answer the basic thrust of Bill’s question, that is, whether quarks and gluons can possibly be held together merely by the force of gravity.

  7. Oliver says

    Unless you’re a black hole skeptic, you probably already accept that gravity can hold together quarks by overcome any repulsive force between hadrons and individual quarks alike. The question is whether it’s possible to overcome the former without the latter.

    Astrofiend’s quote of Wikipedia was perfectly responsive: do physicists think there’s a form of quark matter other than hadrons? Yes, and they call it QGP. It’s more interesting in this context than the as-yet-unobserved single quarks because a neutron star’s worth of quarks is going to be more than one.

  8. Astrofiend says

    Cheers Oliver…

    # Chris Says:
    June 30th, 2008 at 9:05 pm

    Indeed Chris, I could have sourced all of the original material, but I couldn’t be assed. The Wikipedia description is succinct, and, in my opinion, worth contributing in response to Bill’s statement – “There has never been a quark detected in isolation; their existence can only be theorized and, in experiments, inferred. Is there a particle physicist who will step forward and say that quarks can form matter other than as constituents of other particles, like protons and electrons? I think not.”

    Well, apparently there is (not having a go at you Bill) – hence the Wikipedia reference. It goes without saying that information sourced on Wikipedia should be taken with a grain of salt – but this fact does not need to be stated every single time Wikipedia is referred to.

    In reference to his other question, namely, can gravity alone hold such an object together – I’m not sure. Quarks carry the ‘charges’ of colour, mass, electric and weak isospin. If the colour force is shielded in a QGP, then that leaves three other forces. I would say seeing that gravity alone among these is universally attractive, and the density of an object such as a quark star is so high, then gravity would dwarf effects from the two intrinsically stronger electromagnetic and weak forces. But really, I’m just guessing.

  9. AJames says

    Probably a dumb question… but how much smaller would a quark dwarf star be compared to a neutron star? (The article does not say)

    Furthermore, again the question of preservation of angular momentum is neglected here. I thought all neutron stars were flat rapidly rotating disks and were not round at all?

    I also agree with the proposal that “coloured” quarks are theoretical particles used to explain the differences in neutron and protons, and they explain the strong force binding atoms together. Surely the best way to image quark (dwarf) stars as free “quark soup” – where quarks become free as electrons do in the Fermi Sea within stars.

  10. Adam says

    Hi All

    Strange or quark stars are held together by the colour-force NOT gravity. What gravity does is overcome their mutual repulsion and reduces the baryons into free quarks. But, theoretically, a chunk of “quarkonium” can have zero net colour charge and be stable, even down to quite small masses.

    Neutronium – the free neutron “sea” of a neutron star – isn’t stable and would explode violently from neutron decay without the neutron star’s gravity to hold it together.

    The data on the physical characteristics of nuclear matter has huge error-bars so the observations of neutron stars and similar compact objects is providing us with real data on how nuclear matter behaves under extreme conditions.

  11. Aodhhan says

    Good thoughts Bill; It does make you think. A good experiment in this case I think would be to theorize and see at what point do EM bonds become unstable under huge amounts of pressure. At what point do neutrons lose thier ability to confine quarks? Or other conditions?
    While EM is certainly a much stronger force than gravity, it does not have the ‘reach’. The EM bonds on our Sun has no real affect on earth, yet its gravity does.
    I would gather gravity does have some affect on a neutron star in using the neutrons against themselves; crushing each other (towards the center of the sphere) until they become unstable. …just a thought.

    On Wikipedia: I don’t have a problem with someone quoting Dr. Seuss as long as it is relevant and they give credit where it is due. The risk is always that other readers will judge a person/research by its weakest reference.

    AJames: It would depend. How many quarks on average are being held within each neutron? Original temperature and pressure play a role as well. I don’t think we’ll be able to come up with a constant ratio.

  12. john says

    There are more things in heaven and earth than in our philosophy Horatio. Me thinks that God is showing us a sense of humor. We keep on finding stranger things than we can imagine. Carry on fellas.

  13. Matt says

    “Astrofiend, please don’t quote Wikipedia! Try another source that can actually be sourced reliably. Wikipedia is NOT the gospel truth, especially when it comes to complex problems of physics.”

    I strongly disagree with you Chris, in regards to science Wikipedia proved rather trustworthy. Since the topic of QCD is highly complicated only experts would want to contribute to it. Also, when your field of expertise is particle physics, one day you will want to confirm whether Wikipedia got the things your profession is all about right.

    Wikipedia, just like science, is self-correcting. The more expert viewer an article has, the more it will evolve. The problem of vandalism is often exaggerated, especially when the topic is something as ideologically neutral as Quantum Chromodynamics. Who’d want to meddle with that?

  14. R2K says

    There may be quarks, there may be quark stars, and those stars might actually be what we call black holes.

    Now it is time to make observations before we assume we know what the truth is. A good first step would be to make black holes in a particle collider. That could really help us out here.

  15. John M. Kulick says

    http://adsabs.harvard.edu/abs/2008AAS…212.6401L

    The above link goes to one of the most recent papers on this.

    Snowflake

  16. Bill says

    From ScienceWatch (Jul/Aug 2001). “The hypothesis of quark-gluon plasma is still somewhat speculative” (referring to CERN work, and the Brookhaven work of 2005 is by no means definitive in its result). Is there a more recent reference that claims the for-sure creation of this soup?

    I think to claim a macro object made of this speculative stuff is even more speculative.

    Also, there was no predictive power applied in the development of the quark star idea, the hallmark of a sound theory. Someone saw a thing that the standard neutron star theory could not account for, and made a speculative leap. This idea seems to be an attempt to bypass the difficulties of the neutron star idea vs. the actuality of observations that don’t make sense in the context of the theory.

  17. Matt says

    Quantum Chromodynamics is pretty well established, but still not so well understood. I wouldn’t put it in the “speculative” category at all. Experiments at various particle accelerators show the creation of the Quark-Gluon-Plasma, but understanding its behaviour needs further research (go LHC!).

  18. Chris says

    I’ll concede that Wikipedia is *probably* a decent amateur cite for stuff like QCD and probably not subject to intentional vandalism. I’m just concerned that if one makes a theoretical leap off stuff based in Wikipedia, which may apply only in narrow circumstances or under “not so well” understood conditions [as Matt asserts], then the assertion may not be scientifically sound. I realize that this site isn’t strictly scientific, I just want to play devil’s advocate.

    Thus, after having read the article, I don’t see any information on how a quark’s color charge is “screened” at high densities. Is this inferred from the article? Does the quark-gluon plasma, where individual quarks supposedly exist without pairs, necessarily mean that the strong force is not operative or irrelevant?

  19. Chris says

    I wish I could edit my previous post…I read the article again and found info regarding the alleged “screening” of the quark’s color charge in a QGP. But in the introductory paragraph, the article states “[t]his phase consists of (almost) free quarks and gluons, which are the basic building blocks of matter.” Isn’t the “almost” language an important qualifier regarding as to what degree a quark’s color charge may be screened? Does this mean that there is no definitive indications that quarks exist in QGP as free and independent entities?

  20. Drakc says

    With all of this research and discussion going on we are making breakthroughs. I am just a New Eye to this subjuct but If you reread all that has been said there are only a few thing agreed to.

    With the EM fields and gravity working against each other they have to reach a balancing point. This is Influenced directly by the Tempuratue and Mass.
    Depending on where this balance lands we will see different amounts and types of energy discharge and results. Until an object hits the Black Hole stage it is always bleeding energy of some type and will break down to a new form, or Explode and Discharge all of the remaining energy.
    When we do more research I am sure we will find new forms and Frequencies of energy, matter, space, and time but it will take new technology and open minds.
    You apply this to the formation of stars of all types and extend it over the billions of years that it is taking place and all of it can be understood in a sense. Don’t approach any of these subjects with a mind closed to your collegues and their ideas. If you do you block progress.

  21. baley says

    Those stars are indeed strange!

    Sorry I couldn’t resist

  22. RUF says

    Wiki: “…[QGP] consists of (almost) free quarks and gluons, which are the basic building blocks of matter.”

    I don’t believe that gluons have been found to actually exist.

  23. Paul Eaton-Jones says

    If I remember correctly some scientists reportedly “viewed” an isolated quark on an atom of Niobium sometime during the 1980’s during a high energy experiment moving indviidual atoms. They were never able to repeat it however and ‘some’ doubt was expressed at the time as to whether they actually isolated a quark.
    Does anyone remember Blas Cabrerras and his detection of a magnetic monopole in Feb. 1982? Again never replicated but who’s to say these one-off events didn’t or can’t happen?
    Paul.

  24. Covenant says

    I love it when the word “quark” shows up in science. I really do.

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