Quark stars form pulsars or quasars

Quark star

A Quark star (English also strange star, in English "strange star") is a hypothetical compact object that could arise as the product of a supernova (quark nova). In the quark star, matter would be so tightly packed that neutrons would lose their identity and quasi-free quarks would be present (quark-gluon-plasma). The English name stems from the fact that this matter would also contain strange quarks and could therefore be assigned to strange matter.


With the consumption of its nuclear fuel through nuclear fusion, the matter of a star is very strongly compressed by gravity. Depending on the mass of the star, a white dwarf, a neutron star, a (hypothetical) quark star, a (also hypothetical) gravastern or a black hole is created, sometimes accompanied by a supernova or hypernova.

There is an upper mass limit for neutron stars, the Tolman-Oppenheimer-Volkoff limit, the value of which, according to current estimates, is between 1.5 and 3 solar masses;[1] If a neutron star crosses this limit, it collapses and a black hole is created. However, the further a neutron star moves along this limit approachingthe larger the suspected quark-gluon-plasma sphere would be inside it.

According to theoretical models, quark stars could form in X-ray binary stars of low mass. In this, matter is transferred to a neutron star by a companion. According to this, a neutron star with a mass of 1.4 solar masses would have to accrete 0.5 solar masses in order to transform into a quark star. 2S 0921-63 is considered a candidate for this. However, the mass determinations in X-ray binary stars are always fraught with great uncertainties, and a mass of 1.44 solar masses, which is typical for a neutron star, cannot be ruled out.[2]


So far there are no observations that prove that the theoretically possible compression of the neutron matter of an existing neutron star into the quark-gluon plasma of a quark star takes place in the universe. It is possible, however, that many neutron stars have such a plasma, at least in their interior.

Detecting a quark star is considered difficult because its remotely observable properties are similar to those of a neutron star. So far, two pulsars have been discovered as candidates for possible quark stars, one of which has already been eliminated:

  • RX J1856-3754 was discovered by the X-ray satellite ROSAT in 1992, but because of its distance (between 180 and 420 light years) it was not possible to take a photo of it with the Hubble space telescope until 1996. Due to the total radiation, a diameter of only 11 km was calculated, which is too low a value even for a neutron star.[3] However, later measurements showed that only the polar caps shine on this star, so RX J1856-3754 has a much larger diameter than 11 km and is therefore no longer a candidate for a quark star.[4]
  • J0205 + 6449 in supernova remnant 3C58 is assigned to a supernova observed by Japanese and Chinese astronomers in 1181. Because of its great distance of around 10,000 light years from Earth, it has not yet been possible to calculate its diameter, but its luminosity is 16 times less than that of comparable young pulsars. This could be an indication that it is a quark star.[5]


  1. ↑ I. Bombaci: The maximum mass of a neutron star. In: Astronomy and Astrophysics. 305, 1996, pp. 871-877. bibcode: 1996A & A ... 305..871B.
  2. ↑ Chunhua Zhu, Guoliang Lv, Zhaojun Wang, Jinzhong Liu: Low-mass X-ray Binaries with Strange Quark Stars. In: Astrophysics. Solar and Stellar Astrophysics. 2013, arxiv: 1303.2458v1.
  3. ↑ Drake, J. J. et al .: Is RX J185635-375 a Quark Star?. The Astrophysical Journal, Volume 572, Issue 2, 996–1001 (preprint)
  4. ↑ Braje, T. M. et al .: RX J1856-3754: Evidence for a Stiff Equation of State. Astrophysical Journal, Volume 580, 1043-1047 ([arxiv.org/abs/astro-ph/0208069])
  5. ↑ Slane, P. O. et al .: New Constraints on Neutron Star Cooling from Chandra Observations of 3C 58. The Astrophysical Journal, Volume 571, Issue 1, L45 – L49, 2002 (preprint)

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