Let's assume the theoretical quark star exists - and humans have found it. There's a planet orbiting it, and for the purposes of my story, I want it to be habitable.

My question is: Can you have a habitable planet orbiting a quark star?

  • The planet would have to have a reasonable temperature range
  • The planet would be not cause cancer., although this I'm wiling to budge a little on.
  • The planet gets light & heat.
  • Assume the planet is earth-sized, with a similar makeup.
  • Assume 21st century tech.
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    $\begingroup$ Every lit star has a habitable zone - on a quark star it would be a very distant orbit just purely on temperature. The magnetic field would be incredibly intense though (and of course the other high energy radiation as you likely suspect) so your planet would need some form of likely artificial mechanism to shield itself from those things. $\endgroup$ Jan 2 at 21:34
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    $\begingroup$ I'd prefer a yoghurt star in the Milky Way. $\endgroup$
    – Goodies
    Jan 2 at 22:49
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    $\begingroup$ Re the last dot point "Assume 21st century tech" - does this mean you are willing to accept a lifeless planet that can have a colony established on it? If not, what does the tech level refer to? $\endgroup$ Jan 2 at 23:41
  • $\begingroup$ the strange star will have a temperature of 100 billions K and maybe an atmosphere consist of electrons a few compton wavelength thick, if you can find neutron star exceeding Chandrasekhar limit but fall short of the Tolman-Oppenheimer-Volokoff limit maybe you are looking at a quark star ;D $\endgroup$
    – user6760
    Jan 3 at 1:28
  • $\begingroup$ A quark star is so hypothetical that you can give it any properties you want and say, "That's what they discovered." Fun idea, though. $\endgroup$
    – DWKraus
    Jan 3 at 4:38

3 Answers 3


Quark star: It may be purely theoretical, but the mass and size limits in the theory are between the heavy neutron stars and the smallest stellar black holes.

A neutron star from ~6000km (radius of the Earth) is m5-m6 barely-visible star-like object (the quark star would be even dimmer). Then again, its tidal effects at the same distance will tear a human body with ~40kg between the head and the feet. Sorry, no planets bigger than few centimeters at this distance (or closer).

On the other hand, an accretion disk around such object can outshine even the original star by few orders of magnitude and is especially bright in wavelengths outside the visible. As in, extra strong radio and x-ray.

OK, put your planet far away and you get a habitabl-ish planet with rather rough climate (the luminosity of the disk varies a lot) and harsh space weather as well.

If your planet is tilted, your seasons will be 100s or 1000s of years long (the orbital period of the planet around the star). Your people may need to migrate in the meantime.


Strange planets can be very small.


How big could a planet made of strange matter with 1g be? It might be less than a pea. Strange matter is dense.

Searching For Strange Quark Planets

It is interesting to note that, under the SQM hypothesis, quark matter is bounded by strong interaction but not gravity. So, SQM can even exist stably in the form of small chunks in the universe. It implies that planets composed of strange quark matter can also exist stably 8,9. Strange quark planets are very different from normal planets. They have a much higher mean density and a much smaller radius, which provide us with some effective new methods to test the SQM hypothesis... For a strange quark planet, its mean density can be as high as 4 × 10^14 g cm−3...

I calculated here that a strange quark matter planet with density 4 * 10 ^5 would have a surface gravity of 1.14g and a radius of 0.1 km. That is a surface area of 33 acres. I take away that a strange matter planet can be pretty much any size desired.

The main point of the linked article is that such planets are so dense they can orbit very close to their parent strange quark star - closer than planets made of normal matter. You can put it as close as it needs to be to keep warm which might be very close.

Strange quark stars are like neutron stars in that they kick out most of their energy as Xrays. I here propose that your habitable strange matter planet has an atmosphere (by definition) and just like Earth, that xray-opaque atmosphere will soak up the xrays. The energy from the xrays will be re-emitted as visible light. The heat source will be the glowing sky.

Possibly, if this scenario is not wild enough yet, the strange matter planet can be tidally locked to its sun. Then the planet can serve as a barrier to prevent persons on the dark side from being radiated. No radiation will penetrate the superdense strange matter planet.

  • $\begingroup$ When I redo the calculation for for a quark star density of 4x10^14 I get 1.14g gravity for a diameter of 0.1 micron that is 100 nanometer which is about the size of a covid virus. $\endgroup$
    – Goodies
    Jan 3 at 0:07
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    $\begingroup$ A micro-planet with 1g on the surface will not have an atmosphere. $\endgroup$ Jan 3 at 3:10
  • $\begingroup$ @Loren Pechtel: maybe it could scoop up gas from space, or comets? Goodies: yes. I decided to have it be less dense than that. They posit different possible densities in the article so I thought that was ok. $\endgroup$
    – Willk
    Jan 3 at 4:20
  • $\begingroup$ @Willk it will have an escape velocity in the area of 50 m/s. The mean thermal velocity of air at room temperature is about 10 times that. $\endgroup$ Jan 3 at 17:11
  • $\begingroup$ @Willk The problem is that it can't hold one. Holding an atmosphere is a function of temperature & escape velocity. Surface gravity doesn't even appear in the equation. For a typical planet they will be related because both surface gravity and escape velocity are related to size, but once you start playing with objects of non-standard density the relationship goes away. An Earth orbit size non-rotating Dyson Sphere is a milligravity environment and yet would hold a terrestrial atmosphere. $\endgroup$ Jan 3 at 17:56

Note that your link says a quark star would be found inside a neutron star. For practical purposes this means you model it as a neutron star, the quark interior doesn't matter. Thus your world is a pulsar planet. You've got some serious problems--the energy emission is low which means the habitable zone is close in--which means tidal locking. You've got an eyeball planet, it's only going to be habitable in the twilight zone.

Degenerate stars are not pure. The surface of all degenerate stars is normal matter, then electron degeneracy. That's it for a white dwarf, a neutron star has a further layer of neutron degeneracy. A quark star (if it exists) adds a further layer of degenerate quarks.


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