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Are neutron stars the second-smallest and second-densest type of stellar objects after black holes?

NoParrot Fact Check · September 9, 2026

Fact-checked by NoParrot's 4-model methodology · Last verified September 9, 2026

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55

NoParrot Score

Mostly consistent

Claim breakdown

Verified
1
Uncertain
2
Disputed
0

Synthesis

Neutron stars are generally considered the second-smallest and second-densest type of stellar object after black holes, among confirmed stellar remnants. Neutron stars have typical densities around 10^14 to 10^15 grams per cubic centimeter, which is comparable to the density of atomic nuclei, and have radii of about 10–13 km. In contrast, black holes are more compact, with event horizon radii for stellar-mass black holes typically being a few kilometers.

While neutron stars are extremely dense, the density of black holes is a more ambiguous concept. Black holes are often described as infinitely dense at their singularity, but their volume inside the event horizon is not physically well-defined. The size and density of black holes are conceptually different from those of neutron stars. In standard astrophysics, the hierarchy of black holes, neutron stars, and white dwarfs holds.

Hypothetical objects like quark stars, if they exist, could potentially be smaller and denser than neutron stars, thus altering the ordering of compact stellar remnants. However, quark stars have not been confirmed observationally and remain unobserved.

What each model said

  • Gemini ✓ 1 ✗ 1
    Yes, neutron stars are the second-smallest and second-densest type of stellar objects after black holes. * **Density:** Black holes are considered infinitely dense at their singularity. Neutron stars are the next densest objects known, with densities typically around 10^14 to 10^15 grams per cubic centimeter. * **Size:** Stellar-mass black holes are defined by their event horizon, which can be smaller than a neutron star's radius (e.g., a 3-solar-mass black hole has an event horizon radius of about 9 km). Neutron stars typically have radii of about 10-12 km.
  • Claude ✓ 1 ⚠ 2 ✗ 1
    Yes, that's correct. Neutron stars are the second-smallest and second-densest known stellar objects after black holes. - **Size**: Neutron stars typically have radii of about 10–12 km. Stellar-mass black holes have even smaller event horizons (a Schwarzschild radius of ~3 km per solar mass, so roughly 6–9 km for typical stellar black holes). - **Density**: Neutron stars reach densities of ~10¹⁷ kg/m³ (comparable to atomic nuclei). Black holes are considered denser, though their "density" is a somewhat ambiguous concept since their mass is concentrated at a singularity. One caveat: hypothetical…
  • GPT ⚠ 3 ✗ 2
    Yes—among **confirmed stellar remnants**, neutron stars are generally the **smallest and densest objects after black holes**. Key caveats: - **Black holes are not really “stellar objects” in the normal sense**; they are collapsed spacetime regions, and their “density” is not straightforward because the volume inside the event horizon is not physically well-defined. - **Neutron stars** have radii of about **10–13 km** and masses around **1–2 solar masses**, giving densities near or above **atomic nuclear density**. - **White dwarfs** are much larger and less dense: roughly Earth-sized, with den…
  • Grok ✓ 1 ⚠ 2 ✗ 1
    Yes. Neutron stars rank as the second-smallest and second-densest known stellar remnants after black holes. Compact stellar remnants follow this density and size sequence for objects of comparable mass: - Black holes reach effectively infinite density at the singularity; their event-horizon radii for stellar-mass cases are typically a few kilometers. - Neutron stars have average densities around 10¹⁷ kg m⁻³ and radii of roughly 10–14 km. - White dwarfs are next, with densities around 10⁹ kg m⁻³ and radii near Earth’s size (~0.01 solar radii). - Ordinary stars and planets are orders of magnitud…

Models Used

  • Gemini
  • Claude
  • GPT
  • Grok

Disclaimer: This page summarizes the output of 4 frontier large-language models at a single point in time. NoParrot Score reflects cross-model consensus, not absolute truth. Models can be wrong, and consensus can be wrong with them. Treat this page as a research aid, not a final verdict.

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