Earth’s mass would fit in a marble
Compressed into a black hole, Earth would have a horizon about 1.8 centimeters across.
Scale Guide
Black holes to scale
Explore the scaleBlack holes have no material surface. This guide compares horizon diameters derived from mass estimates, from a stellar remnant to black holes in galactic and cluster cores.
Shared scale
Horizon size grows with mass
Shared physical scale
423billion km
A glowing accretion flow, a lensed emission ring, the central shadow and the event horizon are different structures. The plotted values use mass to estimate a Schwarzschild-scale horizon diameter; spin and modeling choices can change the exact geometry.
Double the mass and the horizon doubles in diameter: about 6 kilometers per solar mass for a non-spinning black hole. Real black holes rotate, and no horizon has been photographed directly, so the circles are model-derived size references.
Stellar scale
A black hole can be small by astronomical standards
Cygnus X-1 contains a black hole of about 21 solar masses. Its Schwarzschild diameter is only about 120 kilometers, while the X-ray-emitting accretion flow and binary system extend much farther. Beside it is the Crab Pulsar, a neutron star about 20 kilometers wide.
Shared physical scale
96.6km
Middle scale
Low- and intermediate-mass black holes are hard to pin down
NGC 4395 hosts an unusually low-mass active galactic nucleus. HLX-1 is a strong intermediate-mass candidate whose quoted mass depends on modeling its variable X-ray source. Black holes in this range may show how the first seeds grew into supermassive ones.
Shared physical scale
96,681km
Galactic centers
Supermassive black holes sit at galaxy centers
Sagittarius A* anchors the Milky Way and M87* the giant elliptical galaxy M87. Stellar and gas motions constrain their masses, and the Event Horizon Telescope has imaged the lensed emission ring around both. M87* also launches a relativistic jet thousands of light-years long.
Shared physical scale
29.6billion km
Extreme end
The largest candidates are the least certain
Holm 15A* has a dynamical mass estimate; TON 618’s mass is inferred from quasar spectroscopy; Phoenix A* is a model-dependent candidate. Their different methods and uncertainties prevent a simple precision ranking, even though all occupy the ultramassive range.
Shared physical scale
467billion km
Scale anchors
Worth remembering
Sagittarius A* would fit inside Mercury’s orbit
The Milky Way’s central black hole has a horizon about 24.5 million kilometers wide, about a fifth of the diameter of Mercury’s orbit.
Our galaxy’s black hole is a lightweight
M87* is about 1,500 times more massive than Sagittarius A*, and its horizon is about 1,500 times wider.
M87* is bigger than the planetary Solar System
M87*’s horizon is about 250 AU across, roughly four times the diameter of Neptune’s orbit.
Profiles
Eight black holes across the full horizon scale
Mass estimates, inferred horizon diameters and caveats for the eight black holes above.
Cygnus X-1 was the first cosmic object widely accepted as a black hole. It blazes in X-rays because the black hole is stripping hot gas from a massive blue supergiant companion and funneling it into a compact accretion flow.
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The black hole in NGC 4395 powers an active galactic nucleus inside a small bulgeless galaxy. Its existence helped show that a galaxy does not need a large central bulge to host a feeding central black hole.
Visual creditscaleofspace.org / CC BY-NC 4.0
HLX-1 is one of the strongest known candidates for an intermediate-mass black hole and lies off the plane of ESO 243-49. Hubble observations suggest it may be the stripped core of a cannibalized dwarf galaxy, leaving a midsize black hole with a small cluster of young stars around it.
Visual creditscaleofspace.org / CC BY-NC 4.0
Sagittarius A* is the supermassive black hole at the center of the Milky Way. Event Horizon Telescope observations imaged the glowing material around it, resolving a radio ring about 64 million kilometers across around a black hole of roughly 4.3 million solar masses.
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M87* is the supermassive black hole at the center of Messier 87. The Event Horizon Telescope’s 2019 image resolved a bright emission ring around the black hole’s shadow; neither feature is the event horizon itself.
Visual creditscaleofspace.org / CC BY-NC 4.0
Holm 15A* is the ultramassive black hole in the central galaxy of the Abell 85 galaxy cluster, measured at about 40 billion solar masses. That makes its event horizon enormous, while Holm 15A’s unusually diffuse center preserves evidence of the mergers that helped build it.
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TON 618 is a hyperluminous quasar powered by one of the most massive black holes known. We see it from a far younger universe, and the quasar is so overwhelmingly bright that the galaxy around it is largely lost in the glare.
Visual creditscaleofspace.org / CC BY-NC 4.0
Phoenix A* is the central black hole candidate in the Phoenix Cluster, an extreme cool-core galaxy cluster where the active nucleus has not fully shut down star formation. Its often quoted horizon scale comes from a model-based mass estimate near 100 billion solar masses, not from a direct orbital measurement.
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The horizons in this guide range from about 120 kilometers for Cygnus X-1 to roughly 590 billion kilometers for Phoenix A*, a factor of about five billion.
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About
Scale of Space is a scroll-based journey through the universe, placing objects on a single logarithmic scale so you can compare size across an unbroken range.
Guides explain selected parts of that range, while focused views filter the objects by subject.