Scale insight
Scale Comparison
Sagittarius A* vs M87*, to scale
Both objects became famous through black-hole imaging, but they do not belong to the same horizon scale. Put side by side, the black hole at the center of M87 occupies a far larger mass regime than the one in the Milky Way.
Shared physical scale
21.2billion km
These two black holes are often grouped together because both were resolved by the Event Horizon Telescope, but scale immediately separates them. Sagittarius A* is the central black hole of our own galaxy. M87* belongs to a much more massive galactic system and sits in a very different mass range.
That distinction matters because horizon size is not decorative here. For black holes, it is one of the clearest direct clues to mass. A shared imaging technique does not imply shared scale.
Objects
Open each object in context
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 source about 52 million kilometers across around a black hole of roughly 4.3 million solar masses.
Visual creditscaleofspace.org / CC BY-NC 4.0
M87* is the supermassive black hole at the center of Messier 87. The Event Horizon Telescope’s 2019 image of its glowing ring became the first direct image of a black hole’s immediate surroundings, turning a previously inferred boundary into a measurable true-scale object.
Visual creditscaleofspace.org / CC BY-NC 4.0
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Between the smallest and the largest, perspective is everything.
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 turn parts of that scale into curated essays, while focused views let you explore the same range through specific groups of objects.