A viral post describes our galaxy’s black hole, Sagittarius A*, as “completely invisible”. No light escapes from inside its horizon, but we see its effects: stars orbiting 4.3 million solar masses, and its shadow, imaged in 2022. The post’s deeper question is real. In 1976 Stephen Hawking argued that evaporating black holes would erase information, which quantum mechanics forbids. Since 2019, simplified theoretical models suggest the information can get out, but this is untested and how it happens is unknown. We separate what we observe from what we calculate.
A post that went viral on X this week describes Sagittarius A*, the black hole at the centre of our galaxy, as “completely invisible” and says black holes “break physics”. It touches one of the deepest open questions in science: can a black hole destroy information? We looked at the question by separating what we observe from what we calculate in theory.
What we observe
Sagittarius A* holds about 4.3 million solar masses and lies about 27,000 light-years away. Its event horizon is about 25 million kilometres across (roughly 15.8 million miles), about 18 times the width of the Sun. No light reaches us from inside the horizon, so in that sense the black hole itself cannot be seen. What we can observe is its influence: for decades astronomers have tracked stars racing around it, work that won Reinhard Genzel and Andrea Ghez the 2020 Nobel Prize, and on 12 May 2022 the Event Horizon Telescope released an image of its shadow, the dark region outlined by the glowing gas around it.
Black holeSagittarius A* (Sgr A*)
Mass≈ 4.3 million Suns
Event horizon≈ 25 million km across
Distance≈ 27,000 light-years
Hawking temperature≈ 0.000 000 000 000 01 K
Time to evaporate≈ 10⁸⁷ years
How a black hole evaporates, and the curve that says information escapes
Original Astrometrik animation, not to scale. Left: things fall into the black hole while pairs of particles appear at the horizon and one escapes as Hawking radiation, so the hole slowly shrinks. Right: the entropy of the radiation. Hawking’s 1976 calculation keeps rising (information lost); Don Page showed that if information is kept, the curve must turn over halfway and fall back to zero. Since 2019, calculations in simplified theoretical models reproduce that turn; it has not been observed.
Hawking’s problem, now 50 years old
In 1974 Stephen Hawking showed that, once quantum physics is taken into account, black holes are not completely black: they glow faintly and slowly lose mass. In 1976 he drew the unsettling conclusion: the glow seems to be pure heat, carrying no trace of what fell in, so when the hole finally evaporates the information would be gone. Quantum mechanics forbids that: the full state of a system should always, in principle, be recoverable.
Strictly speaking, the tension does not come from relativity alone: it appears when quantum effects are added to it, in Hawking’s own calculation of the radiation. For Sagittarius A* the process is unimaginably slow: its Hawking temperature is about a hundred-trillionth of a degree above absolute zero, colder than the cosmic microwave background, so today it absorbs far more than it emits.
Is it solved? Not yet
In 1993 Don Page showed what the radiation must do if information survives: its entropy must rise, peak around halfway through the evaporation and fall back to zero. In 2019 two teams (Geoff Penington, and Ahmed Almheiri, Netta Engelhardt and colleagues) found a way to calculate this “Page curve”, using “islands” inside the black hole and, in a related method, “replica wormholes”. In these calculations the curve comes out as it should if information escapes.
These are results in simplified theoretical settings, mostly lower-dimensional models of gravity and holographic frameworks, not for a real, rotating black hole like Sagittarius A*, and nothing of the kind has been observed. As physicist Raphael Bousso put it, “We now can compute the Page curve, and I don’t know why.” How information would get out is still unknown, and the methods are debated.
Fuzzballs, wormholes and other ideas
String theory offers “fuzzballs”: black holes with no singularity at all, just a tangled quantum surface that stores and re-emits everything. The wormholes in the 2019 work are mathematical shortcuts in the calculation of entropy, not doorways you could travel through. Other proposals suggest that evaporation stops and leaves a tiny stable remnant holding the information. Some headlines in 2026 claimed the paradox was “finally solved”, but these are untested theories. The fair summary: there is real progress, no consensus and no experiment yet.
Watch: the black hole paradox in under a minute
Our short animated video explains Hawking’s information paradox with Sagittarius A*.
The post’s statements, in context
Each statement, looked at by separating what is observed from what is calculated:
Correct“15 million miles wide, 4 million solar masses”Close: the event horizon is about 15.8 million miles (25 million km) across, the mass about 4.3 million Suns.
Needs context“Completely invisible”No light reaches us from inside the horizon. We observe its effects instead: stars orbiting it, and its shadow against glowing gas, imaged in 2022.
Needs context“Relativity says destroyed, quantum says preserved”A fair shorthand. Strictly, the tension appears when quantum effects (Hawking radiation) are added to relativity.
Correct“Physicists have been losing sleep for 50 years”Yes: Hawking’s information-loss paper appeared in 1976.
Analogy“The same principle that stops an LLM hallucinating a token”Works as a loose analogy about information being preserved; it is not a physical equivalence.
Needs context“Wormholes suggest black holes are doorways”In the recent calculations, wormholes are mathematical tools for computing entropy, not passages.
Correct“Nobody has solved it yet”Fair: theoretical models since 2019 reproduce the Page curve, but no mechanism is agreed and nothing has been observed.
Every black hole glows at a temperature set by its mass: the smaller, the hotter. Choose a mass to see its event horizon, Hawking temperature and evaporation time.
Universe’s age: 1.4 × 10¹⁰ years. Background sky: 2.7 K, so heavy black holes are still growing.
See where Sgr A* is
Sagittarius A* lies in the direction of Sagittarius, in the brightest part of the summer Milky Way; in October it sets in the south-west soon after dark. The black hole itself is not visible to the eye; the ring marks its position.
The camera view points the way with arrows; once you find it, you can take its photo and share it.
Frequently asked questions
What is the black hole information paradox?
Hawking showed in 1974 that black holes emit faint radiation and evaporate. In 1976 he argued that this radiation carries no information about what fell in, which would destroy information, something quantum mechanics forbids.
Has the information paradox been solved?
Not yet. Since 2019, calculations with islands and replica wormholes reproduce the Page curve in simplified theoretical models, which suggests information can come out. They have not been tested on real black holes, and how information would escape is still unknown.
How big is Sagittarius A*?
About 4.3 million solar masses, with an event horizon about 25 million kilometres across, about 18 times the width of the Sun.
Is Sagittarius A* invisible?
No light comes from inside its event horizon, so the black hole itself cannot be seen. We detect it through its effects: stars orbiting it, and the shadow it casts against the glowing gas around it, imaged by the Event Horizon Telescope in 2022.
Positions and times were recalculated with Astronomy Engine, the sky-calculation library Astrometrik uses; times for Vienna and Istanbul are local time. The artwork on this page was drawn by Astrometrik.