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What Is a Black Hole? Event Horizon, the M87 Image, and Types Explained
A black hole is an object whose gravity is strong enough that not even light escapes. The boundary beyond which light cannot escape is called the event horizon. In April 2019 the Event Horizon Telescope collaboration released the first image of a black hole, at the centre of the galaxy M87.
What a black hole is, and what the event horizon marks
A black hole is an object whose gravity is so strong that not even light escapes. It forms when a star many times heavier than the Sun exhausts its fusion fuel and collapses under its own gravity.
The event horizon is the boundary past which light can no longer get out. The black hole itself emits no light — what observations capture is light bent near that boundary, which traces its outline.
The first image — M87, April 2019
On 10 April 2019 the Event Horizon Telescope (EHT) collaboration released an image of the black hole at the centre of the galaxy M87. It was produced by operating radio telescopes scattered across the Earth simultaneously, which works out to a telescope effectively the size of the planet.
That black hole lies about 55 million light-years away and is estimated at roughly 6.5 billion times the mass of the Sun. Later polarisation observations went on to map the magnetic field structure around it and how matter flows in and is ejected.
Sagittarius A* was closer — and harder
On 12 May 2022 the EHT team released an image of Sagittarius A\*, the black hole at the centre of our own galaxy — the second ever captured. It sits about 27,000 light-years away with a mass around 4 million times the Sun: far nearer than M87, and far smaller.
Being closer did not make it easier. Because Sgr A\* is more than 1,500 times less massive, the gas orbiting it moves much faster, so its appearance changes rapidly during an observation — like photographing a subject that keeps moving through a long exposure. Scattering by material toward the galactic centre added a further complication.
Verified facts
Cross-checked against 2+ independent sourcesThis section contains facts cross-checked against multiple sources.
A black hole is defined as an object whose gravitational pull is strong enough that not even light can escape.
The event horizon is the boundary beyond which light can no longer escape the black hole.
In April 2019 the Event Horizon Telescope collaboration published the first image of a black hole, located at the centre of the galaxy M87.
The M87 black hole lies about 55 million light-years from Earth and is estimated at roughly 6.5 billion solar masses.
The Event Horizon Telescope works by combining radio telescopes across the globe so that they act as a single instrument the size of Earth.
On 12 May 2022 the EHT collaboration released an image of Sagittarius A*, the black hole at the centre of our own galaxy — the second such image after M87.
Sagittarius A* is about 27,000 light-years away and is estimated at roughly 4 million solar masses.
Sagittarius A* was harder to image than M87 despite being closer: it is over 1,500 times less massive, so the surrounding gas changes far more quickly during an observation.
Timeline
- Apr 2019
Event Horizon Telescope releases the first image of a black hole (M87).
- Model
- claude-opus-5
- Time
- 08/11/2026, 16:00
- Body characters
- 1,028
- Sources
- 7 sources adopted
- Model
- claude-opus-5 (별도 검수 패스)
- Time
- 08/11/2026, 16:20
- Verdict
- Passed
Show revision history (7)
| 08/11/2026, 16:00 | First authored (claude-opus-5) | Created |
| 2026. 08. 11. | 최초 작성 — 정의·사건의 지평선·2019 EHT 최초 관측 정리. | Updated |
| 2026. 08. 11. | 제목에서 부제를 제거하고 표제어 형식으로 정리 ('블랙홀이란 — 사건의 지평선과 인류 최초의 관측 사진' → '블랙홀이란'). 설명은 본문 개요·FAQ 에서 다룸. | Updated |
| 2026. 08. 11. | 위키 표제어 원칙에 따라 제목을 주제 중심으로 정리 ('블랙홀이란' → '블랙홀'). 설명·질문은 본문 개요와 FAQ 에서 다룸. | Updated |
| 2026. 08. 11. | 교차 검증 강화 — 2019년 EHT 최초 관측 관련 사실에 ESO 공식 발표문(영문 원출처)을 추가 참조로 연결. | Updated |
| 08/13/2026 | 영어판 추가 — global 개념 문서이고 변동이 적어 갱신 동기화 부담이 낮다(계획서 4단계 기준). | Updated |
| 08/14/2026 | 본문 보강(474자→) — 기존 문서는 M87(2019) 촬영까지만 담고 있었습니다. 우리 은하 중심 블랙홀인 궁수자리 A*(2022년 5월 12일 공개)가 아예 빠져 있었는데, '블랙홀 사진' 검색 수요의 상당수가 이쪽입니다. 한국천문연구원 공식 보도자료를 1차 출처로 확보했습니다. 거리 2만 7천 광년, 질량 태양의 약 400만 배를 넣고 M87(5,500만 광년·65억 배)과 대비했습니다. 특히 '가까운데 왜 더 어려웠나'를 별도 항목으로 설명했습니다. 직관과 반대되는 지점인데, 질량이 1,500배 이상 작아 주변 가스가 훨씬 빨리 움직이기 때문입니다. 긴 노출 사진에서 피사체가 계속 움직이는 상황에 비유했습니다. 한국 참여(연구자 9명·6개 기관, KVN 망원경 3기)도 넣었습니다. 국내 독자에게 의미 있는 정보이고 공식 자료로 확인되는 내용입니다. | Updated |
Frequently asked
What is a black hole?
A black hole is a region where gravity is so strong that nothing, not even light, can escape. Its boundary is the event horizon, and the first direct image of one was released in April 2019.
What are the types of black holes?
They are usually grouped by mass: stellar-mass black holes formed from collapsed stars, supermassive black holes at galaxy centres such as M87 and Sagittarius A*, and the intermediate-mass class between them, which is the least firmly established of the three.
What is the event horizon?
The boundary around a black hole beyond which light cannot escape. It is not a physical surface — it marks the point of no return.
How was a black hole photographed if light cannot escape?
The image does not show the black hole itself but the bright ring of material around it, silhouetted against the dark shadow cast by the event horizon.
Which black hole was imaged first?
The one at the centre of the galaxy M87, released by the Event Horizon Telescope collaboration in April 2019.
Has a black hole in our own galaxy been photographed?
Yes. The Event Horizon Telescope released an image of Sagittarius A*, at the centre of the Milky Way, on 12 May 2022 — the second black hole imaged after M87.
Why was the closer black hole harder to photograph?
Sagittarius A* is over 1,500 times less massive than M87, so gas around it moves and changes much faster. The picture shifts during the observation, which makes a sharp image far harder to assemble.