# How a black hole forms and what happens at the edge

> A process map exported from forks.world (https://forks.world). Author: Brian. Source: https://forks.world/p/cmv21nnnh000ml2064why3upb
> It describes who does what, in what order, and with which technology. Read the plain-language sections first; the JSON at the end is the exact, complete data.

## Summary

- 14 steps across 2 layers
- Persona: A massive star, The core, Space around it, An astronaut

## How to read this file

- A process is made of **layers**. The main layer is the top level; any step of kind `subprocess` opens a detail layer with its own lanes and steps.
- **Lanes** are either persona (people/roles) or technology (systems). Each step belongs to one lane; `using` lists tools a person uses for that step.
- Step kinds: `start`, `task`, `decision` (its arrows carry the answer as a label), `subprocess`, `end`.

## How a black hole forms and what happens at the edge

Lanes:
- A massive star: person / role (id `star`)
- The core: person / role (id `core`)
- Space around it: person / role (id `space`)
- An astronaut: person / role (id `you`)

Steps, in the order they run:

1. **A star more than 20 times the Sun burns through its fuel** [subprocess; A massive star; id `b1`], links to the published process "The life and death of a star" (https://forks.world/p/cmv0idz7h000jjw06rb65zt7m; full text at https://forks.world/api/public/cmv0idz7h000jjw06rb65zt7m/export)
   - then Fusion stops and the core can no longer hold itself up
2. **Fusion stops and the core can no longer hold itself up** [task; The core; id `b2`]
   - then The core collapses in a fraction of a second
3. **The core collapses in a fraction of a second** [task; The core; id `b3`]
   - then Outer layers blast off in a supernova
4. **Outer layers blast off in a supernova** [task; A massive star; id `b4`]
   - then Is what is left heavier than about 3 Suns?
5. **Is what is left heavier than about 3 Suns?** [decision; The core; id `b5`]
   - if "Yes" go to Gravity crushes it into a point: a black hole; if "No" go to It becomes a neutron star instead
6. **Gravity crushes it into a point: a black hole** [subprocess; The core; id `b6`], opens the detail layer "Falling in"
   - then Nothing, not even light, escapes inside the event horizon
7. **Nothing, not even light, escapes inside the event horizon** [task; Space around it; id `b7`]
   - then Gas falling in heats up and glows, so we can see it
8. **Gas falling in heats up and glows, so we can see it** [task; Space around it; id `b8`]
   - then Two black holes spiral together and send gravity waves across space
9. **Two black holes spiral together and send gravity waves across space** [subprocess; Space around it; id `b9`], links to the published process "How LIGO hears gravitational waves" (https://forks.world/p/cmv0kpwmj000ejv06mxozx3gs; full text at https://forks.world/api/public/cmv0kpwmj000ejv06mxozx3gs/export)
   - (no next step recorded)
10. **It becomes a neutron star instead** [end; The core; id `b5a`]

```mermaid
flowchart LR
  subgraph l_star["A massive star"]
    n_b1[["A star more than 20 times the Sun burns through its fuel"]]
    n_b4["Outer layers blast off in a supernova"]
  end
  subgraph l_core["The core"]
    n_b2["Fusion stops and the core can no longer hold itself up"]
    n_b3["The core collapses in a fraction of a second"]
    n_b5{"Is what is left heavier than about 3 Suns?"}
    n_b5a(["It becomes a neutron star instead"])
    n_b6[["Gravity crushes it into a point: a black hole"]]
  end
  subgraph l_space["Space around it"]
    n_b7["Nothing, not even light, escapes inside the event horizon"]
    n_b8["Gas falling in heats up and glows, so we can see it"]
    n_b9[["Two black holes spiral together and send gravity waves across space"]]
  end
  n_b1 --> n_b2
  n_b2 --> n_b3
  n_b3 --> n_b4
  n_b4 --> n_b5
  n_b5 -->|"Yes"| n_b6
  n_b5 -->|"No"| n_b5a
  n_b6 --> n_b7
  n_b7 --> n_b8
  n_b8 --> n_b9
```

### Falling in (detail of step "Gravity crushes it into a point: a black hole")

Lanes:
- An astronaut: person / role (id `you`)
- Space around it: person / role (id `space`)

Steps, in the order they run:

1. **You approach the event horizon** [start; An astronaut; id `e1`]
   - then Time slows down as seen from far away
2. **Time slows down as seen from far away** [task; Space around it; id `e2`]
   - then You cross the horizon and feel nothing special
3. **You cross the horizon and feel nothing special** [task; An astronaut; id `e3`]
   - then Tidal forces stretch you into a thin stream
4. **Tidal forces stretch you into a thin stream** [end; An astronaut; id `e4`]

```mermaid
flowchart LR
  subgraph l_you["An astronaut"]
    n_e1(["You approach the event horizon"])
    n_e3["You cross the horizon and feel nothing special"]
    n_e4(["Tidal forces stretch you into a thin stream"])
  end
  subgraph l_space["Space around it"]
    n_e2["Time slows down as seen from far away"]
  end
  n_e1 --> n_e2
  n_e2 --> n_e3
  n_e3 --> n_e4
```

## Full data (JSON)

```json
{
  "title": "How a black hole forms and what happens at the edge",
  "maps": {
    "m_edge": {
      "id": "m_edge",
      "lanes": [
        {
          "id": "you",
          "name": "An astronaut",
          "type": "person"
        },
        {
          "id": "space",
          "name": "Space around it",
          "type": "person"
        }
      ],
      "steps": [
        {
          "id": "e1",
          "kind": "start",
          "lane": "you",
          "next": [
            {
              "to": "e2"
            }
          ],
          "uses": [],
          "label": "You approach the event horizon"
        },
        {
          "id": "e2",
          "kind": "task",
          "lane": "space",
          "next": [
            {
              "to": "e3"
            }
          ],
          "uses": [],
          "label": "Time slows down as seen from far away"
        },
        {
          "id": "e3",
          "kind": "task",
          "lane": "you",
          "next": [
            {
              "to": "e4"
            }
          ],
          "uses": [],
          "label": "You cross the horizon and feel nothing special"
        },
        {
          "id": "e4",
          "kind": "end",
          "lane": "you",
          "next": [],
          "uses": [],
          "label": "Tidal forces stretch you into a thin stream"
        }
      ],
      "title": "Falling in",
      "parent": {
        "map": "m_root",
        "step": "b6"
      }
    },
    "m_root": {
      "id": "m_root",
      "lanes": [
        {
          "id": "star",
          "name": "A massive star",
          "type": "person"
        },
        {
          "id": "core",
          "name": "The core",
          "type": "person"
        },
        {
          "id": "space",
          "name": "Space around it",
          "type": "person"
        },
        {
          "id": "you",
          "name": "An astronaut",
          "type": "person"
        }
      ],
      "steps": [
        {
          "id": "b1",
          "kind": "subprocess",
          "lane": "star",
          "link": {
            "id": "cmv0idz7h000jjw06rb65zt7m",
            "scope": "public",
            "title": "The life and death of a star"
          },
          "next": [
            {
              "to": "b2"
            }
          ],
          "uses": [],
          "label": "A star more than 20 times the Sun burns through its fuel"
        },
        {
          "id": "b2",
          "kind": "task",
          "lane": "core",
          "next": [
            {
              "to": "b3"
            }
          ],
          "uses": [],
          "label": "Fusion stops and the core can no longer hold itself up"
        },
        {
          "id": "b3",
          "kind": "task",
          "lane": "core",
          "next": [
            {
              "to": "b4"
            }
          ],
          "uses": [],
          "label": "The core collapses in a fraction of a second"
        },
        {
          "id": "b4",
          "kind": "task",
          "lane": "star",
          "next": [
            {
              "to": "b5"
            }
          ],
          "uses": [],
          "label": "Outer layers blast off in a supernova"
        },
        {
          "id": "b5",
          "kind": "decision",
          "lane": "core",
          "next": [
            {
              "to": "b6",
              "label": "Yes"
            },
            {
              "to": "b5a",
              "label": "No"
            }
          ],
          "uses": [],
          "label": "Is what is left heavier than about 3 Suns?"
        },
        {
          "id": "b5a",
          "kind": "end",
          "lane": "core",
          "next": [],
          "uses": [],
          "label": "It becomes a neutron star instead"
        },
        {
          "id": "b6",
          "kind": "subprocess",
          "lane": "core",
          "next": [
            {
              "to": "b7"
            }
          ],
          "uses": [],
          "child": "m_edge",
          "label": "Gravity crushes it into a point: a black hole"
        },
        {
          "id": "b7",
          "kind": "task",
          "lane": "space",
          "next": [
            {
              "to": "b8"
            }
          ],
          "uses": [],
          "label": "Nothing, not even light, escapes inside the event horizon"
        },
        {
          "id": "b8",
          "kind": "task",
          "lane": "space",
          "next": [
            {
              "to": "b9"
            }
          ],
          "uses": [],
          "label": "Gas falling in heats up and glows, so we can see it"
        },
        {
          "id": "b9",
          "kind": "subprocess",
          "lane": "space",
          "link": {
            "id": "cmv0kpwmj000ejv06mxozx3gs",
            "scope": "public",
            "title": "How LIGO hears gravitational waves"
          },
          "next": [],
          "uses": [],
          "label": "Two black holes spiral together and send gravity waves across space"
        }
      ],
      "title": "How a black hole forms and what happens at the edge",
      "parent": null
    }
  }
}
```