Fun fact: I looked this up in the online version of the Duden (the predominant German dictionary). It does have an entry "Black Hole" (so the English term!) but not for "schwarzes Loch", which is the normal German term for it.
(In the printed versions, you might need to go to the Universalwörterbuch or so to find the English entry, it might not be in the normal "Die deutsche Rechtschreibung"; I have not checked.)
> Duden
Just the name gives me flashbacks to German-lessons in highschool.
The Duden is not official since 1996.
Since 2004 the official guidelines for the german speaking countries (Germany, Austria, Swiss, Belgium, South Tirol, Liechtenstein, Romania, Hungary - see this founding document with the list: https://www.rechtschreibrat.com/DOX/wiener_erklaerung.pdf) are covered by the Rechtschreibrat (https://www.rechtschreibrat.com/).
The official german dictionary is here: https://grammis.ids-mannheim.de/rechtschreibung/6774