Talk:Quasar

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Record for the most distant known quasar

Hi there, in the quasars article it says: "31.7 billion light-years away" but in the linked article about UHZ1 it says "UHZ1 is at a distance of 13.2 billion light-years" Could it be a Typo? Bye! 2A02:2454:8628:E300:DD04:6F54:9840:36F (talk) 06:06, 15 November 2024 (UTC)[reply]

It could also be that 31.7 billion ly is how far away it is now due to its motion away from us and the expansion of the universe, as opposed to the distance its light has traveled to reach us (13.2 billion ly). See, for example, https://www.forbes.com/sites/startswithabang/2018/02/23/if-the-universe-is-13-8-billion-years-old-how-can-we-see-46-billion-light-years-away/. A graph there does indeed show a current distance of roughly 30 billion ly for something at z=9.6, which corresponds to something we currently see at 13.2 billion ly. If this is the case it would be good explain it in the article. DKMell (talk) 18:49, 18 November 2024 (UTC)[reply]

The problem is that there are different distance measures in cosmology, and a statement like this lacks essential information if it doesn't specify whether the listed distance is a luminosity distance, a light-travel time distance, etc. In general I think it is better not to list distances in this way at all, but instead to specify the look-back time, or the age of the universe when the light we currently observe from the object was emitted. Aldebarium (talk) 21:40, 18 November 2024 (UTC)[reply]