Talk:Red giant

Table

It would be useful to show a table of how many red giants exist in total right now; at the least denoting the date and a rough number. Right now visitors can not quickly obtain this information - are there 100 red giants? 1000? 100000? Nobody knows right now from this wikipedia article alone. That should be changed in the long run; a rough estimate is fine. 2A02:8388:1604:CA80:0:0:0:1 (talk) 16:43, 26 May 2019 (UTC)

How should we explain why a red giant expands?

Currently it is stated fairly baldly that it does, but some explanation would be better. Unfortunately, a detailed water-tight explanation is probably too complex to be understood by most readers. Can we fudge it with some sort of shell-mirroring explanation? The mirroring is true enough; the full details of why are again quite complex, but with a bit of hand-waving it should be possible to come up with something that will convince most people. Once the mirror principle is accepted, all sorts of aspects of red giant evolution become very easy to explain. Or do we head off down the convection path? That isn't really the reason why red giants expand in the first place, although it explains why they expand more after they initially become red giants. Most people would probably just buy that it was all down to convection, though. Lithopsian (talk) 19:06, 6 June 2019 (UTC)

Closest red giant?

Some sources name Gacrux as the closest R.G. to the Sun, but Arcturus is actually closer. What's the right answer? -- A man without a country (talk) 17:08, 17 July 2019 (UTC)

The article explains it. γ Crucis is the closest class M giant, but K0 Arcturus is closer. Lithopsian (talk) 17:32, 17 July 2019 (UTC)

Thanks. I copied that into preamble. I think preamble also has to answer such questions as:

• What exactly causes RGs to be luminous?
• What is current share of RGs in the Milky Way?
• What is the share of stars which will become RGs in the Milky Way?
• What is the fate of RG stars?

A man without a country (talk) 15:51, 23 July 2019 (UTC)

The lead doesn't have to contain the entire article ;) Most of this information is already in the article. Red giants are luminous for a variety of reasons, partly dependant on your viewpoint, but basically their interiors are hotter and hence fusing at a higher rate than main sequence stars of the same mass (on average, there are exceptions). The fraction of stars that are red giants varies depending on which set of stars you look at; for example, young clusters will contain no red giants while they are (relatively) very common in old globular clusters where young stars are no longer being born. In the solar neighbourhood, around half of one percent of stars are giants, most of those of spectral type K. The only stars that do not become red giants are the tiny number of the most massive, and the least massive red dwarfs, although red dwarfs do make up about three quarters of all stars. Exact statistics depend on who you ask. The evolution of red giants is explained in the article; the simple answer is that in almost all cases they become white dwarfs, but the term red giant covers stars in several different evolutionary phases not all of which immediately progress to a white dwarf. Lithopsian (talk) 19:48, 23 July 2019 (UTC)

Well, there are rules on WP leads. Lead should introduce to subject and summarize the article. And these questions are not from my sole curiosity: they are from lead section in White dwarf, which is marked as good article. -- A man without a country (talk) 20:38, 23 July 2019 (UTC)

I suggest expanding the body first, referenced with reliable sources. Then you can try for a concise lead that summarises the important points. Just adding factoids to the lead will always make a mess. The comparison to white dwarf is apt, since red giants are arguably just as notable. That article is nearly five times as long, and that completeness is one of the reasons it was promoted to FA. Things have slipped a little since, but it is still a decent article. One complication here is that red giant covers several different types of star that are fully discussed in other articles. The new lead makes this a little clearer than it was, but it should still be explained properly in the body, probably with explicit sections and {{main article}} links. Lithopsian (talk) 19:51, 24 July 2019 (UTC)

The Sun as a Red Giant

In the section that talks about the Sun too eventually becoming a red giant, why isn't the possibility of the Sun swallowing up the Earth discussed in more detail, as well as the fact that all life on Earth will probably end long before the Sun even becomes a red giant? The possibility of whether if the Sun will actually indeed swallow up the Earth as a red giant is still an open question even today, although it's more likely that it actually will. — Preceding unsigned comment added by 23.28.197.157 (talk) 12:41, 10 April 2021 (UTC) What about the fact that Titan will probably become habitable as a result of the Sun becoming a red giant?

These things are, or could be, covered in a separate article. The link is right there in the article. This article is about red giants, not about the Sun. Lithopsian (talk) 19:49, 12 April 2021 (UTC)

"Prospects for habitability"

An anonymous editor is trying to add a table to this section of... red giants that could have habitable planets, or something like that. This has several problems:

• It is completely unsourced.
• It includes red supergiants, which are not red giants.
• It includes stars with circumstellar disks. Circumstellar disks are not potentially habitable planets; you might as well list all red giants with planets in that case.
• The two actual planets that are listed are KOI-4902.01 and KOI-5878.01. These are both planet candidates that have not been confirmed. In addition, the Exoplanet Archive lists semi-major axes of less than 1 AU for both candidates, so if their host stars really are red giants as claimed, they would be too hot to be potentially habitable. The listed insolations are Earth-to-Mars-like, but these were presumably calculated based on the assumption that their host stars are on the main sequence.
• If those two planet candidates actually exist and orbit red giants, they might be former habitable planets, that were habitable when their host stars were on the main sequence? But without sources, that's all way too speculative to be in Wikipedia.

SevenSpheres (talk) 18:26, 8 November 2025 (UTC)

For the two KOI candidates, the stars are orange giants, according to NASA Exoplanet Archive and TICv8. Both sources say that these stars’ radius is 2.3 and 5.6 solar radii and both are K type.

For the other red giants, NASA said that frozen planeys in the outer system may thaw into habitable planets, and circumstellar disks are “second chance” of planet formation. ~2025-32241-73 (talk) 01:13, 9 November 2025 (UTC)

And circumstellar disks doesn’t guarantee habitability, but just make the chance greater. ~2025-32241-73 (talk) 01:17, 9 November 2025 (UTC)

any statement requires a citation from at least one reliable source within the text and cannot go beyond what the source says, per WP:OR and WP:SYNTH. "NASA said that frozen planets from the outer system may thaw into habitable planets" does not cover the possibility of specific RG exoplanets being habitable. ArkHyena_woop! (she/they/it) 02:11, 9 November 2025 (UTC)

How about the KOIs? It has detailed sources ~2025-31927-24 (talk) 08:22, 9 November 2025 (UTC)

There's data for them in the Exoplanet Archive, but it doesn't explicitly say that they're potentially habitable planets orbiting giant stars. As mentioned above my own interpretation of the data is different; the host stars do appear to be giants based on their properties (though you can't just make up spectral types), but if that's the case the planets shouldn't be in the habitable zone and the listed insolations are wrong. In any case that's all OR/SYNTH. SevenSpheres (talk) 18:14, 9 November 2025 (UTC)

Maybe that the KOIs are red giants is the older data while newer data says the KOIs are Main Sequence. ~2025-32510-50 (talk) 09:15, 10 November 2025 (UTC)

The stars’ type, semimajor axis and orbital period is not proven yet. Need to study further to prove whether the planets are habitable or not. ~2025-33244-19 (talk) 07:31, 13 November 2025 (UTC)