7

The answer is of order 1 million years to cool from a standard end of He burning temperature of just over $10^8$ K to the top end of the white dwarf temperature range you give in your question. The details would depend exactly on the mass and composition of the white dwarf and there are also some theoretical uncertainties in neutrino cooling rates. The ...


5

Low mass stars like the Sun do become very large prior to He ignition in the core. The exact value depends a bit on models for mass loss from the extended atmosphere (e.g. Guo et al. 2016), but estimates of 250 times its current size are possible (Schroeder & Smith 2008; Spiegel & Madhusudhan 2012). At this radius both Mercury and Venus are engulfed. ...


5

The Sun will not become a red giant for approximately 7 billion years, so there is little chance that Proxima Cen will be anywhere near it. [EDIT: To answer a comment, the current helocentric radial velocity of Proxima Cen is -22 km/s. The Sun's escape velocity at the distance of Proxima Cen is about 0.1 km/s. So the Sun and Proxima Cen are totally unbound. ...


3

Higher mass stars will have shorter lives. Even though they have more fuel for nucleosynthesis, they burn this fuel much quicker than lower mass stars. Generally, you should think of "red-giant" as an evolutionary phase and not a particular type of star. Looking at the Scheller et al. (Aston. Astrophys. Suppl., 96, 269, 1992) data given in one of ...


3

Where does the evolution actually stop? Is the Helium Core Flash the last thing a Sun-like stars experiences or does it in fact follow the rest of the tractory? Stars with masses below about 2 solar masses undergo a helium flash but their evolution does continue afterwards, as shown in the second diagram (Fig. 13.4). So no, the core flash is not the last ...


2

In response to the question of how plants would look in this hypothetical arrangement, it's important to know that green plants did not evolve to maximize our sun's energy because they were not always the dominant photosynthetic organism on Earth. They specifically evolved in the margins around the purple sulfuric bacteria which were once the dominant sun ...


1

The sun, when it becomes a red giant, will be more 100 times more luminous than it is now, but that only gives it an absolute magnitude of about -1, and an apparent magnitude at 4 light-years of about -5: similar to Venus. It is possible for this to cast a very faint shadow, but you need a very dark place to see it. The sun will still be much too small to ...


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