What kinds of stars have viable habitable zones other than G-type stars, and what would life be like orbiting them? [closed]

Question

What would foliage, landscape, and quality of life on dwarf stars and blue stars? Would it be possible for a human to live without high-tech devices and such?

Answer 1

Part One: Habitable Zones.

All stars have habitable zones around them, hollow spheres between where a planet would receive too much energy from the star and become too hot for liquid surface water. and where a planet would receive too little energy from the star and become too cold for liquid surface water.

But:

One)

It is simple to use the ratio between the luminosity of a star and the luminosity of the Sun to compare the size of that star's habitable zone with that of the Sun. Unfortunately the size of the Sun's habitable zone is not known with certainty.

Here is a link to a list of extimates of the inner or other edges, or both, of the Sun's circumstellar habitable zone made in the last 58 years.

https://en.wikipedia.org/wiki/Circumstellar_habitable_zone#Solar_System_estimates

Note the large differences between some of the estimates.

Someone can be certain that planet is in the habitable zone if it receives as much radiation from the star as Earth gets from the Sun. I call the distance from a star where a planet gets as much radiation as Earth gets from the Sun the Earth Equivalent Distance or EED. Some cautious scientists limit the circumstellar habitable zone to a very narrow band around the EED, as you can see from the list, while others accept a much broader habitable zone.

Two)

Difference in the mass, radius, averae density, surface gravity, escape velocity, magnetosphere, hydrosphere, and atmosphere of a planet can affect how much radiation from its star it needs to be habitable, and thus how close or how far from the star it could be. Thus the inner and outer edges of a star's habitable zone are rather fuzzy, since various characteristics of a planet affect the distances where it can have liquid water.

Three)

All planets have elliptical orbits and not perfectly circular orbits. Planets vary greatlyin how elliptical their orbits are. So some planets of some stars may har v eorbits which are in the habitable zone only part of the time.

Four)

Some stars are variable. And some variable stars have very irregular variations, but others have very regular variations. And I suppose that it is theoretically possible that somewhere in the universe there is a planet with highly ellipical orbit around a very regular variable star, where the parameters of the planet's orbit and the star's variation match well enough that the planet is always in the star's habitable zone.

But I wouldn't bet on it.

Five) Many stars are part of binary (double) stars systems, and some stars are part of multiple star systems.

The two stars in a binary system orbit around their center of gravity, often in highly ellipical orbits where the deistance between them changes greatly.

It is possible for a planet to orbit around one of the stars in a binary system in what is called a noncircumbinary or S-type orbit.

It is possible for a planet to orbit around both of the stars in a binary system in what is called a circumbinary or P-type orbit.

The masses and orbits of the two stars will determine whether S-type orbits, P-type orbits, or both will be stable for long ages of time in the system.

If the two stars are widely separated each star can have its own habitable zone for planets in S-Type orbits.

If the two stars are closely separated they will have common habitable zone for planets in P-type orbits.

And probably therer are many systems where the gravitational forces of the stars prevent stable planetary orbits in the habitable zones.

Part Two: Stars That Can Have Planets Habitable for Humans.

There is a scientific study of what is necessary for a planet to be habitable for humans. Habitable Planets for Man, Stephen H. Dole, 1964.

https://www.rand.org/content/dam/rand/pubs/commercial_books/2007/RAND_CB179-1.pdf

It does discuss what types of stars could have planets which are (naturally) habitable for huumans.

More recent discussions of planetary habitability discuss the possible habitabiity of worlds for liquid water using life in general and not for humans in particular. On Earth there are many environments with flourish life forms which are deadly for unprotected humans, so not all planets habitable for liquid water using life in general would be habitable for humans in particular.