When contemplating the possibility of other life in the universe, the main starting point
for any star system is, well, it’s parent star.
First and foremost, for life to be possible in a star system, the star itself must allow
for it.
There are many that do not, for example giant stars that simply don’t live long enough
for life to arise before they explode as supernovas.
And while there are exceptions, very odd but still possible habitable zones such as those
around pulsars, most stars that are considered to have habitable zones fall into several
classes of stable star.
But the life that might arise at these stars may evolve very differently from earth due
to the conditions these stars present to their habitable planets.
The first class is the ubiquitous red dwarfs, the type M stars.
This class has advantages and disadvantages for life.
One the one hand, they are the most abundant stars in the Milky Way by far, offering billions
of chances for life in this galaxy alone.
Secondly, they are very long lived, allowing life a comparatively enormous amount of time
to arise and evolve, far longer than what we have with our sun.
But they can also be violent stars, especially when young, producing giant flares and radiation
that may make any planets within their habitable zones unsuitable for life.
Also they are small stars with habitable zones very close in.
This creates a situation where planets within those zones could be tidally locked, meaning
one face of the planet always faces the star.
This could create a very different kind of habitable world than earth, sometimes called
eyeball worlds.
These planets could have intense desert sides that are permanently baked by the star, but
also a side permanently in the dark.
At the twilight edge there could be a zone where liquid water might be present, and if
the atmosphere is active enough might transfer heat to the dark side of the planet and allow
for water there as well, and possibly life that may well be adapted for low light, or
completely dark conditions.
Given that earth life has produced biolumenescence, one wonders what life on an eyeball world
might be like
But in the end, the habitable zones around red dwarfs are probably not ideal locations
for life to arise, but it also doesn’t seem entirely impossible, and there’s always
the question of liquid water zones underneath shells of ice, like our own Europa, which
could allow life to arise under the protection of that shell.
And given the longevity of red dwarfs they may prove useful for space faring civilizations
looking to colonize very long-lived stars, and thusly may be attractive for SETI searches.
The next class of star may be the most hospitable for earth-like life.
Even more so than our own sun.
These are the slightly larger type K orange dwarfs, and have several advantages over the
red dwarfs.
One, they too are a common type of star, though not as common as the red dwarfs.
They are also a bit larger and brighter, so the habitable zone for these stars lies further
out, favoring life because close proximity to star is generally not good.
And, they live significantly longer than our own sun, providing evolution and life more
time to develop and evolve.
These kinds of stars could be garden spots for life, providing longevity, stability and
a good habitable zone, so far as we know.
It’s difficult to imagine a place that might be better for life than our own solar system,
since we know a star like the sun can produce life and a civilization.
But the orange dwarfs might be better for that than the sun, and it’s possible that
our star is an outlier that alien scientists might dismiss as unlikely to produce intelligent
life.
Yet, our type G so-called yellow dwarf star did exactly that, though it emits more green
light than any other visible light -- and it’s actually rather large as far as stars
go, more like a giant than a dwarf.
So what other type G stars could do it?
Well, sunlike stars are certainly of interest to SETI.
But we don’t really know how slow or how fast evolution can occur.
If it occurs slowly, and earth got lucky in producing intelligence, then sun-like stars
will drop in likelyhood for hosting intelligent civilizations.
After all, ours won’t be hosting it forever.
The sun’s luminosity is increasing and it will slowly bake Earth long before it reaches
its red giant stage.
But there is also the possibility that evolution could produce intelligence much faster than
it did here on earth.
If that’s the case, then the type F stars come into question.
These stars are larger than the sun, but live a bit shorter of a lifetime.
But generally speaking, still billions of years.
These stars are powerful.
They would bathe their planets in ultraviolet light, but their habitable zones would be
further out.
And they have raised eyebrows before, the infamous KIC 8462852 is a type F star.
And, the possibilities regarding their habitable zones are not well-explored, but they are
a maybe.
But going into the stars larger than this class, we start to run into the brick wall
of instability and short life … and supernovas.
But that also offers a possibility.
Given that those stars tend to go supernova, which can pose a threat to a civilization,
what happens if you see a galaxy devoid of these kinds of stars?
What if a galaxy is detected that trends towards redder, more stable stars and has almost no
blue stars?
This concept is known as a red spiral, a galaxy that lacks these stars.
And there are candidates for this.
Natural explanations are on that table of course, and are more likely, such as dust
blocking certain wavelengths of light, but just maybe someone might have removed their
dangerous stars.
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Thanks for listening!
I am futurist and science fiction author John Michael Godier and be sure to check out my
books at your favorite online book retailer and subscribe to my channels for regular,
in-depth explorations into the interesting, weird and unknown aspects of this amazing
universe in which we live.