Re: If the universe continues to expand, will not all stars disappear visually?

People with the most acute eyesight, under
the darkest of skies on Earth, can see down to
the apparent brightness of the planet Uranus. The
brightest supergiant stars, placed at a comparison
distance of 10 parsecs (approximately 32 light-years)
would intrinsically shine about 160,000 times brighter
than Uranus.  Thus it could be seen as similar to
Uranus in brightness if it were 400 times farther than
32 light-years, or about 13,000 light-years away. (400
is the square root of 160,000.) So, a supergiant star
at about 13,000 light-years defines the distance limit
for humans spotting the light of a single star.

This distance isn't even half-way to the center of our
own Milky Way!  How do we then see the outlines of our
own Galaxy, or any of the Galaxies much farther away?
The answer is simple:  we see the combined light of many
bright stars, in regions which appear too small for our
eyes to resolve.  If a typical galaxy contains 1 billion
supergiant stars, it's a billion times brighter than one
star and appears as bright as that star even if it's
30,000 times more distant (30,000 is approximately the
square root of a billion).  Thus, the limits to human
vision lie at about 30,000 x 13,000 light-years, or
roughly half a billion light-years distance. Even so, we
can't see most of the galaxies within that limit, with the
unaided human eye.  Their light is too spread out (unlike
stars).

Moreover, this limit is only about 1/25th of the way to
the farthest galaxy known via telescopic observations.
Telescopes can see objects much farther than human eyes
can, since they collect a lot more light than the pupil
entrance to our eyes can. Right now, the biggest telescope
mirrors are about 10 meters, or 1 million times larger in
area than our eyes. They can thus see objects 1,000 times
more distant - single stars in galaxies 13 million light
years away; entire distant galaxies to the known edge of
the universe.

Now, while it is true that the whole universe is expanding,
gravity is fighting against that expansion and actually wins
on the scale of a galaxy, and even in clusters of galaxies.
For instance, the Andromeda Galaxy, and several other members
of our Local Group of galaxies, are moving toward the Milky
Way.  Thus, we won't have the problem of stars in our Galaxy
becoming too distant for us to see them unaided - as long
as our Galaxy keeps on producing stars.  Likewise for other
galaxies in our local, gravity-bound cluster.

What would our Galaxy need to keep on doing that?  It would
need an unlimited supply of hydrogen and helium.  OK, its
supply is not endless, so eventually stars will use up all
their hydrogen and helium fuel and there won't be enough to
ignite baby stars.  When, in the distant future, the night
sky appears completely black, it won't be due to the light
being too distant, but due to visible light not being
emitted at all.