Will galactic filament indefinitely expand while its galaxy clusters

[James Goetz]

Exciting discoveries of weak gravitational lensing suggest the
existence of galactic filaments made of dark matter that are the size
of galactic superclusters (https://doi.org/10.1093/mnras/stx517).
My questions involves the future of the galactic filaments while
space indefinitely expands between the galaxy clusters within each
galactic filament. Will the filaments indefinitely expand with the
indefinite expansion of space or will the filaments divide because
of an event horizon? For example, event horizon paradigms suggest
that the expansion of space will eventually isolate each galaxy
cluster from each other galaxy cluster. Perhaps we do not yet have
enough information to calculate this because we know little about
dark matter.

[[Mod. note -- I think your last statement is *definitely* true:
we don't know enough about dark matter to calculate this. -- jt]]

[James Goetz]

I guess that we can track the development of the filaments while the
respective galaxy clusters continue to disperse. We should eventually
be able to detect change or no change in their spacial dimensions and
density; while change in length is inevitable. For example, if they
grow in length without losing width, depth, and density, then that
would support that they will develop forever. I am not making any
predictions about how they develop, but tracking their changes will
help us to predict their future regardless if we ever directly direct
dark matter.

[James Goetz]

I emailed the question to the paper coauthor Michael Hudson, and
he replied:

In a nutshell, the filaments, like the rest of the Universe will
still expand indefinitely in the current picture.

The event horizon is analogous to a horizon on Earth, I.e. It is a
distance to which light can travel. It is not a physical force that,
for example, tears anything apart or generates some kind of tangible
barrier.

Mike Hudson, Professor
Dept. of Physics & Astronomy
University of Waterloo
Waterloo, ON N2L 3G1 Canada


[[Mod. note -- Ted Bunn's "Black Holes FAQ" is an excellent reference
to learn more about event horizons:
http://cfpa.berkeley.edu/Education/BHfaq.html
-- jt]]

[Steve Willner]

In article <15f79c53-3337-4211...@googlegroups.com>,

James Goetz <jimgo...@gmail.com> writes:
> Exciting discoveries of weak gravitational lensing suggest the
> existence of galactic filaments made of dark matter that are the size
> of galactic superclusters (https://doi.org/10.1093/mnras/stx517).

Remarkable work.

> My questions involves the future of the galactic filaments while
> space indefinitely expands between the galaxy clusters within each
> galactic filament. Will the filaments indefinitely expand with the
> indefinite expansion of space or will the filaments divide because
> of an event horizon?

What you are asking is whether the filaments are massive enough to be
gravitationally bound. Given the mass of >10^13 Msun, I'd be
surprised if not, but I haven't done any calculation. A detailed
model would require knowing velocites, and the outcome might depend
on the distribution of dark matter around the filament: whether
there's one halo or two.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123 swil...@cfa.harvard.edu
Cambridge, MA 02138 USA

[James Goetz]

> [[Mod. note -- Ted Bunn's "Black Holes FAQ" is an excellent
> reference to learn more about event horizons:
> http://cfpa.berkeley.edu/Education/BHfaq.html
> -- jt]]

Good point about black holes. I neglected that the event
horizons involve future galaxy-cluster-sized black holes
within a supercluster.