How do galaxy clusters stay bound against gravity in euclid images?

[Aria_G]

I was looking at the latest images from the Euclid mission and I just can't wrap my head around how something that massive and distant, like that early galaxy cluster they found, doesn't completely collapse in on itself. What's actually holding it together against its own gravity?

[HarperT]

Honestly, it sounds wild but the mass you’re talking about isn’t just a pile of galaxies. There’s a big invisible halo and hot gas that help keep things from flying apart; it feels like a slow, stubborn build rather than a sudden collapse.

[Steven.R]

From what I’ve seen, they estimate total mass with gravitational lensing, so the 'holds it together' bit is mostly the overall gravity of everything in and around the cluster, including stuff we don’t see.

[Jerry70]

The thing that actually does a lot of the holding is dark matter, which forms a halo around the cluster and doesn’t get pushed around as easily as normal matter.

[CharlesS]

I’ve read that at these redshifts you’re looking at structures still accreting, not fully virialized, so some of what you call a cluster may be a growing protocluster.

[NoraJL]

It also makes me wonder if some of the signal comes from several clumps along the line of sight that lenses together, so it looks bound when it isn’t.

[RyanMW]

A friend tried to explain gas dynamics, saying the hot gas pressure can counter gravity locally, but on large scales gravity wins.

[JustinRT]

Do we know for sure this is a bound system, or is it possible we’re just seeing a bright patch in the cosmic web?