Visible galaxies account for only 1 percent of a cluster's massㅡX-ray studies typically reveal ten times as much sparsely scattered, superhot gas, concentrated towards the centre of a cluster. The gas is believed to be heated and driven off during the galaxy mergers that give rise to elliptical galaxies, becoming energetic enough to escape the gravity of individual galaxies while remaining bound to the cluster as a whole.
I think the grammar of this sentence is incorrect because it doesn't have a target for comparison. I can't not grasp the meaning. Does that sentence mean that Visible galaxies are ten times as much sparsely scattered as (for what??) and the superhot gas have been concentrated towards the centre of a cluster. Is that right? (I'm not good at English, so there can be some mistakes in my question I do not intend.)
If you need more context concerned, please refer to the image I attached below.