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<blockquote data-quote="freyar" data-source="post: 6753123" data-attributes="member: 40227">On lensing, AbdulAlhazred is correct.&nbsp; It's also true that, within a biggish galaxy like ours, we don't know if many/most of the subhalos have been smoothed out by the gravitational effects of normal matter (which are more important than dark matter in the inner parts of galaxies like ours).&nbsp; So we wouldn't necessarily see much (micro)lensing in our galaxy from subhalos.&nbsp; If we're talking about lensing of very far away galaxies, we're talking about strong gravitational lensing, which requires a lot of mass.&nbsp; Typically the only thing large enough to make a lens we'd see is a cluster of galaxies and associated dark matter halo, and we do find that that kind of lens is very common.Based on various types of evidence, dark matter structures did form first, and normal matter then fell into the dense regions of dark matter.&nbsp; Here's a reasonable picture of how things look today: there are these really big clouds of dark matter that hold clusters of galaxies together.&nbsp; Inside these cluster halos are large amounts of intergalactic gas and also smaller halos of dark matter, which by-and-large contain galaxies.&nbsp; Some are reasonably big, like our Milky Way, some are dwarf galaxies (generally satellites of galaxies like ours) that may either have very little normal matter or may be separated from their original dark matter halos by tidal effects, and some are really big monster-sized galaxies formed by the collision of other galaxies.&nbsp; Inside the galaxies, there are probably subhalos and other structures, but we don't have as good of a picture of that.&nbsp; The cluster-sized halos of galaxies themselves form into large walls and seem to lie at the intersection of filaments of dark matter.&nbsp; On the flip side, the walls surround large voids with very little matter of any kind (dark or normal).&nbsp; On the average, on very very large distances, the universe is pretty smooth though, and in fact this is what we see in the cosmic microwave background light, which is uniform with fluctuations of only one part in 100,000 roughly.</blockquote>

[QUOTE="freyar, post: 6753123, member: 40227"] On lensing, AbdulAlhazred is correct. It's also true that, within a biggish galaxy like ours, we don't know if many/most of the subhalos have been smoothed out by the gravitational effects of normal matter (which are more important than dark matter in the inner parts of galaxies like ours). So we wouldn't necessarily see much (micro)lensing in our galaxy from subhalos. If we're talking about lensing of very far away galaxies, we're talking about strong gravitational lensing, which requires a lot of mass. Typically the only thing large enough to make a lens we'd see is a cluster of galaxies and associated dark matter halo, and we do find that that kind of lens is very common. Based on various types of evidence, dark matter structures did form first, and normal matter then fell into the dense regions of dark matter. Here's a reasonable picture of how things look today: there are these really big clouds of dark matter that hold clusters of galaxies together. Inside these cluster halos are large amounts of intergalactic gas and also smaller halos of dark matter, which by-and-large contain galaxies. Some are reasonably big, like our Milky Way, some are dwarf galaxies (generally satellites of galaxies like ours) that may either have very little normal matter or may be separated from their original dark matter halos by tidal effects, and some are really big monster-sized galaxies formed by the collision of other galaxies. Inside the galaxies, there are probably subhalos and other structures, but we don't have as good of a picture of that. The cluster-sized halos of galaxies themselves form into large walls and seem to lie at the intersection of filaments of dark matter. On the flip side, the walls surround large voids with very little matter of any kind (dark or normal). On the average, on very very large distances, the universe is pretty smooth though, and in fact this is what we see in the cosmic microwave background light, which is uniform with fluctuations of only one part in 100,000 roughly. [/QUOTE]

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