Stirring Things Up
Today's Cassini photo was taken September 25. Saturn's F Ring is pulled into knots and curls by the influence of unseen satellites. These objects have not been seen, but we can detect their influence. Small Black Holes could be closer than we think, maybe in our neighbourhood.
The infra-red photo below is from the Spitzer Space Telescope. 210 million years ago the dwarf galaxy M32 smashed into Andromeda, creating ripples in the bigger galaxy's disk. Andromeda is slowly approaching our galaxy and will collide with us in 5-10 billion years. There is unseen mass between them, possibly ten times a galaxy's mass pulling the Milky Way and Andromeda together.
Expansion of the Universe is not uniform. Individual motions of galaxies can oppose the Hubble flow, like trout swimming upstream. The Milky Way and thousands of other galaxies are falling at 600 km/sec toward an unseen mass called the Great Attractor. This object has the mass of 10^16 Suns or 100,000 galaxies! It may be a true Black Hole, so monstrously massive that nothing can escape. There is evidence of another Great Attractor some 700 million years away.
These monsters could be common, yet they are not counted in mass surveys. The missing 2/3 ascribed to "dark energy" may be hidden from us. It is foolish to think that humans know all that is out there. That is like Wile E. Coyote, Super Genius not realising that he is falling into an abyss.
Final photo is from the Hubble space Telescope. The Antennae galaxies NGC 4038 and NGC 4039 are in the process of colliding. I prefer to call this "mating."
A physicist can go with the flow, avoid risk, and not stand out. One can profess that the Universe is dominated by "dark energy" and the Sun circles the Earth. Such people end up complaining about their unsatisfying lives because they never make a difference. It is much more fun to stir things up!