I went to a guest lecture from a professional astronomer
thirty years ago and after it was over, went up to him and asked about M51A,
the Whirlpool Galaxy. It seems to obviously be connected
to the smaller galaxy, M51B. Radio astronomy has
determined there is a connection between the two
galaxies and both are about 25 million light years away.
Here's the kicker. They have radically different red shifts.
M51B should be no where near M51A.
In my naivete, I asked the astronomer about the
discrepancy. His face reddened and he told me
they're weren't about to throw away, I forget his
exact words, all their research based on one anomaly.
I have since learned that an astronomer named Arp
argued that redshift was not due to Hubble expansion
or physical movement of the objects, but must have a
non-cosmological or "intrinsic" origin.
Follow up studies have shown that Arp's hypothesis
cannot be discarded easily.
Time will tell.