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Radrook is offline
Feb4-12, 12:14 PM
P: 334
This article briefly discusses how the intrinsic galactic forces [density waves radiating outward from the core]and the tidal forces involved in galactic collisions differ in the creation and deformation of spiral galaxy hub bars.

Dynamical Properties of Tidally Induced Galactic Bars
Miwa, Toshinobu; Noguchi, Masafumi
Astrophysical Journal v.499, p.149

When the tidal perturbation is relatively weak, it works only as a trigger of bar formation, and the bar properties are determined largely by the internal structure of the target galaxy. On the other hand, a sufficiently strong tidal perturbation washes out the intrinsic property of the target galaxy and imposes on the bar a common characteristic determined by the parameters of the tidal encounter.

Barred Spiral Galaxies Are Latecomers to the Universe

Kartik Sheth
Spitzer Science Center, California Institute of Technology, Calif.

July 29, 2008: In a landmark study of more than 2,000 spiral galaxies from the largest galaxy census conducted by NASA's Hubble Space Telescope, astronomers found that so-called barred spiral galaxies were far less plentiful 7 billion years ago than they are today, in the local universe. The study's results confirm the idea that bars are a sign of galaxies reaching full maturity as the "formative years" end. The observations are part of the Cosmic Evolution Survey (COSMOS).
I assume that the writer is applying that galactic "maturity" criterion as evidenced by the bar only to spiral galaxies and not claiming that eventually all galaxies become barred spiral ones when they mature.