Editing Triangulum Galaxy (section)

===Star formation===
[[File:M33.tif|thumb|[[NGC 604]], a star-forming region in the Triangulum Galaxy, as imaged by the [[Hubble Space Telescope]]]]

In the central 4′ region of this galaxy, atomic gas is being efficiently converted to molecular gas, resulting in a strong [[Spectral line|spectral emission]] of [[carbon monoxide|CO]]. This effect occurs as giant [[molecular cloud]]s condense out of the surrounding [[interstellar medium]]. A similar process is taking place outside the central 4′, but at a less efficient pace. About 10% of the gas content in this galaxy is in the molecular form.<ref name=apj602/><ref name=aaa493/>

[[Star formation]] is taking place at a rate that is strongly correlated with local gas density, and the rate per unit area is higher than in the neighboring [[Andromeda Galaxy]]. (The rate of star formation is about 3.4 solar masses&nbsp;Gyr<sup>−1</sup>&nbsp;pc<sup>−2</sup> in the Triangulum Galaxy, compared to 0.74 in Andromeda.<ref name="aaa495"/>) The total integrated rate of star formation in the Triangulum Galaxy is about {{nowrap|0.45 ± 0.1 [[solar mass]]es per year}}. It is uncertain whether this net rate is currently decreasing or remaining constant.<ref name=apj602/><ref name=aaa493/>

Based on analysis of the chemical composition of this galaxy, it appears to be divided into two distinct components with differing histories. The inner disk within a radius of {{Convert|30|e3ly|kpc|abbr=on|sigfig=1}} has a typical composition gradient that decreases linearly from the core. Beyond this radius, out to about {{Convert|82|e3ly|kpc|abbr=on}}, the gradient is much flatter. This suggests a different star formation history between the inner disk and the outer disk and halo, and may be explained by a scenario of "inside-out" galaxy formation.<ref name=aaa506/> This occurs when gas is accumulated at large radii later in a galaxy's life space, while the gas at the core becomes exhausted. The result is a decrease in the average age of stars with increasing radius from the galaxy core.<ref name=apjl695/>