metallicity造句

Different theories predict how this metallicity gradient changes over billions of years.

Because we see the galaxy when it was young, this result suggests spiral discs start off with steep metallicity gradients.

The metallicity of a star measures the amount of "metals" it has —that is, any element heavier than helium.

In this model, a mass of gas collapses and creates lots of stars at the disc's centre, where the stars quickly boost the metallicity.

Benson says that the steep metallicity gradient agrees with the long-standing but unconfirmed idea that spiral galaxies form their discs of stars from the inside out.

Because stars congregate at a galaxy's centre, the metallicity in most nearby spirals is greatest there and drops toward the edge.

In addition, last year other astronomers reported a steep metallicity gradient in an even farther galaxy, but that galaxy is not a spiral, so its relevance to the Milky Way is less clear.

If astronomers could observe metallicity gradients in spiral galaxies billions of light-years away, we could see how steep the gradients were billions of years ago and thus how they change over time.