TEXTO PARA A QUESTÃO
As astronomers gaze into the depths of , they do so with
unease: They don't know precisely what the universe is made of.
Surprisingly, no one knows the stars' exact chemical
composition: how many carbon, nitrogen and oxygen atoms
[5] they have relative to hydrogen, the most common element.
These numbers are crucial, because they affect how stars
live and die, what types of planets form and even how readily
life might arise on other world's.
Twenty years ago, astronomers expressed confidence ∈ the
[10] numbers they had been working with. Now, not so much. The
problem lies not ∈ the far corners of the cosmos, but much
closer to home. Astonishingly, scientists don't know exactly
what the sun is made of. As a result, they don't know what the
other stars are made of, either.
[15] “The sun is a fundamental yardstick,” says Martin Asplund,
an astrophysicist at the Max Planck Institute for Astrophysics, ∈
Germany. “When we determine the abundance of a certain
element ∈a⋆ or a galaxy or a gas cloud anywhere ∈ the
universe, we use the sun as a reference point.”
[20] The sun's location ∈ the Milky Way also makes it a good
representative of the entire galaxy. Most stars reside ∈ giant
galaxies like the Milky Way, which makes the sun a touchstone
for the entire cosmos.
For nearly a century, astronomers have judged stars normal
[25] or not by seeing whether their chemical compositions match the
sun's. Most stars near us do; some don't.
Scientific American. 1 July 2020. Adaptado.
Conforme o texto, um critério tradicionalmente utilizado por astrônomos para avaliar estrelas envolve
