We have to go back to 1925 when a scandal shook the world of science. The most reputable astronomers of the time declared that the Sun was made of the same mixture of elements as the Earth’s crust, that is, oxygen, silicon, aluminum and iron -which make up 90% of its composition-. However, a young recent graduate student named Cecilia Payne published a groundbreaking thesis arguing that this was not true: they were wrong. Payne claimed that stars, in general (our star included, obviously), were made primarily of hydrogen and not of the elements that made up the Earth’s crust.
He was right?
That’s right, and thanks to this thesis Payne earned a prominent place in science despite the fact that his name is not known to many of us. She is the woman who discovered what stars are made of. Yes indeed; in her time, her conclusion was ridiculed for the mere fact of being a woman (they claimed that her results were “clearly impossible” ) but time proved her right.
Even so, and despite later becoming the first woman to head a department at Harvard, precisely that of astronomy , she was paid considerably less than their male counterparts at the university. A gender pay gap that we continue to face today.
The recipe for a star
Stars are mainly made of 75% hydrogen and 24% helium of the total mass (the remaining percentage is a small amount of other chemical elements, also present in the rest of the universe, such as nitrogen, iron or carbon. ). It is precisely hydrogen and helium that are responsible for its high energy and, therefore, its brightness.
How is the composition of stars analyzed today?
The most common method astronomers use to determine the composition of stars, planets, and other objects is spectroscopy, a branch applied not only to astronomy, but also to chemistry, biology, and physics, of course (among other disciplines scientific).
Currently, this process uses instruments with a grating that diffuses light from an object by wavelength. This scattered light is called a spectrum. Each element, and combination of elements, has a unique fingerprint that astronomers can search for in the spectrum of a given object . Identifying those fingerprints is what allows scientists to determine what that object is made of.
Because the wavelengths at which absorption lines occur are unique to each element, astronomers can measure the position of the lines to determine which elements are present. In the same way, the amount of light that is absorbed can also provide information on how much of each element is on the object.
The birth of a star
Stars arise due to a powerful force: gravity. Clouds of gas and dust can begin to compact and flatten, increasing their density. These dense clumps of gas also get hotter and hotter in the center. When the central gas reaches a certain temperature (millions of degrees) something fantastic happens: the hydrogen atoms come together to form helium. Thus, with this process of nuclear fusion, a lot of energy is released and this is how a star begins its life.
A curiosity: did you know that the universe is mostly empty? There is barely less than one atom per cubic meter.
