Stars are luminous spheroids of plasma that hold their shape due to their own gravity. These glow thanks to the thermonuclear fusion of hydrogen into helium, since the reaction releases a huge amount of energy that radiates into outer space. How many types of stars are there?

In other words, stars are engines of cosmic energy that produce heat, ultraviolet rays, X-rays, and other forms of radiation.

When we look up to the sky far from an urban nucleus, an overwhelming feeling of trifle invades us: from Earth, a human being can observe some 3,000 different stars , but it is estimated that in each galaxy there could be some 100,000 million stellar bodies, in turn multiplied by the 100,000 million galaxies that could exist. These figures are incomprehensible to the human being, but they make it more than clear to us how ephemeral the existence of the individual is on the largest scales.

When we talk about stars, we usually focus our attention on the constellations, the physical limitations of the celestial vault. Our species tends to organize everything that surrounds it, and for this reason we find sense in creating shapes, patterns and maps from concepts that are practically inconceivable from a physical point of view. With the intention of breaking the classification by constellations a bit, today we present the types of stars, but based on their temperature, mass and spectrum .

What are the types of stars?

From a merely informative point of view, a star can be defined as a star or celestial body that shines with its own light in the sky. In other words, it is about each of the celestial bodies that are identified at night when looking up, excluding only the moon, since it does not generate light (but reflects the solar).

We could talk about protostars, T Tauri stars, giant red stars and many more varieties, but we are interested in sticking to a specific classification and continuing with it, from beginning to end. Therefore, to show you the 7 types of stars we have chosen the Harvard classification system . This criterion is based on the spectrum of each stellar body, or what is the same, the elements that the atoms that compose it absorb. Go for it. How many types of stars are there?

1. Class 0

This class includes stars of type 0 or 0-type, extremely luminous and with radiation emitted in the ultraviolet range . If they are observed in a sequential order with respect to the rest, they are the “largest” of all, with a bluish-white hue. Some of the largest massive stars fall into this category.

These stars have temperatures that exceed 30,000 degrees Kelvin, a figure inconceivable for the average human being. In any case, it should be noted that the heat emitted by these bodies is measured by the “effective temperature”, or what is the same, the temperature of a black body that would emit the same total amount of electromagnetic radiation as that of the analyzed element. It is used to estimate the heat emitted in an entity whose emissivity curve is not known.

Class 0 stars (and all variants) are characterized by the relative strength of certain spectral lines, which are the result of an excess or a lack of photons in a narrow range of frequencies (compared to nearby frequencies). On this occasion, the defining spectral lines are HeII (Helium II), prominent at 454.1 nm and 420.0 nm.

In summary, and to keep the space as informative as possible, class 0 stars are very large, very hot and with bluish tones. Do not worry, because once all these terms have been settled, we will go faster in the following variants.

2. Class B

Like class 0 stars, they are very bright and blue stars. They are smaller than the former, but still harbor 2 to 16 times more mass than the Sun and also reach 10,000 to 30,000 degrees Kelvin . Due to their high energy activity and reactivity, class B stars live for a relatively short time period.

These stars are defined by the spectral lines of type He I, in the violet spectrum. There are 9 subdivisions within this class, and the intensity of the hydrogen lines increases constantly in all of them. Again, we maintain the informative spirit saying that they are smaller than class 0, with a blue chromaticity, but still immeasurable in size and with an extremely high energy activity.

3. Class A

These stars are some of the most common to the naked eye , that is, the ones we observe when we look at the sky. About 0.625% (1 in 160) of the “normal” stars in the solar system are of this type. Its temperature ranges between 7,500 and 10,000 degrees Kelvin, its mass is 1.4 to 2.1 times that of the sun, and its chromaticity is white. How many types of stars are there?

The spectrum of these stellar bodies is defined by strong Balmer lines , the set of lines that result from the emission of the hydrogen atom when an electron transits between levels. The hydrogen lines in this type of stellar body, therefore, are very high.

4. Class F

In this group, the so-called H and K lines of calcium stand out , in addition to the characteristic lines of hydrogen, in this case weaker. The effective temperature of these stellar bodies ranges between 6,000 and 7,500 degrees Kelvin, their chromaticity is white-yellowish and their mass is relatively similar to that of the Sun (1.04 to 1.4 solar masses).

5. Class G

Sun: the star that gives us life, one that allows you read these words and life exist is included .

Solar-type or G-class stars are the most common as well, representing 1 in 13 (7.5%) of those observable in the solar system. Its effective temperature is 5,200 to 6,000 degrees Kelvin, the chromaticity is yellow (like the Sun itself) and the mass is 0.8 to 1.04 solar masses.

6. Class K

From here, we enter the categories of stars “colder” than the Sun , although they are in magnitudes that are still inconceivable to humans. Its mass is 0.45 to 0.8 times that of the sun, the chromaticity is pale orange, and the temperature of these celestial bodies ranges from 3,700 degrees Kelvin to 5,200 K. In these stars, the hydrogen lines are extremely weak, if present. They represent 12.1% of the stars when using our system. How many types of stars are there?

7. Class M

Stars with very low hydrogen lines (like those of the K class), but which represent 75% of the stars that make up the solar system. Interestingly, they produce “so little light” that they are invisible to the human eye, unless special devices are used . Its temperature is 2,400 to 3,700 degrees Kelvin, the chromaticity is orange-red and the total mass corresponds to 0.08-0.45 solar masses.

In this group are the stars known as “red dwarfs”, “red giants” and “red supergiants”. They all share the following points: their mass and diameter values ​​are less than half those of the Sun and the temperature does not increase beyond 4,000 degrees Kelvin.

Summary

This complex journey through the stellar world tells us something very clear: the classification of stars goes far beyond the giants, small and protostars. With this range based on spectrum, mass and temperature, all celestial bodies can be encompassed, without the need to resort to extremely complex terminology, reserved only for a few astrophysicists.

In addition, we have relied on Balmer lines (for hydrogen) to quantify the “visibility” of a star and its typology, but it should also be noted that there are others, such as the H and K lines for calcium, sodium lines and others. Of course, the world of astronomy reports an enormous amount of information, as interesting as it is difficult to understand. How many types of stars are there?