The 7 types of stars (and their characteristics)

An overview of the main types of stars according to the Harvard classification system.

Stars are luminous plasma spheroids that maintain their shape due to their own gravity. They shine thanks to the thermonuclear fusion of hydrogen into helium, as the reaction releases an enormous amount of energy that radiates out into outer space.

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 at the sky far from an urban center, an overwhelming feeling of nothingness comes over us: From Earth, a human being can observe about 3,000 different stars.But it is estimated that in each galaxy there could be about 100 billion stellar bodies, in turn multiplied by the 100 billion 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 speak of stars, we tend to focus our attention on the constellations, the physical limitations of the celestial vault. Our species tends to organize everything around it, and so we find meaning in creating shapes, patterns and maps from concepts that are practically inconceivable from a physical point of view. With the intention of breaking a little the classification by constellations, today we expose you types of stars, but based on their temperature, mass and spectrum..

What are the types of stars?

From a purely informative point of view, a star can be defined as a star or celestial body that shines with its own light in the firmament. In other words, we are talking about each of the celestial bodies that are identified at night when we look up, excluding only the moon, since it does not generate light (but reflects the sun's light).

We could talk about protostars, T Tauri stars, red giant stars and many more varieties, but we see the interest to stick to a specific classification and stick with it, from beginning to end. Therefore, in order 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 absorb the atoms that compose it. Let's go to it.

Class 0

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

These stars have temperatures exceeding 30,000 degrees Kelvin, a figure inconceivable to the average human being. However, it should be noted that the heat emitted by these bodies is measured by the "effective temperature", i.e., the temperature of a black body that would emit the same total amount of electromagnetic radiation as that of the element being analyzed. 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 the emissivity curve. 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). (compared to nearby frequencies). Here, the defining spectral lines are HeII (Helium II), prominent at 454.1 nm and 420.0 nm.

In short, and to keep the space as informative as possible, class 0 stars are very large, very hot and with bluish tones. Don't worry, because once all these terms are settled, we will go faster in the following variants.

2. Class B

Like class 0 stars, they are very luminous and blue stars. They are smaller than the first ones, but still They have 2 to 16 times more mass than the Sun and also reach 10,000 to 30,000 Kelvin degrees.. Due to their high energetic activity and reactivity, B-class stars live a relatively short time period.

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

3. Class A

These stars are some of the most common to the naked eyethat is, the ones we observe when we look at the sky. Approximately 0.625% (1 in 160) of the "normal" stars in the solar system are of this type. Their temperature ranges between 7,500 and 10,000 degrees Kelvin, their mass is 1.4 to 2.1 times that of the sun and their chromaticity is white.

The spectrum of these stellar bodies is defined by a strong Balmer lines, the set of lines resulting from the Balmer lines.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 are therefore very high.

4. Class F

In this group, the so-called H and K lines of the calciumThe effective temperature of these stellar bodies ranges between 6000 and 500 degrees Kelvin. The effective temperature of these stellar bodies ranges between 6,000 and 7,500 degrees Kelvin, their chromaticity is yellowish-white and the mass is relatively similar to that of the Sun (from 1.04 to 1.4 solar masses).

5. Class G

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

Solar-type or G-class stars are also among the most common, representing 1 in 13 (7.5%) of the observable stars in the solar system. Their 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 that are "cooler" than the Sunalthough they are at magnitudes that are still inconceivable to humans. Their 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, hydrogen lines are extremely faint, if present at all. They represent 12.1% of the stars in our system.

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. Curiously, produce "so little light" that they are invisible to the human eye, unless special apparatus is used.. Their 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". All of them 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 one thing very clearly: the classification of stars goes far beyond giants, small stars and protostars. With this range based on spectrum, mass and temperature, all celestial bodies can be encompassed, without resorting to extremely complex terminology, reserved only for a few astrophysicists.

In addition, we have relied on the Balmer (hydrogen) lines 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 of 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.