Components of the Universe

We explain what the observable components of the universe and their characteristics are. Also, what are the types of matter and energy.

What are the components of the universe?

The components of the universe, better called astronomical objects or celestial bodies, are the different types of natural objects that make up the observable structure of the universe that is, they can be seen with the naked eye or through observation devices.

The universe is infinite. Therefore, there are enormous expanses of vacuum inside, interrupted by voluminous accumulations of matter and energy that, depending on their composition and dynamics, can give rise to different types of astronomical objects.

From an astrophysical point of view, the universe is composed of two types of matter and energy:

• Baryonic matter (matter) that is, the observable matter as we know it on our planet, which in space constitutes different solid, liquid, gaseous and plasma structures.
• Radiation (energy) a type of energy composed of light particles (photons) that are emitted by different fundamental phenomena and reactions of matter.
• Dark matter (matter) a type of matter that cannot be observed, since it does not emit electromagnetic radiation, but which constitutes 26.8% of the matter in the universe.
• Dark energy (energy) a form of imprecise, undetectable energy of constant density, which pushes the universe towards its expansion. Although its presence at the moment is part of a cosmological theorization, it is thought that 70% of the energy in the universe would be of this type.

The astronomical objects that can be observed through telescopes (some through a homemade one, others through super-powerful telescopes such as the Hubble Space Telescope) are made up of baryonic matter, that is, ordinary matter. The main observable components of the universe are indicated below.

See also: Celestial bodies

The galaxies

a galaxy It is a set of stars that rotate around a common axis, dragging with them many other components materials such as planets, asteroids and comets, or extensive clouds of dust and gas (mainly hydrogen and helium), known as nebulae.

Nebulae give galaxies their usual whitish appearance, as occurs with the galaxy where the solar system is located, the Milky Way. This galaxy is so called because its appearance is reminiscent of a stream of spilled milk, which the ancient Greeks attributed in their mythology to the breast milk of the goddess Hera (Juno for the Romans).

There are approximately 170 billion galaxies in the universe grouped in clusters or local groups. Each one can range from hundreds to millions of light years in extent, and be organized according to a more or less recognizable pattern: spiral galaxies, elliptical galaxies or irregular galaxies. An average galaxy has between 200 and 400 million different stars.

The stars

a star It is an incandescent and luminous star, composed of chemical elements in continuous combustion. Stars can be understood as enormous and continuous space explosions, which retain their spherical shape due to the action of their own gravity, large enough to prevent their components from spreading throughout the universe. The Sun is the best example of what a star is.

Most stars are made of hydrogen, helium, and other light chemical elements subjected by gravity to immense pressures that cause their nuclear fusion. Thus, enormous amounts of energy and radiation are unleashed, and heavier materials are also created, which at the end of the star's life cycle will give rise to other types of celestial bodies. Seen in this way, stars are great furnaces in which new forms of matter are continually being forged.

There are stars of different types, depending on their size, luminosity and temperature reached. According to the Morgan-Keenan (MK) classification system, there are seven types of stars or “spectral classes”: O, B, A, F, G, K and M.

• Type O stars. They are the hottest and their temperatures are around 33,000 degrees Kelvin (K). Their color tends towards blue and they have a luminosity equivalent to 30,000 times that of the Sun. Likewise, they usually have around 16 times the mass of the Sun and a radius 6.6 times larger.
• Type B stars. They are the next stars with the greatest heat and luminosity, whose light is bluish or whitish blue. Its temperature ranges between 10,000 and 33,000 K and its luminosity is 25,000 times that of the Sun. These stars have between 2.1 and 16 times the solar mass and a radius between 1.8 and 6.6 times larger than that of the Sun. Sun.
• Type A stars. They are hot and luminous stars, with white light that in the distance can appear a little bluish. They are the stars with the greatest presence of hydrogen lines on the entire scale, whose temperature is between 7,500 and 10,000 K, and whose luminosity is between 5 and 25 times that of the Sun. Their average mass ranges between 5 and 1.4 times the of the Sun, and its radius is between 1.4 and 1.8 times the solar radius.
• F-type stars. They are the “intermediate” stars of the scale, with a white-yellowish light between 1.5 and 5 times more intense than that of the Sun. Their temperature is around 6000 or 7500 K, and they are slightly larger than the Sun (between 1. 04 and 1.5 times its mass, and between 1.15 and 1.4 times its radius).
• G-type stars. They are the first stars with the lowest brightness and temperature on the scale, whose yellowish light can be perceived as whitish yellow in the distance. Their temperature ranges between 5,200 and 6,000 K, and their comparison with the Sun is in much more equal terms: they have between 0.8 and 1.04 times the solar mass, between 0.96 and 1.15 times the radius solar, and between 0.6 and 1.5 times the luminosity of the Sun.
• K-type stars. They are the intermediate stars of the cold spectrum of the classification, with an average temperature of 3700 to 5200 K. Its orange light has between 0.08 and 0.6 times the intensity of solar light, and its size is slightly smaller than that of the Sun: between 0.45 and 0.8 times the solar mass and between 0.7 and 0 .96 times its radius.
• M-type stars. They are the coldest stars known, whose temperature is less than 3700 K. With red or orange-red light barely 0.08 times as luminous as sunlight, they are small stars with 0.45 solar masses or less, and a radius less than 0.7 times the solar.

A number from 0 (maximum) to 9 (minimum) is added to this stellar classification to indicate the temperature level of a star within its corresponding category. In this way, the Sun is a G2 type star, that is, one of the hottest in the G category. The hotter a star is, the higher levels of energy and radiation it emits; and the colder it is, the more heavy elements (metals and rare earths) are deposited within it.

the planets

a planet It is a solid, spherical and opaque celestial body that orbits another of greater mass, usually a star along an exclusive orbit, that is, free of other planets or planetoids. The name “planets” comes from ancient Greek. planets (“wandering”) in reference to their continuous displacement. The best example of a planet is Earth

Since planets form from already existing clouds of gases and celestial dust, the composition and characteristics of one planet can vary significantly from those of another, and depend largely on its proximity or distance from a star. For example, the planet Mercury has a very weak and tenuous atmosphere, composed of light gases, due to its proximity to the Sun; while Jupiter's atmosphere, hundreds of millions of kilometers further away, is dense and composed of hydrogen, helium and heavy organic gases such as ethane, methane and ammonia.

There are many ways to classify planets. One of the best known is according to its structure and distinguishes between:

• terrestrial planets (Earth-like), which tend to be small, solid and rocky, that is, extremely dense. Earth, Mars and Mercury are examples of this type of planets.
• Jovian planets (similar to Jupiter), which tend to be large, gaseous and of low density, although they are presumed to have a solid core at the heart of their ball of gases. Jupiter, Saturn and Uranus are examples of this type of planets.

Apart from these two categories, there is also talk of dwarf planets or planetoids, which are those celestial bodies very similar to a planet but small in size, incapable of exercising orbital dominance (that is, of having an exclusive orbit). Pluto and Ceres are examples of this type of dwarf planets.

The satellites

a natural satellite It is a celestial body that orbits a larger planet, as it is trapped in its gravitational field. Of very variable size, nature and proportions, satellites can be spherical, like the Moon, or irregular like Deimos, one of the largest satellites of Mars.

Although they have their own orbit around the planet, satellites They accompany it throughout its own orbit around the star. It may be a single satellite, as is the case with the Earth, or dozens of them, such as Jupiter, of which 92 have been counted to date. Satellites should not be confused with planetary rings, which are sets of particles, dust and gases that orbit a planet, forming a visually homogeneous disk, as occurs with Saturn.

The asteroids

an asteroid It is a minor, solid, rocky celestial body too small to be a planet and too large to be a meteoroid. Of variable, often irregular size and shape, these scattered fragments of matter can be found alone or forming asteroid fields that is, more or less dense agglomerations. In the solar system there is an asteroid belt between the orbits of Mars and Jupiter.

Strictly speaking, asteroids are little more than space rocks. lack an atmosphere and do not respond to their own gravitational field. While some remain stable within a field or belt, others move along more or less erratic orbits around a star, which is why they can lead to large stellar impacts.

The comets

a comet It is a celestial body in motion generally composed of rocks, dust and ice particles that, when approaching a hot star like the Sun, evaporate and leave behind a recognizable trail, known as line.

The comets They move along elliptical and prolonged orbits of great eccentricity. They differ from asteroids, whose size may be similar, in that have their own atmosphere fruit of the wear of the materials that make up its core or coma. The pseudo atmosphere of a comet does not depend, like the atmosphere of the planets, on its gravitational attraction.

There are, however, very old comets whose transit around the Sun has depleted their ice reserves. In these cases, they are considered extinct comets and they are not very different from an asteroid. Even so, the distinction between comets and asteroids is a source of debate among astronomy specialists.

The meteoroids

a meteoroid It is a very minor celestial body, less than 50 meters in diameter generally the product of the fragmentation of some larger body, such as a comet or an asteroid. Composed of minerals and metals of various kinds, these fragments pursue an erratic trajectory which often causes them to become trapped in the gravitational field of some planet.

When a meteoroid enters the planetary atmosphere, it is called meteor. Normally, atmospheric friction heats it and disintegrates it, reducing it to harmless dust. In other cases, solid fragments reach the planetary surface and are called meteorites

References

• “What are the fundamental components of the universe?” at the Vitoria Planetarium.
• “Components of the universe” in ICT Resources of the Ministry of Education of Spain.
• “What are the largest structures in the universe?” in El País (Spain).
• “What is the Universe made of?” at The European Space Agency.
• “Universe (astronomy)” in The Encyclopaedia Britannica.