Astronomical objects are structures in space that can be studied. They're not too small to be part of something else, but not so big that they have their own basic parts. Let's look at some examples.

One example is a galaxy like the Milky Way. A galaxy is a group of stars and other things around a nucleus, which is usually a black hole. The stars are the basic parts of a galaxy, no matter what stage of life they're in.

But, an arm of a galaxy or the galaxy itself is not an astronomical object. It's too complex to study with simple laws. The layers of a star are also too simple to capture everything that's happening inside.

A star, on the other hand, is a great example of an astronomical can that that scale.

Overall, astronomical are in space that study to learn more about the universe.

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Here, we only deal with ‘old’ astronomical objects in that we only consider astronomical objects that have already undergone previous processes before acquiring their actual nature. For instance, space dust is one of the most common astronomical objects, which gives rise to stars or planets over time. However, we are more interested in objects like the stars themselves rather than their early stages in the form of space dust.

What are the main astronomical objects?

We are going to make a list of astronomical objects, which includes some objects whose characteristics we won’t explore before we then focus on three main types of astronomical objects: supernovae, neutron stars, and black holes.

Various astronomical objects

Let's take a look at some different types of astronomical objects starting't, which are the astronomical objects to Earth.

Sometimes, the differences between categories can be a bit arbitrary. For example, Pluto was recently reclassified as a dwarf planet instead of a regular planet, but it's not considered a satellite either.

Moving on, we'll be focusing on three main types of astronomical objects: supernovae, neutron stars, and black holes.

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Some other types of astronomical objects are stars, white dwarfs, space dust, meteors, comets, pulsars, quasars, etc. Although white dwarfs are the late stages in the life of most stars, their differences regarding their structure and the processes happening inside them lead us to classify them as different astronomical objects.

The detection, classification, and measurement of properties of these objects are one of the main goals of astrophysics. Quantities, such as the luminosity of astronomical objects, their size, temperature, etc., are the basic attributes we consider when we classify them.

Supernovae

To fully comprehend supernovae, neutron stars, and black holes, it's important to have a basic understanding of a star's life cycle.

Stars are fueled by their mass, as nuclear reactions inside them convert mass into energy. After undergoing certain processes, stars undergo transformations that are primarily determined by their mass.

If the star's mass is less than eight solar masses, it will eventually become a white dwarf. If the mass falls between eight and twenty-five solar masses, the star will become a neutron star. If the mass is greater than twenty-five solar masses, it will become a black hole. In the cases of black holes and neutron stars, the stars typically explode, leaving behind remnants known as supernovae.

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Supernovae are highly luminous astronomical events that are classified as objects due to their accurately describable properties, such as luminosity laws and chemical compositions. As explosive events, their duration is relatively short in the grand scheme of the universe, and their size is not widely studied due to their rapid expansion.

Supernovae resulting from the collapse of a star's core are classified as Ib, Ic, and II. Their properties over time are well-known and used to measure various quantities, including their distance from Earth.

Type Ia supernovae are a special type that originates from white dwarfs. This is possible because, although low-mass stars eventually become white dwarfs, there are processes, such as nearby stars or systems releasing mass, that can cause a white dwarf to gain mass, leading to a type Ia supernova.

Spectral analyses are commonly performed on supernovae to identify the elements and components present in the explosion and their proportions. These analyses help in understanding the star's age, type, and other characteristics. Additionally, these analyses reveal that heavy elements in the universe are almost always created during supernova-related events.

Neutron stars

When a star with a mass between eight and twenty-five solar masses collapses, it becomes a neutron star. This object is the result of complex reactions occurring inside a collapsing star, where its external layers are expelled and recombine into neutrons. The fermionic nature of neutrons causes them to not be able to be arbitrarily close together, which leads to the creation of a force known as 'degeneration pressure', responsible for the existence

Black holes

Black holes are one of the most famous objects found in the universe. They are the remnants of a supernova when the mass of the original star exceeded an approximate value of twenty-five solar masses. The huge mass implies that the collapse of the core of the star cannot be stopped by any kind of force that gives rise to objects like white dwarfs or neutron stars. This collapse continues to exceed a threshold where the density is ‘too high’. This huge density leads to the astronomical object generating a gravitational attraction so intense that not even light can escape it. In these objects, the density is infinite and concentrated in a small point. Traditional physics is unable to describe it, even general relativity, which calls for the introduction of quantum physics, yielding a puzzle that is not yet solved. The fact that not even light can escape beyond the ‘horizon event’, the threshold distance determining whether something can escape from the influence of the black hole, prevents useful measurements. We cannot extract information from inside a black hole. This means that we must make indirect observations to determine their presence. For instance, active nuclei of galaxies are believed to be supermassive black holes with mass spinning around them. This comes from the fact that a huge amount of mass is predicted to be in a very small region. Even though we cannot measure the size (no light or information is reaching us), we can estimate it from the behaviour of the surrounding matter and the amount of mass causing it to spin.

Regarding the size of black holes, there is a simple formula that allows us to calculate the radius of the horizon event:

Here, G is the universal constant of gravitation (with an approximate value of 6.67⋅10-11 m3/s2⋅kg), M is the mass of the black hole, and c is the speed of light.

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Astronomical objects are structures in the universe that can be described by simple laws. Examples of astronomical objects include stars, planets, black holes, white dwarfs, comets, and more.

Supernovae are explosions that often mark the end of a star's life. They have well-known properties that depend on the remnant they leave behind. Neutron stars are one possible remnant of a supernova. They are believed to be very small, dense, and fast-spinning bodies formed by neutrons. However, fundamental properties of neutron stars are still unknown.

Black holes are the extreme case of a remnant of a supernova. They are the densest objects in the universe and are very mysterious because they do not let any light escape. Fundamental properties of black holes are still unknown, and no available theoretical model has accurately described them yet.

Astronomical Objects

What astronomical objects are there in the universe?

There are many: stars, planets, space dust, comets, meteors, black holes, quasars, pulsars, neutron stars, white dwarfs, satellites, etc.

How do you determine the size of an astronomical object?

There are techniques based on direct observation (with a telescope and knowing the distance between us and the object) or on indirect observation and estimation (using models for luminosity, for instance).

Are stars astronomical objects?

Yes, they are the basic constituents of galaxies.

How do we find astronomical objects?

By observation of the universe with telescopes in any frequency available and direct or indirect observation.

Is the earth an astronomical object?

Yes, the earth is a planet.

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