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This article was copied from CASE Science News “The Entire Universe Is My Zoo – Astrochemistry”

The entire universe is like a “molecular zoo”. By studying the molecular spectrum, we can know the molecular distribution, temperature and other properties; And because different molecules have different “habits,” we can also tell that this is an interstellar molecular environment.

astrochemistryWhat is that?

Astronomy is the natural science that studies the celestial bodies in the universe. In addition to “astrophysics” with which the general public is better known, the universe has many aspects, one of which is the topic of this article: “astrochemistry”.

Both are sciences that study “materials,” but physics and chemistry observe the world in different ways. Astrochemistry focuses on the “atoms, molecules, and ions in the different celestial environments” in the universe, studying their composition, distribution, and interactions with each other or their interactions with the environment. (For convenience’s sake, we will collectively refer to molecules, ions, etc. as molecules.)

Although astronomy is one of the oldest sciences, the topic of astrochemistry did not begin to emerge until the mid-20th century. The reason is simple: because particles cannot be seen! The star is so big that you might not be able to see it clearly with a telescope, let alone the molecule you can’t see right in front of your eyes?

Therefore, to study the particles in the universe, we must rely on special techniques; Among them, one of the most important techniques is “spectroscopy”.

A spectrum is a pattern that arranges light by wavelength or frequency, like a “rainbow” is a type of spectrum, a pattern of sunlight separated according to different frequencies. In addition to visible light, there are many wavelengths that are not visible to the naked eye, such as radio waves, infrared, ultraviolet, X-rays, etc.

Each molecule has its own spectrum, if we want to know what the molecule’s spectrum looks like, in addition to experimental measurements, we can use computers to perform accurate simulation calculations for predictions. Spectra of particles are like ‘fingerprints’, just as police compare collected fingerprints to a database to see who left the fingerprint. Astronomers compare the observed spectra with the database. Comparing to see which particles are on the other side of the distant stars, even their content, temperature, etc. (Fig. 1).

To learn more about how astronomers use spectroscopy, you can refer to: “Deconstructing Light: Spectra in Astronomy”.

why the universe“Molecular Zoo”？

the animalsIt often reflects the local environment, for example, when you see a hippopotamus, you know there is an environment with water and grass; When you see sakura salmon, you know that there is a current with a low water temperature. ^[3]Treat the universe as a molecular animalThe same is true for gardens, observing the distribution and content of molecules can also allow us to infer the physical environment. At present, we have observed more than 200 kinds of particles from interstellar space, and here are some common interstellar particles!

Molecular hydrogen, H₂）

The most abundant molecules in the universe are also the main components of the “molecular cloud”. There are approximately 10,000 hydrogen molecules per cubic centimeter in the molecular cloud (10⁴ poison^-3）。

Molecular clouds are where stars and planets are born, so understanding the distribution of hydrogen molecules can help us study star formation. At the same time, hydrogen molecules can react with heavy elements and be catalysts for many chemical reactions, producing other molecules such as carbon monoxide (CO) and carbon dioxide (CO).₂), the cyano radical (CN), etc.

The hydrogen molecule is very important to astrochemistry. Unfortunately, it is almost impossible to observe in an environment where the average temperature of the molecular cloud exceeds 200 degrees below zero (because it is a symmetric molecule, interested readers can learn more about it).^[5][6]

carbon monoxide (CO)

Carbon monoxide is distributed in interstellar regions of low temperature and high density. It is the second most common interstellar molecule.

Compared to hydrogen molecules, carbon monoxide is much easier to notice, so it’s easier for astronomers to tell the distribution of molecular clouds from carbon monoxide images. Since it is almost impossible to directly observe molecular clouds with visible light, early scientists had no idea that there were so many molecular clouds around, and only opened their eyes after noticing a picture of carbon monoxide. ^[5][6][7]

Ammonia (Ammonia, NH₃）

Ammonia can also be easily observed as a molecule. The first molecule observed in history was ammonia. Ammonia has many spectral lines, and the intensity of these spectral lines is very sensitive to environmental changes and can correspond to many different interstellar environments. Observing ammonia allows us to more accurately derive the environmental conditions there ^[8][9]。

The environment in the universe has changed a lot, and chemical reactions in different environments can be completely different. In the universe, diffuse cloud, dense cloud, hot core formed by stars, and other regions where a large number of particles have been detected, the temperature distribution ranges from 10 K to 1000 K (about -200 degrees to +800 degrees Celsius), the density ranges From one hundred particles per cubic centimeter to ten trillion particles (10² poison^-3～ 10¹³ poison^-3) Both!

Here we will present several interstellar environments with high molecular content.

star forming region

A place with high density within the molecular cloud where stars are formed. The Orion KL nebula (Orion KL) is the most active star-forming region in the Orion macromolecular cloud. There are many “complex saturated organic molecules” shown here, such as: methanol (CH₃OH), methyl formate (HCOOCH₃) etc, there are also some long chain carbon molecules, such as: cyano acetylene (HCCCN)^[10]。

Comet 67P/Churyumov-Gerasimenko (Comet 67P/CG)

In recent years of monitoring data, scientists have observed extremely high levels of molecular oxygen (O₂) which surprised them a lot. Because oxygen molecules can easily interact and become other molecules in the universe, but in a volatile environment like a comet, there can be a high content of oxygen molecules, which means that these oxygen molecules are likely to form in a comet. time, it is already in the surrounding environment and is frozen on the comet ^[11][12]。

The scope of the astrochemistry involved is very broad, spanning many different fields. The whole universe is a “molecular zoo”. Astronomers observe particles in these universes to find out what kind of environment there are in distant celestial bodies. Many organic molecules have also been discovered in interstellar space, and the study of these molecules can help us understand the origin of life, and this is the main direction of astrochemical research.

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