With the advancement of science and technology, human beings have been able to observe and understand many aspects of the universe, such as the origin, structure, composition, and history of the universe. However, there are still many unknowns and mysteries in the universe, such as the expansion of the universe, dark matter, dark energy, etc. These unknowns and mysteries make up 95% of the universe and are known as the "Dark Universe".
In June 2022, the European Space Agency (ESA) and NASA jointly launched the Euclid Space Telescope (Euclid), a space telescope dedicated to exploring dark matter and dark energy, to unravel the mysteries of the dark universe.
Euclid Space Telescope (Euclid)
It will produce the largest three-dimensional map of the universe ever created, covering nearly a third of the sky, including billions of galaxies 10 billion light-years from Earth. The mission of the Euclid Space Telescope is to measure the distribution and influence of dark matter and dark energy by observing the shape, redshift, and evolution of galaxies, thereby revealing their nature and nature. The Euclid Space Telescope will bring a revolutionary breakthrough to mankind's understanding of the universe and will also make important predictions for mankind about the future of the universe.
3D map of the universe
Dark matter: the invisible skeleton of the universe
Dark matter is a substance that does not emit light, emits or absorbs any electromagnetic waves, and it can only be detected by gravity. Dark matter accounts for about 26% ±1% of the energy density of matter in the universe, far exceeding the 4.9% of visible matter. The existence of dark matter can explain some phenomena in astronomical observations, such as the rotation curve of galaxies, the gravitational lensing effect of galaxy clusters, and the anisotropic spectrum of cosmic microwave background radiation. The nature of dark matter is not yet clear, it may be one or more unknown elementary particles, it may be one or more unknown composite particles, or one or more unknown celestial bodies, or one or more unknown physical phenomena.
The Euclid Space Telescope will use the deformation of galaxies to detect the distribution of dark matter, a manifestation of the gravitational lensing effect. Gravitational lensing is the deflection of light light as it passes through the vicinity of a massive celestial body due to the curvature of space-time, as if it had passed through a lens. Gravitational lensing effect can be divided into strong gravitational lensing effect and weak gravitational lensing effect, the former will produce obvious distortion, such as multiple images, arc structures, ring structures, etc., and the latter will only produce small distortions, such as stretching or compression of shapes.
By analyzing the distortions of these lens images, astronomers can map the distribution of dark matter within galaxy clusters
The principle of using the deformation of galaxies to detect the distribution of dark matter is as follows: when we observe a distant galaxy, its light may pass through one or more intermediate objects, such as a cluster of galaxies, before reaching us. These intermediate celestial bodies exert a gravitational lensing effect on the light, causing the shape of the galaxies we see to change. If we know the original shape of the galaxy, or assume that the shape of the galaxy is random, then we can deduce the mass distribution of the intermediate object based on the deformation of the galaxy, and thus determine the distribution of dark matter in it. This is the method of using the deformation of galaxies to detect the distribution of dark matter, also known as the weak gravitational lensing method.
Gravitational lensing effect
In addition to the method of using the deformation of galaxies to detect the distribution of dark matter, there are other methods, such as the method of using the motion of galaxies to detect the distribution of dark matter, also known as the kinetic method. This method uses the speed of galaxies or the internal motion of galaxy clusters to infer the distribution of dark matter, which provides additional gravitational pull to maintain the stability of galaxies or clusters.
Dark energy: the mysterious driving force of the universe
Dark energy is a force that accelerates the expansion of the universe, accounting for about 68.9% ± 0.6% of the energy density of matter in the universe, far exceeding the sum of visible matter and dark matter. The presence of dark energy can explain some phenomena in astronomical observations, such as the brightness of distant supernovae, the anisotropic spectrum of cosmic microwave background radiation, and the formation of large-scale structures in the universe. The nature of dark energy is not yet clear, it may be one or more unknown energy fields, it may be one or more unknown physical constants, or one or more unknown physical phenomena.
The Euclid Space Telescope will use the redshift of galaxies to detect the effects of dark energy, a manifestation of the Doppler effect. The Doppler effect refers to a change in the wavelength of light caused by the relative motion between a light source and an observer, just as the whistle of a train sounds different when it is closer and farther away. The redshift of galaxies refers to the increase in wavelength of the spectrum of galaxies due to the expansion of the universe after the propagation through cosmic space, like a Doppler effect. The redshift of galaxies can reflect the distance of galaxies from us, as well as the rate at which the universe is expanding.
If we know the brightness of galaxies, or assume that the brightness of galaxies is constant, then we can derail the distance of the galaxies based on the redshift of the galaxies, and thus determine the expansion rate of the universe. This is the method of using the redshift of galaxies to detect the effects of dark energy, also known as the supernova standard candle method.
In addition to using the redshift of galaxies to detect the action of dark energy, there are other methods, such as the method of detecting the effect of dark energy by using the formation of large-scale structures of the universe, also known as the Bain acoustic oscillation method. This method is to infer the role of dark energy based on the fluctuations in the density of matter in the universe, because dark energy affects the amplitude and phase of the fluctuations in the density of matter in the universe, and thus affects the distribution of galaxies in the universe.
The Evolution of Galaxies: A History Book of the Universe
The evolution of galaxies refers to the process of formation and development of galaxies, which is affected by factors such as the material composition of the universe, the rate of expansion, and density fluctuations. The evolution of galaxies can reflect the history of the universe and the role of various substances and forces in the universe. If we know the age of galaxies, or assume that the age of galaxies is certain, then we can deduce the history of the universe based on the evolution of galaxies, so as to determine the material composition, expansion rate, density fluctuations and other parameters of the universe. This is the method of using the evolution of galaxies to probe the history of the universe, also known as galaxy evolution.
The principle of using the evolution of galaxies to probe the history of the universe is as follows: when we observe a distant galaxy, its light experiences a cosmic time delay before it reaches us, so that we see the galaxy as it used to be, not as it is now. This is equivalent to seeing the history of galaxies, so that we can understand the history of the universe. By observing galaxies at different distances, we can see what different phases of the universe look like, so that we can detect the evolution of the universe. For example, we can observe the shape, size, color, brightness, chemical composition, structure, activity and other characteristics of galaxies, so as to infer the age, temperature, mass, metallicity, formation mode, evolution path and other information of galaxies.
In addition to the method of using the evolution of galaxies to detect the history of the universe, there are other methods, such as the method of using the anisotropic spectrum of cosmic microwave background radiation to detect the history of the universe, also known as the cosmic microwave background radiation method. This method is to infer the history of the universe based on the temperature and unevenness of polarization of microwave radiation in the universe, because microwave radiation in the universe is the earliest light in the universe, which records the initial state and evolution of the universe.
The significance and value of the Euclid Space Telescope
The Euclid Space Telescope is an unprecedented space exploration project, which will bring a revolutionary breakthrough to mankind's understanding of the universe and will also make important predictions for mankind's future of the universe. The significance and value of the Euclid Space Telescope are as follows:
- It will reveal the nature and nature of dark matter and dark energy, solve one of the greatest mysteries of cosmology, and will also provide important tests and enlightenment for the basic theories of physics.
- It will create a three-dimensional map of the universe, show the structure and evolution of the universe, and will also provide valuable data and resources for astronomical observation and research.
- It will explore the origin and destiny of the universe, answer one of the ultimate questions of the universe, and will also provide deep food for thought and enlightenment for human philosophy and culture.
The Euclid Space Telescope is a bold attempt and challenge to the universe by mankind, which will open up a new horizon and field, let us see a broader and more wonderful universe, and also let us have a clearer and more comprehensive understanding of ourselves and the world.
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