On September 29, 2021, NASA announced that it will launch the "Roman" space telescope (hereinafter referred to as Roman) before May 2027.
Roman's original name was "Wide Field Infrared Survey Telescope". Plans for the telescope were formally proposed as early as 2010, but the implementation of the plan has been repeatedly delayed for a variety of reasons. The 2.4-meter-diameter wide-angle primary mirror of the Roman will be equipped with two scientific instruments: one is a multi-band visible light and infrared light camera with more than 300 million pixels, the wide-angle camera, whose resolution exceeds that of the "Hubble" Space Telescope (hereinafter referred to as Hubble). No.); the second is a high-contrast, small-field camera and a spectrometer, the Coronal Imager, which uses a new starlight suppression technology to perform observations in the visible and near-infrared light bands.
The design of NASA's previous "Joint Dark Energy" mission can be seen in the design of Roman, but the Roman mission has expanded in many ways, including the use of gravitational microlensing to search for planets outside the solar system (exoplanets for short). planet). So, what do scientists expect from the Roman?
Lohmann's wide-angle instrument (schematic diagram)
Roman's Coronal Imager (schematic)
Using Gravitational Microlensing to Find Black Holes (Schematic)
Testing the theory of the accelerating expansion of the universe
The Roman team pointed out that the space telescope plans to carry out groundbreaking detections of millions of galaxies distributed in space and time, thereby screening different theories about the mechanism of the acceleration of the expansion of the universe. Romain will use a variety of techniques to achieve this discrimination, which mainly apply the principles of spectroscopy, which explores the color composition of light. The technology will allow scientists to accurately measure the expansion rate of the universe at different times, and use it to trace the evolution of the universe.
Installation scene of the main mirror of the Roman
Paint a grand picture of the universe
In addition to exploring the expansion rate of the universe, Roman will provide clues to other cosmic mysteries, help scientists understand the first generation of galaxies, map dark matter, and even reverse the space-time structure of the local group of galaxies in the Milky Way, which is closer to Earth. It is expected that the cosmic picture provided by Roman will be very grand, to help scientists decipher the mysteries of the universe in unprecedented ways. Each image provided by Roman will contain precise measurements of numerous celestial objects that scientists can use to conduct statistical studies that would not be possible with telescopes with a narrow field of view.
Romain draws a picture of the universe (imagination)
With Roman's current design, the telescope's spectroscopic survey in just seven months after liftoff can cover nearly 2,000 square degrees, or about 5 percent of the entire sky's field of view. The survey will reveal the exact distances from Earth for the 10 million galaxies that formed between 3 billion and 6 billion years after the universe formed, the cosmic puberty. Roman was able to do this because the light reaching its mirror surface had embarked on its journey as early as the young age of the universe. Such measurements will help scientists map the web-like macrostructure of the universe. They will also pinpoint the distances from Earth of the 2 million galaxies that formed earlier in the universe (only 2 billion to 3 billion years after the universe formed). It is a hitherto unexplored object in the macroscopic structure of the universe.
Universe at different times
Explore the expansion of the universe
Almost all the information we get from space comes from light. Roman will use spectroscopy to study celestial objects, from which it can get some information about luminous objects, including the speed at which the object is moving away from Earth. Scientists call this phenomenon of celestial bodies moving away from Earth "redshift" because: when a celestial body recedes, the wavelengths of all light received by Earth from the celestial body are stretched and shifted to a redder wavelength of light.
In the 1920s, two American astronomers, including Edwin Hubble, made a startling discovery: With very few exceptions, the vast majority of galaxies were moving away from Earth and away from each other, at a rate determined by Distances between galaxies and Earth, and between galaxies and galaxies. Galaxies leave Earth precisely because of the expansion of the universe, and by determining the speed at which galaxies are moving away from Earth, scientists can know the distance between the galaxy and Earth—the higher the spectral redshift of a galaxy, the faster the galaxy is moving away from Earth.
By measuring the precise positions of tens of millions of galaxies, Roman's spectroscopic survey will help scientists create a three-dimensional map of the universe. By understanding how the distribution of galaxies changes over time and distance, scientists can get a glimpse of how fast the universe was expanding at different times. Roman will also correlate galactic distances with echoes of sound waves from the time just after the cosmic explosion. These sound waves, known as "baryon acoustic oscillations," grow over time due to cosmic expansion and leave characteristic imprints on the universe by affecting the distribution of galaxies. For any modern galaxy, we are more likely to find another galaxy some 500 million light-years away. And further away or closer to the galaxy, the odds of finding another galaxy are lower—one of the hallmarks of baryon acoustic oscillations.
Identify two important theories
It stands to reason that the gravitational force within the universe should have caused the expansion of the universe to slow down. But scientists were surprised to find that the expansion of the universe is accelerating, which means that existing theories of the universe are either wrong or incomplete. So, what is the situation? To answer this question, scientists have put forward two speculations: one is that there is dark energy in the universe; the other is that Einstein's theory of gravity, the general theory of relativity, needs to be revised. Whichever of these two scenarios holds true, the mystery of the accelerating expansion of the universe will be solved.
Modifying the equations that describe fundamental phenomena like gravity may sound extreme, but it's happened before. Newton's laws of gravity cannot explain some phenomena that scientists have observed, such as a small but mysterious precession of Mercury's orbit. Scientists eventually realized that this precession was perfectly explained by Einstein's theory of general relativity. The shift from Newton's theory of gravity to Einstein's theory of gravity eventually gave birth to modern physics by changing the way we observe space-time. Since then, scientists no longer regard time and space as independent and constant, but as interconnected and constantly changing.
The accelerating expansion of the universe may suggest that Einstein's theory of gravity is not entirely correct either. On the scale of the solar system, general relativity is absolutely correct. But in the larger universe, scientists seem to have less confidence in general relativity. The Roman team simulated the function of the Roman spacecraft, believing that the large and far-reaching three-dimensional images of the universe will help to identify existing theories about the expansion of the universe. Should dark energy be used to explain the accelerated expansion of the universe, or should it be explained by a modification of Einstein's theory of gravity? Roman can verify both cases at the same time.
Scientists speculate that there are many planets similar to Earth in the universe (imagination)
Exploring space dust in search of Earth-like
The Roman team also pointed out that Roman can detect planets located in the habitable zone of nearby planetary systems (the temperature around the star is not too high, so liquid water may exist in the region of space near the star. These regions are called planetary systems habitable). A special type of dust in the zone). Identifying the amount of this type of dust in these systems will help scientists learn more about the formation mechanisms of rocky planets and find habitable planets—Earth-like ones—through future missions.
In the solar system, ecliptic dust—mostly small rocky particles left behind by asteroid collisions and comets disintegrating—is distributed in the asteroid belt from near the sun to between Mars and Jupiter. From a certain distance, ecliptic dust is second only to the brightness of the sun in the solar system. In other planetary systems, the name has been changed to extra-ecliptic dust, which creates halos that scatter light from the host star, making it difficult for us to see other planets.
If it is found that there is not much extra-ecliptic dust around a star, it will be relatively easy for future missions to detect possible planets around that star. And if there is a lot of extra-ecliptic dust, scientists can also explore all kinds of interesting mysteries: Are the sources of this dust also asteroids and comets? How does this dust affect the brightness and distribution of the planets they hide? In other words, detecting extra-ecliptic dust is a win-win for scientific exploration.
Earth may not be alone in the universe
Reveal hidden planets
By exploring extra-ecliptic dust, scientists can find clues about what other planetary systems look like. Because a greater number of comets produce more extra-ecliptic dust, the amount of extra-ecliptic dust is indicative of comet activity. By exploring the distribution of extra-ecliptic dust, scientists can speculate on the conditions of surrounding planets, as planets may affect extra-ecliptic dust with their own gravity, for example by creating blank tracks in the dust.
Scientists point out that they still know very little about extra-ecliptic dust because they are so close to their host star that they are overwhelmed by the star's dazzling light and difficult to observe. While it's not certain what Roman will find in different planetary systems, scientists are looking forward to it: after all, Roman's instruments can explore habitable zones in planetary systems, and Roman is the only one so far possible to do this kind of work. Exploring spacecraft.
Roman will likely use a coronal imager to block out the starlight of its host star, allowing precise measurements of visible light reflected by dust in planetary systems. Such measurements are difficult for telescopes located on Earth's surface because ground-based telescopes have difficulty seeing through Earth's turbulent atmosphere, making it difficult to observe extra-ecliptic dust.
Equipped with special sensors and deformable mirrors, Roman's coronal imager actively measures and cancels starlight in real time, providing images with much higher precision than Hubble's passive coronagraph can provide. Scientists may find warmer dust orbiting the host star in relatively close proximity.
Pathway for future missions
Hubble has observed cryogenic debris disks farther away from their host star (much farther from the Sun than Neptune), but no spacecraft or ground-based telescope has yet been able to image the warm dust in the habitable zone. While previous detection projects have predicted extra-ecliptic dust in the habitable zone, the Lohmann imagery will be much more sensitive, thanks to the high-tech coronagraph and Lohmann's stability in space Location. Roman will orbit Lagrange L2 at a distance of 1.6 million kilometers from Earth, rather than in low-Earth orbit like Hubble, which means Roman's observations will not be as sensitive as Hubble's. Environmental conditions interfere, so Roman's observations will be more precise.
Find planets by discovering debris disks (imaginary)
Photographing warm debris close to the host star is important because the material composition of these debris differs from that of the outer edge of the dust disk: close to the host star, the dust disk is dominated by rocky grains; farther away, The dust disk is dominated by ice grains. In these two regions, the debris is produced by different processes, so by detecting the chemical composition of the extra-ecliptic dust, it is possible to obtain information that cannot be obtained by simply observing the outer region of the dust disk, allowing scientists to understand the mechanisms that shape planetary systems. , providing important reference information for future missions to photograph the habitable zone of a planet. Specifically, by knowing how much extra-ecliptic dust a potential planet is obscured, scientists can determine how large a telescope is needed to see through that dust. In this regard, Roman's Coronal Imager will lay the groundwork for the search for Earth-like planets.
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