In recent years, more and more people have begun to celebrate the New Year in an elegant way, and "watching exhibitions during the Spring Festival" and "celebrating the New Year with art" have become a new trend. For example, during the 2023 Spring Festival, many Shanghai citizens and tourists visited the "Jade Rabbit Elf" special exhibition to welcome the Spring Festival in the Year of the Rabbit held at the Shanghai Museum. The Spring Festival of 2024 is getting closer and closer. If you are planning to see the exhibition, did you know that there is a magnificent nebula "art exhibition" in the distant space hundreds of light years away in the universe?
Who has such great ability to show us such an "art exhibition"? It is the famous "James Webb Space Telescope".
01 Hubble successor: James·webb space telescope
The James Webb Space Telescope (JWST, hereinafter referred to as the Webb Telescope) is a collaboration between NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA). As the successor of the Hubble Space Telescope, it is currently the most complex and expensive astronomical telescope in the world; equipped with four scientific instruments:Near-infrared camera (NIRCam), near-infrared spectrometer (NIRSpec), mid-infrared instrument (MIRI), fine guidance sensor/near-infrared imager, and seamless spectrometer (FGS/NIRISS). As can be seen from the names of these instruments, unlike the Hubble Telescope,The Webb telescope mainly observes infrared bands(See Figure 1),Wavelengths greater than the visible light band seen by the human eye. Its main tasks includeSearch for the first-generation galaxies formed after the Big Bang, study the evolution of galaxies, observe the birth process of stars and planetary systems, and measure the chemical composition of planets and exoplanets in the solar system to explore the possibility of life in them..
Figure 1. Hubble and Webb Space Telescope observation bands (Image source: webbspacetelescopemediakit/NASA)
The Webb Telescope's powerful primary mirror (6.5-meter diameter) can provide unprecedented resolution and sensitivity. People expect it to present us with a clearer and more magnificent picture of the universe. In July 2022, the first batch of scientific images from the Webb Telescope were released, which included a nebula filled with gas and dust - the Carina Nebula (upper right in Figure 2). It was considered by many netizens to be the most beautiful of the first batch of scientific images. The author used it as the desktop wallpaper of my computer. In July 2023, to commemorate the first anniversary of scientific operation, the Webb Telescope released a stunning nebula image - the Rho Ophiuchi cloud (Figure 3). This image resembles an impressionistic painting and was selected by Nature magazine as one of the top ten scientific images in 2023. The Webb Telescope is like the Monet in space, vividly showing the beauty of light and shadow in the universe.
Figure 2. The first scientific images released by the Webb Telescope. Upper left: the Southern Ring Nebula in two infrared bands; upper right: a corner of the Carina Nebula (NGC 3324); lower left: Stephen's Quintet; lower right: galaxy cluster SMACS0723. (Pictures from NASA, ESA, CSA, and STScI)
Figure 3. A corner of the Ophiuchus Nebula captured by the Webb Telescope. Each star's dazzling six-pointed starburst is due to the construction of the Webb Telescope's primary and secondary mirrors. (Pictures from NASA, ESA, CSA, STScI, Klaus Pontoppidan (STScI), Alyssa Pagan (STScI))
02 The magnificent nebula: the cradle of star birth
The Carina Nebula and the Ophiuchus Nebula captured by the Webb Telescope are both star-forming regions—that is, where stars are born.Observing these sky regions is one of the core scientific goals of the Webb Telescope, and is expected to reveal to us the secrets of star birth.. The Ophiuchus Nebula is the closest star-forming region to us, about 390 light-years away. Astronomers believe thatA huge molecular cloud will collapse into thousands or even millions of stars. These molecular clouds are star-forming regions. They are mainly composed of about 70% hydrogen, 28% helium, and a small amount of other elements.. The typical scale of molecular clouds is tens to hundreds of light years, the mass is tens of thousands to millions of solar masses, and the temperature is very low, about minus 250 degrees Celsius. These molecular clouds are not a uniform whole and have many complex structures inside. The collapse of molecular clouds requires gravitational instabilities, which together with the effects of turbulence, rotation and magnetic fields, determine the spatial and mass distribution of molecular cloud clumps, which are the regions where stars and star clusters form.Many molecular cloud clusters or sub-clusters will collapse together, so stars are born in groups., like brothers and sisters in a big family, scattered everywhere as time goes by.Astronomers estimate that our sun has thousands of siblings.
The collapse of the molecular cloud clump gradually increases the temperature of the center, forming an object called a protostar. This protostar has not yet begun nuclear fusion because the core temperature is not high enough to sustain nuclear reactions. The protostar will rely on gravity to accretion the surrounding gas to form an accretion disk (see Figure 4).As the mass of the protostar continues to increase, the internal temperature and pressure gradually increase, eventually reaching a level sufficient to initiate nuclear fusion and become a star.. The greater the mass, the shorter the time required for this process.For a solar-mass star, that's about 50 million years, a very short infancy compared to the Sun's 10 billion-year lifespan. When the accretion of the protostar ends or is about to end, the remaining gas and dust on the accretion disk will collide and gather to form a core, accreting the surrounding gas and dust, and eventually forming a planet around the star.
Figure 4. Twenty different protostars and their accretion disks. (Pictures from ALMA(ESO/NAOJ/NRAO), S.Andrewsetal.;NRAO/AUI/NSF, S.Dagnello)
For decades, astronomers have gradually understood the general process of how interstellar gas nebulae collapse into stars and their surrounding planets, but there are still many unclear details and many unresolved questions. The answers to these questions may shed light on the origins of the solar system and even the origins of life. Therefore, the Webb Telescope regards observing the star formation process as one of its core scientific goals.
03The splendid and colorful star cradle,How on earth was it photographed?
Star-forming regions are filled with dust, which blocks light (think haze), making it impossible to see the details inside the star-forming region and the stars being formed.Infrared light can penetrate this dust, which is the observation band of the Webb Telescope.Therefore, compared to the Hubble Telescope, the Webb Telescope not only has clearer details (high resolution) can also see more clearly (see celestial objects obscured by dust). The left side of Figure 5 is the famous "Pillars of Creation" (a small part of the Eagle Nebula) photographed by Hubble. These dark brown pillars spurting out are dust. The picture on the right is the same area photographed by the Webb Telescope. It can be seen that Webb's photo is significantly more transparent, and many areas and stars obscured by dust are revealed in the Hubble photo.
Figure 5. Part of the Eagle Nebula as captured by the Hubble (left) and Webb (right) telescopes. (Pictures from NASA, ESA, CSA, STScI; Joseph DePasquale (STScI), Anton M. Koekemoer (STScI), Alyssa Pagan (STScI).)
Our human eyes cannot see infrared light, so why can we see so many colorful photos taken by Webb?actually,All the colors we usually see can be synthesized using several basic colors, for example, various display devices and digital cameras use the three primary colors of red, green, and blue to synthesize other colors; printers use cyan, red, and yellow to synthesize various color pictures.The color in astronomical observations actually corresponds to a very narrow band, and one color can be seen by observing in one band, for example, you can see a red world with a red lens, which is equivalent to only red light passing through the lens. This kind of lens is called in astronomyfilter.
For the Ophiuchus Nebula observed by Webb (Figure 3), it usesnear infrared cameraPhotographed, used in totalFive types of filtersTake the pictures separately, and then assign a color visible to the human eye to each picture, and finally synthesize the gorgeous "colorful" nebulae we see, among which:
Filter F187N (center wavelength 1.874 microns) is designated blue
Filter F200W (1.990 micron) is light blue
Filter F335W (3.365 micron) is cyan
Filter F444W (4.421 micron) is yellow
Filter F470N (4.707 micron) is red
The wavelength of the filter increases in sequence, and the wavelength of the specified color also increases in sequence..
The Ophiuchus Nebula region photographed in Figure 3 contains about 50 newly born stars, most of which are similar in size to our sun.Our solar system may have been born in such a nebula 4.5 billion years ago. There is a bright star in the center of the structure like a stalactite cave on the lower left. This is the only star in this area that is much larger than the sun. This young star cannot restrain its inner enthusiasm and releases blazing light and star wind. Like carving knives, it is carving the wall (dust) of the nebula and slowly eroding it, forming what we see. This void is also filled with a faint cyan haze-like gas - polycyclic aromatic hydrocarbons (PAHs), which are a type of hydrocarbon organic compounds that are very common in the interstellar medium, and their radiation characteristics are around 3.3 microns. The red stalagmite-like structure on the upper right is a newly born star breaking through the outer envelope, producing jets in opposite directions, just like a newborn baby stretching its arms for the first time. The red color is radiation from molecular hydrogen because it has a radiation signature near 4.693 microns. There is an approximately triangular dark area in the central area, indicating that the thick dust blocks even infrared light.
The vastness of the universe not only feasts our eyes because of its magnificence and brilliance, but also allows us to gain true knowledge because of its hidden mysteries. Continuously exploring the universe means exploring oneself, and always being in awe of the universe means being in awe of oneself!
References:
https://www.nature.com/immersive/d41586-023-03872-z/index.html
https://webbtelescope.org/news/webb-science-writers-guide/science-with-webb
https://webbtelescope.org/contents/news-releases/2023/news-2023-128
Author: Yan Zhen, researcher at Shanghai Observatory, Chinese Academy of Sciences
Produced by: Popular Science China
Producer: China Science and Technology Press Co., Ltd., China Science and Technology (Beijing) Digital Media Co., Ltd.