Do you notice the "stars" of these eight corners in the photo taken by Weibu?

On July 12, 2022, James Webb Space Telescope (hereinafter referred to as "Weibu") released the first full color photo. Among them, there are eight corners of the "stars" on some images.

Webu's first full -color map was taken by near -infrared cameras. Some celestial bodies displayed in the figure appeared. Image source: NASA, ESA, CSA, STSCI

Why did Weibaba shoot such an octagonal star? Are the octagonal stars in Wubu's photos of all stars? Why are the obvious degree of angle in the image of different wavelengths different? Here, let's reveal the answers to these questions.

Why did Webb the octagonal star?

The eight horns of these octagonal stars are caused by the diffraction of light. The diffraction of light refers to the phenomenon of the spread of light by bypassing obstacles. For reflecting telescopes, the main mirror is responsible for reflecting the starlight to the sub -mirror surface, and the latter further reflects the light to the detector/camera or the third mirror. In the actual observation of the telescope, the main mirror itself and the bracket of the auxiliary mirror will cause diffraction phenomena.

The structure of the Weibu Space Telescope, the diffraction is related to the main mirror, the auxiliary mirror and its bracket. The source of the picture: NASA

The diffraction of the main mirror surface is caused by its edges. The diffraction pattern generated by its edge is determined by its edge, and the direction of the diffraction light is perpendicular to the edge. If the main mirror is N -edge, the produced diffraction light is perpendicular to the N -strip side, respectively. When the main focus surface is passed, the center coincides to form N -pair angle. For the positive N edge, if n is an occlusal number, N pairs of angle will overlap to N/2 pairs (n); if n is a strange number, N pairs of the angle does not overlap each other, and it will still be displayed as N pairs (2N). If the main mirror is round, it is equivalent to infinite multiple edges. The split angles produced are along the radius and are existing in all directions, so as to form a concentric diffraction ring and do not display the horn.

The main mirror of different shapes produces different shapes and different numbers. Image source: (CMGLEE)

Light -shot auxiliary mirror brackets will also produce diffraction phenomena. If the bracket of the auxiliary mirror has N edges, it will also produce the perpendicular to the diffraction light. After passing through the main focus surface, the N -pair angle is also formed. As long as the projection of the two edges of the bracket in the main mirror is located on the same line or parallel, the corresponding angle will overlap, resulting in a decrease in the number of horn, as shown below.

Different positions of the sub -mirror bracket generate different shapes and different numbers. The left side is a stent schematic, and the second column is paired with a pair of fangs; the third column is the angle of the angle that enters the main focus surface. Image source: NASA, ESA, CSA, Leah Hustak (STSCI), Joseph DEPASQUALE (STSCI)

The combination of the main mirror of different shapes and different sub -mirror brackets produces different forms of diffraction angles. Take the famous Hubble Space Telescope (hereinafter referred to as "Halbal") as an example. Its main mirror surface is round and the bracket is a cross -shaped 4 -type edge. Therefore Faste 4 horn, such as the image of Sirius taken by Hubble in the figure below.

Sirius (white circle in the picture in the picture) and Sirius (small white point in the lower left corner) taken on October 15, 2003. For example, Sirius B is excluded, and this photo is excessively exposed, so the diffraction ring of its main mirror is particularly obvious. Four horn is caused by the diffraction of the bracket. Image source: NASA, ESA, H. Bond (STSCI), and M. Barsstow (University of Leicter)

Weibu's main mirror surface is spliced ​​from multiple hexagonal mirrors. The bracket of the pair of mirror surface has three edges, as shown in the figure below.

Weibu's main mirror shape and auxiliary mirror bracket shape. The left is the side view, and the right is a positive view. Image source: NASA, ESA, CSA, Leah Hustak (STSCI), Joseph DEPASQUALE (STSCI)

Therefore, the main mirror of Weibu produces 6 long angles, and the bracket produces 6 short angles, a total of 12 angles. However, the experts designed an angle to overlap the 4 short -angle generated by the auxiliary mirror bracket with the 4 long angles generated by the main mirror surface, only 6 long, 2 shorts, and 8 angles.

Web's main mirror produces 6 long angles, and the auxiliary mirror produces 6 short angles. The 4 of the latter are overlapped with the 4 of the former. Essence Image source: NASA, ESA, CSA, Leah Hustak (STSCI), Joseph DEPASQUALE (STSCI)

The full color picture of NGC 3324 in the nebula shot by Webbu. In the figure, the celestial body of the octopus is a star in the galaxy. Image source: NASA, ESA, CSA, and STSCI

Only those point celestials that look particularly bright can produce angles. Of course, the celestial bodies that look particularly bright in the telescope push the stars in the Milky Way. In fact, most of the deep -field maps, the south -ring star clouds, the "Stephen Five Beauty" and the vast majority of the octagonal stars in the bottom of the ship are celestial bodies in the galaxy. Are the octagonal stars in Wubu's photos of all stars?

the answer is negative. As we said above, the vast majority of dot -shaped sources with angle are stars in the galaxy. We emphasize that "most of them" is because there are exceptions -some octagonal stars are other celestial bodies.

The core of the NGC 7319 (at the top of the "Stephen Five Inspection" image) taken by Webb is an anti -example: its medium -infrared image shows obvious octagonal fangs, but it is not a star, but a bright active galaxy nucleus.

"Stephen Five Inquiry" shot by Webb. Near -infrared images taken on the left for the near -infrared camera, and the middle infrared image taken on the right for Miri. The core of the NGC 7319 located at the top of the middle and infrared images shows obvious octagonal fangs. Image source: NASA, ESA, CSA, STSCI

NGC 7319 core strong medium infrared radiation means that its core peripherals are rich in dust. Dust to varying degrees, the strong column of ultraviolet rays, visible light and near -infrared rays from the core area are obscured. After the dust itself was heated by ultraviolet rays and visible light, the temperature rose, and a strong medium -infrared radiation was emitted.

The active galaxy nuclear is much smaller than the galaxy. If they are extremely bright, then from the distant distance, it is like a bright star. When shooting them with some telescopes, the angle will also be displayed. This is the case of the octagonal mang of the image.

It must be pointed out that before Webb, other telescopes have already taken some bright active galaxies, which also shows obvious diffraction angles. In the figure below, 3C273 is a star -like body taken by Hubble (the brightest category in the active galaxy nucleus), which shows a obvious four -corner.

The visible light image shot by Hubble's WFPC2 star 3C273 (located in the center of the graph) has obvious ring -shaped diffraction patterns and four corners. 3C273 is the first star -like body discovered by humans. Image source: ESA/Hubble & Nasa

The huge brightness of the active galaxy is a mystery. However, research in the past few decades has basically reached a consensus in theory: there are huge black holes in the center of the core core of the active galaxy, and the gas and dust around the black holes fall around the black hole to form a "accumulation disk"; In the process of falling into the black hole, a part of its gravitational potential energy will be converted into internal energy, which increases its temperature and emits very bright ultraviolet, visible light, and infrared radiation. Ultraviolet rays and visible light heat the surrounding dust, so that they emit infrared radiation.

Structure diagram of the galaxy nucleus. The central black spots are black holes, and the disk around the black hole is an accounting disk (torus). Picture source: NASA

The dust around the active galaxy is often circular. If the observer and the active galaxy nucleus happen to be blocked by the dust loop, the strong light from the suction disk of the active galaxy will be covered. In this case, the medium -infrared radiation of the dust ring itself is more prominent.

Due to the excellent detection ability of Weibu in China, it has a unique advantage in studying the dust of the periphery of the galaxy. The research on the infrared radiation emitted by these dusts has an important role in the physical nature of people's understanding of the dust of the galaxy nucleus and even the geometric shape of the dust ring.

The system of black holes in the active galaxy and the system composition of the product will also emit jet (Jet). These jets are perpendicular to the direction of the accumulation disk. The speed is close to the speed of light in the vacuum, and a large amount of radio radiation will generate inside the injection. However, only a part of the active galaxy nucleus will generate injection. In the diagram of the stars 3C 273 above, the strip -shaped object on the left of the center is a jet emitted.

Why are the obvious degree of angle in the image of different wavelengths different?

There is also a feature posted by Webb: The picture taken by the same object, the significant degree of nearly infrared and the middle infrared angle is not the same.

Taking two images of NGC 7319 taken by Weibu as an example. The core of this galaxy's near -infrared image only vaguely shows the horn, and its middle infrared image shows a very obvious octagonal mang. This is because the core of NGC 7319's core dust is much brighter than near -infrared radiation.

The star in the center of the South Ring -shaped Nebula (NGC 3132) also reflects the characteristics of "different levels of the angle of different bands", but the situation is completely opposite: the horns in the middle infrared image are weaker It's much more. This is because the star temperature is high, and its middle infrared is much darker than near infrared radiation.

The South Ring Nebula (NGC 3132) shot by Webb. Near -infrared images taken on the left for the near -infrared camera, and the middle infrared image taken on the right for Miri. Image source: NASA, ESA, CSA, STSCI

Of course, the significant level of the horn is also related to the wavelength itself (the long -wave diffraction phenomenon is more obvious than the short wave) and the exposure time.

In fact, in fact, in addition to the "stars" of eight corners, there are many places worth analyzing these details that Wabu obtained. Essence

At that time, Zhuangzi sighed pessimisticly: "My life also has the end, and I know that there is no end. With the end of the end, there is no end." So, do we still need to explore hard? Our answer is -of course! It is the interpretation of the ocean -style ocean -style ocean -style exploration of generations of scientists that allow humans to solve the secrets of all things and the universe themselves step by step, so that humans can get rid of the unknown state and get the fun brought by knowledge.

In the vast universe, humans are small; but in the exploration of unknown, humans are great. Exploring endlessly, I hope we will go with us.

Produced: Popular Science China

Author: Wang Shanqin

Producer: China Science Popularization Expo

The China Science Popularization Expo is the Science Popular Science Platform of the Chinese Academy of Sciences. It is sponsored by the Computer Network Information Center of the Chinese Academy of Sciences. Relying on the high -end scientific resources of the Chinese Academy of Sciences, it is committed to spreading cutting -edge scientific knowledge and providing fun science and education services.

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