Why can't Hubble see the first galaxies in the universe?

The starry sky at night is the only window for human beings to communicate with the universe. On a clear, completely dark night without any light pollution, we can see about 6,000-7,000 stars with the naked eye, including the five planets of our sun (Uranus and Neptune are invisible to the naked eye). Besides these, we can also see the milky way and some vague nebulae in the night sky, such as Andromeda and Magellan galaxy.

Now we know that these vague nebulae are Sing Tao in the distant universe, independent of the Milky Way. In our Hubble volume, there are at least about 200 billion such galaxies, like the Milky Way, floating alone in the universe, like a lonely boat in the sea. We can know that the vastness of our universe and countless galaxies contained in it are entirely due to the emergence and development of telescopes.

Because in 1609, before Galileo made his first astronomical observation with his homemade telescope, we humans were still demonstrating the model of the solar system. Kepler's law of planetary motion has just been put forward, and Heliocentrism's model has been initially established. Newton didn't put forward the law of universal gravitation until 1687, which explained the essential reason why planets move around their parent stars.

With the establishment of the solar system model, people's eyes began to turn to the distant starry sky and entered the stage of establishing the universe model. The appearance of telescopes has also freed people from the limitation of observing the sky with the naked eye. A large number of dim stars and star aggregates that were previously invisible to the naked eye have been found in the sky, and those strange ambiguities have been found in the sky? Nebula? .

After decades of debate and observation, it was not until 1924 that the aperture, optical technology and astrophotography technology of the telescope were improved unprecedentedly, while Edwin? Hubble used the 254 cm reflecting telescope at Mount Wilson Observatory to observe the Andromeda Nebula to find out these so-called? Nebula? In fact, it is a galaxy, and it is found that the galaxies in the universe are moving away from us. Edwin? Hubble's discovery brought human vision out of the Milky Way and created galactic astronomy. On the basis of Hubble's discovery, people established an expanding big bang universe model, and modern astronomy began.

1990 The launch of Hubble telescope brought human vision to the deep space of the universe. In fact, with the cooperation of Hubble telescope and Spitzer infrared telescope, human beings are very close to the first galaxies and even the first stars born in the early universe! In recent years, we have been constantly refreshing the records of the farthest and oldest galaxies in the universe. For example, the EGSY8p7 galaxy and UDFj-39546284 discovered by Hubble are one of the very old galaxies in the universe, which were born 65.438+0.323 billion years ago and 65.438+0.34 billion years ago, respectively, 30 billion and 33 billion light years away from us. We should know the history of the whole universe.

But these two galaxies are not the oldest galaxies in the universe, because Hubble has not yet detected the first galaxy in the universe, which is the limit of the Hubble telescope we will talk about next.

You might think that as long as we aim Hubble at an area in the sky, expose it for a long time and collect more photons, can we see the first galaxies after the birth of the universe? There is no problem in theory, which is also a common method for Hubble to observe distant galaxies, but Hubble cannot receive more photon information after exposure for a certain period of time. Because Hubble telescope has its inherent limitations, it can be said that it is doomed to be unsuitable for observing distant galaxies.

The biggest factor limiting Hubble is the aperture of the main mirror and its working band. The aperture determines the number of photons that Hubble can collect, even if the exposure time is prolonged. The working band determines what wavelength of photons it can accept, because the telescope will not collect photons in the whole band when it works, which will cause interference from other signals, so we will only choose one band for observation. Observing celestial bodies in different bands will bring very different appearances and attributes.

You see, the above picture is also a supernova remnant, and we can get different effects by observing it in different bands. Figure 1 shows the sensing of very large array radio telescope under radio waves, figure 2 shows Spitzer infrared telescope in near infrared band, figure 3 shows the imaging of Hubble telescope in visible band, figure 4 shows the imaging of Astro- 1 telescope in ultraviolet light, and figures 4 and 5 show the imaging of Chandra X-ray Observatory at higher energy.

Therefore, the observation band is very important for target imaging, and the main working band of Hubble telescope is visible light. Although we added an infrared filter to Hubble in the later maintenance, the infrared band is still a serious problem for Hubble. So what does this have to do with distant galaxies?

The galaxies we see in the universe today are actually no different from the newly born galaxies in the early universe. They all rely on the nuclear fusion of stars to radiate energy, but the early galaxies were smaller, contained more blue giant, and emitted more energy, and a large part of them were in the ultraviolet band.

However, if these lights want to reach the earth, they must go through a hellish journey and fly tens of billions of light years. In this journey, the energy of light will be attenuated, that is, the loss of energy will lengthen the wavelength of light, but this has little effect. The biggest influence on light energy/wavelength is that our universe is expanding, and the expanding space will lead to the stretching of light wavelength. After a long journey, the ultraviolet light originally emitted by distant galaxies has shifted to the infrared band.

If we continue to use Hubble's visible light band to find those very distant galaxies in the universe, we can only find nothing. Therefore, Hubble's observation ability is limited. If the observation distance is longer, more serious problems will occur, which is beyond Hubble's power at present.

We know that in the millions of years after the birth of the universe, there were no stars, no galaxies, only a large number of neutral gas clouds. These gas clouds only gathered under the action of gravity in the next 50 million to 654.38 billion years, and ignited nuclear fusion, forming the first stars and galaxies. However, the light emitted by the initially formed star will hit neutral atoms and will be absorbed no matter which direction it travels. We call this period the dark age of the universe. So Hubble can't see any light in the dark ages of the universe under visible light.

But far infrared rays can be very immune to neutral hydrogen and can pass through these obstacles without hindrance, so we need to build a more powerful infrared telescope to detect these early galaxies in the universe. This is James? The significance of the Webb telescope mission. It is 0/00 times more sensitive than Spitzer infrared telescope. However, it is very important that although the infrared light originally emitted by distant galaxies is not blocked by neutral hydrogen, with the red shift caused by the expansion of the universe, a large part of infrared light has entered the far infrared band or even the microwave band.

If the light in the early dark ages is completely extended to the microwave band by the universe, it will be mixed with photons radiated from the microwave background of the universe, then we will never be able to detect the original galaxies and stars. Therefore, we urgently need the Webb telescope to take off to take over Hubble's work.