Shulou(Shulou.com)11/24 Report--

In various pictures of the Milky way, the Milky way as a whole looks like a plate with a central bulge and a spiral around it. But how do we know what the Milky way looks like as a whole in the Milky way? As the saying goes, "you can't know the true face of Lushan Mountain only because you are in these mountains." if you want to directly understand what the galaxy as a whole looks like, the best way is to observe it from the outside of the galaxy.

But even Voyager 1, the farthest probe so far, has only flown out of the solar system's heliosphere, which is just out of the influence of the solar wind. If bounded by the Oort Cloud, it hasn't even left the door of the solar system. At its speed, it will take at least tens of thousands of years to fly completely out of the solar system.

Someone said, "Why do detectors always fly out along the ecliptic, can't we launch up and down the solar system, so we should be able to fly out soon?"

First of all, the purpose of most probes is to detect planets. Whether they are eight planets or dwarf planets or asteroids, their orbits are basically on the ecliptic, so most probes can only fly like this.

Second, even if Voyager is a probe flying to extrasolar interstellar space, saving fuel as much as possible is the first consideration. After all, the efficiency of solar energy is very limited, and as it flies farther and farther, the solar radiation that the spacecraft can receive is getting weaker and weaker. So at present, the usual way is to throw the spacecraft out through the momentum of Jupiter and other big planets, that is, the gravitational slingshot effect.

And the Oort Cloud is seen as a spherical cloud of comets and other small celestial bodies, enveloping the middle stars, planets, and even the Kuiper Belt, like the egg white of an egg, except that the proportion of egg white is much different from that of egg yolk. So if you want to fly out of the Oort cloud of the sphere, whether it is flying horizontally or vertically, it is not much different.

Doesn't the Milky way look like an enlarged version of the solar system? is it the same thing? As a galaxy, its actual situation and structure are more complex.

We know that the solar system is located near the disk of the Milky way and revolves around the center of the Milky way. But the ecliptic plane of the solar system and the galactic plane of the Milky way do not overlap, and the two have an angle of about 60 °.

In this way, from the point of view of the gravitational slingshot of the solar system that relies on the big planets, probes like Voyager can indeed fly up and down the galactic disk from the vertical direction.

In this way, the spacecraft will not be able to take advantage of the speed at which the solar system rotates around the center of the silver, including using other stars to make gravitational slingshots. After all, the directions of the two are basically vertical.

And even if our spacecraft itself has enough power to reach the escape velocity of the Milky way (that is, the fourth cosmic speed), it is still out of reach for mankind to reach the disk of the Milky way.

Because the average thickness of the Milky way disk is more than 1000 light-years, while the fourth cosmic speed is only about 500 kilometers per second. To make a simple calculation, it will take almost 200000 years to get the probe just off the disk. It will take at least millions of years to reach a position where the entire galaxy can be seen.

So sending a probe outside the Milky way to get a full view of the Milky way is feasible in theory, but it is not realistic in practice, and it is still impossible in the foreseeable future.

Although it is impossible to observe the overall structure of the Milky way directly, we can speculate indirectly in other ways, such as "counting stars".

In 1610, Galileo gave the first evidence that the Milky way is made up of a large number of stars through a telescope. More than a hundred years later, Herschel drew the first map of the shape of the Milky way by calculating the number of stars in different regions of the sky. In this picture, the Milky way is just a small area centered around the sun.

Although more accurate measurements have been used since then, this method of "counting stars" has always had drawbacks, such as a large amount of interstellar dust on the silver disk that seriously obscures the line of view. so we have always been a glimpse into the overall appearance of the Milky way.

Things finally took a turn for the better in the 1950s. Because the 21-centimeter line radiated by hydrogen atoms will not be absorbed by interstellar dust, and the interstellar space of the Milky way is filled with a large amount of neutral hydrogen. So the scientists thought that it might be possible to draw the motion of gas in the Milky way with the help of the Doppler shift of spectral lines.

Then through the radio telescope, people actually detected the 21-centimeter line from interstellar space. Soon, a swirling image of the Milky way with a spiral arm structure appeared in front of people for the first time, although there was still a big occlusion in the center of the galaxy.

Later, with the Spitzer telescope put into use, it was found that the center of the Milky way was not a ball as people thought, but like a stick. At this point, the rod spin structure with spiral arms has become what we imagine the Milky way to look like today.

This article comes from the official account of Wechat: Linvo says ID:linvo001, author: Linvo

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.