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

In 1933, Fritz Zwicky was studying several galaxies in the latecomer cluster. This is a cluster of more than 1000 galaxies, about 330 million light-years away. Zwicky found that the galaxies in the cluster are moving so fast that there is not enough mass to hold the cluster together. Today, measuring some parameters of the universe is still tricky, let alone in 1933, so how did Zwicky measure it?

Source Pixabay first of all, we must measure the distance with some kind of standard candle. A standard candle is a star with predictable brightness, such as a Cepheid variable or a type 1a supernova. If we know their actual brightness, we can compare it with the apparent brightness. Because the light obeys the inverse square law, we can get the distance from the ratio of the actual brightness to the apparent brightness.

Next, we're going to use Herotu, which can tell us almost everything about stars. If we know the actual brightness and color of a star, this picture will tell us its radius, its stage of life, and eventually its mass. What Zwicky needs is the overall brightness of a galaxy, and he can estimate the mass of the stars in it.

It's a little difficult to measure speed. These celestial bodies are far away from us, so we can't actually see these things moving. In order to calculate the velocity, we need to measure something called Doppler redshift. When an object is close to or away from us, the frequency / wavelength of the light it emits changes. But we can't see the color change with the naked eye, so we have to transfer the light to the spectrum and then look for the movement of the spectral line.

So Zwicky gets the mass, the velocity, and then applies the law of gravity to see what happens. However, there are many galaxies in the late-developing cluster, so it is very difficult to solve the multi-body problem. Therefore, Zwicky uses the potential force theorem, which correlates the kinetic energy in the system with the time average of the potential energy. Based on the measured galactic velocity and the effective radius of the cluster, we can calculate how much mass is needed. As a result, the measured mass is much less than that obtained by theory.

Zwicky reasoned that there must be invisible dark matter. However, it refers to dark matter different from what is now thought to be dark matter. Zwicky refers to dark matter that does not emit or reflect enough light to make it invisible from the earth. Under this definition, many ordinary things are also dark matter, such as giant cold diffusion gas clouds. Zwicky believes that stars account for only a small part of the mass of the universe, and most of the rest are gas clouds.

In 1951, HaroldEwen and Edward Purcell discovered 21-centimeter hydrogen lines, which enabled us to find all the cold hydrogen between stars and galaxies. Even if hydrogen is cold and in a diffuse gas cloud, it still emits this 21 centimeters of light. This means that we can measure their mass, but it is still not enough to explain the quality problem of Zwicky.

Then in 1962, we used a space probe to discover the first extrasolar X-ray source. The earth's atmosphere absorbs a lot of X-rays from space, so our X-ray detectors must be in space to see it. X-ray astronomy opened up a whole new way of looking at the universe, when we saw something new: hot hydrogen. Unfortunately, it is still not enough to explain the quality problem.

The problem of dark matter did not progress until the early 1970s, when Vera Rubin was using a spectrometer built by Kent Ford to study the rotation of galaxies. She plotted the distribution of hydrogen in several galaxies, but when she studied the rate of rotation of the hydrogen, she found something strange. Based on her hydrogen distribution map, she predicts a decline in the orbital velocity of stars near the outer edge of the galaxy. However, the observed data show something different, and the velocity of the outer edge tends to be flat instead of decreasing.

So she asked herself a question: what if galaxies have more mass than we can see? Yes, it sounds familiar, she's talking about dark matter, which is the same argument that Fritz Zwicky made in the 1930s, but Vera Rubin came up with the right amount of data, which made dark matter a science for the first time.

So let's take a look at the latest material composition. Active stars account for about 1.5% of cosmic matter, planets, moons, asteroids and comets account for about 0.005%, diffuse gas and dust clouds account for about 14.5%, and 84% are unaccounted for. This is what we call dark matter.

This article comes from the official account of Wechat: Vientiane experience (ID:UR4351), author: Eugene Wang

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.