2020-10-27

The universe gave black holes a black body, but humans use it to detect light

By yqqlm yqqlm

When you walk down the street and look at the end of the road, you know which object is closer to you. This is because the surrounding 3D image and the shape of the object can help you build a complete image in your brain, allowing you to distinguish the distance.

getInterUrl?uicrIvZQ=8dddb413c7c602133dcb9a02b3d5b731 - The universe gave black holes a black body, but humans use it to detect light

However, when you look up at the night sky When the stars are fighting, you can only see countless shining star points, but you don’t know which star is closer to us and which one is farther away. You may not even know that the Big Dipper we are most familiar with is actually very far away from each other, some are only 70 light years away from us, and some are 100 light years away. As for the constellations we draw as a plan, the distance between the stars is even more amazing.

This is because, because they are just a light spot and the dark night sky has no other reference, we have no way of judging their distance.

However, as of today, scientists have found many ways to detect the distance of these celestial bodies. We have introduced that the Cepheid variable stars and Type Ia supernovae in the universe are all astrometric tools in the universe. Through their luminosity, scientists can accurately calculate their distance and reflect the celestial bodies around them. The distance from us.

getInterUrl?uicrIvZQ=7349f0690e986b563cda51254ac454f0 - The universe gave black holes a black body, but humans use it to detect light

Astronomer Yue Shen of the University of Illinois at Urbana-Champaign said:”In astronomy, measuring the distance of celestial bodies is the most basic challenge. Therefore, if you can put an extra kit in your pocket, it is definitely something to be excited about.”

But for now, , Scientists’”tools in their pockets” are still relatively limited, and the distances of many celestial bodies have not been fully determined. For example, the well-known Betelgeuse has many different distance data in history, which is caused by the limitation of our current scientific level. Therefore, they have also been looking for new ways to better determine the distance of celestial bodies, so as to draw more accurate maps of the Milky Way and the universe.

Recently, scientists have found a new astrometer in the universe, which may become an important tool for humans to measure the distance of celestial bodies in the future. Interestingly, this tool is exactly what we call a completely invisible celestial body-a black hole. Specifically, it is the echo of the supermassive black hole in the universe.

getInterUrl?uicrIvZQ=ea870c9e20994c43f36c4ed30ebe2d54 - The universe gave black holes a black body, but humans use it to detect light

Then the problem is that the black hole itself cannot be seen by us , It is impossible to observe directly under any electromagnetic wave, how can it allow the information of other celestial bodies to be displayed in front of us?

We know that there are actually many black holes in the Milky Way. Although the number of black holes we have discovered is not large, scientists estimate that the total number of black holes in the Milky Way may reach 1 billion. However, there is another black hole in the Milky Way that is more distinctive, and that is the supermassive black hole in the center of the Milky Way——Sagittarius A *.

Of course, even if its mass reaches 4 million times that of the sun, it is still invisible. However, when the material swallowed by it accelerates and spins like water in a sink and falls into its horizon, a huge accretion disk will be formed. The matter in the accretion disk glows due to the energy generated by friction, which allows us to observe this huge black hole.

getInterUrl?uicrIvZQ=6950c5db6ba02e5e464f6ee33e3bd47d - The universe gave black holes a black body, but humans use it to detect light

Besides the accretion disk, there is a huge dust The cloud, called a ring disk (torus), is shaped like a donut. It is this outer ring that is the key to the newly developed technology for detecting the distance of celestial bodies. This technique is called echo rendering, or reflection rendering.

Around an active supermassive black hole, every time the area of ​​the accretion disk closest to the black hole emits bright light in the visible and ultraviolet bands. When this light propagates to the outer ring, it will produce a kind of”echo”. Specifically:When these electromagnetic waves are absorbed, the dust cloud will be heated as a result, and finally be observed by us in the form of infrared radiation.

For supermassive black holes, the size of the accretion disk is also extremely amazing. For these black holes, it may take several years for light to travel to the outer ring, and then be converted into infrared rays and re-emitted. In the universe, the speed of light is constant, so as long as the time difference between the flare and the reflected wave is calculated, we can easily calculate the distance between the inner edge of the accretion disk and the outer ring.

getInterUrl?uicrIvZQ=b93863ce6ee192902ddb237410a6fba4 - The universe gave black holes a black body, but humans use it to detect light

We just mentioned that the accretion disk’s The luminescence is due to the friction of the swallowed matter. This friction will also cause the temperature of the accretion disk to be extremely high, and the closer to the black hole, the higher the temperature, on the contrary, the farther the place is, the lower the temperature. Research results show that when the temperature is below 1200 degrees Celsius (2200 degrees Fahrenheit), dust clouds will form. In other words, the distance between the outer ring and the inner ring of the accretion disk is directly proportional to the temperature of the accretion disk.

So, as long as you know the distance, you can calculate its temperature. If we know the temperature, we can calculate how much light this area emits. This is the relationship between radius and luminosity, referred to as R-L relationship. After knowing the luminosity, the distance of the celestial body can be calculated.

Of course, it’s easy to say, but not so easy to observe. Scientists need to observe a black hole for a long time to be able to detect its visible and ultraviolet flares and infrared echoes.

getInterUrl?uicrIvZQ=829d8fb3357fba616b336d6614c93f20 - The universe gave black holes a black body, but humans use it to detect light

For this, the University of Illinois at Urbana-Champaign The team of scientists led by Qian Yang is combing and analyzing the black hole flares data collected by ground-based optical telescopes in the last 20 years, and also studied the data collected by NASA’s wide-area infrared detector from 2010 to 2019 to find flares. In the end it was rewarded. In the end, they determined a total of 587 supermassive black holes with both visible light flares and mid-infrared echoes. This is the most complete survey and statistics to date.

It should be noted that the wide-area infrared detector does not cover all infrared bands, so this will have a greater impact on the distance calculation. However, with these data, they were able to prove that the R-L relationship is a relatively reliable tool. At present, they are still doing perfect work.

getInterUrl?uicrIvZQ=b89717421f376d29b9798705c7a008f5 - The universe gave black holes a black body, but humans use it to detect light

Anyway, they still think about their own research Very confident. Yang said:”The advantage of echo mapping is that supermassive black holes will not disappear quickly. Therefore, we can repeatedly detect the dust echo of the same system to improve the measurement of distance.”

<

p >The universe is so vast, and those galaxies are hundreds of millions or even billions of light-years away, which brings us many difficulties in detecting their distances and hinders our understanding of the universe. If we find accurate tools to determine their distance, I believe it will be of great benefit to the development of human astronomy.