Fatal attraction! Why are we so obsessed with black holes?

When you stare into the abyss

The abyss is also staring at you

April 2019

First photo of a black hole released

For the first time, humans truly gazed into the abyss of the universe

(The first photo of a black hole ever taken by humans, image source: @EHT Collaboration, tagged @小黑/星球研究院)

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At this time

Distance people doubt whether black holes exist

More than a hundred years have passed

For black holes

This is just a brief moment

But for humans

It is a long journey that constantly subverts imagination.

It was this ideological storm that lasted for more than a hundred years.

This is what allowed us to write this article.

Take you to the darkest abyss in the universe

(Black hole artist's conception, image source @wikimedia commons)

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So

What exactly is a black hole?

Why does it have such powerful power?

So that all matter, energy and even light

No one can escape its fatal attraction.

(NGC 1097 Fornax barred spiral galaxy, there is a massive black hole at the center of the galaxy, photographer @Yan Zhipeng)

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To answer these questions

First, let's start with an astronomical mystery.

01

Mystery

1964

Scientists have discovered the direction of the Cygnus constellation in the Milky Way.

A blue star discovered by accident

Not only does it have a mass and temperature far exceeding that of ordinary stars,

There are two more puzzling doubts.

(Betelgeuse and the surrounding starry sky. Betelgeuse is also a celestial body with brightness and mass far exceeding that of ordinary stars. This picture is only for reference, not the blue star in Cygnus. Photographer @欧铭枝)

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Doubt 1

As a single star in the Milky Way

It is orbiting around the center of the Milky Way.

It also rotates along another elliptical orbit

(The position of the sun in the Milky Way. It only revolves around the center of the Milky Way without any other orbital motion. Image source: @NASA/JPL-Caltech/ESO/R. Hurt)

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Doubt 2

Near this blue star

Scientists detect strong high-energy radiation

It cannot generate such high energy by itself.

Could it be

Is there another celestial body around this star?

It is its existence that changes the orbit of the star.

And did it produce strong radiation?

But

If such a celestial body really exists

Why can't people see it?

In order to explain these doubts

People remembered an ancient prophecy

02

prophecy

As early as the eighteenth century

Scientists predict

There is a special celestial body in the sky

Its gravitational pull is very strong

So that not even light can escape from it

Therefore, we will not be able to see this celestial body.

This dark object is a "dark star" (please watch it horizontally, the black hole artist's conception of the black hole is located in the center of the brightest area in the picture, image source @ESO/M. Kornmesser)

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However, at that time

All the theories of physics known to man

No one can do anything about this "dark star"

Give a reasonable explanation

Until 1915

Einstein completes the theory of general relativity

The illusory prophecy now has a real theoretical basis

Soon after

German soldier and astronomer Karl Schwarzschild

On the front lines of World War I

Calculated the radius formula of the "dark star"

The "influence" of the "dark star" was described for the first time

This formula is called the Schwarzschild radius

The name "Dark Star" here will be

A more resounding name replaced

Black Hole

(Karl Schwarzschild, Einstein's general theory of relativity predicted the existence of black holes, and Schwarzschild gave the first solution to the theoretical equation, so a type of black hole is named after him, image source @wikimedia commons)

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The Schwarzschild radius shows

The larger the mass of the black hole,

The greater the scope of its "influence"

If the Earth were compressed into a black hole

Then its Schwarzschild radius is only about 9 mm

The size of a dime

(Hubble Telescope and Earth, image source: Visual China)

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Bounded by the Schwarzschild radius

The inside and outside of a black hole are two completely different worlds

Everything that happens inside a black hole

Cannot be seen from the outside

Therefore, this boundary is also called the event horizon.

(Artist's impression of the NGC 3201 black hole, the black hole has an impact on the nearby space-time, image source @ESO/L. Calçada)

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When matter passes through the event horizon and enters the interior of the black hole

Will fall irresistibly toward the center

There is a singularity with infinite density.

There will be no turning back for matter

This sounds so magical

But do such black holes really exist?

03

clue

Just as the study of black holes is booming

Affected by the outbreak of World War II

Many physicists have devoted themselves to the research of atomic bombs

Among them was Oppenheimer, the "father of the atomic bomb"

In the late 1930s, he

Predicted the existence of black holes

In 1942

Oppenheimer was appointed

Chief Scientist of the Manhattan Project

Began to focus on the development of the atomic bomb

that's all

The topic of black holes was gradually forgotten until the discovery of another theoretical celestial body.

Rekindled people's enthusiasm for studying black holes

(Oppenheimer [first from left] is showing photos of the atomic bomb explosion to people around him, picture source: @Visual China)

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1967

Scientists have repeatedly received

A strange signal in the universe

It visits the Earth every 1.337 seconds.

At first scientists thought it was a message from an alien civilization.

Later confirmed

This signal comes from a rapidly rotating neutron star.

A celestial body composed almost entirely of neutrons

It radiates electromagnetic waves from the poles of celestial bodies

Scanning deep space

Like a cosmic beacon

Guiding travelers in the vast universe

(A high-speed rotating neutron star is shown. Shortly after the discovery of the neutron star, John Wheeler first used the term black hole. Image source: @新片场, tagged @小黑/星球研究院)

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Neutron stars are like black holes.

The final fate of all stars

Like creatures on earth

Stars in the universe also have "life and death"

In the star life stage

The burning of its own fuel causes the star to "expand" outward

Thus resisting the attraction between matter

The inward "contraction" caused by

When the two forces reach balance

Stars can maintain a stable existence

(The sun is burning. Nuclear fusion reactions have been taking place inside the sun, which has allowed the sun to exist stably for hundreds of millions of years. Since the mass of celestial bodies such as stars in the universe is usually relatively large, the mass of the sun is generally used as the basic unit when measuring their weight. Photographer @王佳奇)

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But the star's fuel will eventually run out.

At this point the power generated by the burning disappears

The star collapses inwards rapidly under the influence of gravity.

Forming a very dense celestial body

The rest of the excess matter is thrown away

The star dies

What kind of dense celestial body will eventually form?

Depends on the mass of the star

Stars with a mass less than 8 times that of the sun collapse into

White dwarfs with high surface temperatures and small volumes

Its maximum mass is only 1.44 times the mass of the sun

This is also the final ending of our sun

(Sirius has two stars, A and B. Sirius B was identified as a white dwarf in 1915, but its brightness in the starry sky is far less than that of A, so we can only see the light of A on the ground. In ancient Chinese astrology, Sirius is "a sign of invasion". Su Shi wrote in "Jiangchengzi·Mizhou Hunting" that "I can draw a carved bow like a full moon, look northwest, and shoot Sirius", comparing Sirius to the Western Xia on the border of the Northern Song Dynasty. Photographer @Wang Jin)

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Stars with 8 to 30 times the mass of the sun will collapse into

Neutron Star

(The Vela supernova remnant is the remnant left after the star collapsed into a neutron star. The material energy in the remnant area is relatively high, and it appears bright in visible light and X-ray bands. Photographer @有手就行)

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When the mass of the neutron star exceeds 3.2 times the mass of the sun

It will further collapse

Black hole formation

(Please watch horizontally, supermassive black hole artist's conception, image source @NASA/JPL-Caltech)

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Previously

These are the dense objects formed after the death of stars

Only white dwarfs have been confirmed by observation

With the discovery of neutron stars

People have reason to believe

Black Hole

There is a high probability that it really exists

That twinkling beacon of the universe

It seems to be illuminating the direction for humans to find the truth about black holes.

04

the truth

1975

Famous physicist Stephen Hawking

I made a bet with fellow physicist Kip Thorne

Hawking believes that the strange blue star

The unknown celestial body nearby is not a black hole

Kipp's view is the opposite.

In subsequent years of observation

There is growing evidence that

The mass of the unknown object is 8.7 times the mass of the sun.

Exceeding the neutron star limit of 3.2 times the mass of the sun

So it's a black hole.

(Please watch in horizontal mode. The artist imagines the Cygnus X-1 black hole and the blue stars nearby. Cygnus X-1 is the first black hole discovered in human history. Its name indicates that it is the first X-ray source discovered in the constellation Cygnus. X-rays are a type of high-energy electromagnetic waves. Image source: @ESA/Hubble)

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One night in June 1990

Hawking broke into Kip's office with the help of his assistant

Sign the bet and admit defeat

And humorously put a thumbs-up on the bet

In fact, for Hawking, who studies black holes

This is exactly the ending he expected.

(Hawking and Kip Thorne [first from left], in 2021 scientists re-measured the Cygnus X-1 black hole and found it to be 21.2 times the mass of the sun, picture source @Visual China)

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that's all

Humanity discovered the first black hole

So all the previous doubts

There are reasonable explanations

The existence of a black hole causes the surrounding space-time to bend

The blue star revolves around the black hole along a curved orbit.

This is the manifestation of the gravitational effect of a black hole.

(The artist imagines that the existence of the black hole at the center of the Milky Way causes the surrounding stars to move in elliptical motions around it. The blue circle marked is the location of the black hole. Image source: @ESO/M. Parsa/L. Calçada)

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I understand one of the doubts.

Another doubt is solved

The strong gravitational pull of a black hole

Attracting matter from blue stars

Make them spin and fall into a black hole

It accumulates around into a disk-like structure

Accretion disk

(Visual simulation of a black hole accretion disk. Due to the strong gravitational force of the black hole, the accretion disk seen from different angles will have different changes. The light from the accretion disk behind the black hole will bend as it propagates forward. Image source: @NASA's Goddard Space Flight Center/Jeremy Schnittman, marked with @小黑/星球研究院)

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The materials in the disk rub against each other

Producing temperatures of millions of degrees Celsius

This produces high-energy radiation

(Artist's impression of a black hole accreting a star, image source @NASA's Goddard Space Flight Center/Chris Smith (USRA/GESTAR), tagged @小黑/星球研究院)

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also

Not all of the accreted matter falls into the black hole.

Affected by factors such as the black hole's magnetic field

Some of the material will gather into a narrow stream

Spray out

Like a sword piercing deep space

Jet

These ejected materials drift in space

New celestial bodies will be born in the future

(The ultra-long jet structure in the Hercules A galaxy photographed by the Hubble Space Telescope, image source @NASA/ESA)

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Compared to the black hole itself

Its accretion disk and jets are brightly visible.

This has become a powerful tool for astronomers to find black holes.

(Schematic diagram of black hole structure, image source @ESO, ESA/Hubble, M. Kornmesser/N. Bartmann, marked @小黑/星球研究院)

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Not only that

The fatal attraction of black holes leaves more clues

When light passes around a black hole

will inevitably propagate along curved space-time

From the surface phenomenon

Light doesn't go in a straight line anymore

It turns a corner

(The existence of a black hole changes the trajectory of light passing through it, drawn by @小黑/Planet Research Institute)

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When there is another compact object near a black hole

This gravitational force will cause

Two celestial bodies orbiting each other

And eventually merge into a black hole with a larger mass

(Simulation of the orbiting motion of two black holes, image source @NASA, tagged @小黑/星球研究院)

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In the process

The curved spacetime near these two celestial bodies is disturbed

And radiate outward in the form of waves

This is the ripple of time and space

Gravitational waves

(Two compact celestial bodies rotating around each other radiate gravitational waves outward, map by @小黑/Planetary Research Institute)

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In 2015, humans successfully detected the

Gravitational waves from the merger of two black holes

It travels 1.3 billion light years to reach Earth

Scientists have calculated the mass of the binary black hole based on it.

If we say that astronomy before this

Humans use their eyes to see

The successful detection of gravitational waves

This means that humans can use their ears

Listen to the whispers from the universe and time

(Comparison of the masses of black holes in gravitational wave merger events measured by the Laser Interferometer Gravitational-Wave Observatory in the United States. The merger of black holes with other celestial bodies is one of the ways in which the mass of black holes increases. Map by @黑抓/星球研究院)

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Through these methods

Humans have discovered more and more black holes

But in the eyes of physicists, it is incredibly simple

Only three physical quantities are needed to cover all

The first indicator is "how heavy"

That is quality

The second indicator is "whether it rotates"

Usually expressed as angular momentum

The third indicator is "whether it is charged"

Charge

According to their mass, black holes can be divided into three categories.

Black holes with less than 100 times the mass of the sun

Stellar-mass black hole

Most stars in the universe end up with this type of black hole.

Black holes with a mass of more than 1 million times that of the sun

Supermassive black hole

Black holes of this magnitude are usually found at the center of galaxies.

A key figure in galaxy evolution

Between stellar black holes and supermassive black holes

An intermediate-mass black hole

Compared with the previous two black holes

Due to the small number of observations

We still don't know enough about this kind of black hole

(Comparison between the mass of compact objects and the mass of the sun. The sun is not a compact object. The picture is only for comparison. Image source: @NASA/CXC/Visual China/Wang Jiaqi, and drawn by @黑抓/Planetary Research Institute)

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In addition to being classified by quality

According to angular momentum and charge

Black holes can be divided into four types

(The picture below shows the classification of black holes according to rotation and charge, the picture is from @Visual China, marked @黑抓/星球研究院)

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Although so many mysteries of black holes have been discovered

But this is only through

Accretion disk, jet

Gravitational effects, gravitational waves

These indirect ways to find it

Just like we can't see the wind

But it can pass through the sand blown by the wind

And indirectly judging the existence of wind is the same

(Please watch in horizontal mode. Yadan landform is a typical wind erosion landform. Its formation is inseparable from the action of wind. Photographer: @孙祺)

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Human curiosity drives scientists to

"seeing is believing"

What does a black hole look like?

Is it possible to directly make a black hole reveal its true form?

05

Appear

Taking pictures of black holes

This is the answer given by physicists

But this requires

An unprecedentedly large telescope

Aiming to observe supermassive black holes

Event Horizon Telescope

(Event Horizon Telescope, EHT )

Born out of necessity

(Artist's impression of a "eating" black hole. The bright accretion disk and jet prove its existence. Image source: @Aurore Simonnet and NASA's Goddard Space Flight Center)

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first

We need to choose the subject

In order to be able to see and photograph black holes clearly

Large mass and close distance to the Earth are necessary conditions

M87 galaxy near the Milky Way

There just happens to be such a supermassive black hole

It is 6.5 billion times more massive than our sun.

(M87 galaxy is the brightest point in the picture, picture source @ESO)

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Even though this black hole is so huge

But it is still 55 million light-years away from Earth.

See it from Earth

It is equivalent to seeing footprints on the surface of the moon.

This is a great test of the telescope's resolution ability.

(Observing the footprints on the moon from the earth, map by @Zheng Yi/Planetary Research Institute)

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The larger the aperture of the telescope,

The higher the resolution

China's Sky Eye in Guizhou

It is the largest single-aperture radio telescope in the world

Its caliber reaches 500 meters

But this still cannot satisfy the requirements of scientists

Want to take a picture of a black hole?

The telescope aperture must reach "Earth level"

(The "China Sky Eye" located between the mountains, photographer @酷鸟魏建)

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A single telescope won’t work

Then find a way to use multiple telescopes

Scientists use special methods

Uniting radio telescopes around the world

Equivalent to a virtual telescope with a larger aperture

This is very long baseline interferometry

(Very Long Baseline Interferometry)

VLBI for short

The distance between the telescopes is called the baseline

The aperture of the virtual telescope is equivalent to

The longest baseline length

The longer the baseline

The higher the resolution of the virtual telescope,

(Please watch in horizontal mode. The circular array solar radio imaging telescope located in Daocheng, Sichuan, also known as the "Thousand Eyes Dzi Bead". The 313 antennas are equivalent to a virtual telescope. Photographer: @蓝燕斌)

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The eight telescopes involved in the first black hole image are located in

Mexico, Spain, Chile, Antarctica

Hawaii and Arizona in the United States

They form a virtual telescope with an aperture equivalent to the diameter of the Earth.

(Distribution of the EHT telescope array in 2017. The English letters in the figure below are the abbreviations of the English names of the telescopes. Map by @郑艺/Planetary Research Institute)

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The aperture of the telescope is determined

But it doesn’t mean you can start observing right away.

Because we want to combine them perfectly

The observations must be made at the same time

Taking into account many factors such as weather and observation mission arrangements

The 8 radio telescopes involved in the shooting

In 2017, there were only 10 days of observation time in the whole year.

(Please watch in horizontal mode. The James Clerk Maxwell Telescope (JCMT) and the Submillimeter Array (SMA) are located on a mountain 4,000 meters above sea level in Hawaii, USA. The high altitude environment ensures good observation results, and it must be carried out in clear weather because the moisture in the atmosphere will affect the observation. Photographer @虞乐)

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Although the observation time is short

But the data obtained is very rich

The total amount of observation data generated reached 3500TB

If converted into a movie, it would take more than 300 years to watch it all.

Just processing this data

It took 2 years

April 10, 2019

The first photo of a black hole has been released

Scientists jokingly call it "donut"

The bright outer ring is the accretion disk surrounding the black hole.

The shadow in the middle is where the black hole is.

(The first photo of a black hole, image source: @EHT Collaboration, tagged @小黑/Planetary Research Institute)

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The M87 black hole also has a jet about 5,000 light years long.

But this time only the black hole and its accretion disk were captured

"Family Members" Are Not Complete

(The jet structure of the M87 black hole, the long strip shape in the picture, image source @wikimedia commons)

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So in 2018

An international team led by Chinese scientists

Using the same technical means

Re-photographing the M87 black hole in a new observation band

Telescopes with new wavelengths have a wider field of view

Able to see more black hole structures

Not only that

The number of telescopes has also increased from 8 to 16.

Greatly improved the imaging quality of the virtual telescope

(The geographical distribution of telescopes that participated in photographing black holes in 2018 is as follows, map by @郑艺/Planetary Research Institute)

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April 2023

Scientists release a "panoramic photo" of the M87 black hole

For the first time, a black hole and surrounding structures are imaged in one picture

(A panoramic photo of the M87 black hole shows that the jet structure is divided into three parts, shaped like a "trident". Image source: @R.-S. Lu (SHAO)/E. Ros (MPIfR)/ S. Dagnello (NRAO/AUI/NSF), with annotation @小黑/星球研究院)

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5 months later

Chinese scientists have proved

This is the first black hole "seen" by humans

It is rotating

Before that

Is the black hole rotating?

There is no direct observational evidence

(The precession of the M87 black hole jet is shown in the figure. The rotation axis of a spinning object is still rotating around another central axis, which is manifested as precession. Source: @崔玉竹, Intouchable Lab@Openverse, marked with @小黑/星球研究院)

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In addition to the distant M87 black hole

The center of our galaxy

There is also a supermassive black hole

Scientists also took photos of it

(Photos of the Milky Way's black hole and the central region of the Milky Way released in 2022. The black hole photo also looks like a donut. Image source: @NASA/CXC/HST/ EHT Collaboration, marked with @小黑/星球研究院)

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Imaging a black hole is a breakthrough in astronomy

But this is just the first step in exploring black holes.

Scientists will conduct more experiments in the future.

For example, taking "color photos" of black holes in different bands

Even add the time dimension to shoot a "black hole movie"

Maybe then

With more comprehensive observation and understanding

Black holes will no longer be mysterious

06 Ending

Black Hole

With its fatal gravity

Not only attracts everything

It also attracts humans to explore

Its existence

Once beyond human imagination

Even Einstein once doubted

But it was eventually proven to be real.

The universe is so magical

It's not too late to wait until you see it

The journey of exploring black holes also tells us

Just let your thoughts run wild

Only in this way can human beings transcend rigid concepts.

Entering a new world

so

In the next exploration journey

Please let your thoughts continue to run wild

But more than a hundred years

(The starry sky above is full of infinite unknowns and possibilities, photographer @Windsky)▼

This article was created by

Written by: Xinghe

Editor: Li Heili

Image: Zhang Zhaohai

Map: Zhengyi

Design: Xiaohei & Heizha

Proofreading: Wang Kun & Song Nan

Cover credit: NASA/JPL-Caltech

Audit Expert

Feng Haiyuan, PhD in Theoretical Physics from Southern University of Science and Technology

Note: The black hole event horizon and singularity discussed in this article are based on the Schwarzschild black hole background.