Name: how astronomers find black holes
Uploaded: 2023-04-30T11:07:38.000Z
Duration: 1 min 10 s
Channel: JoVE

K12 Standards

north-carolina-k-12-science-standard-course-of-study

North Carolina K-12 Science Standard Course of Study

9-12

Earth and Environmental Science

Earth's Place in the Universe

ESS.EES.1.1

Detection of Black Holes

Event horizon defines a boundary surrounding a black hole, within which the escape velocity exceeds the speed of light.
Since light photons cannot escape, events occurring inside the event horizon cannot be seen. So, how do astronomers detect a black hole then?
The enormous gravity of the black hole attracts any nearby matter close to it. As this matter falls over the event horizon, it forms a whirlpool-like disk around the event horizon, known as an accretion disk.
Just outside the event horizon, the speed of matter is just slightly less than the speed of light. Particles moving with relativistic speeds interact with each other, thereby increasing the temperature of the accretion disk. At very high temperatures, the matter emits X-rays, which the astronomers can detect using the space-based telescopes.
A supermassive black hole at the center of a galaxy can be detected by observing the orbital period of the stars close to it. Using Kepler&#39;s third law of planetary motion, the mass of such a black hole can be estimated.

detection of black holes

Although black holes were theoretically postulated in the 1920s, they remained outside the domain of observational astronomy until the 1970s.
Their closest cousins are neutron stars, which are composed almost entirely of neutrons packed against each other, making them extremely dense. A neutron star has the same mass as the Sun but its diameter is only a few kilometers. Therefore, the escape velocity from their surface is close to the speed of light.
Not until the 1960s, when the first neutron star was discovered, did interest in the existence of black holes become renewed. Evidence for black holes is based upon several types of observations, such as radiation analysis of binary stars (called X-ray binaries), gravitational lensing of the light from distant galaxies, and the motion of visible objects around invisible partners.
The closest and perhaps the most dramatic evidence for a black hole is at the center of our galaxy, the Milky Way. Using data obtained from the W. M. Keck Observatory, astronomers have been able to determine the orbits of several stars near the center of our galaxy. The periods and sizes of these orbits suggest that the stars are orbiting a mass of approximately four million solar masses. Moreover, this mass must reside in the region obtained by the intersection of the stars&#39; orbits. This region is so small that it would fit inside the orbit of Mercury. However, no light is emitted from this region in the visible spectrum.
The only logical conclusion of these observations is that a black hole exists in this region. Astronomical observations of regions outside the Milky Way suggest that black holes with masses millions of times more massive than the Sun are common at the center of galaxies.
This text is adapted from <a href="https://openstax.org/books/university-physics-volume-1/pages/13-7-einsteins-theory-of-gravity">Openstax, University Physics Volume 1, Section 13.7: Einstein&#39;s Theory of Gravity.</a>

Although black holes were theoretically postulated in the 1920s, they remained outside the domain of observational astronomy until the 1970s.
Their ...

Education

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Physics

Unit 1

Gravitation

KEY TERMS AND CONCEPTS

how astronomers find black holes

Black holes are found through indirect astronomical evidence. They were first proposed in the 1920s, but they stayed outside observational astronomy until the 1970s. Their closest known cousins are neutron stars, which are made mostly of packed neutrons and are extremely dense.

A neutron star can have the mass of the Sun while its diameter is only a few kilometers. Because of that, the escape velocity from its surface is close to the speed of light. Interest in black holes rose again in the 1960s, after the first neutron star was discovered.

Astronomers look for black holes using several kinds of observations. These include radiation from binary stars, called X-ray binaries, gravitational lensing of light from distant galaxies, and the motion of visible objects around unseen partners. Each method gives indirect evidence that something massive and invisible is present.

The strongest nearby evidence comes from the center of the Milky Way. Data from the W. M. Keck Observatory show that several stars orbit a hidden mass there. The size and period of those orbits point to about four million solar masses packed into a region so small that it would fit inside Mercury’s orbit.

No visible light comes from that region. For that reason, the best explanation is that a black hole is present. Similar observations outside the Milky Way suggest that black holes millions of times more massive than the Sun are common at the centers of galaxies.

How Astronomers Find Black Holes

gravitation

Newton’s Law Behind Planet Motion

Newton’s law of gravitation links falling objects, the Moon’s orbit, and planetary motion. Before Newton, many people thought the sky and Earth followed different laws. Kepler later described the three laws of planetary motion, but their connection to a deeper force was still unclear. Isaac Newton made that connection in 1665 to 1666. He showed that the same phenomenon explains why objects fall to Earth and why the Moon moves around Earth. He also found that the Moon’s centripetal acceleration...

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newton's law of gravitation

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gravitation between spherically symmetric masses

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Gravitational Potential Inside a Shell

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acceleration due to gravity on earth

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acceleration due to gravity on other planets

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Measuring Gravity on Distant Planets

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apparent weight and the earth's rotation

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potential energy due to gravitation

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Adding Gravitational Forces with Superposition

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escape velocity

Launching a Satellite Beyond Gravity

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circular orbits and critical velocity for satellites

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Orbital Speed and Period in Circular Paths

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energy of a satellite in a circular orbit

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Satellite Orbits and Energy in Space

Satellite orbits and energy in space depend on altitude, orbit shape, and gravity. Thousands of artificial satellites circle Earth every day at many different distances. Satellites below 1,600 km are in low-Earth orbit, or LEO. Research satellites and Earth observation satellites are usually placed in LEO. They mostly move in elliptical orbits, which are oval-shaped paths. Navigation satellites are placed in medium-Earth orbit, or MEO, which ranges from 2,000 km to 36,000 km above Earth’s...

kepler's first law of planetary motion

Planet Orbits as Ellipses

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kepler's second law of planetary motion

Kepler's Equal-Area Planet Motion

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kepler's third law of planetary motion

Kepler’s Planet Distance Law

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tidal forces

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schwarzschild radius and event horizon

Escape Velocity Limits and Black Holes

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Black holes are found through indirect astronomical evidence. They were first proposed in the 1920s, but they stayed outside observational astronomy until the 1970s. Their closest known cousins are neutron stars, which are made mostly of packed neutrons and are extremely dense. A neutron star can have the mass of the Sun while its diameter is only a few kilometers. Because of that, the escape velocity from its surface is close to the speed of light. Interest in black holes rose again in the...

principle of equivalence

Weightlessness and Einstein’s Equivalence

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space-time curvature and the general theory of relativity

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Einstein’s Gravity and Mercury’s Orbit

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key terms and concepts

Learn how astronomers detect black holes using star orbits, X-ray binaries, gravitational lensing, and evidence from the Milky Way's center.

How Astronomers Find Black Holes | JoVE K12

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JoVE Core Physics introduces the theory and application of fundamental physics topics, including kinematics, dynamics, fluid mechanics, statics, waves, and acoustics, with concise and easy-to-understand animated videos. Additionally, the scientist-in-action videos demonstrate the application of related concepts in classical and original research experiments performed in today's laboratories worldwide.

Pennsylvania State Academic Standards

Earth and Space Science

Space Systems

3.3.9-12.B

3.3.9-12.D

Louisiana Student Standards for Science

High School

Earth Science

Earth’s Place In The Universe

HS-ESS1-1

HS-ESS1-2

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Ohio’s Learning Standards and Model Curriculum

Physical Science

The Universe

Stars

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HIgh School

ES.2

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Alabama Course of Study Science

9-12.ESS.1.3.b

Florida Department of Education

SC.912.E.5

SC.912.E.5.5

SC.912.E.5.10

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New York State Science Learning Standards

Earth and Space Sciences

HS-ESS1-3.

Georgia Standards of Excellence

Astronomy

SAST4

SAST4.1

Kepler's First Law of Planetary Motion

In the early 17th century, German astronomer and mathematician Johannes Kepler postulated three laws for the motion of planets in the solar system. He ...

Kepler's Second Law of Planetary Motion

In the early 17th century, German astronomer and mathematician Johannes Kepler postulated three laws for the motion of planets in the solar system. His ...

Kepler's Third Law of Planetary Motion

In the early 17th century, German astronomer and mathematician Johannes Kepler postulated three laws for the motion of planets in the solar system. In ...

Tidal Forces

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Gravity between Spherical Bodies

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Use models to illustrate the formation of the solar system.

Uniform Circular Motion

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Gyroscope: Precession

Precession can be demonstrated effectively through a spinning top. If a spinning top is placed on a flat surface near the surface of the Earth at a ...

simple-harmonic-motion-and-uniform-circular-motion

Simple Harmonic Motion and Uniform Circular Motion

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Use mathematics and computational thinking to analyze Earth's motion through space.

ESS.EES.1.2

Light as Energy

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Nuclear Fusion

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First Law of Thermodynamics

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Energy Dynamics

The Food Chain
Energy is one of the most important abiotic factors in an ecosystem and organisms in an ecosystem are connected by the flow of energy and ...

Use models to illustrate how the sun produces energy.

ESS.EES.1.3

Radiation: Applications

The average temperature of Earth is the subject of much current discussion. Earth is in radiative contact with both the Sun and dark space; it receives ...

What is Weather?

Overview

Weather refers to the current state of atmospheric conditions at a specific time and place. Weather is temporary and is influenced by the ...

What is Climate?

Climate refers to the prevailing weather conditions in a specific area over an extended period. As the saying goes, &#8220;Climate is what you expect. ...

Radiation Pressure: Problem Solving

The radiation pressure applied by an electromagnetic wave on a perfectly absorbing surface equals the energy density of the wave. The wave&#39;s momentum ...

Absorption of Radiation

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where &#963; is the Stefan-Boltzmann constant, a ...

Construct an explanation to infer how incoming solar radiation interacts with Earth systems to support life.

ESS.EES.1.4

Explain how Earth's position relative to the sun influences conditions on Earth.

How Astronomers Find Black Holes

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