Astrophysics

Astrophysics is more than just stargazing.

This story was created for the Google Expeditions project by Vida Systems, now available on Google Arts & Culture.

Astrophysics by Vida Systems, Google Arts & Culture

It is not limited to optical telescopes with which stars, galaxies, and other bodies are observed, but includes subjects like radio astronomy, cosmology, and spectroscopy.

Also, the infrared range of the electromagnetic radiation and weightlessness are investigated.

Introduction

For centuries, astronomy followed the theories of Ptolemy who lived in the 2nd century AD. There, the earth was at the center of the solar system, encircled by the sun and the planets.

It was not until the 15th century that Copernicus proclaimed that the sun was at the center, and that all the planets, even the earth, were circling around it. Most astronomers believe the Universe began in a Big Bang about 14 billion years ago.

The Big Bang

According to the Big Bang theory, the entire Universe was inside a bubble that was thousands of times smaller than a pinhead. It was hotter and denser than anything we can imagine. Then, it suddenly exploded.

Expansion and Contraction

The Big Bang theory is based on the concept of singularity. However, some scientists think that the universe was never a singularity, and it didn't expand at once, but is a continuous process of expansion and contraction.

Principle of Development

The universal principle of development is spiral expansion out of the center towards the periphery. The more the universe expands, the more it cools. We know about this because of relic radiation, which is the leftover radiation from the Big Bang.

Geocentrism by Ptolemy

According to Ptolemy, the earth is right at the center of the universe. All other heavenly bodies (moon, sun, planets, stars) revolve around it in perfect circles. In order to reconcile observations in astronomy with this discovery, it has been necessary to let all heavenly bodies revolve around earth’s orbit in the so-called epicycles, and partly again in orbits around these epicycles.

Through the use of some 80 such orbits, Ptolemy could bring his model into harmony with the observations.

Who Was Ptolemy?

Ptolemy was a Greek astronomer who lived between 85 and 165 A.D. He took the ideas and observations put forth by Aristotle and Hipparchus along with his own, and developed them into his geocentric theory.

Theory of the Spheres

Ptolemy used math to describe how the planets, sun, and stars revolved around the earth. He calculated that each planet moves in its own small circular path, while at the same time moving in a large circle around the earth.

Ptolemy’s Geocentric Model

The geocentric model states that the Earth is at the center of the universe, and all other heavenly bodies circle around it. This theory was thought to be true for 1,400 years, until the time of Copernicus.

Heliocentrism by Copernicus

The Ptolemaic model was not seriously challenged for over 1,300 years. It was Nicolaus Copernicus who changed how we view the positioning of the sun, earth, and other celestial objects in space.

He reasoned that it was the sun at the middle of the known universe, and not the earth, an idea that was strongly opposed at the time. 

Who Was Copernicus?

Copernicus was born on the 19th of February, 1473, and died on the 24th of May, 1543. He was born in Thorn, Royal Prussia, which was part of the Kingdom of Poland at the time.

The Heliocentric Model

The astronomical model that Copernicus developed was called heliocentrism (“helios” means “sun”). It has the sun motionless at the center of the Universe, while the earth and other planets rotate around it in circular paths.

Model Change

The Ptolemaic model was thought to be true for 1,300 years until Copernicus’ heliocentric model. Ptolemy’s model stated that the earth was in the center and the sun revolved around it, but Copernicus found out that it was quite the opposite.

Theory of Relativity by Einstein

The Theory of General Relativity says that large objects cause outer space to bend in the same way a marble laid onto a large thin sheet of rubber would cause the rubber to bend. 

He reasoned that it was the sun at the middle of the known universe, and bend much more than the marble would.

Einstein

Albert Einstein was a German theoretical physicist born in 1879. At the age of 37, he developed and published the general theory of relativity, which would go on to become 1 of the 2 pillars of modern physics. 

Special Theory of Relativity

The Special Theory of Relativity (1905) applies to all physical phenomena as long as gravitation is not significant. Special relativity applies to "flat space-time" — to phenomena that are not significantly influenced by gravity, i.e., don’t spiral around larger objects like planets and stars.

Theory of Relativity

The General Theory of Relativity was developed by Einstein in 1915. The theory states that it is impossible to distinguish or tell the difference between gravity and the force of inertia of a moving object.

The Time-Space Continuum

According to Einstein, gravity is simply the speed with which a body attracts a smaller body — the larger the body, the higher the speed. This means that time determines space and vice versa.

Light Bending in Outer Space

Einstein's general relativity theory is a way to explain gravitation. The main idea is that spacetime is curved by the presence of mass. Photons travel in a straight line in a vacuum. 

A big mass, such as a black hole, may curve space-time so much that a straight line in space-time isn't straight anymore. When we look at photons in space, they seem to bend in a curve through space.

Space-time Continuum

Space and time were combined into 1 entity called “spacetime” because per relativity equations, both space and time coordinates must mix together to accurately describe what we see.

Because space consists of 3 dimensions, and time is 1-dimensional, spacetime must be a 4-dimensional object.

Light

Imagine space like a rubber sheet. If you stretch it and place a mass in the middle and roll a ping-pong ball past the mass, it will curve towards the mass. Similarly, when spacetime is curved, objects will appear to be attracted towards mass. 

Cosmic Bodies

Cosmic bodies like the sun bend this 4-dimensional cosmic grid. The warp, in turn, creates the effect of gravity, redirecting the path of objects that travel into it. The strength of gravity depends on the size of the space-time warp.

Neutron Star

A neutron star is a very small and dense star made almost completely of neutrons. It is a very large nucleus held together by gravity. Neutron stars have a radius of about 6 miles and a mass from about 1.4 to 5 times the mass of the sun.

How Do Neutron Stars Pulsate?

Pulsars are types of neutron stars that spin and send a beam of radio waves. When this beam moves past Earth, it shows up as a pulse (like the light from a lighthouse seen as a flash on the horizon) and therefore are called pulsars.

How Do Neutron Stars Form?

They are usually what is left of very big stars that have exploded (these are called supernovas). Some are what happen to a white dwarf (small star) that has a lot of energy.

Magnetic Field

All stars have a magnetic field inside of them. When a star collapses, it becomes smaller. This means that the magnetism is pushed into a smaller area and the magnetic field is stronger nearer the star.

Do Neutron Stars Die?

There is no clear mechanism for a neutron star to dissipate and then disappear entirely. However there is a means that can cause such stars to experience a loss of mass over very long periods of time.

Orion’s Belt

Orion is one of the largest constellations in the sky and is also one of the easiest to find. The giant figure also contains the Orion Nebula (M42), which has been the subject of many of the most famous astronomical images we have received from the Hubble Space Telescope.

Horsehead Nebula

The Horsehead Nebula, also known as Barnard 33, is a dark nebula in the constellation Orion that is рart of the much larger Orion complex. It's located just to the south of the star Alnitak found on the farthest east on Orion's Belt.

The Flame Nebula

The Flame Nebula, also called NGC 2024, has no well-defined edge. It is found about 900 to 1,500 light years away from Earth. This nebula, рart of the Orion complex, is known as a star-making area.

NGC 2023

An emission and reflection nebula found in the constellation of Orion, NGC 2023 was discovered by William Herschel in 1785. One of the largest reflection nebulae ever discovered, it is also known as LBN 954.

Black Holes

Black holes are the strangest objects in the Universe. A black hole does not have a surface, like a planet or star. Instead, it is a region of space where matter has collapsed in on itself. 

This catastrophic collapse results in a huge amount of mass being concentrated in an incredibly small area. The gravitational pull of this region is so great that nothing can escape – not even light.

Center

The center of a black hole is called the singularity or Inner Event Horizon. This is where gravity's pull is almost impossibly strong. So strong that time and space as we know it don't exist in the singularity.

Diameter

The diameter of a black hole depends on the mass of the original object that becomes a black hole. If Earth became a black hole, it would have a diameter of about 0.017 meters — about the size of a marble.

Spaghettification

Spaghettification is the infinite vertical stretching and horizontal compression of objects into long thin shapes ( like spaghetti). Near black holes, the stretching is so powerful that no object can withstand it, no matter how strong its components. 

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