Black Holes: The Weird Science of the Most Mysterious Objects in the Universe
THE ELECTROMAGNETIC SPECTRUM Light electromagnetic waves and radiation all refer to the same thing electromagnetic energy EM Electromagnetic energy is created when a charged particle such as an electron is accelerated through an electric field This movement produces oscillating electric and This infographic illustrates the range of electromagnetic wavelengths Longer radio waves are less energetic while shorter gamma rays are super energetic Wavelengths in the middle of the range are associated with the light we can see with our eyes Scientists have developed telescopes that can detect a wide range of wavelengths across the spectrum They play a key role in observing black holes
the shorter the wavelength the higher the frequency of the waves and the more energetic the photons The opposite is true too the longer the wavelength the lower the frequency of the waves and the less energetic the photons This range of wavelengths frequencies and energy is known as the electromagnetic spectrum from radio waves low energy to gamma rays high energy In between are the wavelengths of the visible spectrum the light that our eyes can see magnetic fields traveling back and forth at right angles to one another in a packet of energy called a photon Photons travel in a wavelike pattern at the speed of light Unlike sound waves electromagnetic waves can travel through the vacuum of space Scientists describe EM according to wavelength frequency and energy The wavelength measured in meters is the distance between peaks tops of a wave Frequency is the number of waves that form in a given length of time One wave or cycle per second is called a hertz Each photon varies in energy measured in electron volts We say that a higher energy photon is more energetic All three characteristics are related 11
French mathematician and astronomer Pierre-Simon Laplace independently came to the same conclusion just over a decade later In his 1796 book Exposition du système du monde Explanation of the System of the World Laplace referred to black holes as black stars writing It is possible that the greatest luminous light-filled bodies in the universe are invisible You’ve got to give Michell and Laplace major props for predicting the existence of dark or black stars but they made one critical mistake They believed as did Newton that light was made up of tiny particles called corpuscles These corpuscles were thought to have mass and because they had mass gravity would pull on them Scientists such as James Clerk Maxwell soon discovered however that visible light is actually a form of electromagnetic radiation Scientists understood that electromagnetic radiation has no mass As the corpuscle theory of light lost favor so too did the idea of a dark black star WHAT’S THE MATTER As scientists were beginning to understand the nature of light they were also gaining new insight on matter the stuff that makes up the universe at least the stuff that we can detect The concept of the atom had been around since the ancient Greek philosopher Democritus ca 460 370 BCE upended the accepted notion that the universe was made of four elements earth air fire and water He described the universe this way by convention sweet and by convention bitter by convention hot by convention cold by convention color but in reality atoms and void Atoms from the Greek word atomos 12 BLACK HOLES
meaning indivisible Democritus said were different sizes and shapes and they all moved about in a void of nothingness Centuries later English chemist and physicist John Dalton came up with a scientific theory about atoms based on his experiments with gases In 1803 he proposed that each element such as hydrogen carbon or iron had its own kind of atom and that these atoms varied in size and mass He was right but like Democritus he believed that atoms were indivisible little spheres of matter It wasn’t until 1897 that English physicist J J Thomson found a particle even smaller that the atom the electron Thomson proposed that an atom was actually made of a ball of positively charged matter studded with negatively charged electrons It became known as the plum-pudding model in which the bulk of the atom the positively charged pudding was studded with negatively charged electrons In a series of ingenious experiments in 1909 Thomson’s student a New Zealander named Ernest Rutherford showed that at the center of each atom is a small dense and positively charged nucleus He published his results in 1911 In the years that followed scientists established that the nucleus is actually made of smaller particles positively charged protons and neutrons which have no charge A cloud of negatively charged electrons surrounds the nucleus Over time scientists found even more basic building blocks of matter In 1964 for example physicists Murray Gell-Mann and George Zweig proposed that neutrons and electrons are made of even smaller 13 WHAT IS A BLACK HOLE
