Black Holes: The Weird Science of the Most Mysterious Objects in the Universe
The force acting on an object is equal to the mass of that object times its acceleration In mathematical form it is expressed like this F ma where F is force m is mass and a is acceleration For every action there is an equal and opposite reaction Newton used those laws in a thought experiment to try to understand the motion of the planets It went something like this What if he were to shoot a cannonball from the top of a very high mountain where just as in outer space there is no air resistance Without a force to act on it the cannonball would continue in a straight line forever But in reality Newton knew that the cannonball would move forward and eventually drop back to Earth Newton came up with the idea of gravity to name the downward pulling force acting upon the cannonball Isaac Newton 1642 1727 was a physicist and mathematician He laid out what he understood about laws of motion the behavior of fluids and gravitation in his book Philosophiae Naturalis Principia Mathematica The book established Newton’s reputation as one of the greatest minds of science 8 BLACK HOLES
Newton reasoned that the faster the cannonball was moving the farther forward it would travel before dropping to Earth If the cannonball were moving fast enough it would fall into an orbit around Earth instead of into it much as the moon orbits Earth If it moved really fast it would reach escape velocity leaving Earth and its orbit altogether He realized that the same force gravity that pulls an apple to Earth when it falls from a tree could also explain the orbits of the moon around Earth and the planets around the sun Newton’s law of universal gravitation published as part of the Principia states that the gravitational force between any two objects in the universe is proportional to the product of their masses The gravitational force is inversely proportional to the square of the distance between the center of each mass So more massive objects have greater gravitational pull than less massive objects And that gravitational pull gets weaker with distance Fast-forward to 1783 in a village in West Yorkshire England The head of the parish in the village a brilliant clergyman named John Michell had an unusually keen interest in science He met with some of the leading scientists of the time including Benjamin Franklin and published influential papers about the nature of magnetism astronomy and earthquakes He was trying to figure out a way to measure the mass of distant stars He concluded that the gravity of some really massive stars might be so great that not even light could escape them Michell published his calculations in a paper that described a universe with many invisible dark stars The only way to detect them he said would be to observe their gravitational effects on nearby objects 9 WHAT IS A BLACK HOLE
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
