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- 2021 - New discoveries include planets orbiting the stars. How pulsars were used to find these planets. Some discoveries occurred inside Albert Einstein s head, he called a thought experiment. Robert Millikan used oil drops to discover the electric charge on an electron. In 1851 a pendulum was used to learn how fast the Earth was rotating. To learn more read Review Number 2021.
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- In 1992, 60 years after discovering Pluto, astronomers discover a new planet orbiting a distant star. By observing light from the star and measuring wavelengths they could determine that the star moved back and forth as if a planet was circling it. The light was red shifted and blue shifted as the light source moved away from us and then towards us.
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- Pulsars are the remains of supernovae explosions. Their rotation results in rotating beams of light exiting the poles. The rotating Neutron Star is compact only 12 miles in diameter. It is super dense and has a precise , constant rotation. This star with orbiting planets will have a clock lile wobble due the gravitational influence of its orbiting planets.
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- You would think that a supernova explosion would blast away any orbiting planets. However, somehow, orbiting a pulsar was the first exoplanet to be discovered.
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- The teacher asked the students, “How would you discover the size of the Earth before airplanes?”
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- It took the ancients many decades to discover that the Earth was not flat, it was round. They began to realize the curvature when sailing ships went over the horizon, you could still see their sails. Then, they saw a Lunar eclipse with the Earth’s circular shadow on the Moon. Their sailing ships also realized that the stars in the Southern Hemisphere could not be seen in the Northern Hemisphere.
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- You will be surprised to learn who first measured the size of the Earth. It actually happened in 250 BC. Eratosthenes was a Greek scholar who figured out why in the town of Syene they experienced no shadows looking down the well at high noon. But, during the summer solstice at noon the wells in the city of Alexandria did. He measured the distance between the two cities using camel drives. He knew how far camels can walk each day. He measured the angle of the shadow in Alexandria. He used simple geometry. He came up with a calculation that the Earth was round with a circumference of 28,000 miles. Of course his units were not miles, but, his calculation was within 10% of today’s number.
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- Einstein’s experiment was a “thought experiment“. No camels were needed. He thought that if he raced his bicycle along side a beam of light what would he see?
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- He knew that light was an electromagnetic wave. He figured that the light wave would be frozen as he raced along side it at the same speed. Would it be possible for him to travel that fast?? He did the math. What fell out was the Theory of Special Relativity.
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- His next trick was to imagine he was in an elevator with no windows. He cut the cable and went into free fall. He would experience the same weightlessness as in free space. His conclusion was that he could not tell the difference between acceleration and the pull of gravity. Inertial mass and gravitational mass were identical. What fell out of that thought experiment was the math for the Theory of General Relativity.
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- In 1909 Robert Millikan knew that an electric charge existed. He knew the charge was carried by electrons. But, what was the amount of charge carried by each electron. How could he possibly measure one electron?
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- Well, use oil drops , of course.
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- He dropped drops of electrically charged oil drops into a vacuum. Their terminal velocity would be due to the pull of gravity. If you calculate the drops velocity, the density of air left in the vacuum chamber, the density of the oil, the strength of gravity, and “viola” the math can calculate the mass of the drops.
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- Now, apply an electric field around the chamber. When the electric field balanced the falling drops with that gravitational force he could calculate the electric charge on each drop. After many, many measurements he determined the charge on an electron to be 1.6*19^ coulombs. That amount of charge was fundamental. It is always the same for every electron.
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- In 1851 physicist Leon Foucault decided he could suspend a pendulum and the Earth would rotate underneath it. The pendulum would always maintain its original plane. It would trace the rotation of the Earth on the floor beneath it.
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- He constructed his biggest pendulum in the Pantheon in Paris, France. He showed everyone how the Earth was rotating 11.3 degrees per hour. Times 24 hours equals 271 degrees. A more accurate experiment would measure 15 degrees per hour.
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- In the 1950s astronomers were studying mysterious radio waves from unknown sources in the night sky. In 1963 a paper was written declaring the sources to be 2.4 billion light years away. They were so powerful yet appeared as the faintest of stars. They got the name “quasi-stellar objects” , or quasars..
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- Later many of the same objects were found far beyond the Milky Way. Not knowing what they were astronomers came up for many different names for them. Eventually they realized they were all the same objects viewed from different directions and orientations. The energy came from blackholes at the centers of distant galaxies. The material orbiting around and cascading into the center of the blackhole were generating the enormous amount of energy.
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- Now, in 2017, astronomers have discovered gravity waves , which are the stretching of spacetime, followed by a flash of gamma rays. Gamma rays are the highest energy form of light. The source was found to be two neutron stars spiraling around each other, then merging , and maybe creating a blackhole.
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- LIGO, the gravity interferometer in Louisiana, detected the gravitational waves on August 17, 2017. Then there was a second LIGO detection in Washington State milliseconds later. After that a gamma ray burst was detected, 1.74 seconds later. They showed that the two neutron stars were circling each other some 1,500 times before merging.
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Eleven hours later optical and infrared telescopes got the spectrograph identifying the chemical elements, iron and gold created in the collision. These were some of the elements thrown into outer a space to become new stars and planets.
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- On September, 2015, LIGO detected two blackholes merging. They had Solar Masses of, 29 and 36 suns. The merger created a new blackhole of 62 Solar Mass. The remaining 3 Solar Mass was radiated away as gravitational waves traveling at the speed of light, 186,000 miles per second.
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- LIGO’s wave detection is amazing. These two instruments have two perpendicular arms that only stretched their laser beams 1/1000 the width of a proton.
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- In December, 2015, another detection was of a merger of two blackholes, 8 and 14 Solar Mass. Later, on January 4, 2017, LIGO detectors measured a 19 and 31 Solar Mass merger of two blackholes.
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- The blackhole pairs are gravitationally bound. By emitting gravity waves they drain their orbital energy. Eventually, over billions of years, the orbits shrink into a collision. These final seconds are when the gravitational waves are powerful enough for LIGO to detect them.
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- These new detections will allow astronomers to confirm that gravity waves don’t disperse and all frequencies travel at the same speed through space, the speed of light.
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- Neutron stars should also emit gravitational waves. If these high density rotating stars produce circumference bulges of only a few inches they should continuously radiate gravitational waves.
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- These gravity wave detectors may even become sensitive enough to study supernovae explosions and cosmic strings. Who knows what we may find with these new telescopes steadying the cosmos? We might even detect the source of Dark Matter.
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----- 707-536-3272 ---------------- Friday, February 16, 2018 -----
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