- 1687 - Astronomers are no longer limited to visible light when studying the heavens. Today’s technology launches detectors into orbit that can “see” much more of the electromagnetic spectrum, from infrared to Gamma Rays. This review focuses on what astronomers have learned with X-ray telescopes.
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- What if you were like Superman and had X-ray vision? What would the Universe look like? Astronomers have been looking through a slot in the electromagnetic spectrum only 300 nanometers wide for most of history. Visible light spans from blue light at 400 nanometers to red light at 700 nanometers wavelengths.
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- The shorter the wavelength the higher the energy in the radiation.
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------------------------ Energy = Planck’s Constant * Speed of Light / wavelength of light.
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---------------------- E = h * c / w
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- The shorter the wavelength the higher the energy. Infrared radiations with a longer wavelength than visible red light at 700 nanometers was discovered in 1800. For the first time we could see what our eyes could not see. Then shortly after, in 1801 , ultraviolet radiation was discovered with wavelengths shorter than 400 nanometers. Ultraviolet waves carry more energy and can burn the skin with rays you can not see.
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------------------------- Microwaves were discovered in 1864
------------------------ Radio waves in 1887
------------------------ X-rays in 1895
------------------------ Gamma Rays in 1900
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- The slot in the electromagnetic spectrum through which we peer gets wider and wider.
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- Energy wise visible light ranges from 1.6 electron volts to 3.4 electron volts. That is a very little amount of energy, but, all your eyes need to see what’s out there.
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- X-rays with far shorter wavelengths have energy ranging from 3,000 electron volts to 79,000 electron volts. That much energy can penetrate right through your body. Lucky for us the Earth’s atmosphere absorbs this X-ray radiation from space before it gets to the surface of Earth.
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- Astronomers have to go into orbit, into space, to measure and “see” X-ray emissions in outer space. With these new eyes astronomers can study Blackholes, Blazars, supernovae, and our Sun. Images never before seen.
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- The accretion disks of Blackholes contain higher energy because the orbiting particles rub together and friction reaches high enough temperatures to emit X-rays. As material is falling into a Blackhole X-rays are radiating away. This is how astronomers can “see” a Blackhole.
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- Blazars are seen when the jets at the rotating poles of the Blackhole’s accretion disk points directly at our line of sight.
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- NuSTAR is an X-ray orbiting telescope launched in 2012.
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- Chandra X-ray telescope was launched in 1999.
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- Here are some of the astronomical discoveries astronomers have made with their new X-ray eyes:
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- X-ray emission from galaxy clusters have been used to calculate their temperature, density, and mass. Comparing clusters in today’s cosmos with those present 5.5 billion years ago allows the growth of these clusters to be calculated. Modeling slower growth in the past and faster growth in the present has determined that the ratio of repulsive energy is 70% and attractive energy, gravitational energy is 30%. We call the 70% Dark Energy and the 30% matter. Only 5% if the matter is visible, 25% is Dark Matter that we can not see.
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- Every large galaxy has a super massive Blackhole at its center. X-ray emissions come from the hot gasses surrounding an active Blackhole. Calculating the amount of energy released has shown astronomers how Blackholes can create galactic structures a billion times larger than themselves.
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- X-rays have detected hot gases between the galaxies. In fact, the mass of these hot gases exceeds the mass of the galaxies by a factor of 7 times. Normal Matter , that is visible matter, can account for only a small fraction of the total mass present. The rest must be Dark Matter that we can not see.
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- X-rays have discovered several dozen pairs of Blackholes that are circling each other. Eventually the two Blackholes will merge as they loose energy, energy that we believe is radiating away in the form of gravitational waves.
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- X-ray observations of the Blackhole at the center of the Milky Way Galaxy have detected X-ray flares much like the flares radiated by our own Sun.
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- The Supernova 1987 is the nearest to Earth. X-rays track the shockwave that has been heating up cold gas in the interstellar medium as it explodes into space.
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- By measuring the wavelengths of the individual elements formed in the supernova explosion astronomers can map the images of oxygen, silicon, sulfur, magnesium, and iron. The individual elements are tracked as they travel inside the exploding structure of the supernova remnants.
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- Uniform X-ray signals across the sky create an X-ray “ background”. Much like the cosmic microwave background that exists. Although it appears uniform, high resolution from the Chandra telescope has identified enough individual point sources to account for the total background signal. They are Blackholes at the centers of most galaxies.
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- These are a few of the discoveries X-ray telescopes have brought to astronomy. The first observations were made in 1978. NuSTAR is the latest X-ray telescope launched in 2012. Chandra launched in 1999. Chandra measures “ soft X-rays” in the 0.1 to 10,000 electron volt range. NuSTAR measures “ hard X-rays” in the 3 to 78,000 electron volt range.
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- Astronomers can create images detected in X-rays by translating them to lower frequencies and into the range of visible light that our eyes can recognize. This is like heterodyning in AM radios that translates radio waves down to acoustic waves that our ears can recognize. New discoveries are certain to occur, stay tuned.
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