- 3574 - BLACKHOLES - wonders of the universe? The second wonder of the Universe is a massive blackhole at the center of our Milky Way Galaxy. Its name is “Sagittarius A“. If you spot the “teapot” constellation in the southern sky it is just above the spout.
----------- 3574 - BLACKHOLES - wonders of the universe?
- Of course, the Blackhole is a dark spot because the center of our Milky Way is blocked by a large intergalactic dust cloud. Astronomers are tracking stars with infrared telescopes that can see through the dust. Their orbits around Sagittarius A are used to determine the mass of this blackhole.
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- It is 3,600,000 times the mass of our Sun. The only thing we know of that can be that massive in such a small space is a blackhole. It is a calculation not a direct observation.
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- The blackhole is spinning a complete rotation every 10 minutes. As blackholes go in the Universe this one is relatively quiet. There are only small amounts of infrared and X-ray flashes emanating from its accretion disk.
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- In contrast, the accretion disks of blackholes at the center of many galaxies are so active as to out shine all the billions of stars in the galaxy. In the Milky Way we have discovered this blackhole by tracking stars orbiting it.
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- If it were more active we could not even see these neighboring stars. Blackholes are truly black and there are only two ways to describe them or find them. One description is their mass and the other is their rotation. That’s it. No other light or information comes out of a Blackhole.
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- A star exists because nuclear fusion creates heat which creates outward pressure which counterbalances the inward force of gravity. When a star burns all of its fuel it can no longer produce heat, and therefore outward pressure, so the inward force of gravity wins the battle and collapses the star into a “neutron star” or a “singularity“. If the star is large enough and the gravity strong enough the star compresses into a Singularity at the center of a Blackhole.
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- A Blackhole is created because the gravity is so strong no energy can escape. No light, no electromagnetic radiation, no information of any kind can escape the blackhole once it has formed.
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- Normally things can escape a mass by obtaining an escape velocity fast enough to overcome the pull of gravity. The escape velocity for some mass leaving Earth is 25,000 miles per hour . This applies to any mass escaping Earth’s gravity, from a spaceship, to a baseball, to a gas molecule.
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------- The equation that describes this escape velocity is:
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-------------------- Escape velocity^2 = 2 * G * Mass Earth / Radius
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-------------------- Escape velocity^2 = 2 * G * Mass Earth / Radius
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-------------------- Radius of the Earth = 6.378*10^6 meters = 3,963 miles
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-------------------- Velocity = 11,200 meters/second = 25,054 miles per hour
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- The Sun is 300,000 times more massive than the Earth, so the escape velocity for the Sun is much faster, 1,500,000 miles per hour .
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-------------------- The radius of the Sun is 6.9599*10^8 meters = 432,470 miles
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-------------------- Velocity = 6.67*10^5 meters / second = 1.5*10^6 miles per hour, 1,500,000 mph.
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- A star 8 times more massive than the Sun would collapse into a blackhole and have an escape velocity greater than 671,100,000 miles per hour. This is faster than the speed of light. Nothing can exceed the speed of light, so this escape velocity can never be attained, so nothing can escape, so you have a Blackhole.
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- The other interesting part of this equation is that escape velocity depends on the radius. If you compressed the mass of the Earth into a sphere 3/4th inch in diameter it would become a Blackhole. All the Earth’s mass would shrink into a Singularity in the center of this Blackhole.
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-------- Schwarzchild Radius of the Earth if it becomes a Blackhole:
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----------------- Set the escape velocity = the velocity of light
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----------------- c^2 = 2 * G * Mass Earth / radius
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----------------- c^2 is the velocity of light^2 = 9 * 10^16 meters^2 / seconds^2
----------------- G = the Gravitational Constant = 6.67 * 10^-11 meters^3/Kg * sec^2
---------------- Mass of the Earth = 5.97*10^24 kilograms
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- Substitute into the equation and solve for radius:
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---------------- Radius = 8.85 * 10^-3 meters
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---------------- Radius = .348 inches
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- If all the mass of the Sun were compressed to a radius of 2 miles it too would become a Blackhole.
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- To become a blackhole a star must have an escape velocity greater than 300,000 kilometers/second, 671,100,000 miles per hour.
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- Schwarzchild Radius of the Sun if it becomes a Blackhole:
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------------------- Mass of the Sun = 1.9891*10^30 kilograms.
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- Substitute into the equation above and solve for radius:
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------------------- Radius = 2,950 meters = 1.83 miles
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- The radius of the Blackhole is called the “Event Horizon“. It is the spherical surface at a point where gravity overcomes all other forces. It is the line where everything turns black and nothing escapes.
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- There is no material at this surface, no material exists at the Event Horizon. Gravity continues to compress all material into a single point at the center, called the “Singularity“. The Singularity is where all the mass of the Blackhole is concentrated.
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- One misconception about Blackholes is that these become giant vacuum cleaners sucking in everything that is around them. This is not the case. The only force is gravity created by the mass in the Singularity.
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- If we did compress our Sun into a diameter of 4 miles and it became a Blackhole Singularity, all the planets in the Solar System would not notice a difference. All the orbits about the Blackhole would be exactly the same as they are with today‘s Sun.
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- However, they would notice it getting colder as none of the Sun’s radiation would be warming the Solar System any more. Light and heat would disappear when the Sun shrunk into a Blackhole.
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- The equation for gravity remains the same outside the Event Horizon of a Blackhole.
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--------------------- The force of gravity = G * mass1 * mass2 / radius^2
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- There is a Blackhole in the center of most every galaxy. At the center of our Milky Way the Blackhole is 4,000,000 times the mass of our Sun, 4*10^6 Solar Mass. Our Milky Way Blackhole is 26,000 lightyears away rotating once very 30 minutes.
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- Every massive star, >30 Solar Mass, lives for only 4,000,000 years, runs out of fuel, and in one second collapses into a Blackhole. There are millions of these Blackholes throughout our Milky Way Galaxy. The remnants of massive stars with short lives are everywhere. The closest Blackhole is 15 lightyears away, but others are spread all over the galaxy.
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- Most stars in the Universe are not single stars like our Sun. Most are binary stars, two stars orbiting each other. As one star is larger than the other, or one is older than the other, one will collapse into a Blackhole first.
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- The other star continues to orbit the Blackhole. The mass of the Blackhole creates tidal forces on the other star causing its shape to teardrop. The is much the same as the tides on Earth as the Moon causes the oceans on the near side of Earth to rise and the oceans on the far side to rise causing a flattening on the adjacent sides and bulges of high tides on either end facing and farthest from the Moon.
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- The difference with the Binary Blackhole is that the gravity is so great it not only causes the tides it actually pulls material away from the other star. The material spirals into the Blackhole forming an accretion disk around the Event Horizon.
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- The gas and material orbit at near the speed of light. Friction between the fast moving gas and material causes enormous heat, millions of degrees, which in turn creates X-ray radiation. This is how astronomers can see the Blackholes. X-ray telescopes can see the accretion disks of Binary Blackholes light up with a ring of X-rays.
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- The center of the Milky Way being a massive Blackhole, was discovered by studying the stars orbiting around the accretion disk. The stars were studied since 1992, and were found to be moving in ellipses around a center of mass and traveling at 4% the speed of light (12,000 kilometers/ second, 26,800,000 miles per hour). The Black Hole at the center has a mass of 4,000,000 Suns and is only 10 light-seconds in diameter.
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------------------- Calculating the mass of the Milky Way Black Hole using the velocity of an orbiting star.
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------------------- The star is in an elliptical orbit traveling at 4% the speed of light or 12,000 kilometers / second.
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------------------- If we assume the orbit is circular the equation for orbital velocity is:
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------------------- Orbital Velocity^2 = G * Mass / radius
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------------------- The radius is 500 times the Event Horizon = 5.895*10^12 meters. The is 819 light seconds, or 3.6 billion miles.
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Substituting into the equation:
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------------------- Mass of the Blackhole = 127 * 10^36 kilograms.
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------------------- Dividing by the Solar Mass = 64,000,000 solar mass.
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- The calculation using Relativity equations = 4,000,000 solar mass. So, our equations from Kepler start to break down at 4% the speed of light and we have to use Einstein’s relativity equations. I have yet to master those equations.
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--------- The radius of the Event Horizon in the Milky Way Black Hole.
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- If the mass of the Blackhole is 4 million solar mass we can calculate the radius of the Event Horizon.
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------------------- C^2 = 2 * G * Mass Earth / radius
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- Substituting into the equation:
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------------------- Radius = 11.79*10^9 meters = 7.3 million miles
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------------------- Radius = 1.64 light seconds.
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- Again, using relativity equations the answer is 2 million miles, 10 light seconds, but astronomers and theoretical physicists are still wrestling with these calculations. We are getting closer to the right answers, but there is always more to learn.
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- The center bulge of the Milky Way has a mass of 1,000,000,000,000 solar mass. The mass of all the stars is 100,000,000,000 solar mass. That means that 90% of the total mass is Dark Matter and only 10% is ordinary matter found in the stars.
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- The fact that we can see the stars at the center of the Milky Way means that the galaxy’s Blackhole is relatively quiet. The accretion disk does emit some X-rays and some infrared radiation but not enough to outshine the neighboring stars.
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- In many other galaxies the radiation from the Blackhole accretion disk is so bright it appears as a point source outshining all the stars in the whole galaxy, brighter than more than 1,000,000,000,000 of the galaxy’s stars.
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- Blackholes and accretion disks are the source of “Quasars“, “Gamma Ray Bursters“, “Magnetars“, and other astronomical phenomena. When the accretion disks pulls an extensive amount of gas in the orbiting gas becomes ionized creating a magnetic force.
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- The Blackhole itself can not have any magnetic force, but the orbiting gas in the disk can. The magnetic force becomes so great it shoots jets of gas and radiation out the poles of the accretion disk with tremendous energy.
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- Blackhole accretion disk rotations have been measured from one rotation in 10 minutes to 1,000 rotations per second. The energy released in 10 seconds along the gamma ray jets can exceed all the energy released from our Sun over its entire lifetime, 10 billion years.
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- When rotations become extremely fast, approaching the speed of light, the General Theory of Relativity requires distortions in space and time. The Singularity becomes a ring rather than a point.
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- The disk experiences “frame-dragging” that drags space and time around with it, time is slowed, and gravity causes a red-shift in radiation. Blackholes become the labs to study these strange effects of General Relativity as rotational velocities approach the speed of light.
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- We do not understand what happens inside a Blackhole because as the mass concentrates into a Singularity all the Theories of Relativity break down. Gravity can not be calculated at the quantum level.
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- We need a new theory that combines relativity and quantum mechanics for the force of gravity before our math can deal further.
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May 7, 2022 BLACKHOLES - wonders ? 578 592 3567
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