--------------------- #1508 - Are there Blackholes in our own Galaxy?
- Most people have learned by now that there is an enormous Blackhole at the center of the Milky Way Galaxy. It has the name Sagittarius A*. ( pronounced A star ). You can find it on the southern horizon in the Constellation Sagittarius the Archer. The shape of the star constellation is a perfect “teapot”. The Blackhole is at the spout of that teapot just 26,000 lightyears away.
-
- Most people will probably be surprised to learn the astronomers have found 18 other Blackholes in our Galaxy. Blackholes are hard to find. Astronomers estimate that there are millions more Blackholes that remain undetected. Blackholes are invisible because no light can escape. Astronomers can only find Blackholes due to their gravitational effects on neighboring objects. When gas or stars are orbiting an invisible center at abnormally fast speeds, or when the orbiting gas gets superheated and emits X-rays or Gamma Rays, then the invisible center could be a Blackhole.
-
- The invisible center could also be a Neutron Star that is very small and emits almost no radiation. In order to determine which is right astronomers need to make accurate measurements of the mass and the radius of the orbiting gas or star.
-
- Neutron Stars are created when an 8 Solar Mass star ends its life exhausting all of its nuclear fuel. With no fuel to create outward radiation the inward pressure of gravity causes the star to collapse. When all of the star’s mass reaches the center it rebounds into a giant shockwave. It becomes a brilliant supernova explosion that is 10 billion times the brilliance of our Sun. What is left behind is a Neutron Star that is less that 3 Solar Mass and 12 miles in diameter.
-
- Blackholes are created when a 30 Solar Mass star ends its life. The supernova explosion is much greater and the core left behind is greater than the 3 Solar Mass. A dead star of mass greater than 3 Solar Mass has so much gravity not even the neutrons at the core can withstand the pressure. The radius collapses even further. The mass / radius ratio passes the threshold that even light speeds can not achieve the escape velocity needed to leave the core. The core becomes a Blackhole with an Event Horizon right at the point that light is bent backwards into the core never to escape. ( See footnote 2 to learn more about Escape Velocity and why the ratio mass / radius determines when the star becomes a Blackhole. )
-
- Beyond the edge of the Event Horizon gas and particles, and stars, can orbit without being pulled into the Blackhole. However anything that passes inside the Event Horizon is removed from the Universe never to return. How big is the Event Horizon?
-
- For a non-spinning 10 Solar Mass Blackhole the Event Horizon is 37 miles across. For a 20 Solar Mass Blackhole the Event Horizon is 74 miles across. Doubling the mass doubles the diameter. If the Blackhole is spinning and it is spinning at its maximum rate the diameter is half that of a non-spinning Blackhole of the same mass.
-
- Astronomers can never see the Blackhole itself. However, they can see the accretion disk of material that is orbiting beyond the Event Horizon. The friction created by the rapid rotation of gas and particles heats up the gas to millions of degrees. The extremely hot gas begins emitting X-rays. Astronomers detect the X-rays and can make measurements of velocities and radii that will be used to calculate the mass at the center. If it is more than 3 Solar Mass the center must be a Blackhole. Binary Stars orbiting a Blackhole are the easiest to measure and all 18 discovered so far have been X-ray binaries.
-
- A binary pair of stars orbiting each other, and one of the stars is invisible, and, the companion star is the telltale indicator of the mass of the invisible star. Measurements are made of the orbiting speed of the companion star. Distances are measured of the orbits about the center. Knowing the mass and radius will allow calculations to be made of the mass of the invisible star. If it is less than 3 Solar Mass it is a Neutron Star. If it is more than 3 Solar Mass it is a Blackhole.
-
- These measurements have been made accurately on 18 binary Blackholes. 20 more have X-ray signatures of invisible orbiting binaries but measurements are not yet precise enough to definitely say they are Blackholes and not Neutron Stars. Many more Blackholes exist in our Galaxy. But, unless there is a binary star or orbiting X-ray material there is no way to tell the Blackhole is there.
-
- The Blackhole at the center of our Galaxy is 4 million Solar Mass. Its Event Horizon is 15 million miles across, which is the diameter of 17 Suns side by side. The Blackhole is 26,000 lightyears away. 4 million Solar Mass is an enormous mass. But the Galaxy in total is 10^12 Solar Mass. So, 4*10^6 Solar Mass is only 0.0004% of the total Galaxy‘s mass.
-
- Sagittarius A* has a spinning accretion disk that is 140 million miles in circumference completing a rotation ever 24 minutes. The material is traveling 34 million miles per hour. The radius of the orbiting material is 22 million miles.
-
- One other Blackhole among the other 18 is 37,000 lightyears away. It is 10,000 Solar Mass and has a diameter of 4.7 Earths.
-
- Another is 10 Solar Mass and has a diameter of 37 miles, about the size of Rhode Island.
-
- The 18 Blackholes so far discovered are all X-ray Binaries ranging is size from 4 to 15 Solar Mass.
-
- They range in distances is from 3,400 lightyears away to 86,000 lightyears away.
-
- The companion stars range in brightness magnitudes form 8.9 to 18.2 Magnitude. They have orbiting periods ranging from 4.1 hours to 155.3 hours.
-
- The second biggest Blackhole, outside of Sagittarius A*, is Cygnus X-1 having a 15 Solar Mass. Its companion star is a Blue Supergiant Star of 19 Solar Mass. It has a magnitude of 8.9 and can be viewed in the Constellation Cygnus the Swan with an amateur telescope. It is 6,100 lightyears away.
-
- The companion Blue Star orbit’s the Blackhole in 134.4 hours ( 5.6 days ). The average distance between the binaries is half the distance between the Sun and Mercury. The orbiting velocity is 90% of the theoretical maximum and it is the brightest X-ray source in the sky.
-
- Unless a Blackhole actively feeds on material from another star or other material it will not have an accretion disk and it will not be visible. Lonely Blackholes are truly black. Outside our Galaxy almost every other large galaxy has a massive Blackhole at its center. In 1990 most astronomers were not convinced Blackholes even existed. Now, we are convinced they are more common than every imagined. An announcement will be made shortly, stay tuned.
-
------------------------------------------------------------------
(1) Other reviews available #1441, # 1350 about Cygnus X-1, and still 11 others if you want the index.
-
(2) The definition of a Blackhole is a mass of so much gravity even light can not escape. We can calculate Escape Velocity. And, we know the velocity of light is 186,282 miles per second.
-
- Escape Velocity squared is directly proportional to the mass and inversely proportional to the radius.
-
------------------------------ (Ve)^2 = constant * M / r
-
- The bigger the mass the faster the velocity needed to escape its gravity. The smaller the radius the faster the escape velocity needed. Any proportionality can be turned into an equality with the proper “constant of proportionality“. In this case the constant is 2 * the Gravitational Constant.
-
------------------------------- (Ve)^2 = (2*G) * M / r
-
-------------------------- The Gravitational Constant, G = 6.67*10^-11
-------------------------- If we make the Escape Velocity, Ve = the speed of light, then (Ve)^2 = 9*10^16
-
------------------------- 9*10^16 = ( 13.3*10^-11 ) * M / r
------------------------- r = ( 1.5*10^-27 ) * M
-
- If we normalize this equation to us Solar Mass as the unit in kilograms, which is 2*10^30 kilograms, the equation reduces to:
-
--------------------- r = 3 * M
-
- r is in kilometers and M is in Solar Mass.
-
- This becomes a very simple formula to calculate the radius of the Event Horizon of the Blackhole. The Milky Way Blackhole is 4,000,000 Solar Mass. The radius of its Event Horizon is 12,000,000 kilometers. A diameter of about 15 miles.
-
(3) Why is the Escape Velocity squared equal to the ration of Mass to radius?
-
------------------------------- (Ve)^2 = (2*G) * M / r
-
- We get this equation setting the balance or the equality of two opposing Energies, the Kinetic Energy needed to escape the pull of gravity and the Potential Energy of gravity trying to push towards the center not allowing any escape.
-
------------------ The equation for Kinetic Energy = ½ * mass * (velocity)^2
-
------------------ The equation for Potential Energy = G *mass * Mass / radius.
-
- The Event Horizon occurs when these two energies cancel out being equal to each other.
-
------------------ ½ * mass * (velocity)^2 = G * mass * Mass / radius.
-
------------------- ( velocity ) ^2 = (2*G) 8 Mass / radius.
-
- Use this formula to determine how fast you would have to throw a baseball in order to escape Earth’s gravity? From the Earth = 25,000 miles per hour.
-
--------------------------- From the Sun = 1,375,716 miles per hour
-------------------------- From a Blackhole = 670,633,500 miles per hour, but nothing can travel faster than the speed of light so the baseball could never escape.
-
(4) CAUTION: It is important to note that these calculations are illustrative. They are all Isaac Newton’s physics. When we approach the speed of light, when gravity becomes as intense as a Blackhole, light and space bend, time slows, and Albert Einstein’s equations come into play. You need to employ equations of Relativity to get more precise answers to these questions.
-------------------------- ------------------------------------------------------------------
RSVP, please reply with a number to rate this review: #1- learned something new. #2 - Didn’t read it. #3- very interesting. #4- Send another review #___ from the index. #5- Keep em coming. #6- I forwarded copies to some friends. #7- Don‘t send me these anymore! #8- I am forwarding you some questions? Index is available with email and with requested reviews at http://jdetrick.blogspot.com/ Please send feedback, corrections, or recommended improvements to: jamesdetrick@comcast.net.
or, use: “Jim Detrick” www.facebook.com, or , www.twitter.com.
707-536-3272, Saturday, November 3, 2012
No comments:
Post a Comment