--------- #1273 - Are Astronomical Mergers in our Future?
- Mergers are going on all the time in our Universe. Some are large, some are relatively small. Our galaxy is relatively quiet right now. We should use this time to study what might happen when these mergers do occur?
- Attachments - Neutron Stars Merging
- A supercomputer is used to program the laws of physics and simulate what would happen if two orbiting Neutron Stars merged together. The computer create 6 frames of time as the merger progresses.
------------------- Frame ----------- Time ----------------- Width of Image
------------------- 1 ----------- 0.0 seconds ---------
------------------- 2 ----------- 0.007 seconds --------- 0.0 millimeters
------------------- 3 ----------- 0.014 seconds --------- 18 millimeters
------------------- 4 ----------- 0.015 seconds ---------
------------------- 5 ----------- 0.021 seconds ---------
------------------- 6 ----------- 0.026 seconds --------- 20 millimeters
- The width of each frame corresponds to 48 kilometers and is 48 millimeters wide. Therefore the scale is 1 kilometer per millimeter.
- Each Neutron Star is 1.4 Solar Mass.
- To determine how fast the stars are approaching each other measure the distance of separation between frames 0.007 seconds and 0.014 seconds. It is 18 millimeters or 18 kilometers in 0.007 seconds. That corresponds to a velocity of 18 kilometers per 0.007 seconds = 2,600 kilometers / second. 1 km/sec = 2,237 mph. Therefore, the stars are approaching each other in a descending spiral at 5,816,200 miles per hour.
- The last image shows the merger of the two Neutron Stars to be 20 millimeters across. Will it become a Blackhole?
- The radius of a Blackhole is directly proportional to its mass:
----------------- r = constant * M
- A proportionality can be changed in to an equality with the proper constant of proportionality. In this case the constant is:
---------------- r = (2 * G / c^2 ) * M
---------------- where G = Gravitational Constant
---------------- G = 6.67*10^-11 m^3 / ( kg*sec^2)
--------------- c = speed of light
-------------- c = 3*10^8 meters per second
--------------- c^2 = 9 * 10^16 m^2 / sec^2
-------------- r = 1.48 * 10^-27 m * M / kg
-------------- Converting this result in terms of Solar Mass, where Solar Mass = 1.98*10^30 kilograms
-------------- r = 2,930 m * M Solar Mass
- This formula is usually shown as --------------- r = 3* M
where: “r” is kilometers and “M” is in Solar Mass.
- The Neutron Stars each have a mass of 1.4 Solar Mass, so, the total is 2.8 Solar Mass after they merge.
-------------- r = 2.930 km * 2.8 Solar Mass
---------------- r = 8.2 kilometers for the Blackhole.
- The actual diameter of the merger is 20 kilometers, or a radius of 10 kilometers, therefore, the radius is too large to form a Blackhole. The merger will remain a bigger Neutron Star and go supernova. It will not collapse into a Blackhole.
- Exiting from the image of the last frame is a beam of radiation exiting the rotational poles. A protractor is used to measure the width of the beam and it is 30 degrees. What would the width of the beam be when it gets to us? We are 5,000,000 lightyears away. The circumference of the circle at that distance is 2*pi *r = 31.4* 10^9 lightyears. 30 degrees is 1/12th of the circumference. Therefore, the width of the beam when it reaches us is 2.6 billion lightyears.
- The above scenario was a computer model for the merger of two Neutron Stars. Astronomers are currently monitoring the actual merger of two White Dwarf stars. White Dwarfs are remnants of a supernova that are low mass, less than 1.4 Solar Mass. If they were larger they could collapse into a Neutron Star. A White Dwarf with the mass of the Sun is compressed into a volume the size of the Earth. A Neutron Star with the mass of the Sun is compressed into a volume a few kilometers in radius. The reason the star collapsed is the gravity was so intense the electrons collapsed into the nuclei of the atoms forming neutrons. The neutrons are so dense a penny of this material on Earth would weigh 1,000 pounds.
- Because the two stars are orbiting so close together their mutual gravity pulls the equator out of the lower mass star by 3%. If that were the Earth the tides would be 120 miles high. However, at this point the stars are not close enough to each other to begin exchanging material.
- The White Dwarfs complete their orbits in 13 minutes, eclipsing each other every 6 minutes. The orbits are so repetitive, they make an excellent clock. The White Dwarfs are traveling at 370 kilometers per second, which is 1,332,000 miles per hour. At their current rate of descent they will collide in about 900,000 years from now.
- The brighter White Dwarf contains 25 % Solar Mass compressed into the volume the size of Neptune. The companion, dimmer, White Dwarf is 50% Solar Mass compressed into the volume the size of the Earth. The density of these stars is so great a penny of this material on Earth would weigh 1,000 pounds.
- The reason these two stars will not orbit each other forever is because they are loosing energy in the form of gravitational waves. This has not been conclusively proven because we have yet to detect gravity waves. However, General Relativity equations predict that these large rotating masses would create ripples in the fabric of space-time. These ripples, or waves, carry away energy causing the stars to loose angular momentum energy and to spiral into each other on descending orbits. That is what will cause them to collide in 900,000 years from now.
- Neutron Stars merge, White Dwarfs merge, even galaxies are merging. When galaxies merge they create massive Blackholes at their core that are billion of Solar Mass. So far, the Blackhole at the center of our Milky Way Galaxy, named Sagittarius A, is quiet. It is about 4,000,000 Solar Mass with a volume the size of our Solar System. We do not see any mergers in its near future. Nor, do we see the Sun merging with another star in the near future. But, you never know, things could change. An announcement will be made soon, stay tuned.
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707-536-3272, Friday, July 15, 2011
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