- 3582 - BINARY STARS - more common than expected? We think of stars as being single points of light in the night sky. However, most stars are not single, most stars are binaries. Binaries are 2 stars in gravitational orbit around each other, actually around a single point that is their center of gravity.
------------------ 3582 - BINARY STARS - more common than expected?
- When binaries get close enough together they create a balance between their centripetal force and gravity and can exchange material between them. When this happens all sorts of celestial objects can be created:
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----------------- X-Ray binaries
----------------- Variable stars
----------------- Novae
----------------- Supernovae
---------------- Gamma Ray Bursters
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- In the life of a star it is the initial mass that determines its fate. Big stars die young. Medium stars like our Sun lives 10,000,000,000 years. Our Sun is about 5,000,000,000 years old today. Happy Birthday Sun!
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- Small stars and Brown Dwarfs live for an eternity. The fate of binaries gets more complicated with two masses and different chemical compositions. Here are some examples:
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- Eta Carinae is a binary star in the process of ejecting their common envelope.
- ( See Review 832, “ The next Supernova in our Galaxy”.
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- Cygnus X-1 is an X-ray binary.
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- Radio source “PSR1913+16” are binary pulsars in rapidly decaying orbits. The energy calculated in the loss of angular momentum as the orbit shrinks exactly matches the loss by gravitational radiation predicted by Einstein’s Theory of Relativity.
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- Astronomers are trying to detect these gravity waves being emitted from PSR1913+16 using a gigantic laser interferometer. Gravity is a very weak force and we are just learning how to detect this radiation.
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- Stars are formed in the gravitational contraction of dense interstellar clouds of gas and dust. Once a certain point is reached a rapid collapse occurs lasting only 100,000 years. The density of the star core reaches temperatures needed to ignite a thermal nuclear reaction and the star is born.
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- Using AU, astronomical units, as the distance from the Sun to Earth, here are the steps in the gravitational contraction:
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---------------- 200,000 AU ------------ Dark cloud of gas and dust
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---------------- 10,000 AU ----------- Collapse by gravity over 100,000 years
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--------------- 500 AU ----------- Protostar
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-------------------- 100 AU ----------- Star that has completed accumulating its mass.
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----------------------- 50 AU ---------- Star and planets in a solar system after 50 million years.
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- The interstellar clouds of gas and dust are rotating at different rates. The rotations create friction between the gas molecules and electrons are stripped off creating ions and charged particles in the cloud.
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- The giant cloud is supported by these magnetic fields and by the pressure from the hot gases at the center. Magnetic fields are created whenever an electric charged particle is in motion. Electrons are negative charges. The nucleus of hydrogen is a proton which is positively charted.
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- Magnetic fields control the early phases of the cloud’s rotation and contraction. But, at some point the ions and the magnetic field lines move out past the neutral gas. When this happens the rapid collapse ensues. “Rapid” in cosmic terms is less than 100,000 years.
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- If the cloud had a relatively slow rotation than a single star is formed by the collapsing gas.
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- If the cloud had a rapid rotation rate it would form rings in the collapsing gas. When the rotation is rapid enough these rings break apart forming two stars. Extremely rapid rotations will break up the rings causing three or four stars being formed in the collapsing gas. The binary systems are forming at the same time the stars themselves are forming in the gravitational collapse of the interstellar cloud.
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- The fate of these binary stars depends on their initial masses. There are many combinations possible. The stars rotate around a common center of gravity. This creates the combined effects of both gravity and centripetal force.
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- A surface of constant energy is created where these two forces are in balance. This is similar to a topological map have lines of equal elevation. These lines form a surface that is equal elevation a balance between up and down. Across the binaries surface of constant energy material from one star can transfer to another without having to climb or descend. This surface of constant energy is called the “ Roche-lobe” surface.
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- Once material is being exchanged what happens next depends on the combination of masses and chemical composition of the two stars.
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- If the helium star is over 40 solar mass it compacts into a supernova explosion leaving behind a Blackhole.
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- If he helium star is less the 40 but more than 30 solar mass the supernova remnant is a Neutron Star.
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- If the binary system survives the supernova explosion the gas from the secondary star enters the accretion disk of the Neutron Star or Blackhole. The in falling material in the accretion disk becomes a powerful X-ray emission source. That is how astronomers are finding Blackholes.
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- The secondary star in this case will only live for 10,000 to 100,000 years before it too goes supernova. The second supernova in the system can often set the Neutron stars spinning creating “Pulsars“, or even massive “Gamma Ray Bursters“.
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- The “Black Widow Pulsar” in Constellation Sagitta is an example of a millisecond Pulsar orbited by a helium White Dwarf.
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- If the binary White Dwarf stars come together then the merger produces an intense stellar wind creating a planetary nebula around a carbon-oxygen “White Dwarf star“. R, Coronae Borealis stars are an example.
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- By studying a specific region in the sky astronomers have determined the odds of any particular star being a multiple system. Here is the data from the Virgo region:
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---------------- 59% are single stars
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--------------- 35% are binaries
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---------------- 6% are triple stars.
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- Of the 300 protoplanets studied astronomers discovered 33% are found in binary systems. So, over many planets have a two sun system. Nights and days, as well as Spring and Fall would be very confusing. You would need a computer for a wristwatch.
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- Using only binoculars you can find several binary systems in the night sky. See the “Big Dipper” to find Mizar and Alcor.
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May 19, 2022 BINARY STARS - more common than expected? 1063 3582
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--------------------- --- Thursday, May 19, 2022 ---------------------------
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