- 3048 - SHOOTING STARS - Out of the Galaxy? If a star is traveling over 1,000,000 miles per hour it is referred to as a “hypervelocity star“. Some 16 or these hypervelocity stars have been discovered. The first one discovered in 2005 was traveling over 2,000,000 miles per hour. In 2006 and 2007 seven more hypervelocity stars were discovered.
---------------------- 3048 - SHOOTING STARS - Out of the Galaxy?
- One of these stars traveling 1,560,000 miles per hour was 362,000 lightyears from the Milky Way Center. Its velocity exceeded the escape velocity for the galaxy. It will eventually leave the galaxy and keep on going into outer space. How could a star larger than our Sun get propelled to such an extreme velocity?
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- This star’s velocity is moving almost directly away from the Milky Way’s center. The star is rich in heavy metals which is consistent with a young star forming near the galactic center. The star is about 80,000,000 years old and that is enough time for the star to have reached its present location.
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- The basic method to achieve hypervelocity involves the “ Conservation of Momentum”. Binary stars approaching a Blackhole. When one star gets captured at a close approach and pulled in the partner star would be flung out in the opposite direction.
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- Another method could come from one of our satellite Dwarf Galaxies plunging into the Milky Way as they merge. The merger causes stars to reach breakneck speeds. 8 of the 16 stars are clustered in the same direction around the Constellation Leo the Lion. These hypervelocity stars could be the result of such a merger.
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- A Pulsar is a rotating Neutron Star. One Pulsar has been clocked at 2,500,000 miles per hour. A Pulsar is created from the super dense collapsed core of a massive star that exploded as a supernova. This Pulsar originated in the Constellation Cygnus the Swan, 2.5 million years ago. Since then the star has traversed one-third of the night sky.
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- Two other hypervelocity Pulsars have been discovered but their speeds and directions have not been accurately determined to date. Most likely all 3 Neutron Stars were kicked out of supernova explosions for their extreme speeds. Another 6 or the 16 stars are almost certainly from the galactic center super massive Blackhole.
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- One way hypervelocity stars are discovered is by the bow shocks of compressed matter created as the speeding star plows through the intergalactic medium. Stars of low velocity do not create bow shocks.
- Once a 3 dimensional velocity vector is determined for a hypervelocity star the astronomers can follow the path backwards to find the place the star originally came from. If the path comes back to a supernova explosion, astronomers would theorize that binary stars were involved.
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- When 2 heavy stars orbit each other at high velocity, they are held together by gravitational attraction, or potential energy. When one of the stars explodes as a supernova the remaining star leaves its orbit, continuing in a straight line, preserving its kinetic energy as a high velocity exit.
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- Astronomers have discovered the remnants of just such a scenario. “HD77581” binary has an invisible companion “Vela X-1“. Vela X-1 has a perfect bow shock of parabolic form. It is 6,000 lightyears away. It has a space velocity of 90 kilometers per second, 201,330 miles per hour. It has been traveling for 2.5 million years. Working backwards its origin corresponds with a supernova explosion that produced a Neutron Star. This is now a strong X-ray source known as Vela X-1.
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- Another outlier, hypervelocity star is more than 3 times its age for its present location. A good guess is that this hypervelocity star was flung out of the Large Megellanic Cloud galaxy a neighbor galaxy to the Milky Way. The star’s chemical abundance pattern closely matches those of the LMC galaxy rather than the Milky Way’s galactic center stars.
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- To get a star’s 3 dimensional velocity astronomers must measure in 3 perpendicular directions. Radial velocity, receding or coming directly toward us, is measured using the Doppler Shift of the light. The redshift or blue shift.
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- The Transverse velocity, or proper motion across the sky, must be measured by taking a series of positions against more distant objects. For example let’s take the velocity vectors for our Sun. Conventionally the vectors are labeled U, V, and W.
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---------- U = 22,370 miles per hour and is positive in the direction of the Galactic Center.
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---------- V = 11,700 miles per hour and is positive in the direction of the Galactic Rotation.
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---------- W = 16,000 miles per hour and is positive in the direction of the Galactic North Pole.
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--------- The geometric sum of these 3 vectors is a vector velocity of 30,000 miles per hour moving through space relative to the center of the Milky Way.
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February 15, 2021 SHOOTING STARS - Out of the Galaxy? 1133 3048
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