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- 2028 - Hyper-Velocity Stars are destined to leave the galaxy breaking free of its gravity. They are racing in the galaxy’s outer halo 150,000 lightyears from the galaxy center traveling more than 700,000 miles per hour. At that speed it would take 20 minutes to traverse the Earth -Moon distance.
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- ---------------------------------- 2028 - Hyper-Velocity Stars .
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- Could the Earth ever leave the Sun’s gravity and drift off into space? How about the Sun, could it escape the Milky Way Galaxy? Well there are stars that get up enough speed to escape the galaxy’s gravity. There are dozens of them making the trip into intergalactic space.
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- Stars are always weaving in and out , above and below, the Galaxy’s spiral arms. I know when you look into the night skly it looks like everything except the Moon and a few planets are stationary. However, the 200 to 500 billion stars that are in our galaxy are all in constant motion. Some are revered up so fast they are 2 to 3 times the speed of our Sun.
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- The ones called hyper-velocity stars are destined to leave the galaxy breaking free of its gravity. Most of these stars are 2 to 5 times the mass of our Sun with surface temperatures over 18,000 Kelvin. They are racing in the galaxy’s outer halo 150,000 lightyears from the galaxy center traveling more than 700,000 miles per hour. At that speed it would take 20 minutes to traverse the Earth -Moon distance. Or, traverse 1,000 lightyears in just 1 million years.
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- The first hyper-velocity star was discovered in 2005. The star was 350,000 lightyears from the center of the galaxy. We are 26,000 lightyears from the center. The star was traveling 1,510,000 miles per hour away from the center. Astronomers believe that the super massive blackhole at the center slingshot the star out of the center.
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- Mathematically it is called a ‘3-body exchange” between the blackhole and a binary pair of stars. The blackhole captures one of the stars and slings the other star out of the galaxy. This gravitational slingshot could potentially eject a star at near the speed of light out of the galaxy.
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- The galaxies halo contains several old metal-poor, low-mass stars that were likely been ejected there. The best explanation for their existence there involves a binary star that travels too close to a massive blackhole. The blackhole captures one star into a highly eccentric orbit than ejects the other has a hypervelocity star.
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- The radian velocity of the star is determined by examining its light spectrum. If the star is moving towards us its spectrum wavelengths are shifted to shorter wavelengths. If the star is moving away from us, its spectral lines shift to longer wavelengths. The higher the velocity the greater the shift.
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- Once we know the star’s radian velocity as viewed from Earth we can calculate how fast it is moving relative to the Galactic center. This is the star’s “radian velocity“, its motion “across” our line of sight is called “proper motion”. It is much harder to precisely measure this velocity. In order to measure proper motion we must observe the shift in the star’s position relative to more distant stars.
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-These hyper-velocity stars have extreme velocities but their proper motions across the sky is less than 1 milli-arcsecond per year. This is equivalent to the angular size of a dime viewed at a distance of 2,300 miles away. Quite a technical challenge. It requires using satellites specifically designed to make this measurement.
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-Astronomers are learning that a trajectory outward from the center of the galaxy would not necessarily be in a straight line. Theorist are speculating that dark matter could shape the trajectory quite differently. On the other hand by plotting the trajectory astronomers could better map out the unseen dark matter surrounding our galaxy.
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- Astronomers hope to learn a lot more studying these hyper- velocity stars. There could be thousands more that we have not yet discovered. Studying these hyper-velocity stars and how they deviate from a straight line could help us map out the shape and orientation of the dark matter halo. Dark matter remains one of the major mysteries in astronomy today. We need to learn much more to understand what it is and how it affects our world. Stay tuned. There is a lot going on out there.
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----- 707-536-3272 ---------------- Tuesday, February 27, 2018 -----
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