- 2062 - Galaxies
- spin and velocities. All disk galaxies rotate about once every billion years,
no matter their size or mass. The
conclusion is that stars orbiting at the edges of galaxies have the same order
of magnitude orbital periods. The
galaxies in the expanding universe are
separating from each other faster than expected. There is still more to learn.
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LEARN MORE, FEEDBACK ENCOURAGED
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----------------------------- 2062 -
Galaxies - spin and velocities
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In March 2018, some astronomers announced the discovery that all disk
galaxies rotate about once every billion years, no matter their size or mass. This
measurement is made on the extreme edge of the galaxy disk. To their surprise
they did not find a dense galaxy rotating more quickly, while another with the
same size but lower density rotating more slowly.
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- The
radial velocities of neutral hydrogen in the outer disks was measured for many
galaxies.
The galaxies ranged from small dwarf irregulars to massive spiral galaxies. These galaxies differed in both size and rotational velocity by up to a factor of 30. With these velocity measurements, the researchers were able to calculate the rotational period for each of the galaxies. The conclusion was that the outer rims of all disk galaxies take roughly a billion years to complete one rotation.
The galaxies ranged from small dwarf irregulars to massive spiral galaxies. These galaxies differed in both size and rotational velocity by up to a factor of 30. With these velocity measurements, the researchers were able to calculate the rotational period for each of the galaxies. The conclusion was that the outer rims of all disk galaxies take roughly a billion years to complete one rotation.
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on theoretical models, the astronomers expected to find only sparse populations
of young stars and interstellar gas on the outskirts of these galaxies. But
instead, they discovered a significant population of much older stars mingling
with the young stars and gas.
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How does Dark Matter enter into or influence this phenomena?
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- The conclusion is that stars orbiting at the
edges of galaxies have the same order of magnitude orbital periods. This is like Kepler finding that planets
orbiting the Sun sweep out equal areas in equal time. A planet has to move faster
when it is closest to the Sun and slower when further away. Newton
then showed that this was due to a "1 / radius squared" gravitational force.
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- Newton's
laws of gravity explained the relationship that Kepler found when Kepler studied
the data that Tycho found. Who can be the next Newton by coming up with a
galactic dynamics model that shows that the outer edge of galaxies will have
orbital periods of roughly the same magnitude, close to 1 billion years
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- Our
Sun's galactic rotation period is 240 million years. . Our Milky Way galaxy
spiral pattern rotation period is 220–360 million years. Not all disk galaxies rotate once every
billion years, given this one example and this one measureement. But , is this the outer edge being measured,
and is the galaxy really rotating like a phonograph record? Maybe the rotation is like a lawn sprinkler and
the outer edges lag in the rotation and take longer to complete one rotation?
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galaxy rotation is not the only mystery.
The galaxies in the expanding universe are separating from each other faster than
expected.
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Hubble Space Telescope measures the distance to other galaxies by examining a
type of star that varies in brightness. These stars, called Cepheid variables,
brighten and dim in a predictable way that lets researchers judge the distance
to them. This data is then used to measure the universe's expansion rate, known
as the Hubble constant.
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new findings show that Cepheid variables in our Milky Way galaxy are up to 10
times farther away than any previously analyzed for a star of this kind. These Cepheids
are more challenging to measure than others because they reside between 6,000
and 12,000 lightyears from Earth. To handle that distance, the researchers
developed a new scanning technique that allowed the Hubble Space Telescope to
periodically measure a star's position at a rate of 1,000 times per minute,
thus increasing the accuracy of the stars' true brightness and distance.
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- The
Planck satellite mapped leftover radiation from the Big Bang, known as the Cosmic Microwave Background. The
Planck data revealed a Hubble constant between 67 and 69 kilometers per second
per megaparsec. (A megaparsec is roughly 3 million light-years) This is about 9 percent lower than that of
the new Hubble measurements, which estimate that the universe is expanding at
73 kilometers per second per megaparsec, suggesting that galaxies are moving
faster than expected. ( In more familiar
units, this is 49,306 miles per hour per million lightyears distance.)
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- One
possible explanation for the discrepancy is that dark energy is driving
galaxies farther apart with greater intensity. In this case, the acceleration
of the universe may not have a constant value but rather may change over time.
It is also possible that elusive dark matter, which accounts for 80 percent of
the matter in the universe, interacts more strongly with visible matter or
radiation than we thought.
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- Another
possible explanation includes a new kind of subatomic particle that travels
close to the speed of light and would be affected only by gravity. Researchers
named the superfast particles "sterile neutrinos".
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- Any
of these scenarios would change the contents of the early universe, leading to
inconsistencies in current theoretical models.
These inconsistencies would result in an incorrect value for the Hubble
constant of the expansion rate for the universe. There is more to learn, stay tuned.
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------------------------- Monday, April 16, 2018
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