- 2082 - Dark matter is one of the most important, least understood
building blocks of our universe. This gravitationally inferred matter accounts
for 85 percent of the universe’s mass and is believed to form the underlying
foundations upon which all galaxies are built. Our current understanding of
dark matter is not entirely correct. This should not be a complete surprise
considering we have yet to detect direct evidence of the elusive material.
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----------------------------------- 2082 -
Dark Matter - throws us a curve
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- We were first
introduced to dark matter in 1930. And,
we still do not know what it is in 2018.
Fred Zwicky first suggested dark matter existed because something was
holding the galaxies from flying apart. We have evidence that it is 26% of all
the matter-energy in the universe.
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- The way the
spiral galaxies rotate and the laws of physics as we understand them require
the outer most stars to be flying away like water from a lawn sprinkler. Something
in a halo around most galaxies is holding everything together. We call it dark matter.
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- Dark matter is one of the most important, least understood
building blocks of our universe. This gravitationally inferred matter accounts
for 85 percent of the universe’s mass and is believed to form the underlying
foundations upon which all galaxies are built.
-
- We thought that every galaxy had dark matter and that dark matter is how a galaxy begins to form. This invisible, mysterious substance is the most dominant aspect of any galaxy. So just when we begin to define what it is we find a galaxy without evidence of a dark matter presence. It challenges the standard ideas of how we think galaxies work, and it shows that dark matter must have its own separate existence apart from what we find in other galaxies.”
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- The oddball galaxy in question, NGC1052-DF2 is a small galaxy in a collection of galaxies dominated by the much larger elliptical NGC 1052. The relatively innocuous galaxy DF2 only stood out to the researchers when they noticed it appeared differently in images taken by different surveys. DF2 looked like a blob of dim and diffuse light in some images, then appeared as a group of point-like sources in other images.
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- DF2 was considered an ultra-diffuse galaxy due to its large size and transparent appearance. It is located about 65 million lightyears away. Although the galaxy is about as large as the Milky Way but contains 200 times fewer stars.
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- 10 globular clusters, large, spherical groups of typically old stars, on the outskirts of DF2 were rotating around DF2 three times more slowly than they would be if the galaxy contained a typical amount of dark matter in addition to its sparse amount of normal matter. The researchers calculated the galaxy’s overall mass and found that, if there is any dark matter at all, it’s very little. The stars in the galaxy can account for all the mass, and there doesn’t seem to be any room for dark matter.
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- We thought that every galaxy had dark matter and that dark matter is how a galaxy begins to form. This invisible, mysterious substance is the most dominant aspect of any galaxy. So just when we begin to define what it is we find a galaxy without evidence of a dark matter presence. It challenges the standard ideas of how we think galaxies work, and it shows that dark matter must have its own separate existence apart from what we find in other galaxies.”
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- The oddball galaxy in question, NGC1052-DF2 is a small galaxy in a collection of galaxies dominated by the much larger elliptical NGC 1052. The relatively innocuous galaxy DF2 only stood out to the researchers when they noticed it appeared differently in images taken by different surveys. DF2 looked like a blob of dim and diffuse light in some images, then appeared as a group of point-like sources in other images.
-
- DF2 was considered an ultra-diffuse galaxy due to its large size and transparent appearance. It is located about 65 million lightyears away. Although the galaxy is about as large as the Milky Way but contains 200 times fewer stars.
-
- 10 globular clusters, large, spherical groups of typically old stars, on the outskirts of DF2 were rotating around DF2 three times more slowly than they would be if the galaxy contained a typical amount of dark matter in addition to its sparse amount of normal matter. The researchers calculated the galaxy’s overall mass and found that, if there is any dark matter at all, it’s very little. The stars in the galaxy can account for all the mass, and there doesn’t seem to be any room for dark matter.
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- To determine how quickly the globular
clusters were rotating around DF2, the researchers analyzed the absorption
lines of spectra. This allowed them to
determine each cluster’s velocity, which they then used to calculate the
overall mass of the galaxy. (See
appendix of other reviews that explain how these calculations are made.)
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The finding that DF2 apparently has very little, if any, dark matter
caught the researchers off guard because it is the first galaxy ever found to
be lacking the pervasive material. There is no theory that predicted these
types of galaxies. The galaxy is a complete mystery, as everything about it is
strange. How you actually go about
forming a galaxy like DF2 is completely unknown.
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- Maybe DF2 is actually a tidal dwarf galaxy. This type of galaxy can form during galactic mergers, which often fling out ordinary matter that is made up of protons, neutrons, and electrons, called baryonic matter.. However, DF2 appears to have fewer metals than would be expected for a normal tidal dwarf galaxy.
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- Maybe DF2 is actually a tidal dwarf galaxy. This type of galaxy can form during galactic mergers, which often fling out ordinary matter that is made up of protons, neutrons, and electrons, called baryonic matter.. However, DF2 appears to have fewer metals than would be expected for a normal tidal dwarf galaxy.
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- No matter how DF2 formed, the astronomer's findings demonstrate that dark matter is indeed a physical building block that can be separated from baryonic matter, and, as a result, the findings also cast doubt on some alternative theories to dark matter.
- No matter how DF2 formed, the astronomer's findings demonstrate that dark matter is indeed a physical building block that can be separated from baryonic matter, and, as a result, the findings also cast doubt on some alternative theories to dark matter.
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One such theory modifies how
gravity works over distance and is called MOND.
This theory eliminates the need
for dark matter proposing that the gravitational force acts differently on
low-acceleration objects, such as those found on the outer fringes of galaxies.
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- This result poses a very strong challenge to MOND. In MOND, the extra gravitational forces observed on galactic scales are woven into the equations, meaning that wherever you see galaxies, you should see the effect of the modified gravity. However, in this galaxy, there is no need for the extra gravity to explain its kinematics. This suggests that galaxies and dark matter are separable components and that dark matter is a material substance.
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- Before astronomers can make any sweeping conclusions about the true nature of our universe, these studies of extraordinary findings must first be verified and replicated
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- This result poses a very strong challenge to MOND. In MOND, the extra gravitational forces observed on galactic scales are woven into the equations, meaning that wherever you see galaxies, you should see the effect of the modified gravity. However, in this galaxy, there is no need for the extra gravity to explain its kinematics. This suggests that galaxies and dark matter are separable components and that dark matter is a material substance.
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- Before astronomers can make any sweeping conclusions about the true nature of our universe, these studies of extraordinary findings must first be verified and replicated
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- Our first conclusion is that our current understanding of dark matter is not entirely correct. This should not be a complete surprise considering we have yet to detect direct evidence of the elusive material. Confusing results force scientists to look at a problem in different ways, which typically leads them to revise and update their theories so they better describe reality.
- Our first conclusion is that our current understanding of dark matter is not entirely correct. This should not be a complete surprise considering we have yet to detect direct evidence of the elusive material. Confusing results force scientists to look at a problem in different ways, which typically leads them to revise and update their theories so they better describe reality.
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- Baryonic matter is defined as the type of matter composed of atoms that we can see. Dark matter is a form of non-baryonic matter that reacts with the force of gravity but does not interact with ordinary matter.
- Baryonic matter is defined as the type of matter composed of atoms that we can see. Dark matter is a form of non-baryonic matter that reacts with the force of gravity but does not interact with ordinary matter.
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- Observations
suggest that dark matter is "cold" meaning that it travels much
slower than the speed of light. It clumps together more than fast-moving
"hot" dark matter.
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- Here are some
of the theories being pursued. It could be weakly interacting massive
particles called WIMPS. It could be
"axions" which are lighter
than WIMPS but much more plentiful. It could be heavy sterile neutrinos not yet
discovered past the three known varieties of neutrinos. Or, it could be low
mass blackholes.
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- Whatever it
is it needs to account for 80% of all the matter in the universe. It neither emits or absorbs light, electromagnetic
radiation. It does interact with the
rest of the universe through gravity. It
affects the rotation of galaxies. It gravitationally
distorts light passing through galaxy clusters. It accounts for the abundance
of the light elements hydrogen and helium produced in the first minutes of the
expanding universe.
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- Over the past 15 years experiments, at the Large
Hadron Collider, has failed to detect individual particles of dark matter. No signs of these elusive particles have appeared.
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- Astronomers
have studied hundreds of galaxy rotations.
All having similar flat rotation structures requiring that they reside
within massive halos of dark matter. Now we have to deal with some exceptions.
Stay tuned there is still more to learn.
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-
- OTHER REVIEWS
AVAILABE ABOUT DARK
MATTER:
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- 1934 - Can
dark matter make blackholes? Dark
matter outweighs normal matter 5 to 1.
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- 1888 - What
is the universe made of?
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- 1850 - If
dark matter is 90% of all matter in the Universe we have more to learn beyond
today' physics.
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- 1823 - Dark
matter and the extinctions of the dinosaurs.
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- 1820 - Does
the math then concludes to be consistent with these laws we need to create an
unobserved distribution of new mass.
- 1636 - Using
the temperature of X-ray hot gas to determine the mass of galaxy clusters.
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- 1535 -
Gravity lenses find dark matter and planets. Listing of 11 more reviews about dark matter.
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------------------------- Sunday, April 29, 2018 --------------------------------
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