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https://arstechnica.com/science/2017...h-white-dwarf/
Prompted by this article and finding myself with a fair amount of downtime this morning, I will impart boredom onto you all with another installment of “Physics with Samir”:
Albert Einstein’s, arguably, biggest contribution to theoretical physics was not what won him the Nobel Prize in 1921 (photoelectric effect); it was the General Theory of Relativity. In the broad strokes, the General Theory of Relativity is the theoretical construct that any object with a non-zero mass will distort or warp the space-time field local to that object and the magnitude or strength of that distortion is directly proportional to the mass of that object.
What do you mean “warp”?
The fairly ubiquitous representation of this is to imagine a large bedsheet stretched out and suspended off the ground. Space-time is actually 4-dimensional: the 3-dimensional directional or Cartesian space (x-, y-, and z-axes or front/back, left/right, and up/down) and 1-dimensional time (forward/backward), but for simplicity, we will use our bedsheet to illustrate space-time in 2-dimensions. To imagine third dimension, just envision that the bedsheet can be rotated or flipped about any axis on the plane of the bedsheet. Now, if I were to take a marble and place it on our bedsheet, the weight of the marble would push the bedsheet downward in conical shape centered on the marble. If I was to take a baseball, the same effect would result except that the baseball, being heavier or, more accurately, more massive, the depth of the conical shape would be much greater. If I were to repeat this process with a basketball, a bowling ball, etc., the depths of the “cones” or distortions, we would find, would be proportional to the weights or masses of the objects on the bedsheet—the heavier the object, the larger the cone.
The distortions caused by non-zero mass objects can affect other objects by exerting an attractive force on them called gravity. Sometimes, the distortion is strong enough to affect the path that light takes near that object causing the path to bend inward toward the object. This is called gravitational lensing.
The first observation of gravitational lensing was during a solar eclipse in 1919. Without the blinding effects of staring at or near the sun as it was obfuscated by the moon, the apparent positions of the stars in the direction of the sun were observed to have shifted slight as the light from the stars was bent, or lensed, back toward the observers.
This effect can be seen on much larger scales, too. The large gravitational fields (space-time distortions) created by large galaxies or clusters of galaxies also lens light. This effect was observed in images of the Abell 2281 galaxy cluster.
Go here for picture of Abell 2281.
The distorted images of the background galaxies are a result of the light from those galaxies being lensed by the Abell 2281 cluster. The distortions are interesting because the lensed AND lensing galaxies are so large that the light is not coming from a point source; light originating from one side of the lensed galaxy could travel along a different path around the lensing galaxies than light originating from the other side of the lensed galaxies. This causes the elongated “smeared” images of the lensed galaxies. Additionally, light originating from the same side of the lensed galaxy could take two different paths through the lensing galaxies causing the same lensed galaxy to have more than one image (these appeared as “orange” images in the picture above).
Much like with optical lensing, we can determine refractive properties of the lensing medium based on the images observed—knowing what we should see compared to what we actually see, we can know what changed the image. When calculations were made of the amount of mass needed to create the lensed images and compared to the observations, the amount of mass needed was approximately 3 times that of what was actually observed. A hypothesis was offered to explain the mass deficiency needed to accurately predict the geometric distortions observed; this was the birth of dark matter, but I leave that as a topic for another time.
Prompted by this article and finding myself with a fair amount of downtime this morning, I will impart boredom onto you all with another installment of “Physics with Samir”:
Albert Einstein’s, arguably, biggest contribution to theoretical physics was not what won him the Nobel Prize in 1921 (photoelectric effect); it was the General Theory of Relativity. In the broad strokes, the General Theory of Relativity is the theoretical construct that any object with a non-zero mass will distort or warp the space-time field local to that object and the magnitude or strength of that distortion is directly proportional to the mass of that object.
What do you mean “warp”?
The fairly ubiquitous representation of this is to imagine a large bedsheet stretched out and suspended off the ground. Space-time is actually 4-dimensional: the 3-dimensional directional or Cartesian space (x-, y-, and z-axes or front/back, left/right, and up/down) and 1-dimensional time (forward/backward), but for simplicity, we will use our bedsheet to illustrate space-time in 2-dimensions. To imagine third dimension, just envision that the bedsheet can be rotated or flipped about any axis on the plane of the bedsheet. Now, if I were to take a marble and place it on our bedsheet, the weight of the marble would push the bedsheet downward in conical shape centered on the marble. If I was to take a baseball, the same effect would result except that the baseball, being heavier or, more accurately, more massive, the depth of the conical shape would be much greater. If I were to repeat this process with a basketball, a bowling ball, etc., the depths of the “cones” or distortions, we would find, would be proportional to the weights or masses of the objects on the bedsheet—the heavier the object, the larger the cone.
The distortions caused by non-zero mass objects can affect other objects by exerting an attractive force on them called gravity. Sometimes, the distortion is strong enough to affect the path that light takes near that object causing the path to bend inward toward the object. This is called gravitational lensing.
The first observation of gravitational lensing was during a solar eclipse in 1919. Without the blinding effects of staring at or near the sun as it was obfuscated by the moon, the apparent positions of the stars in the direction of the sun were observed to have shifted slight as the light from the stars was bent, or lensed, back toward the observers.
This effect can be seen on much larger scales, too. The large gravitational fields (space-time distortions) created by large galaxies or clusters of galaxies also lens light. This effect was observed in images of the Abell 2281 galaxy cluster.
Go here for picture of Abell 2281.
The distorted images of the background galaxies are a result of the light from those galaxies being lensed by the Abell 2281 cluster. The distortions are interesting because the lensed AND lensing galaxies are so large that the light is not coming from a point source; light originating from one side of the lensed galaxy could travel along a different path around the lensing galaxies than light originating from the other side of the lensed galaxies. This causes the elongated “smeared” images of the lensed galaxies. Additionally, light originating from the same side of the lensed galaxy could take two different paths through the lensing galaxies causing the same lensed galaxy to have more than one image (these appeared as “orange” images in the picture above).
Much like with optical lensing, we can determine refractive properties of the lensing medium based on the images observed—knowing what we should see compared to what we actually see, we can know what changed the image. When calculations were made of the amount of mass needed to create the lensed images and compared to the observations, the amount of mass needed was approximately 3 times that of what was actually observed. A hypothesis was offered to explain the mass deficiency needed to accurately predict the geometric distortions observed; this was the birth of dark matter, but I leave that as a topic for another time.
Last edited by Rev. Rob Large; Jun 8, 2017 at 11:57 AM.
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TLDR (kidding, kidding).
This is also how scientists locate black holes and other anomalies in a fabric of space, no? I know that's your reference to dark matter, but essentially, that deflection is what shows us "there's something there exerting gravitational force equal to X" even if other "conventional" methods of ascertaining size, position, and mass/density of a heavenly body (oh, my) fail.
This is also how scientists locate black holes and other anomalies in a fabric of space, no? I know that's your reference to dark matter, but essentially, that deflection is what shows us "there's something there exerting gravitational force equal to X" even if other "conventional" methods of ascertaining size, position, and mass/density of a heavenly body (oh, my) fail.
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kidatari
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