“unidentified”Dark matterIt is said that the mystery of gravity in the universe can be explained without postulating “dark matter.”Modified Newtonian mechanics“It’s an interesting hypothesis, but it doesn’t have a lot of support. In particular, the effect of modified Newtonian mechanics on the scale of the solar system, which is shorter than the scale of stars and galaxies, has not been explained before.”
A research team led by Katherine Brown of Hamilton College and Harsh Mathur of Case Western Reserve University has revealed that the orbits of trans-Neptunian objects are biased when they mimic the orbits of trans-Neptunian objects under modified Newtonian mechanics. This is it,The first case demonstrates the effectiveness of modified Newtonian mechanics over short distancesIn addition,It denies the “Planet Nine” hypothesis that there is an unknown planet in the outer solar systemIt is something that must be done.
However, due to limitations in the amount of data underlying the results,The possibility that this result is the result of chance and can be easily reversed cannot be excluded.Brown and Mathur themselves warn against this.
■ “Modified Newtonian mechanics” that denies “dark matter”
The amount of matter in our universe can be estimated by measuring the gravitational effects caused by matter, such as the rotation speed of galaxies. However, the total amount of matter estimated from gravitational observations is about five times the amount of “normal” matter that can be observed using electromagnetic waves such as visible light. This great discrepancy can only be explained if we consider that in addition to the matter that can be observed by electromagnetic waves, there is also an unknown matter that can be observed by gravity but not by electromagnetic waves. “Dark matter” is a term that refers to this unknown substance, and discovering its true identity is considered one of the greatest challenges in astronomy.
However, despite many years of research and observational experiments, the true nature of dark matter is still unknown, and the truth is that it is difficult to narrow down the candidates, let alone discover it.
Most scientists believe that whatever the true nature of dark matter is, it requires major revisions to currently accepted theories of physics. For this reason, a few scientists are thinking: “Maybe dark matter doesn’t exist in the first place?” In this case, it is the theory of gravity that needs to be revised.
One proposed modified theory of gravity is “modified Newtonian mechanics”. In modified Newtonian mechanics, by modifying Newton’s equation of motion that describes the motion of a body, the inverse square law, which states that “gravity weakens inversely with the square of the distance,” is not entirely true, and we assume that the translation is inversely proportional to the first force. If modified Newtonian mechanics is correct, there is no need to consider the existence of dark matter.
However, Newton’s modified mechanics denies the theory of general relativity, which has withstood rigorous tests and cannot be said to have gained much support. In addition, modified Newtonian mechanics is very difficult to verify, because the inverse square law appears to apply at distances of up to tens of billions of kilometres, i.e. within the interior of the solar system.
■Does modified Newtonian mechanics also deny the existence of “Planet Nine”?
Brown and Mathur’s research team conducted a simulation study, believing that modified Newtonian mechanics might conflict with the “Planet Nine” hypothesis, another mystery surrounding the outer solar system.
Outside the orbit of Neptune, the outermost of the eight planets in the solar system, there are countless celestial bodies called “trans-solar objects.” In examining these orbits, it has been pointed out that although the celestial bodies should be evenly distributed in all directions, there is a bias in that they are actually distributed in a specific direction.
This can be explained by the belief that there are large-mass bodies in the outer solar system that have not yet been discovered, and that they disturb the orbits of outer solar system bodies through gravity. The estimated mass and the fact that it obliterates surrounding objects corresponds to the definition of a planet in our solar system, which was adopted in 2006, so this planet was named “Planet Nine”, the unknown ninth planet. However, Planet Nine has not yet been discovered, and some researchers believe it does not actually exist.
Brown and Mathur believed that this Planet Nine hypothesis was incompatible with modified Newtonian mechanics, so they simulated changes in the orbits of post-Neptunian objects under the assumption of a gravitational field based on modified Newtonian mechanics, and the results were compared with actual observations.
As a result of the simulation,Trans-Neptunian objects are affected by the Milky Way’s gravitational field, and the long axis of their elliptical orbits points toward the center of the Milky Way.This has been shown. This result matched well with the actual orbits of six trans-Neptunian objects, such as asteroid 90377 Sedna, which is known to have a highly precise elliptical shape. This is the first result showing that modified Newtonian mechanics works even at a short distance within the solar system, and based on modified Newtonian mechanics, it suggests that Planet Nine may not exist.
■Preliminary research results that can be easily reversed
However, based on the results of this study, it cannot be said that modified Newtonian mechanics is correct.The orbit data used in this research is not accurate enough to be used for verification, and we cannot rule out the possibility that the simulation results match reality. Since the modified Newtonian mechanics itself has been subjected to harsh conditions when verified using other methods, there is a strong possibility that the modified Newtonian mechanics itself will be rejected. So,This result can be easily reversed.
Also, the existence of Planet Nine can be denied without assuming modified Newtonian mechanics. Trans-Neptunian objects are extremely difficult to observe because they are located far away, literally on the outer edge of the solar system. It is very likely that the deviation in orbit, which is the basis for the existence of Planet Nine, is the result of observation bias due to the small number of observations of objects in the outer solar system. Additional astronomical observations are essential to find answers to questions such as dark matter, modified Newtonian mechanics, and Planet Nine.
Written by Riri Aya