The history of science is full of debates between warring factions. Even today, astronomers debate the big ideas — such as the various models that describe the motion of stars and galaxies, from invisible dark matter to claims that our understanding of the laws of physics is wrong. Each side points to different evidence supporting their position. Now, A.J new leaf Posted in natural astronomy Ziff claims a key observation, and in doing so strengthens the case for the universe being filled with invisible matter.
Modern astronomy makes an unusual claim. While powerful observatories, such as the Hubble Space Telescope and the newer James Webb Telescope, can see billions of stars and galaxies, those amazing images are only a small fraction of the matter in the universe. In addition to glowing stars and the invisible clouds of gas that reside in the space between them, most astrophysicists believe that the universe is filled with a substance called dark matter that neither emits nor absorbs light.
It should come as no surprise, then, that dark matter has not been detected directly; It can only be observed by the effect of gravity on visible matter. According to the theory, dark matter is about five times more abundant than normal matter.
The evidence for dark matter
There is a lot of evidence supporting the idea of dark matter, but the easiest explanation for it has to do with the rotation of galaxies. galaxies They are huge clusters of stars in space, containing several billion stars. The Milky Way, the galaxy in which our planet is located, is estimated to contain between 200 and 400 billion stars.
Galaxies rotate, which means that the stars revolve around the galactic center, not much different from how the planets revolve around the sun in our solar system. Although each planet is gravitating towards the sun, its speed is such that it rotates in an almost circular path. Speed and gravity balance each other out, with planets farther from the sun moving slower than those closer to it.
In galaxies, it’s pretty much the same, and the laws of physics make similar predictions, specifically that stars farther from the galactic center move more slowly than stars closer to it. However, when astronomers measure the speed of stars in the outskirts of galaxies, they find that they are moving faster than expected. If the laws of gravity and motion are correct, the only explanation is that the extra, invisible matter increases the gravity these fast-moving stars experience.
Dark matter discussion
However, a minority of scientists reject the dark matter hypothesis as implausible. Instead, they believe that the accepted laws of physics are incorrect. According to them, either the laws governing the motion of astronomical bodies are wrong, or our theory of gravity does not work on galactic scales. For both guesses, these researchers have developed a host of new physics theories, governed by different equations than those taught in physics classes.
Both camps — the dark matter proponents and the modified physics community — point to different sets of astronomical data to support their position. Both groups can point to observations that support their guesses and dislike the other. While most astronomers embrace the idea of dark matter, there was one hard-to-interpret observation on the dark matter camp: the distribution of small galaxies surrounding larger galaxies.
These smaller galaxies are called “satellite galaxies”. The two explanations — dark matter and modified physics — make different predictions about how satellite galaxies are arranged around galaxies like the Milky Way. Over the past half century or so, astronomers have realized that observations favor the camp of modified physics.
The Milky Way is a spiral galaxy, which means it looks a bit like a spinning disk, about 100,000 light-years wide and 12,000 light-years thick – a cosmic pizza pan. This is what visible stars and galaxies look like. However, the dark matter theory says that dark matter is essentially a large spherical cloud, perhaps 700,000 light-years across, with the Milky Way galaxy at the center. Because dark matter is important in the formation of galaxies, dark matter theory proposes that satellite galaxies of the Milky Way must be spherically distributed around it.
On the other hand, if dark matter is not real, and the correct explanation for rapidly rotating galaxies is that the laws of physics must be modified, scientists expect that satellite galaxies should orbit the Milky Way at about the same level as the Milky Way. The Way – Essentially extensions of the Milky Way itself. When astronomers measure the position of 11 galaxies belonging to the Milky Way, they find that they lie in the plane of the Milky Way. Moreover, the observed formation is very unlikely from a dark matter point of view. So, that’s a win for the modified gravity crowd.
Another win for dark matter
the paper recently published in Astrological naturey takes another look at this observation using very accurate data measured by Gaia satellite. Gaia was designed to measure the location and direction of motion of up to a billion stars, and galaxies belonging to the Milky Way were included in the study.
What the paper found was that the methodology used to determine the orbital plane of the satellite group of galaxies was strongly influenced by two satellite galaxies, named Leo 1 and Leo 2, that were the most distant (about 700,000 to 800,000 light-years) from the center of the Milky Way. (The mathematical method weights the influence of satellite galaxies by the square of the distance between them.)
The two Leo galaxies are currently located roughly in the plane of the Milky Way. However, other, closer satellite galaxies are distributed spherically, though not quite as well. If the Leo moons are excluded from the analysis, the data no longer strongly favors the modified physics hypothesis. Importantly, when the motion of the Leo galaxies is measured by the Gaia satellite, the authors find that their location in the plane of the Milky Way is tentative. When they project their location a billion years into the past or future (the blink of an eye, in cosmological terms), these galaxies no longer exist on the galactic plane.
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In other words, when the hyperfocus on Leo satellite galaxies caused by the algorithm is taken into account, along with the temporary alignment in the galactic plane, the observations of satellite galaxies of the Milky Way are now fully consistent with the dark matter hypothesis.
Granted, one measurement is not enough to make a final decision in a debate. However, one of the strongest examples of data favoring modified physics and disturbing dark matter seems to no longer have its effect before. Given the broad support from other data for dark matter, this paper strengthened the case.