Astronomers have discovered a strange galaxy that has no dark matter
three years ago, Filippo Transnational And his colleagues observed the distribution of a strange galaxy that looked like a collection of cities scattered with stars and gas; But unlike other galaxies, including the Milky Way, these galaxies did not appear to have massive masses of dark matter that could hold these star cities together by gravity. Scientists have selected one of these galaxies for further study. The galaxy is about 250 million light-years from Earth. Researchers have placed 27 radio telescopic antennas from New Mexico’s massive array (VLA) toward the galaxy.
After collecting the data, the researchers created a map of stars and gas that confirmed the initial theories. “The amount of dark matter in this galaxy was much, much lower than expected,” said Fraternali, an astronomer at the Captain Astronomical Institute at the University of Groningen in the Netherlands.
If researchers or their competitors find other similar galaxies, a challenge to understanding dark matter will begin, which has been the dominant theory for the past twenty years. Fraternali and his team published their findings in the December issue of the Monthly Notices of the Royal Astronomical Society.
Based on decades of telescopic observations and computer simulations, scientists have identified dark matter as the hidden skeleton of the universe. It consists of massive masses of invisible particles and hosts large and small galaxies. The transcendental is not the first person to see this exception; Because a few years ago Peter Vanducom, Astronomer Yale and colleagues discovered similar galaxies with the Hubble Space Telescope that appeared to have no dark matter. Vandocom says:
These galaxies were discovered in 2018 and created a series of controversial debates; Because this finding was very unexpected and we could hardly explain it.
The galaxies previously observed are in a crowded environment. In these environments, galaxies pass by each other, possibly stealing dark matter. However, the transnational galaxy is completely isolated and has no disturbing neighbors; As a result, the scarcity of dark matter in this galaxy cannot be justified. “This is a very important result,” Vandokum added. “How can stars and gas coexist in an environment without the help of dark matter?”
Astronomers mapped stars (blue) and gas (green) to a strange galaxy called AGC 114905
These are strange objects Super-scattered galaxies (Ultra diffuse galaxies) and are classified into very specific categories in terms of mass. These galaxies are small; But they have spread far and wide. Some of them are the size of the Milky Way; But their number of stars is only one hundredth of the Milky Way or even less. Also, these galaxies are almost transparent and difficult to observe in the night sky. Miria Montes“Astronomers at the Baltimore Space Telescope Institute of Science say:
These galaxies have a smaller center; As a result, they are difficult to observe. Today, with better telescopes and deeper observations, they can be better observed.
Vera Rubin He was one of the first astronomers in the 1960s to measure the speed of stars around the center of galaxies, raising the possibility of dark matter. He showed that the stars in the galaxy’s inner orbit have different speeds than the more outer orbits. Based on the rotation of these stars, the scientists calculated the mass required for their continuous orbital motion.
In many of these galaxies, this mass was many times greater than the total number of stars. Scientists solved this problem with the hypothesis that dark matter emits no light, and concluded that this matter probably makes up the rest of the galaxy’s mass.
Transnatal measurements and his team showed that such a scattered galaxy did not need to rely on dark matter; Because the velocities of rotation were exactly the same as the mass of the stars and the gas of the galaxy, no additional negligible mass was required. Montes and his team also studied such galaxies, including their outer slopes; But at least for now, this galaxy-like galaxy remains a complex mystery.
The galaxy AGC 114905 does not conform to any of the definitions of dark matter
The transcendentalist believes that their target galaxy, AGC 114905, has a strange feature: aberration. Some galaxies are like flying saucers, and if a telescope could see them from a distance, they would be easier for astronomers to observe; Because they can see the rotating stars on one side of the galactic disk moving towards us and the stars moving away from us on the other side. If they can measure the speed of these stars, they can estimate the mass of the galaxy and dark matter.
However, according to transnational calculations, the AGC 114905 deviates slightly more than 30 degrees; As a result, astronomers have calculated the mass correctly for this amount of deviation. If they make a mistake about the degree of deviation, there is a lot of room for dark matter in the measurements.
Assuming the researchers’ calculations are correct, it is not yet clear what exception their galaxy is. Is this galaxy really a strange cosmic mass that no one can comprehend, or can it be a spark for bigger issues in dark matter theories?
The galaxy has not yet conformed to any of the proposed definitions for the origin of superconducting galaxies; As a result, astronomers speculate that such a galaxy, with a small amount of dark matter, could be the remnant of a pair of larger galaxies that, passing side by side, exerted gravitational forces on each other, leaving a puffy bubble of stars and gases; But there are no giant galactic neighbors around the galaxy; Therefore, this explanation is not correct.
According to another theory, the galaxy could be a remnant of past stellar explosions. All stars eventually die, and this death occurs in some stars in the form of a supernova explosion. Over time, supernovae eject parts of galaxies and repel materials, including gas clouds. However, this is not the case for AGC 114905; Because this galaxy is still full of gas, which is the building block and fuel for new stars. If this galaxy had been denser in earlier periods, it could be said that a large part of the compact clusters of today’s stars are an indicator of a denser past; But this galaxy lacks such clusters.
In fact, AGC 114905 does not appear to apply to any of the dark matter models. Decades of scientists like Lara Cells, UC Riverside astrophysicist simulated the universe on powerful computers and tried to show dark matter models that reconstruct astronomers’ observations. “We quickly looked at the simulations and found nothing like this galaxy,” says Sells.
The transcendental galaxy and others may point to the need for alternatives to dark matter. When scientists point to the existence of dark matter, they are actually making hypotheses about the function of gravity; But what happens if gravity acts a little differently than they imagined?
Fraternali et al. In his project One of the theories of a possible winner called MOND Or they tested modified Newtonian dynamics to replace dark matter, which includes Newton’s law of gravity with a slight change. This theory is called a physicist Milgrom cases He proposed in the 1980s that the standard physics of gravity, which describes the motion of objects at high gravitational velocities such as the planets in our solar system, might not apply to slow stars at the edge of the galaxy disk.
According to this theory, the difference between the expected velocities of stars in galaxies and their velocities is not a sign of lost mass; It is a mathematical error. Although the model MOND well describes normal galaxies, it can not justify the rotation of the transnatal puffy galaxy.
In general, it is too early to conclude that AGC 114905 is incompatible with dark matter theories. For now, Fratarnali and others will continue to study these strange galaxies, and the James Webb Space Telescope will raise hopes for these studies. Vandocom concludes:
It’s not like looking at the edge of the universe or trying to discover small planets next to a star. This research will be done with the tools we have.