The Bullet Cluster was considered the main evidence for the existence of dark matter for more than two decades. Now it is working against that theory. New data from the James Webb Space Telescope show that the observed effects can be explained without invoking an invisible substance.
A Double Collision and an Invisible Framework
The Bullet Cluster formed as a result of the collision of two giant galaxy systems. It took place approximately 4 billion years ago at a distance of about 3.7 billion light-years from Earth. The collision speed exceeded 2,500 kilometers per second.
During this event, the hot gas from the interstellar space of both systems experienced friction, heated up, and slowed down. In composite images combining Webb data and X-ray telescope observations, these clouds are conventionally shown in pink. The galaxies themselves passed through one another almost without obstruction, since the distances between individual stars inside them are too great for frequent collisions. As a result, the visible concentrations of stars separated from their gas and continued moving forward.
Gravitational lensing, meaning the bending of light from distant objects, should have been strongest near the gas clouds. That is where most of the cluster’s ordinary matter is concentrated. However, observations showed the opposite. The strongest distortion of light occurred where the galaxies ended up.
This paradox became the main evidence in favor of dark matter. Something invisible and massive passed through along with the galaxies and did not experience friction, because it does not participate in electromagnetic interaction.
Remnants of Massive Stars Instead of Dark Matter
Scientists led by Dong Zhang of the Helmholtz Institute for Radiation and Nuclear Physics at the University of Bonn proposed an alternative. They stated that the Bullet Cluster actually agrees particularly well with the scenario of modified Newtonian dynamics, or MOND. This model does not require dark matter at all to explain the motion of galaxies.
The role of the invisible mass in this case may be played by remnants of massive stars. These are neutron stars and black holes left behind after supernova explosions. They are just as invisible to direct-observation telescopes as dark matter, but they create enormous gravity. In the standard model, which assumes the existence of dark matter, the amount of dark matter required in the cluster would have to be reduced by approximately half after taking such remnants into account.
The new Webb data made it possible to count the number of stars and heavy elements in the cluster more accurately. Dr. Indranil Banik of the Institute of Cosmology and Gravitation at the University of Portsmouth showed that this amount of ordinary matter, including stellar remnants, is sufficient to produce the observed lensing effect.
Reassessment of the Main Argument
For a long time, MOND could not explain the Bullet Cluster phenomenon, which is why it lost ground to the standard model. Now the same object has turned into an argument in its favor. The new study, published in the peer-reviewed journal Physical Review D, effectively deprives the standard cosmological model of one of its most convincing pieces of evidence.
However, the authors do not claim that dark matter does not exist. They only show that the Globular Cluster may no longer be considered as unequivocal evidence for its existence. To assess the validity of this conclusion, similar studies need to be carried out for other galaxy clusters in the process of collision.
According to universetoday.com
