Astronomers at Yale University have identified a third galaxy, NGC-DF9, located 67 million light-years from Earth, and appears to lack dark matter, a theoretical invisible substance necessary for most galaxy formation. This discovery joins the previously identified DF2 and DF4, and all nine galaxies including DF9 are now shown aligned in a straight line. The line of galaxies lacking dark matter has never been seen before, said researcher Michael Kim, a doctoral student in astrophysics at Yale University’s Graduate School of Arts and Sciences. The researchers suggest a violent collision separates the gas from the dark matter, allowing DF9 to form solely from ordinary matter, providing a new window into the nature of dark matter itself. This discovery challenges current assumptions about how galaxies form and suggests that dark matter can behave independently of ordinary matter.
DF9 joins DF2 and DF4: third dark matter-free galaxy discovered
This discovery, detailed in The Astrophysical Journal, follows the previous identification of DF2 and DF4 as being similarly deficient in the invisible matter that is thought to make up the majority of the universe’s mass. The researchers determined DF9’s mass by measuring the velocities of stars inside it, and found a total of 100 million solar masses, consistent with visible matter alone. This contrasts sharply with the expected mass of more than 10 billion solar masses if dark matter were present, reinforcing the anomaly. The team, led by Peter van Dokkum, used the Cosmic Web Imager of the WM Keck Observatory in Hawaii to analyze the faint light emitted by DF9, initially misidentifying it as a supermassive black hole.
This careful analysis revealed the unique composition of the galaxy and confirmed its place among galaxies devoid of dark matter. Until now, it was assumed that galaxies form inside clumps of dark matter called “halos,” Kim suggested, but this system shows that stars and galaxies can originate outside these halos during extreme events. This challenges theories that assume dark matter is a modification of gravity, supporting the idea that it is a physical substance capable of independent action. The team is now searching for the gas remaining from the initial collision using telescopes including the newly created Mothra telescope, in the hope of improving their understanding of this unusual galaxy formation process.
This system shows that stars and galaxies can form outside of dark matter “halos” in extreme events, and indicates that dark matter is physical matter that can act independently of ordinary matter or gas, challenging alternative theories that dark matter is gravity.
The Cosmic Web Imager confirms the low mass and stellar composition of DF9
Confirmation of the formation of DF9 was based on observations from the WM Keck Observatory. This galaxy joins DF2 and DF4 in a strange alignment, forming a straight line with seven other galaxies, a configuration that has led to a re-evaluation of galaxy formation processes. The team suggests a violent collision as the catalyst for this unusual formation, suggesting that the collision stripped the gas of dark matter, allowing the gas to assemble into new galaxies along a linear path. The existence of galaxies forming independently of dark matter supports the idea that dark matter is a distinct physical substance, capable of separating from ordinary matter during extreme events. More observations are planned, including one using the new Mothra telescope, to search for gas remaining from the initial collision and improve this emerging picture of the galaxy’s evolution.
They found that DF9’s mass is equivalent to 100 million suns, which is consistent with the expected amount of visible matter in a galaxy of this size, and nothing else.
The galaxy collision theory explains the linear arrangement of dark matter-poor galaxies
NGC-DF9, a dwarf galaxy located 67 million light-years away, has become the third known galaxy to show a striking absence of dark matter, joining DF2 and DF4 in challenging traditional cosmological models. The discovery, published in the Astrophysical Journal, extends beyond individual anomalies; Researchers have identified a distinct alignment, where nine galaxies, including DF9, appear to form a straight line across vast cosmic distances. This process, illustrated in artist renderings, explains the linear formation and shared properties of the dark matter deficiency between DF2, DF4, and now DF9.
A line of galaxies lacking dark matter has never been seen before.
