A galaxy without dark matter: New measurements deepen the ‘complete mystery’

The mysterious galaxy NGC 1052-DF2 (DF2 for short) appears to be completely lacking in dark matter – and how it formed remains a “total mystery”. This is what a group of astronomers who used the Hubble Space Telescope to collect new data on DF2 said. It first caused a stir in 2018, when the first research data suggested that the motions of stars there could be explained almost exclusively by their gravity; There was very little space for dark matter. Then other measurements suggested that the galaxy was much closer to us, and the mystery seemed to be solved. But it is now certain that it is very far away, so there is still more dark matter missing. The researchers face a conundrum.

mysterious dark matter

Dark matter has not been directly observed yet, what exactly is one of the biggest questions in modern physics. The shape of matter, which has been described only theoretically so far, can be observed only through the force of gravity. This means that the motions of stars in the Milky Way cannot be explained by the gravitational pull of all visible objects alone; Invisible dark matter affects their orbits. This applies to all galaxies explored so far. A survey introduced in 2018 made NGC 1052-DF2 the first known counterexample. It is the size of the Milky Way, but contains 200 times fewer stars. With the calculated proportion of dark matter, the hyper-open galaxy reaches only 0.25% of the expected value.

If the galaxy is much closer to us than expected, that could explain the huge discrepancy and solve the mystery, as has been said over and over again. This is why Yale University’s Zili Shen team has 2020 Detailed measurements using the Hubble Space Telescope On the red giant stars at the edge of the galaxy in order to determine the difficulty of determining the distance more accurately. Accordingly, it is 72 million light-years away from us and not 65 million light-years as it was assumed in 2018. They couldn’t confirm the distance of 42 million light-years only, which was announced in the meantime, until the mystery was solved. Instead, the “complete mystery” about DF2 only deepened, as they explained Now in Astrophysical Journal Letters. How the galaxy arose is inexplicable.

The team also shows that in 2020, another galaxy, NGC 1052-DF4, was discovered, and it appears to be completely devoid of the mysterious dark matter. Since the two galaxies are relatively close together, researchers believe the absence is due to a common composition. The new measurements would have shown, however, that at 6.5 million light-years the distance is farther than expected. In addition, there is a theory of DF4, according to which another galaxy can tear dark matter. There are no candidates for DF2. The team explains that further exploration of galaxies and the search for similar galaxies could in any case provide more insights into the nature of dark matter. In addition, the discovery of galaxies with and without dark matter confirms the fact that the mysterious form of matter actually exists.

(mo)