Van Dokkum's group upgraded the rotation speed of Dragonfly 44. It was found that mond was vindicated. McGaugh said thatDragonfly 44 is an example of how these data evolve.
The slower rotation speed implied that the halo is smaller than they thought. Van Dokkum disagrees with the result of the 2020 halo count. The size of the halo is uncertain, but it may be less massive than first thought.
The mystery has been compounded by a new discovery.
According to a paper published in August, Dragonfly 44 is between 10 billion and 13 billion years old.
It shouldn't be as big as the one in Dragonfly 44. Early-universe objects tend to be smaller than later-universe objects.
It should have been torn apart by now. It's possible that Dragonfly 44 has a large dark matter halo after all. "That's a really fun explanation, so that's why I like it, but I don't know if it's right"
The "high spin" hypothesis suggests that two small galaxies merged while rotating in the same direction, and that the resulting galaxy, Dragonfly 44, was the result. It puffed out and blew out its star-making material because of this.
Astronomers have cataloged a wide range of other ultra-diffuse galaxies, despite the scrutiny of Dragonfly 44. The findings are forcing them to think differently.
Dark matter seems to be missing from some new UDGs. The group of Van Dokkum spotted a trail of others nearby. The team speculated in Nature that the trail was formed in the aftermath of a collision. The dark matter kept going even though the flow of gas slowed. A string of dark matter-free galaxies were formed by the compressed gas.
There are two UDGs that point to a different theory. The UDG seems to have been ripped apart by the force of a heavy nearby galaxy. This can't explain the location of Dragonfly 44.
The September paper reported star formation in a UDG that was contrary to the idea that they only harbor old stars.
Dark matter theory may be supported by a range of UDGs that are different inside and out. Van Dokkum said that the stars are moving very fast in one galaxy and very slowly in the other.
If there are genuine outliers within the UDG population, that is a problem for MOND. That doesn't mean dark matter is a better interpretation.
New telescopes will be required to answer definitive questions. When distant galaxies appeared in the early universe, the James Webb Space Telescope spotted them and will help test and refine the ideas.
Van Dokkum said that we don't know what's out there. Even after all these decades of studying the sky, we haven't discovered many large, very close by, and unusual galaxies that are in our current catalog.
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