Sunday, 22 July, 2018

Unique, oddball galaxy is strangely devoid of dark matter

3_28_Milky Way Galaxy without any dark matter baffles astronomers
Grady Vargas | 30 March, 2018, 00:46

For a galaxy like NGC1052-DF2, you'd expect to see about one hundred times more dark matter than visible matter-but astronomers found it has nearly no dark matter. On the other hand, he said, "this shows that dark matter is separate from galaxies".

"Finding a galaxy without dark matter is unexpected, because this invisible mysterious substance is the most dominant aspect of a galaxy", said Dokuum.

Theories like modified Newtonian dynamics and a new idea called emergent gravity propose that there is no dark matter. If there were no such thing as dark matter and the current laws of physics were just slightly wrong, you'd expect the laws to be just as wrong in NGC 1052-DF2 as they are everywhere else.

"There are simulations of the universe starting back near the Big Bang that show dark matter was produced and actually gravitationally attracted normal matter to it, and that's how the galaxies were formed", said Dan Bauer, a physicist at Fermi National Accelerator Laboratory, who studies dark matter and did not work on the paper.

Paradoxically, the discovery of a galaxy without dark matter may actually confirm that the stuff actually exists by contradicting hypotheses advanced by dark matter doubters. Confusing things further, the galaxy appears extremely similar to others that are almost entirely composed of dark matter.

But more detailed observations by the Dragonfly Telephoto Array, a DIY-style observatory cobbled together from Canon camera lenses to study faint, extended objects in the sky, caught van Dokkum and his team's interest. They found that the clusters were moving at relatively low speeds - less than 23,000 miles (37,000 km) per hour.

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NGC 1052-DF2 resides about 65 million light-years away in the NGC 1052 Group, which is dominated by a massive elliptical galaxy called NGC 1052.

The discovery of NGC1052-DF2 will hopefully go a long way in the future study of dark matter, which sounds odd, but its lack of dark matter will help scientist understand why it occurs in other places.

In fact, the best fit for the motion of the globular clusters is a galaxy with no dark matter at all, although the uncertainties are high enough that there could be equal amounts of matter and dark matter present.

Closer monitorings utilizing the Hubble and also 10-meter Keck telescopes revealed that the item, now described NGC1052- DF2, belonged to a lately uncovered course of things called ultra-diffuse galaxies. It is about the size of our own galaxy, but only one-hundredth of its stars, while - unlike ours - it does not have a black hole in its center. From those measurements, the team calculated the galaxy's mass.

The researchers describe the galaxy as looking like "a diffuse blob sprinkled with very compact star clusters". Given that there isn't a trace of the dark matter, data suggests that it's made entirely of normal matter. Since it does not, that particular explanation for dark matter, and why we can't see it, becomes less likely. "How do you create a galaxy without dark matter first?"

To develop more understanding of the unusual galaxy, the researchers then used both NASA's Hubble Space Telescope and the Gemini Observatory in Hawaii. It could be that NGC 1052-DF2 was once a placid mass of gas and has been recently perturbed by another unseen galaxy nearby, sparking star formation. The galaxy is a complete mystery, as everything about it is unusual. "But for now, I think the evidence for dark matter greatly outweighs the evidence against it".

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