Category: df2

Ask Ethan: What’s The Real Story Behind …

Ask Ethan: What’s The Real Story Behind This Dark Matter-Free Galaxy?

“I read a study that said the mystery of a galaxy with no dark matter has been solved. But I thought that this anomalous galaxy was previously touted as evidence FOR dark matter? What’s really going on here, Ethan?”

Imagine you looked at the Universe, and saw a galaxy unlike any other. Whereas every other galaxy we’ve ever looked at exhibited a large discrepancy between the amount of matter that’s present in stars and the total amount of gravitational mass we’d infer, this new galaxy appears to have no dark matter at all. What would you do? If you’re being a responsible scientist, you’d try to knock down this galaxy by any scrupulous means possible. You’d wonder if you had mis-estimated one of its properties. You’d try to re-confirm the measurements with different instruments and techniques. And you’d wonder if there weren’t an alternative explanation for what we were seeing.

Well, if you read that the galaxy has dark matter after all, and the mystery has been resolved, you should definitely read this instead. The story is far from over, and even if the new team’s results hold up, there’s still a mystery at play here.

5 Ways To Make A Galaxy With No Dark Matter “…

5 Ways To Make A Galaxy With No Dark Matter

2.) Ejected from galactic mergers. When two galaxies smash together, they usually merge entirely, but sometimes there is ejected material. Sufficient amounts could create a baryons-only galaxy.”

Last week, astronomers announced the discovery of the ultra-diffuse galaxy NGC 1052-DF2 (or DF2), which appears to be completely free of dark matter. Other similar galaxies have been seen before, but all contain more, not less, dark matter than you’d have expected on average. This first galaxy ever seen without the gravitation-altering effects of dark matter was touted to defy theory, but it does no such thing. In fact, there are many explanations that lead directly to galaxies such as DF2 as an inevitable consequence, including one that was put forth in a predictive fashion as much as 20 years ago.

Come find out the five ways to make a galaxy without dark matter, and learn why this is such an important test of dark matter theory itself!