Galaxy with missing dark matter

Galaxy without any dark matter baffles astronomers

Galaxy without any dark matter baffles astronomers

(It's dark because it's light-less.) In 2003, the Wilkinson Microwave Anisotropy Probe (WMAP), which carefully and precisely measured the relic radiation from what we can only call the beginning of the universe (but, of course, there was no beginning in the normal sense of the word or even an explosion in the normal sense of that word), showed the universe is flat and that these unusual and light-less particles made up about 24 percent of everything.

There have been several ideas that have floated around regarding the true nature of dark matter, and discoveries like this will only push astronomers to unlocking its secrets. "So it only makes sense if dark matter is a real substance, that can be present or not, separately from the regular matter", Mack added. The result of this would be that a signature usually attributed to dark matter should always be detected, and is an unavoidable effect of the presence of ordinary matter.

So, when astronomers look at the galaxies, our own Milky Way included, they find that the normal matter - stars, dust, nebulae, etc - are moving so fast that they'll all just fly apart from one another. Data from observations made on this and other instruments around the world eliminated all other explanations but one: this galaxy did not interact with or have any dark matter.

"Instead we saw the opposite, leading to this remarkable conclusion that there's actually no room for dark matter at all in this thing", van Dokkum says.

Roughly 65 million light-years away from Earth is a galaxy called NGC 1052-DF2 (DF2 for short). His favorite: That the galaxy formed in the very early universe in a way astronomers have never seen or understood. "It is pretty weird".

"Something like this has never been seen", said Prof Pieter van Dokkum, of Yale University, the study's senior author. In spite of the fact that we can't straightforwardly watch it, we know dark matter is there in light of the fact that we can perceive how its gravity influences ordinary matter. Usllay galaxies have a larger mass than can be accounted for just by the ordinary matter inside them. 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. From those measurements, the team calculated the galaxy's mass.

By observing it with the Hubble telescope, Pieter van Dokkum likens it to "a big blob through which we can see". Even the globular clusters are oddballs: they are twice as large as typical stellar groupings seen in other galaxies.

Based on this understanding, the team studying DF2 thought they had a pretty good idea how much dark matter it contained.

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So, DF2 is definitely an oddball. But upon further study, an global team of astronomers was surprised to discover that it had no dark matter, something that has been seen as crucial in the formation of galaxies.

Dark matter also connects giant clusters of galaxies with thin tendrils, forming an enormous cosmic web that gives the universe its structure. "Not sure what to make of it, but it is definitely intriguing", she said.

The galaxy has very few stars, but many of them are grouped together in unusually bright clusters. But a small, distant galaxy is challenging everything we thought we knew about galaxy formation. The faster they're moving, the more dark matter there must be.

Oddly enough, this galaxy with very little dark matter actually helps to confirm the existence of dark matter. The leading dark matter theory predicts that this "sea" of particles moves around a galaxy in deep, plunging orbits like comets around the sun.

Alternatively, in the absence of any direct dark-matter detections, some theorists have suggested its existence is illusory-and that something else drives galaxy evolution and gravitational lensing.

What's next for this research?

The researchers suggest that the somewhat-odd appearance of the globular clusters is probably related to the galaxy's unexpected properties, and they announced they're working on a paper that will describe those.

"We're now undertaking a survey to find more objects like DF2", says Abraham.

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