Scientists discover galaxy that appears to lack dark matter
Scientists discover galaxy that appears to lack dark matter
Galaxy without any dark matter baffles astronomers
30 March, 2018, 00:48
This galaxy, NGC 1052-DF2, is the size of the Milky Way but only has 1/200 the amount of stars, with no dense center or spiral arms or black hole. What has scientists so curious about this galaxy is that it is unusually transparent and appears to contain no dark matter.
Although it has never been directly observed, scientists are confident that this elusive material exists because of the gravitational effects it appears to have on astronomical objects.
The scientists then used larger telescopes - including the W.M. Keck Observatory in Hawaii and the HubbleSpace Telescope - to do followup observations. "I spent an hour just staring at this image", van Dokkum said as he recalled first seeing the Hubble image of NGC 1052-DF2. "It's so rare, particularly these days after so many years of Hubble, that you get an image of something and you say, 'I've never seen that before.' This thing is astonishing: a huge blob that you can look through. It is literally a see-through galaxy", he added.
But none of the ultra-diffuse galaxies discovered so far have been found to be lacking in dark matter. By looking at the dynamical properties of ten globular clusters - essentially, a very large ball of stars - orbiting the galaxy, it allowed the team to work out an independent value of the galaxies mass. Dokkum said that the discovery challenges the standard ideas of galaxy formation. In other words, dark matter doesn't seem to be exerting its gravity on normal matter in that galaxy.
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. "How do you create a galaxy without dark matter first?" "But what would you get if there were no dark matter at all?"
Ultra-Diffuse galaxies had actually been recognized formerly in various other galaxy collections. That would only make sense if there was no dark matter at all acting on them, a finding confirmed when the researchers subsequently calculated the mass of the galaxy. "This whole story is one of dark matter being the scaffolding on which every galaxy is built", said van Dokkum. In one, a sudden explosion of massive star-birth inside the galaxy could have cleared out all of its gas and dark matter. Of course, they point out that most of the things we've found that look similar have turned out to have an excess of dark matter, so there's a lot we still need to figure out here. The researchers then set about measuring the movements of the clusters as a way to estimate the galaxy's total mass.
The galaxy, charmingly named NGC1052-DF2, is about 65 million light-years away and is about one two-hundredths the mass of our own Milky Way galaxy. Yet in this unusual galaxy, the projected signatures of these exotic effects are not seen.
The team is already hunting for more dark-matter deficient galaxies.
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. The gas crunched together in balls, lit up as stars, and formed planets and galaxies. The researchers, led by Mr. Peter van Downey of the University of Yale, USA, made the relevant publication in Nature magazine and relayed by the Athenian News Agency.
Dark matter does not emit electromagnetic radiation, and remains immune to direct observation.
But that doesn't mean the results in this paper provide ideal support for dark matter theories either.
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