Located 6.5 billion light years from our own Milky Way galaxy, is the ghostly looking NGC 1052-DF2 the first dark matter free galaxy ever discovered?
By: Ringo Bones
Back in 2015, a Harvard University astronomer named Pieter van Dokkum used the Dragonfly Telephoto Array in order to investigate faint astronomical objects, and these include ultra diffuse galaxies that look quite ghostly in comparison to our own Milky Way galaxy. Then as recently as March 28, 2018, Dokkum and his team of astronomers published their findings on why the galaxy NGC 1052-DF2 looks so diffuse and ghostly in comparison to a typical galaxy like our Milky Way – that is the ghostly looking galaxy is devoid of dark matter.
Even though Earth-based detectors / traps containing liquid xenon, ultrapure germanium and gallium has yet to confirm the existence of this elusive substance, cosmologists and theoretical physicists had reached a consensus for about two decades now that dark matter is essential in the formation of galaxies. Since the 1950s, astronomers noticed that the amount of visible matter in a typical galaxy is not enough to hold all of the stars, gases and dust in place and from flying up given its rate of rotation – even the subsequent discovery of super-massive black holes in the centers of galaxies is not enough to hold all of it together; which makes 85-percent of the bulk of the Universe hitherto unseen hence the concept of dark matter.
Unusually ghostly and transparent, NGC 1052-DF2 (the NGC stands for New General Catalog as a new designation for the classification of nebulae, stars and galaxies – as opposed to the older M or Messier catalogue system) is about the size of our Milky Way galaxy and yet it contains 200 times fewer stars and 400 times less dark matter than our own galaxy and also lies 6.5 billion light years away from us. If this turns out to be true, NGC 1052-DF2 may be the first galaxy of its kind that is made up only of ordinary matter. Current astrophysical laws as we know then dictates that dark matter is thought to be very essential to the fabric of the Universe as we understand it.
The study of this ghostly galaxy has recently been published in the science journal Nature. The authors of the study weren’t initially on the hunt for dark-matter-free galaxies instead they had set out to take a closer look at ultra-diffuse galaxies. These are similar in size to the spiral galaxies we’re more familiar with but have a fraction of the number of stars. When Prof. Pieter von Dokkum, lead author of the study, first spotted NGC 1052-DF2 said: “I stared a lot at that image and just marveled at it... its like a ghostly glow in the sky…”
Galaxy NGC 1052-DF2 has very few stars but many of them are grouped together in unusually bright clusters. When the team studied the behavior of these clusters, they found that the stars seemed to account for all of the galaxy’s mass, leaving no room for dark matter. In a typical spiral galaxy like our Milky Way, there’s about five times more dark matter than regular matter. And as you go further out from the galaxy, you’ll find fewer stars and more dark matter. The dark matter halo is much more extended than the stars are in a typical spiral galaxy.