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.
