NEIGHBOURING GALAXY TO BLAME FOR BIZARRE CASE OF MISSING DARK MATTER
Observations made by the Hubble Space Telescope solves two-year mystery
It’s all NGC 1035’s fault. That’s what observations made by an international team of researchers using the Hubble Space Telescope have suggested is the cause of a mysterious disturbance in a galaxy, far, far away. They’ve discovered that NGC 1035 is a massive galaxy that’s so big it is tearing its smaller neighbouring galaxy apart piece by piece, starting with its dark matter. The phenomenon is known as ‘tidal disruption’, but until now has remained hidden from view.
The story started in 2018 when astronomers discovered a galaxy, around 65 million light-years away, unlike any they’d seen before. What made this galaxy, named NGC 1052-DF2, exceptional was that most of its dark matter (the elusive substance known to make up 80 per cent of the Universe’s mass) was missing. The finding left the astronomers puzzled, as dark matter plays a key role in the current models of galaxy formation and evolution. Without it, the clouds of primordial gas made up of hydrogen and helium created in the Big Bang would lack the necessary gravitational pull to start collapsing and forming new galaxies.
A year later, another galaxy with missing dark matter (this one named NGC 1052-DF4 and 45 million light-years away) was discovered, proving that NGC 1052-DF2 wasn’t unique.
Now, new evidence gathered by Hubble has been used by a team of researchers led by Dr Mireia Montes of the University of New South Wales in Australia, to suggest that NGC 1052-DF4’s dark matter is being stripped by the gravitational pull of its massive neighbour NGC 1035. The smaller galaxy’s dark matter is the first thing to be torn away by the larger galaxy as the tidal disruption takes hold, with the stars succumbing at a later stage.
“We used Hubble in two ways to discover that NGC 1052-DF4 is experiencing an interaction,” said Montes. “This includes studying the galaxy’s light and the galaxy’s distribution of globular clusters.”
Globular clusters are spherical clusters of stars thought to have formed in the episodes of intense star formation that shaped galaxies. Their compact size and luminosity make them easy to observe.
Thanks to Hubble’s high-resolution imagery (and with help from the Gran Telescopio Canarias and the IAC80 telescope, both in the Canary Islands), the team could identify NGC 1052-DF4’s globular cluster population. This enabled them to construct a 3D picture of what’s happening in the galaxy. The alignment of its globular clusters suggests that they’re being stripped from their host and that tidal disruption is occurring.
“This discovery reconciles existing knowledge of how galaxies form and evolve with the most favourable cosmological model,” said Montes.
“The story started in 2018 when astronomers discovered a galaxy, around 65 million light-years away, unlike any they’d seen before”