“The nature of dark matter is one of the biggest mysteries in science and we need to use any related new data to tackle it,” says astronomer Avi Loeb with the Harvard-Smithsonian Center for Astrophysics. Dark matter is “dark” in the sense that it hardly interacts with anything, particularly with light. While dark matter may be too elusive to be found in particle experiments, it can reveal its presence in astronomical observations.
At the Boundaries of Fundamental Physics
Dark matter pushes at the boundaries of the known fundamental laws of physics. Leading candidates for dark matter that have so far defied every type of detector designed to find it. Because of its huge gravitational footprint in space, we know dark matter must make up about 85 percent of the total mass of the universe, but we don’t yet know what it’s made of, but if it has anything to do with any scalar particles, it may be older than the Big Bang, suggest physicists, who, sounding like creators of science-fiction have imagined new kinds of dark matter ranging from planet-sized particles to highly-speculative dark-matter life.
Hubble’s Clues to Missing Dark Matter
But what astrophysicists do know, is that new data from the Hubble Space Telescope explains the reason behind the missing dark matter in NGC 1052-DF4, which resides 45 million light-years from Earth. Astronomers discovered that the missing enigmatic matter can be explained by the effects of tidal disruption from gravity forces of the neighboring massive galaxy NGC 1035 that are stripping NGC 1052-DF4 of dark matter. while the stars feel the effects of the interaction with another galaxy at a later stage.
Until now, the removal of dark matter in this way has remained hidden until astronomers using Hubble’s high resolution could observe extremely deep images that can reveal extremely faint features including identifying the galaxy’s globular clusters population.
“We used Hubble in two ways to discover that NGC 1052-DF4 is experiencing an interaction, This includes studying the galaxy’s light and the galaxy’s distribution of globular clusters,” explained STScI Fellow at the Space Telescope Science Institute, Mireia Montes of the University of New South Wales in Australia, who led an international team of astronomers to study the galaxy using deep optical imaging including 10.4-metre Gran Telescopio Canarias (GTC) telescope and the IAC80 telescope in the Canaries, Spain, to complement Hubble’s observations,
This image at the top of the page shows the region around the galaxy NGC 1052-DF4, taken by the IAC80 telescope at the Teide Observatory in Tenerife. The figure highlights the main galaxies in the field-of-view, including NGC 1052-DF4 (center of the image), and its neighbor NGC 1035 (center left).
Globular Clusters Reveal Clues
Globular clusters — the oldest visible objects in the universe thought to have formed soon after the Universe began nearly 13.8 billion years ago, at the same time as, or perhaps even before, the first galaxies formed. They are thought to form in the episodes of intense star formation that shaped galaxies. Each contains hundreds of thousands to occasionally over ten million stars all born at essentially the same time, and densely packed into a spherical volume with diameter over a thousand times smaller than the diameter of the Milky Way. Their compact sizes and luminosity make them easily observable and they are therefore good tracers of the properties of their host galaxy.
By studying and characterizing the spatial distribution of the clusters in NGC 1052-DF4, astronomers can develop insight into the present state of the galaxy itself. The alignment of these clusters suggests they are being “stripped” from their host galaxy, and this supports the conclusion that tidal disruption is occurring.
Tidal Tails Confirm a Disruption Event
By studying the galaxy’s light, the astronomers also found evidence of tidal tails, which are formed of material moving away from NGC1052-DF4—this further supports the conclusion that this is a disruption event. Additional analysis concluded that the central parts of the galaxy remain untouched and only ∼ 7% of the stellar mass of the galaxy is hosted in these tidal tails. This means that dark matter, which is less concentrated than stars, was previously and preferentially stripped from the galaxy, and now the outer stellar component is starting to be stripped as well.
Stars Showing Effects After Evaporation of Dark Matter
“This result is a good indicator that, while the dark matter of the galaxy was evaporated from the system, the stars are only now starting to suffer the disruption mechanism,” explained team member Ignacio Trujillo of the Instituto de Astrofísica de Canarias in Spain. “In time, NGC1052-DF4 will be cannibalized by the large system around NGC1035, with at least some of their stars floating free in deep space.”
“A Sigh of Relief”
The discovery of evidence to support the mechanism of tidal disruption as the explanation for the galaxy’s missing dark matter has not only solved an astronomical conundrum, but has also brought a sigh of relief to astronomers. Without it, scientists would be faced with having to revise our understanding of the laws of gravity.
“This discovery reconciles existing knowledge of how galaxies form and evolve with the most favorable cosmological model,” added Montes.
The Daily Galaxy, Max Goldberg, via ESA/Hubble Information Centre