Tiny, cold clumps of dark matter seen by Hubble backs key prediction in dark matter physics

The finding suggests to astrophysicists that dark matter is a lot 'colder' than they knew, in smaller scales.


Scientists, mathematicians and astrophysicists alike have been investigating a mysterious, ubiquitous and seemingly-invisible substance that has gone by the name of 'dark matter' for a few decades now. Still, this frustrating quest for answers only seems to be turning up more mysterious with time.

While many theories suggest dark matter exists, overwhelming evidence suggests that dark matter makes up the bulk of the Universe’s mass, and makes up the very scaffolding that holds galaxies and its contents together in the "vacuum" of space.

Pursuing evidence of the "invisible mass" hasn't been easy, but scientists have managed to "detect" them using indirect methods (like the ones used to study black holes, while we've only ever "seen" a black hole once in human history). What they're measuring is how the combined gravity of dark matter affects the motions of stars and galaxies.

 Tiny, cold clumps of dark matter seen by Hubble backs key prediction in dark matter physics

Each of these Hubble Space Telescope snapshots reveals four distorted images of a background quasar — an extremely bright region in the centre of some distant galaxies — and its host galaxy surrounding the core of a foreground massive galaxy. Image: NASA-JPL

In a new study, researchers have found evidence of dark matter, in clumps, around galaxies that are relatively medium and large in size. With a new observation technique and data from the Hubble telescope, a group of UCLA and NASA JPL astronomers has stumbled on dark matter forming much smaller clumps than previously thought.

Without any reassurance from visuals of the "small size" clumps, researchers have developed alternative theories, like that of "warm dark matter." The idea suggests that dark matter is fast-moving, zipping along so quickly that it doesn't merge and form small pockets. The JPL-UCLA study has contradictory evidence to this scenario, providing evidence that dark matter is "colder" than the warm dark matter theory suggests.

An illustration showing how light from a faraway quasar (a super-bright region in the center of some distant galaxies) is altered by a massive foreground galaxy. The galaxy's powerful gravity warps and magnifies the quasar's light, producing four distorted images of the quasar, in a process called 'gravitational lensing'. Image: NASA

An illustration showing how light from a faraway quasar (a super-bright region in the centre of some distant galaxies) is altered by a massive foreground galaxy. The galaxy's powerful gravity warps and magnifies the quasar's light, producing four distorted images of the quasar, in a process called 'gravitational lensing'. Image: NASA

"Astronomers have carried out other observational tests of dark matter theories before, but ours provides the strongest evidence yet for the presence of small clumps of cold dark matter," Anna Nierenberg of NASA's Jet Propulsion Laboratory in Pasadena, California, leader of the Hubble survey said in a press release. "By combining the latest theoretical predictions, statistical tools and new Hubble observations, we now have a much more robust result than was previously possible...dark matter is colder than we knew at smaller scales."

The results confirm a fundamental prediction in the "cold dark matter" theory in astrophysics. The team presented their findings at the 235th meeting of the American Astronomical Society (AAS), held 4–8 January 2020 in Honolulu, Hawaii.

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