NASA | GSFC | STScI | HubbleSite | 2020 Jan 08
Using NASA's Hubble Space Telescope and a new observing technique, astronomers have found that dark matter forms much smaller clumps than previously known. This result confirms one of the fundamental predictions of the widely accepted "cold dark matter" theory.Each of these Hubble Space Telescope snapshots reveals four distorted images of a
background quasar and its host galaxy surrounding the central core of a foreground
massive galaxy. The gravity of the massive foreground galaxy is acting like a magnifying
glass by warping the quasar’s light in an effect called gravitational lensing. ... The
presence of the dark matter concentrations alters the apparent brightness and
position of each distorted quasar image. Astronomers compared these measurements
with predictions of how the quasar images would look without the influence of the
dark matter clumps. The researchers used these measurements to calculate the masses
of the tiny dark matter concentrations. Hubble's Wide Field Camera 3 captured the near
infrared light from each quasar and dispersed it into its component colors for study with
spectroscopy. The images were taken between 2015 and 2018.
Credits: NASA, ESA, A. Nierenberg (JPL) and T. Treu (UCLA)
All galaxies, according to this theory, form and are embedded within clouds of dark matter. Dark matter itself consists of slow-moving, or “cold,” particles that come together to form structures ranging from hundreds of thousands of times the mass of the Milky Way galaxy to clumps no more massive than the heft of a commercial airplane. (In this context, "cold" refers to the particles' speed.)
The Hubble observation yields new insights into the nature of dark matter and how it behaves. "We made a very compelling observational test for the cold dark matter model and it passes with flying colors," said Tommaso Treu of the University of California, Los Angeles (UCLA), a member of the observing team.
Dark matter is an invisible form of matter that makes up the bulk of the universe's mass and creates the scaffolding upon which galaxies are built. Although astronomers cannot see dark matter, they can detect its presence indirectly by measuring how its gravity affects stars and galaxies. Detecting the smallest dark matter formations by looking for embedded stars can be difficult or impossible, because they contain very few stars.
While dark matter concentrations have been detected around large- and medium-sized galaxies, much smaller clumps of dark matter have not been found until now. In the absence of observational evidence for such small-scale clumps, some researchers have developed alternative theories, including "warm dark matter." This idea suggests that dark matter particles are fast moving, zipping along too quickly to merge and form smaller concentrations. The new observations do not support this scenario, finding that dark matter is "colder" than it would have to be in the warm dark matter alternative theory. ...
Warm dark matter chills out: constraints on the halo mass function and the free-streaming
length of dark matter with 8 quadruple-image strong gravitational lenses ~ Daniel Gilman et al
- arXiv.org > astro-ph > [ur=https://arxiv.org/abs/1908.06983l]arXiv:1908.06983[/url] > 19 Aug 2019 (v1), 11 Nov 2019 (v4)