Astronomers Spot Strongest Proof Yet for Cold Dark Matter "Clumps" in Universe Using New Observation Techniques with Hubble
Astronomers using an innovative new observation technique on the Hubble Telescope have uncovered the strongest proof yet for the existence of dark matter in outer space and that it forms in tangled clumps throughout the universe – some of them very small – and strengthening current theories we have about this little-understood invisible form of matter.
"We made a very compelling observational test for the cold dark matter model and it passes with flying colors," Tommaso Treu, a member of the observing team from the University of California Los Angeles, said in NASA's official statement.
Dark matter is a theoretical form of matter that emits neither light nor energy. It is somehow very definitely there: scientists have observed dark matter's gravity acting on stars and galaxies – and the math all adds up – but we don't have the technology to actually see it. Yet scientists believe that it makes up as much as 80% of our universe.
There are many theories about dark matter. The "cold dark matter" theory seems to be the most popular. In this case, "cold" refers to how extremely slowly the dark matter particles are moving. The theory holds that the slow-moving particles of dark matter come together to form tangled clouds and clumps. They could be huge – "hundreds of thousands of times the size of the Milky Way" – or the size of a 747 airplane. Galaxies are born within these clouds of dark matter, and dark matter then impacts the motions of both the galaxies and their stars.
Scientists used a groundbreaking new technique to "see" dark matter. They trained Hubble on a series of quasars located 10 billion light-years away from Earth. Quasars are jets of intensely bright light beaming from the accretion disc of searing hot dust and gas that surrounds a black hole. NASA calls them "streetlights" of the universe. The team studied the light from the quasars, and observed how the galaxies (located 2 billion light-years away from Earth) between the quasar and Hubble bent the quasars' light with its gravity.
Credit: NASA, ESA and D. Player (STScI)
This is called "gravitational lensing" and it did, indeed, act as a magnifying lens – giving us multiple perspectives and enabling the researchers to map out clumps of dark matter between us, the quasar, and the galaxies in between. Astronomers then compared these images against their calculations for how the quasar would look without dark matter.
"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."
Credit: NASA, ESA, A. Nierenberg (JPL) and T. Treu (UCLA)
"Small dark matter clumps act as small cracks on the magnifying glass, altering the brightness and position of the four quasar images compared to what you would expect to see if the glass were smooth," explained Daniel Gilman, another team member from UCLA.
Simon Birrer, also of UCLA, added, "Particle physicists would not even talk about dark matter if the cosmologists didn't say it's there, based on observations of its effects."
Anna Nierenberg, the Hubble survey leader at NASA's Jet Propulsion Laboratory, concluded:
"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."