New Hubble images add to the dark matter puzzle

The images and our best computer models don't agree.

galaxy cluster MACSJ 1206
  • Scientists can detect the gravitational effects of invisible dark matter.
  • Dark matter causes visual distortions of what's behind it.
  • The greater the distortion, the greater the amount of dark matter. Maybe.

    • Dark matter is believed to be important stuff, the glue that holds together the dust, gas, and stars that make up galaxies. It's the organizing force for the universe's large-scale structure, the shape you'd see if you were able to zoom way, way out, and it comprises most of a galaxy's mass.

      We don't know precisely what dark matter is, since it doesn't emit or reflect light, or absorb it for that matter, rendering it invisible to our instruments. However, we can see what dark matter does, insofar as light from objects behind dark matter warps and is magnified as it makes its way toward us. That visual distortion is referred to as dark matter's "lensing" effect, as it's similar to what you might see passing a magnifying glass over an object.

      Now a new study of images from the Hubble Space Telescope combined with spectra from the European Southern Observatory's Very Large Telescope (VLT) in Chile finds that there's either a lot more dark matter than computer models predict, or there's a major puzzle piece missing from what we thought we knew about dark matter's behavior.

      A trio of intriguing galaxy clusters

      The three galaxy clusters imaged for the study

      Credit: NASA, ESA, G. Caminha (University of Groningen), M. Meneghetti (Observatory of Astrophysics and Space Science of Bologna), P. Natarajan (Yale University), and the CLASH team.

      The discrepancy has to do with images of three galaxy clusters captured by Hubble's Wide Field Camera 3 and Advanced Camera for Surveys as part of two Hubble projects: The Frontier Fields and the Cluster Lensing And Supernova survey with Hubble (CLASH) programs. The three clusters are called MACS J1206.2-0847, MACS J0416.1-2403, and Abell S1063.

      Such imagery can be used for authenticating — or exposing flaws in —predictive computer models of dark matter's behavior, locations, and concentrations.

      Lead author Massimo Meneghetti of the INAF-Observatory of Astrophysics and Space Science of Bologna, Italy, says that "galaxy clusters are ideal laboratories in which to study whether the numerical simulations of the Universe that are currently available reproduce well what we can infer from gravitational lensing."

      Mapping dark matter

      The assumption has been that the greater the lensing effect, the higher the concentration of dark matter.

      As scientists analyzed the clusters' large-scale lensing — the massive arc and elongation visual effects produced by dark matter — they noticed areas of smaller-scale lensing within that larger distortion. The scientists interpret these as concentrations of dark matter within individual galaxies inside the clusters.

      The researchers used spectrographic data from the VLT to determine the mass of these smaller lenses. Pietro Bergamini of the INAF-Observatory of Astrophysics and Space Science in Bologna, Italy explains, "The speed of the stars gave us an estimate of each individual galaxy's mass, including the amount of dark matter." The leader of the spectrographic aspect of the study was Piero Rosati of the Università degli Studi di Ferrara, Italy who recalls, "the data from Hubble and the VLT provided excellent synergy. We were able to associate the galaxies with each cluster and estimate their distances."

      This work allowed the team to develop a thoroughly calibrated, high-resolution map of dark matter concentrations throughout the three clusters.

      But the models say...

      However, when the researchers compared their map to the concentrations of dark matter computer models predicted for galaxies bearing the same general characteristics, something was way off. Some small-scale areas of the map had 10 times the amount of lensing — and presumably 10 times the amount of dark matter — than the model predicted.

      "The results of these analyses further demonstrate how observations and numerical simulations go hand in hand," notes one team member, Elena Rasia of the INAF-Astronomical Observatory of Trieste, Italy. Another, Stefano Borgani of the Università degli Studi di Trieste, Italy, adds that "with advanced cosmological simulations, we can match the quality of observations analyzed in our paper, permitting detailed comparisons like never before."

      "We have done a lot of testing of the data in this study," Meneghetti says, "and we are sure that this mismatch indicates that some physical ingredient is missing either from the simulations or from our understanding of the nature of dark matter." Priyamvada Natarajan of Yale University in Connecticut agrees: "There's a feature of the real Universe that we are simply not capturing in our current theoretical models."

      Given that any theory in science lasts only until a better one comes along, Natarajan views the discrepancy as an opportunity, saying, "this could signal a gap in our current understanding of the nature of dark matter and its properties, as these exquisite data have permitted us to probe the detailed distribution of dark matter on the smallest scales."

      At this point, it's unclear exactly what the conflict signifies. Do these smaller areas have unexpectedly high concentrations of dark matter? Or can dark matter, under certain currently unknown conditions, produce a tenfold increase in lensing beyond what we've been expecting, breaking the assumption that more lensing means more dark matter?

      Obviously, the scientific community has barely begun to understand this mystery.

      What does kindness look like? It wears a mask.

      Northwell Health CEO Michael Dowling has an important favor to ask of the American people.

      Sponsored by Northwell Health
      • Michael Dowling is president and CEO of Northwell Health, the largest health care system in New York state. In this PSA, speaking as someone whose company has seen more COVID-19 patients than any other in the country, Dowling implores Americans to wear masks—not only for their own health, but for the health of those around them.
      • The CDC reports that there have been close to 7.9 million cases of coronavirus reported in the United States since January. Around 216,000 people have died from the virus so far with hundreds more added to the tally every day. Several labs around the world are working on solutions, but there is currently no vaccine for COVID-19.
      • The most basic thing that everyone can do to help slow the spread is to practice social distancing, wash your hands, and to wear a mask. The CDC recommends that everyone ages two and up wear a mask that is two or more layers of material and that covers the nose, mouth, and chin. Gaiters and face shields have been shown to be less effective at blocking droplets. Homemade face coverings are acceptable, but wearers should make sure they are constructed out of the proper materials and that they are washed between uses. Wearing a mask is the most important thing you can do to save lives in your community.
      Keep reading Show less

      Science confirms: Earth has more than one 'moon'

      Two massive clouds of dust in orbit around the Earth have been discussed for years and finally proven to exist.

      J. Sliz-Balogh, A. Barta and G. Horvath
      Surprising Science
      • Hungarian astronomers have proven the existence of two "pseudo-satellites" in orbit around the earth.
      • These dust clouds were first discovered in the sixties, but are so difficult to spot that scientists have debated their existence since then.
      • The findings may be used to decide where to put satellites in the future and will have to be considered when interplanetary space missions are undertaken.
      Keep reading Show less

      Scientists stumble across new organs in the human head

      New cancer-scanning technology reveals a previously unknown detail of human anatomy.

      Credit: Valstar et al., Netherlands Cancer Institute
      Surprising Science
      • Scientists using new scanning technology and hunting for prostate tumors get a surprise.
      • Behind the nasopharynx is a set of salivary glands that no one knew about.
      • Finding the glands may allow for more complication-free radiation therapies.
      Keep reading Show less

      Millennials reconsidering finances and future under COVID-19

      A new survey found that 27 percent of millennials are saving more money due to the pandemic, but most can't stay within their budgets.

      Personal Growth
    • Millennials have been labeled the "unluckiest generation in U.S. history" after the one-two financial punch of the Great Recession and the pandemic shutdowns.
    • A recent survey found that about a third of millennials felt financially unprepared for the pandemic and have begun saving.
    • To achieve financial freedom, millennials will need to take control of their finances and reinterpret their relationship with the economy.
    • Keep reading Show less
      Personal Growth

      6 easy ways to transition to a plant-based diet

      Your health and the health of the planet are not indistinguishable.

      Scroll down to load more…