As astronomers peer through telescopes across the cosmos, dust clouds may distort the light from distant objects, leading to inaccurate observations, which new research out of the Max Planck Institute for Astronomy (MPIA) is attempting to mitigate.
The effects of dust clouds on observations can vary, from a reddening effect, altering the perceived color, to an “extinction,” leaving the objects to appear fainter than they genuinely are. By producing a 3D dust map in unrivalled detail, the Max Planck team aims to enable astronomers to understand their observations more accurately.
Dust Data Discovered
Space dust presents unique problems for astronomers due to how unevenly particles absorb and scatter light. The reddening effect is due to the dust’s preference to absorb shorter wavelength light toward the blue end of the spectrum. By blocking light as it moves across space, dust clouds generate an extinction curve, causing a dimming effect. By understanding the wavelength-absorption properties of a particular dust cloud, astronomers can glean detailed information about its composition, as well as the types of radiation in its region.
The European Space Agency’s (ESA) Gaia mission collected crucial spectroscopic information, allowing MPIA PhD candidate Xiangyu Zhang and his advisor Gregory Green to develop their dust map of the Milky Way galaxy. After combing through Gaia’s June 2022 data report, the third release from the mission, Zhang and Green found that 130 million spectra out of 220 million were ideal for their map.
Astronomers Reconstruct Dust
The first challenge was getting the data into workable shape, as Gaia collects coarse, low-resolution spectra information. Fortunately, 1% of the stars in the data set are available in high-resolution spectroscopies from the National Astronomical Observatories of China’s LAMOST survey. By correlating the two data sets, the pair could determine essential properties of the stars, such as surface temperature.
The MPIA researchers generated spectra models by feeding data on stars and intermediary dust clouds to a neural network. They then compared those models to the GAIA data, using statistical analysis to identify dust properties between Earth and those stars. The pair reconstructed the first 3D map of cosmic dust’s extinction curve across the Milky Way from that information. Their work is unprecedented, accounting for 130 million stars, with the closest earlier study only covering one million.
Understanding Dust
Dust plays a crucial role in the universe. It shields giant gas clouds from surrounding radiation during star formations. Discs of such gas and dust are the building blocks of planets long after stars begin to shine. Within the Milky Way, dust grains hold the majority of elements heavier than hydrogen and helium.
While scientists have long been aware of the importance of dust on a cosmic scale, the map reveals even more surprising information. Going into the project, scientific consensus had been that the higher the particle density, the greater the extinction curve should be. Instead, the pair found that intermediate density offered the steepest extinction. Zhang and Green hypothesize that molecules called polycyclic aromatic hydrocarbons (PAHs) are driving the steep curve instead of the dust particles directly. Intriguingly, PAH may have also played a role in the rise of life. Zhang and Green are at work on new methods to test their PAH hypothesis.
The paper “Three-dimensional maps of the Interstellar Dust Extinction Curve Within the Milky Way Galaxy” appeared on March 13, 2025 in Science.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.