Astronomers Reveal Detailed 3D Map of Cosmic Dust

Astronomers Reveal Detailed 3D Map of Cosmic Dust
by Robert Schreiber
Berlin, Germany (SPX) Mar 14, 2025

Observing distant stars and galaxies comes with a challenge: how much of what we see is affected by cosmic dust? The presence of interstellar dust clouds can make celestial objects appear redder and dimmer than they actually are, an effect known as reddening and extinction. To address this, two astronomers have created an intricate 3D map that provides an unprecedented view of dust distribution in the Milky Way, offering a clearer perspective on the universe.

Cosmic dust interacts with starlight in a distinct way-absorbing shorter wavelengths (blue light) more strongly than longer wavelengths (red light). The specific wavelength-dependent absorption pattern, known as the extinction curve, reveals critical insights into dust composition and the local space environment.

Using Data from 130 Million Star Spectra

Xiangyu Zhang, a PhD student at the Max Planck Institute for Astronomy (MPIA), and his advisor, Gregory Green, an independent research leader at MPIA, leveraged data from the European Space Agency's Gaia mission. Over its 10.5-year span, Gaia mapped the positions and properties of over a billion stars. From its third data release (DR3), made public in June 2022, Zhang and Green identified 130 million suitable star spectra for their dust analysis.

Despite Gaia's low-resolution spectra, the astronomers found a workaround. They incorporated high-resolution spectroscopic data from China's LAMOST survey for 1% of their chosen stars. These reference data points allowed them to determine key stellar properties, such as surface temperature and spectral type.

Constructing the 3D Dust Map

To extract dust characteristics from the vast dataset, Zhang and Green trained a neural network to generate synthetic star spectra based on known stellar properties and dust effects. Comparing these models with actual Gaia observations, they used Bayesian statistical methods to infer the dust properties affecting 130 million stars.

The result is the first detailed, three-dimensional map of interstellar dust extinction curves. Previous dust maps included only about one million stars-this latest work expands that number dramatically, improving the accuracy of cosmic dust measurements.

More Than Just an Obstruction

While dust can hinder astronomical observations, it plays a crucial role in cosmic evolution. Stars form within massive dust-laden gas clouds, and young stars are often encircled by dusty disks where planets begin to take shape. Dust grains themselves act as building blocks for planetary material, including Earth-like worlds. Additionally, within the interstellar medium, most elements heavier than hydrogen and helium are locked within these tiny dust particles.

Surprising Dust Properties

Beyond mapping dust distribution, Zhang and Green discovered an unexpected trend in extinction curves. Conventional theories predicted that in denser dust regions, the extinction curve should flatten as larger dust grains form, reducing the effect of shorter wavelengths. However, the data revealed a steepening of the extinction curve in intermediate-density regions, meaning that shorter wavelengths were absorbed even more strongly.

The astronomers suggest this could be due to the growth of polycyclic aromatic hydrocarbons (PAHs), a class of molecules abundant in interstellar space and potentially significant in the origins of life. They plan further observations to test this hypothesis.

Research Report:Three-dimensional maps of the interstellar dust extinction curve within the Milky Way galaxy