Supernova W44 May Be Igniting New Stars

Left: Three-color image of G034.77-00.55 showing its position (black circle) between the SNR W44 (blue circle) and the HII region G034.758-00.681 (green circle). Red is 24 um emission, green is 8 um emission, and blue shows a combined JVLA+GBT 21 cm continuum. The white square indicates the extent of the ALMA image.
Top right: Integrated intensity map of the N2H + (1-0) emission toward the shock front in G034.77. Magenta contours highlight the shape of the cloud and SiO(2-1) emission is shown as black contours. The dense gas is organised into two fragmented filaments.
Bottom right: Position of the cores (yellow) and overlaid mass surface density map (color scale). 
_{See Cosentino et al. 2025 for extended data references.}

Supernova remnants (SNRs) are among the most energetic events in galaxies, but their role in triggering star formation remains debated. Evidence is growing that such shocks can compress ambient gas enough to initiate collapse, but direct observational proof is scarce. The SNR W44, about 20000 years old and located 2.9 kpc away, is interacting with the nearby infrared dark cloud G034.7700.55, making this system a compelling laboratory to study shock-induced star formation.

Cosentino et al. (2025) used 3-arcsec angular resolution ALMA images of the dense gas tracer N₂H⁺(1-0) to identify core-like structures at the interface of the shock between the SNR and the cloud. They find several core-like objects distributed along two filaments across the cloud, parallel to the direction of the shock front. The gas associated with the cores has velocity consistent with that of the material that has been compressed by the shock. The cores have masses up to 20 M_sun and density larger than 10⁵ cm^-3. The majority of the detected cores appear bound and unstable, meaning they could collapse to form stars. It is therefore likely that the shock from the supernova remnant W44 has triggered early-stage star formation in the nearby infrared dark cloud G034.77.

The paper has been accepted for publication in A&A. The preprint can be found here.


Contributed by Giuliana Cosentino

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