Spiral Galaxies Surprise with Powerful Radio Jets express
It was once believed that only elliptical galaxies could spawn giant streams of radio emission — radio jets emanating from central supermassive black holes. A new study proves otherwise: spiral galaxies also host powerful radio fountains. Researchers selected 15 such objects using Hubble images and radio sky data.
To picture the difference, imagine a spinning plate with a fountain at its center. Water jets shoot straight up and down, perpendicular to the plane. In the same way, radio jets in spiral galaxies burst out near the rotation axis, at a slight angle to the poles. We see most of these galaxies almost edge-on, and their jets end in bright 'hot spots'. Light analysis of the nuclei revealed that matter is simultaneously falling into the black hole and new stars are being born.
Unexpected twist: many candidates turned out to be false positives. Radio jets from distant sources simply shone right through a spiral galaxy, creating an illusion. Such systems offer a rare chance to study invisible magnetic fields inside galactic disks. This discovery builds on the work of Karl Jansky, who first detected a cosmic radio signal a century ago.
Original abstract
as written by the authors arXiv:2603.07788
We present a sample of large double radio sources hosted by spiral galaxies (Spiral Double Radio Active Galactic Nuclei, SDRAGNs). Candidates were selected during Radio Galaxy Zoo, and refined using Sloan Digital Sky Survey images. The most promising were targeted in the Zoo Gems Hubble Space Telescope program, yielding images for 36 candidates. We assess the likelihood of each spiral galaxy being the genuine host of the radio emission finding 15 new high-probability SDRAGNs. SDRAGN hosts are seen preferentially close to edge-on. SDRAGNs predominantly show FR II radio structures and optical pseudobulges. Accounting for sample selection effects, the radio-jet axes lie preferentially near the poles of the galaxy disks; we find a constant probability distribution for intrinsic pole-jet angles < 30 degrees, ramping to zero at 60 degrees. We have obtained optical spectra for all these new SDRAGNs. Among both previous and new SDRAGN samples, 8/25 show Seyfert 2 signatures, 6/25 show central star formation, and 5/25 show LINER emission strong enough to indicate AGN or shock ionization, broadly similar to radio galaxies in elliptical hosts with the addition of star formation (diluting or masking weak AGN signatures). SDRAGNs include FR II sources seen at unusually low radio power, and preferentially occur in significant galaxy overdensities on 1-Mpc scales. Our "false alarms" - systems where HST data show the spiral to not be the actual host galaxy - include radio sources seen through large parts of foreground spiral disks, potentially useful for Faraday-rotation studies of disk magnetic fields.
Some candidates turned out to be false: radio emission from distant sources was shining through a spiral galaxy, creating an illusion. Such systems are a unique laboratory for studying magnetic fields in galactic disks.