In the new study, published in the Monthly Notices of the Royal Astronomical Society, researchers unraveled the structure and evolution of the spiral galaxy 2MASX J23453268−0449256, which is three times the size of the Milky Way.
The galaxy is especially interesting because it produces enormous jets of energy stretching millions of light-years. These jets are a characteristic of elliptical galaxies and unexpected in spiral galaxies as traditionally scientists believed that such activity could disrupt the definite structure of a spiral galaxy.
“This discovery is more than just an oddity—it forces us to rethink how galaxies evolve and how supermassive black holes grow in them and shape their environments,” said lead author Professor Joydeep Bagchi of Christ University, Bangalore.
“If a spiral galaxy can not only survive but thrive under such extreme conditions, what does this mean for the future of galaxies like our own Milky Way?”
300 μJy beam−1. The major and minor axes of the synthesized elliptical beam are 10.35 arcsec×7.23 arcsec at PA 45.24∘. The AGN core is detected at 5.5 mJy beam−1 brightness. Noteworthy is the rare occurrence of two nested pairs of radio lobes. The extremely large extent of the emission is evident with the inner and outer radio lobe pairs extending over ∼387 kpc (∼4.52 arcmin) and ∼1.6 Mpc (∼19.1 arcmin), respectively. The white dotted ellipse represents an outline of the optical galaxy zoomed by a factor of
∼4 for clarity. The scale bar represents 500 kpc. The inset image shows zoomed-in details of the inner radio-double observed with VLA at 4.8 GHz and 19.8 arcsec×13.3 arcsec restoring beam at PA 178.5° (lower left corner). Contour levels are (−0.1, 0.1, 0.2, 0.4, 0.8, 1.6, and 3.2 mJy beam−1). The scale bar represents 50 kpc. The ellipse represents a zoomed outline of the optical galaxy. The inner double has an edge-brightened FR-II (Fanaroff & Riley 1974) morphology, being fed by jets, but the outer lobes have a peculiar filamentary and diffuse structure, possibly decaying relics of jet activity that had ceased millions of years ago. Image credit: Joydeep Bagchi et al. Unveiling the bulge–disc structure, AGN feedback, and baryon landscape in a massive spiral galaxy with Mpc-scale radio jet
Using observations from the Hubble Space Telescope, the Giant Metrewave Radio Telescope, the Atacama Large Millimeter Wave Array and multi-wavelength analyses, the researchers detected an enormous supermassive black hole at its heart and radio jets that are among the largest known for any spiral galaxy, making it a rare phenomenon.
Model A. Grey-scale images and galfit modelling of the inner 25 arcsec × 25 arcsec of spiral galaxy J2345 in all three HST/WFC3 filters, shown with a log scale. Top row: H band, middle row: I band, and bottom row: Bband. Left image panels show the HST input image of the galaxy, middle image panels show the best-fitting galfit model, and right panels show the residual image. Spiral arms were not included in the galfit model. Image credit: Joydeep Bagchi et al. Unveiling the bulge–disc structure, AGN feedback, and baryon landscape in a massive spiral galaxy with Mpc-scale radio jet
When looking carefully at J2345−0449, astronomers noticed it doesn’t have a typical round-shaped center, known as a bulge, that most large galaxies have. Instead, this galaxy has a flat, disk-shaped bulge called a pseudo-bulge.
They also found a small bar-shaped structure made of stars near its center and a ring of stars around it. These discoveries suggest this galaxy formed calmly, without major collisions or interactions with other galaxies.
The galaxy’s powerful jets, coming from a supermassive black hole at its center, extend far beyond its spiral arms. These jets appear in radio images as two sets of lobes, with newer inner jets nested inside older outer ones. Researchers believe these jets are influencing how stars form, especially reducing star formation in the galaxy’s center despite plenty of available gas.
Astronomers also detected a vast halo of extremely hot gas, visible in X-ray images, extending well beyond the galaxy itself. This discovery helped scientists confirm predictions about how much normal matter (baryons) a galaxy like this should have, helping solve a longstanding mystery known as the “missing baryons” problem.
By using observations across many types of light—like ultraviolet, optical, infrared, radio, and X-ray—scientists built a complete picture of this galaxy.
They were able to measure accurately the amount of stars, dust, and the rate at which new stars are forming, clearly showing how the jets from the black hole affect the galaxy’s evolution. They also discovered that J23453268−0449256 contains 10 times more dark matter than the Milky Way, which is crucial for the stability of its fast-spinning disk.
This galaxy, with its unusual spiral shape, lack of traditional bulge, massive halo, and huge jets, provides scientists a special chance to test and refine our understanding of galaxy formation and evolution.
“Understanding these rare galaxies could provide vital clues about the unseen forces governing the universe—including the nature of dark matter, the long-term fate of galaxies, and the origin of life,” said co-author Shankar Ray, a Ph.D. student at Christ University, Bangalore.
References:
1 Unveiling the bulge–disc structure, AGN feedback, and baryon landscape in a massive spiral galaxy with Mpc-scale radio jets – Joydeep Bagchi et al. – Monthly Notices of the Royal Astronomical Society – March 20, 2025 – – OPEN ACCESS