Astronomers Catch a Nearby Black Hole in a Years-Long Radio Outburst Never Seen Before, Offering a Window Into the Early Universe

Overview

A black hole at the center of a spiral galaxy 1.8 billion light-years away has been shining exceptionally brightly in radio light for more than eight years, a transition into a long-lasting radio-bright state that researchers say has never been observed before. The galaxy, cataloged as SDSS J110546.07+145202.4, sits in the constellation Leo, according to the Max Planck Institute for Radio Astronomy (MPIfR), which led the international research effort.

What We Know

The black hole at the galaxy’s center is comparatively low in mass but is increasing exceptionally fast through the accretion of matter. The intensity of its radio emission has increased more than 20-fold in a short period and shows no signs of weakening, and for more than eight years the galaxy has been shining in the radio regime at about 10 quadrillion (10¹⁶) times the intensity of the sun.

The research team, led by Stefanie Komossa of the Max Planck Institute for Radio Astronomy, drew on observations from the 100-meter Effelsberg radio telescope, CSIRO’s Australia Telescope Compact Array, the Very Long Baseline Array, and SKA telescopes. “Luminous radio radiation from rapidly growing, lightweight black holes is rare to begin with. Their transition into a long-lasting, radio-bright state has never been observed before,” Komossa said, according to MPIfR.

Co-author Phil Edwards of CSIRO said, “We are dealing with the prototype of a new class of galaxies that undergo rapid changes in radio emission,” according to MPIfR. Kovi Rose of the Sydney Institute for Astronomy, another co-author, added that “such high-energy events can provide astronomers with a wealth of insights,” as reported by Universe Today.

The findings, published as “SDSS J110546.07+145202.4: The first long-duration radio changing-look NLS1 galaxy” in The Astrophysical Journal, classify the object as a narrow-line Seyfert 1 (NLS1) galaxy, according to the study preprint on arXiv. The paper reports a monochromatic radio luminosity of 7×10⁴⁰ erg per second at 4.85 gigahertz, an X-ray spectrum with a photon index of about 2.5, and a radio spectral energy distribution that peaks at a low turnover frequency of roughly 2.1 gigahertz, according to the preprint. The authors describe the outburst as “remarkably long-lived,” having lasted at least eight years at roughly constant flux density, per the same paper.

What We Don’t Know

The exact mechanism that triggered the sustained radio brightening is not settled. The MPIfR team suspects that more matter has been falling into the black hole for several years, triggering a jet — a concentrated beam of particles moving at nearly the speed of light — but the underlying physical trigger remains undetermined, according to CSIRO. The study preprint notes the authors weighed alternative explanations, including gravitational lensing, a black hole merger, and a tidal disruption event, before concluding that a change in accretion rate most likely triggered the jet activity.

Analysis

Researchers frame the galaxy’s low redshift combined with its comparatively low-mass, rapidly accreting black hole as a nearby proxy for conditions thought to have governed black hole growth in the early universe. The study preprint states that the system “offer[s] a unique perspective of the physical processes of radio-jet ignition that are expected to operate in the early Universe around growing SMBHs,” giving astronomers a rare opportunity to study, in real time and close to home, a process that ordinarily unfolds only in galaxies too distant and too faint to observe in comparable detail.