At the heart of the Sombrero Galaxy sits a black hole weighing a billion Suns. It has enough fuel to outshine its entire galaxy, yet it glimmers at less than a billionth of its potential brightness.
Located roughly 30 million light-years from Earth in the constellation Virgo, the Sombrero Galaxy (Messier 104) hosts one of the most massive black holes ever found in the local universe—roughly 250 times heavier than Sagittarius A* at the center of the Milky Way. Astronomers led by John Kormendy first weighed this giant in the 1990s using the Canada-France-Hawaii Telescope and the Hubble Space Telescope. By measuring the Doppler shifts of starlight near the core, they found stars whipping around an invisible central pivot at speeds far too high to be explained by the gravity of the stars alone. Subsequent dynamical models place the black hole's mass between 600 million and 1 billion solar masses, giving a billion-solar-mass event horizon a radius of nearly 20 astronomical units, or roughly the distance from the Sun to Uranus.
A black hole of that size is big enough to drive a blinding quasar, and observations with the Chandra X-ray Observatory confirm that the galaxy's central bulge holds plenty of hot, diffuse gas drifting inward to feed it. Yet the core remains strangely dim, classified as a low-luminosity active galactic nucleus.
Rather than settling into a dense, incandescent disk, the infalling gas forms what astrophysicists call a radiatively inefficient accretion flow: a hot, tenuous cloud in which gas plunges across the event horizon before it has time to radiate away its heat. The small fraction of energy that does escape powers a compact radio source and a pair of miniature relativistic jets spanning just a few light-years, resolved by high-resolution radio interferometry.
In late 2024, the James Webb Space Telescope's Mid-Infrared Instrument offered the clearest view yet of the black hole's immediate surroundings. In visible light, the glowing dome of ancient stars that gives the Sombrero its hat-like crown obscures the interior. At mid-infrared wavelengths, the glare of those old stars vanishes, revealing a smooth inner disk with the active black hole gleaming as a solitary pinpoint at the center.