A decade ago, we didn’t know if dwarf galaxies had black holes. Today, half of the ones we see aren’t where we expected.
Normally, galaxies have supermassive black holes millions to billions of times the Sun’s mass.
So far, they’ve always been found at the host galaxy’s center, driven there by gravitational interactions and astrophysical dynamics.
Their presence is detectable when matter falls in, causing radio and X-ray emission activity.
However, dwarf galaxies — much smaller and lower in mass — are expected to have black holes measuring just ~10,000–1,000,000 solar masses.
Over 100 dwarf galaxies are now known to possess these black holes, with the first verified one discovered in 2011.
However, solely finding radio emissions isn’t enough: active black holes and star-formation bursts can create that signal.
Researchers led by Dr. Amy Reines just conducted the first large-scale radio survey looking for black holes in dwarf galaxies.
Using the Very Large Array, her team surveyed 111 dwarf galaxies, and found 13 of them that showed evidence for massive black holes.
Remarkably, approximately half of the black holes were not located at the galaxy’s centers, but were significantly off-kilter.
The reason is straightforward but fascinating: the quiet galaxies have centered black holes, but merging/interacting galaxies have them off-center.
Perhaps, when they finish settling down, their black holes will be centered after all.
Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.Ethan Siegel is the author of Beyond the Galaxy and Treknology. You can pre-order his third book, currently in development: the Encyclopaedia Cosmologica.