Sen—A new study using data from NASA’s Wide-field Infrared Survey Explorer (WISE) has turned up what might be the cosmic seeds from which a black hole will sprout. The results are helping scientists piece together the evolution of supermassive black holes that dominate the hearts of all galaxies.

Black holes come in a range of sizes. The smallest, only a few times greater in mass than our Sun, form from exploding stars. The biggest, billions of times the mass of our Sun, grow together with their host galaxies over time, deep in the interiors. But how this process works is an ongoing mystery.

WISE addressed this question by looking for black holes in smaller, “dwarf” galaxies. These galaxies have not undergone much change, so they are more pristine than their heavier counterparts. They resemble the types of galaxies that might have existed when the Universe was young, and thus offer a glimpse into the nurseries of supermassive black holes.

Using data of the entire sky taken by WISE in infrared light, up to hundreds of dwarf galaxies have been discovered in which buried black holes may be lurking. The researchers found that the dwarf galaxies’ black holes may be about 1,000 to 10,000 times the mass of our Sun, larger than expected for these small galaxies.

“Our findings suggest the original seeds of supermassive black holes are quite massive themselves,” said Shobita Satyapal of George Mason University, lead author of the new research.

The galaxy NGC 4395 is shown here in infrared light, captured by NASA's Spitzer Space Telescope. Image credit: NASA/JPL-Caltech.

The galaxy NGC 4395 is shown here in infrared light, captured by NASA’s Spitzer Space Telescope. Image credit: NASA/JPL-Caltech.

The galaxy NGC 4395 is “bulgeless” because it lacks a large collection of stars at its centre. Astronomers have found more evidence that such bulgeless galaxies, contrary to previous theories, do harbor supermassive black holes.

Daniel Stern, an astronomer specializing in black holes at NASA’s Jet Propulsion Laboratory, who was not a part of the new study, says the research demonstrates the power of an all-sky survey like WISE to find the rarest black holes. “Though it will take more research to confirm whether the dwarf galaxies are indeed dominated by actively feeding black holes, this is exactly what WISE was designed to do: find interesting objects that stand out from the pack.”

The discovery of dwarf galaxy black holes that are bigger than expected suggests that galaxy mergers are not necessary to create big black holes. Dwarf galaxies don’t have a history of galactic smash-ups, and yet their black holes are already relatively big.

Instead, supermassive black holes might form very early in the history of the Universe. Or, they might grow harmoniously with their host galaxies, feeding off surrounding gas.

“We still don’t know how the monstrous black holes that reside in galaxy centers formed,” said Satyapal. “But finding big black holes in tiny galaxies shows us that big black holes must somehow have been created in the early Universe, before galaxies collided with other galaxies.”

WISE was put into hibernation upon completing its primary mission in 2011. In September 2013, it was reactivated, renamed NEOWISE and assigned a new mission to assist NASA’s efforts to identify the population of potentially hazardous near-Earth objects. NEOWISE will also characterize previously known asteroids and comets to better understand their sizes and compositions.

Source: Jenny Winder