Supermassive black holes can be up to a billion times more massive than our sun. New findings show these gigantic, mysterious bodies may have been born large, rather than accumulating in size over billions of years.
The smallest black holes are only a few times more massive than our home star. They are created when massive stars die and explode. The largest of these strange objects can grow to be thousands or millions of times larger than the Sun. How they do this largely remains a mystery, although several theories are being offered. All galaxies contain super-massive black holes at their centers.
The Wide-field Infrared Survey Explorer (WISE) observatory, operated by NASA, was used to examine black holes in tiny dwarf galaxies. Astronomers studied systems which have undergone little change for billions of years. This allows study of the conditions in the early days of galaxy formation, as well as providing data on the formation of supermassive black holes. By looking at dwarf galaxies, the researchers hoped to get a glimpse of what galaxies may have looked like long ago.
Wise Observatory images have revealed hundreds of previously-unknown dwarf galaxies, each of which contains black holes. These features usually contain between 1,000 and 10,000 solar masses.
"[T]his is exactly what WISE was designed to do: find interesting objects that stand out from the pack," Daniel Stern, a black hole specialist at Jet Propulsion Laboratory, said. Stern was not involved in the investigation.
Astronomers looked for thermal radiation from these bodies, radiating in the infrared part of the electromagnetic spectrum. They wanted to know how quickly these bodies grow over time, as they consume everything around them.
One theory states that in the early days of galaxy formation, collisions and mergers between galaxies was more common than it is today. Based on this school of thought, these collisions would lead to super-massive black holes growing as they merge. Astronomers found galactic black holes were more massive than expected. This suggests the features start large, rather than become more massive over time.
"We still don't know how the monstrous black holes that reside in galaxy centers formed. 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," Shobita Satyapal of George Mason University, lead author of the paper announcing the study, said.
Analysis of black holes in dwarf galaxies was published in the Astrophysical Journal.
