Often described as destructive monsters that hold light captive, black holes play a less nasty role in the latest research from NASA’s Hubble Space Telescope. A black hole at the heart of the dwarf galaxy Henize 2-10 is creating stars rather than engulfing them. The black hole is apparently contributing to the firestorm of new star formation taking place in the galaxy. The dwarf galaxy is 30 million light-years away, in the southern constellation of Pyxis.
A decade ago, this small galaxy sparked a debate among astronomers over whether dwarf galaxies harbored black holes commensurate with the supermassive behemoths found at the cores of larger galaxies. This new discovery has tiny Henize 2-10, containing only a tenth the number of stars found in our Milky Way, poised to play a big role in solving the mystery of the origin of supermassive black holes.
The Hubble Space Telescope is an international cooperation project between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland operates the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.
“Ten years ago, as a grad student thinking I would dedicate my career to forming stars, I looked at Henize 2-10 data and everything changed,” said Amy Reines, who has published the first evidence of a black hole in the galaxy. in 2011 and is the principal investigator on the new Hubble observations, published in the January 19 issue of Nature.
“Early on, I knew something unusual and special was happening at Henize 2-10, and now Hubble has provided a very clear picture of the connection between the black hole and a nearby star-forming region located 230 light-years from the black hole,” Reines said.
This connection is a gas outlet that extends through space like an umbilical cord to a luminous stellar nursery. The region was already harboring a dense cocoon of gas when the low-velocity outflow arrived. Hubble spectroscopy shows the flow was moving at around 1 million miles per hour, slamming into the dense gas like a garden hose hitting a pile of dirt and spilling out. Newborn star clusters dot the path of outflow propagation, their ages also calculated by Hubble.
This is the opposite effect of what is seen in large galaxies, where matter falling towards the black hole is carried away by the surrounding magnetic fields, forming blazing jets of plasma moving at near speed light. Clouds of gas caught in the path of the jets would be heated far beyond their ability to cool and form stars. But with Henize 2-10’s less massive black hole and its smoother flow, the gas was compressed just enough to precipitate new star formation.
“Only 30 million light-years away, Henize 2-10 is close enough that Hubble could very clearly capture both imagery and spectroscopic evidence of a black hole outflow. The added surprise was that, rather than to suppress star formation, the outflow triggered the birth of new stars,” said Zachary Schutte, a graduate student at Reines and lead author of the new study.
Since first discovering distinct radio and X-ray emissions in Henize 2-10, Reines believes they likely originated from a massive black hole, though not as supermassive as seen in larger galaxies. Other astronomers, however, thought the radiation was more likely emitted by a supernova remnant, which would be a familiar occurrence in a galaxy that is rapidly pumping out massive, rapidly exploding stars.
“Hubble’s incredible resolution clearly shows a corkscrew-like pattern in gas velocities, which we can fit to the model of a precessional flow or oscillation of a black hole. A supernova remnant n wouldn’t have that pattern, and so it’s actually our absolute proof that it’s a black hole,” Reines said.
Reines expects more research to be conducted on black holes in dwarf galaxies in the future, with the goal of using them as clues to the mystery of how supermassive black holes formed in the early universe. It’s a persistent puzzle for astronomers. The relationship between the mass of the galaxy and its black hole may provide clues. The Henize 2-10 black hole measures about 1 million solar masses. In large galaxies, black holes can be over a billion times the mass of our Sun. The more massive the host galaxy, the more massive the central black hole.
Current theories about the origin of supermassive black holes fall into three categories: 1) they formed as smaller stellar-mass black holes, from the implosion of stars, and somehow gathered enough of matter to become supermassive, 2) special conditions in the early universe allowed the formation of supermassive stars, which collapsed to form massive “seeds” of black holes early on, or 3) the seeds of future Supermassive black holes are born in dense star clusters, where the overall mass of the cluster would have been sufficient to somehow create them from gravitational collapse.
So far, none of these black hole seeding theories have taken the lead. Dwarf galaxies like Henize 2-10 offer promising potential clues because they have remained small over cosmic time, rather than undergoing the growth and mergers of large galaxies like the Milky Way. Astronomers believe that black holes in dwarf galaxies could serve as analogs to black holes in the early universe, when they were just beginning to form and grow.
“The era of the first black holes is not something that we have been able to see, so it really became the big question: where did they come from? Dwarf galaxies may retain some memory of the seeding scenario black holes that have otherwise been lost in time and space,” Reines said.
Video: https://youtu.be/YJbxIdZ-3fg