Hubble finds evidence of galaxy star birth regulated by black hole fountain

Astronomers have uncovered a unique process for how the universe’s largest elliptical galaxies continue making stars long after their peak years of star birth.

NASA’s Hubble Space Telescope’s exquisite high resolution and ultraviolet-light sensitivity allowed the astronomers to see brilliant knots of hot, blue stars forming along the jets of active black holes found in the centers of giant elliptical galaxies.

Combining Hubble data with observations from a suite of ground-based and space telescopes, two independent teams found that the black hole, jets, and newborn stars are all parts of a self-regulating cycle. High-energy jets shooting from the black hole heat a halo of surrounding gas, controlling the rate at which the gas cools and falls into the galaxy.

“Think of the gas surrounding a galaxy as an atmosphere,” explained the lead of the first study, Megan Donahue of Michigan State University.

“That atmosphere can contain material in different states, just like our own atmosphere has gas, clouds, and rain. What we are seeing is a process like a thunderstorm.

 As the jets propel gas outward from the center of the galaxy, some of that gas cools and precipitates into cold clumps that fall back toward the galaxy’s center like raindrops.”

“The ‘raindrops’ eventually cool enough to become star-forming clouds of cold molecular gas, and the far-ultraviolet capabilities of Hubble allowed us to directly observe these ‘showers’ of star formation,” explained the lead of the second study, Grant Tremblay of Yale University.

“We know that these showers are linked to the jets because they’re found in filaments and tendrils that wrap around the jets or hug the edges of giant bubbles that the jets have inflated,” said Tremblay. “And they end up making a swirling ‘puddle’ of star-forming gas around the central black hole.”

But what should be a monsoon of raining gas is reduced to a mere drizzle by the black hole.

While some outwardly flowing gas will cool, the black hole heats the rest of the gas around a galaxy, which prevents the whole gaseous envelope from cooling more quickly.

The suite of telescopes shows how galaxy ecosystems work, including the black hole and its influence on its host galaxy and the gas surrounding that galaxy.