What Black Hole Winds Tell You about Galaxies

This illustration shows gusts of charged particles streaming in all directions from a black hole at the center of a galaxy. NASA/JPL-Caltech

Black holes suck. Their gravitational pull is so powerful that black holes famously grab anything near them in space—even light. But black holes also, it turns out, blow. If they’re gobbling up any nearby matter, black holes actually stream charged subatomic particles. And that, astronomers now say, has huge consequences for the life of nearby stars and the shape of whole galaxies.

Supermassive black holes like the ones at the center of some galaxies are surrounded by gas and dust spiraling into the maw. As all that stuff gets pulled in, the pieces rub against each other. That friction becomes energy, radiation that turns the atoms of the dust-disc into charged particles. All that stuff then rushes outward at speeds approaching a third of the speed of light. “We’ve known for a while now that every galaxy like the Milky Way has a supermassive black hole at its heart, and we also know there’s a connection between the mass of the black hole and the mass of the galaxy,” says Fiona Harrison, an astronomer at Caltech who worked on the new research. “But it’s a mystery why. One hypothesis is that through blows like this, black holes can actually affect galaxies on large scales.”

That expanding bubble of ions packs a serious punch—like about 10 trillion suns’ worth. It blows away the random bits of gas and dust always hanging around a galactic core. But gas and dust are the raw materials for building new stars. Once it’s gone: No more new stars.

Harrison and her colleagues were looking at x-ray data from a black hole 2 billion light years away, in the heart of a quasar unpoetically called PDS 456. Earlier observations from a space telescope called XMM-Newton, in orbit between Earth and the moon, revealed the wind, but blowing more narrowly. Adding in data from a telescope in low-Earth orbit, NuSTAR, showed the wind blowing outward in every direction. The scientists had never seen that before. “We’re trying to tell the narrative story of galaxy formation,” says Roger Blandford, an astrophysicist at Stanford University. “We understand quite a lot of the physics, but it has to be guided by observations. This is a good measurement that will help along the way.”