New stars can form in black hole winds

New stars may be born in the hostile winds that emerge from black holes, according to a study.

Black-hole-wind-sweeping-away-galactic-gas

An artist’s impression of a large-scale galaxy outflow driven (inset) by the winds from a supermassive black hole at the centre. Image Credit: ESA/ATG medialab

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New molecules can form in the winds that blow from black holes, enabling new stars to be born in hostile environments, according to a study.

The discovery, if true, could explain how large numbers of molecules can exist in the winds powered by supermassive black holes at the centres of galaxies.

Molecules are mostly found in the coldest parts of the cosmos, so finding molecules in the hot, energetic outflows generated by black holes is something of an astronomical puzzle.

But rather than molecules surviving the extreme heat of black hole outflows, the study suggests molecules are actually being born in these environments.

“When a black hole wind sweeps up gas from its host galaxy, the gas is heated to high temperatures, which destroys any existing molecules,” says Alexander Richings of Northwestern University’s Center for Interdisciplinary Research and Exploration in Astrophysics, who created the computer simulations that enabled the discovery.

“By modeling the molecular chemistry in computer simulations of black hole winds, we found that this swept-up gas can subsequently cool and form new molecules.”

An artist’s illustration based on a Hubble Space Telescope image of the Pinwheel Galaxy, M101. It depicts a supermassive black hole at the centre of the galaxy blasting out winds from the centre.Credit: NASA/JPL-Caltech
An artist’s illustration based on a Hubble Space Telescope image of the Pinwheel Galaxy, M101. It depicts a supermassive black hole at the centre of the galaxy blasting out winds from the centre.
Credit: NASA/JPL-Caltech

In 2015, astronomers discovered energetic outflows containing gases of highly ionized atoms pouring from supermassive black holes at the centres of most galaxies.

In 2017, stars were observed forming in these so-called winds, which should be impossible given the extreme conditions of these outflows.

But Richings and his study co-author Claude-André Faucher-Giguère, an assistant professor in Northwestern University’s Weinberg College of Arts and Sciences, have found that new molecules like hydrogen, carbon monoxide and water can actually form in black hole winds.

This image of the Pinwheel Galaxy, or M101, combines data in the infrared, visible, ultraviolet and x-rays from four of NASA’s space telescopes. This multi-spectral view shows that both young and old stars are evenly distributed along M101’s tightly-wound spiral arms. Such composite images allow astronomers to see how features in one part of the spectrum match up with those seen in other parts. It is like seeing with a regular camera, an ultraviolet camera, night-vision goggles and X-Ray vision, all at once! The Pinwheel Galaxy is in the constellation of Ursa Major (also known as the Big Dipper). It is about 70% larger than our own Milky Way Galaxy, with a diameter of about 170,000 light years, and sits at a distance of 21 million light years from Earth. The red colors in the image show infrared light, as seen by the Spitzer Space Telescope. These areas show the heat emitted by dusty lanes in the galaxy, where stars are forming. The yellow component is visible light, observed by the Hubble Space Telescope. Most of this light comes from stars, and they trace the same spiral structure as the dust lanes seen in the infrared. The blue areas are ultraviolet light, given out by hot, young stars that formed about 1 million years ago. The Galaxy Evolution Explorer (GALEX) captured this component of the image. Finally, the hottest areas are shown in purple, where the Chandra X-ray observatory observed the X-ray emission from exploded stars, million-degree gas, and material colliding around black holes. Credit: NASA/JPL
The Pinwheel Galaxy, or M101. Image Credit: NASA/JPL
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“This is the first time that the molecule formation process has been simulated in full detail, and in our view it is a very compelling explanation for the observation that molecules are ubiquitous in supermassive black hole winds, which has been one of the major outstanding problems in the field,” says Faucher-Giguère.