For the first time, researchers have measured rapidly varying temperatures in hot gas flowing from the vicinity of a black hole.
Artist impression illustrating a supermassive black hole with X-ray emission emanating from its inner region (pink) and ultra-fast winds streaming from the surrounding disk (purple). Image credit: ESA.
Outflowing gas is a common feature of supermassive black holes that reside in the center of giant galaxies.
Millions to billions of times more massive than the Sun, these black holes feed off the surrounding gas that swirls around them.
Space telescopes see this as bright emissions, including X-rays, from the innermost part of the disc around the black hole.
Occasionally, the black holes eat too much and burp out an ultra-fast wind. These winds are an important characteristic to study because they could have a strong influence on regulating the growth of the host galaxy by clearing the surrounding gas away and therefore suppressing the birth of stars.
Using ESA’s XMM-Newton and NASA’s Nuclear Spectroscopic Telescope Array (NuSTAR) telescopes, a research team led by Michael Parker from Cambridge’s Institute of Astronomy has now made the most detailed observation yet of such an outflow, coming from a nearby supermassive black hole.
This black hole is located in the active galaxy IRAS 13224-3809 in the constellation Centaurus.
The winds recorded from the black hole reach 159 million mph (71,000 km/s) — 0.24 times the speed of light — putting it in the top 5% of fastest known black hole winds.
“We know that supermassive black holes affect the environment of their host galaxies, and powerful winds arising from near the black hole may be one means for them to do so,” said NuSTAR principal investigator Dr. Fiona Harrison, from the California Institute of Technology.
“The rapid variability, observed for the first time, is providing clues as to how these winds form and how much energy they may carry out into the galaxy.”
XMM-Newton focused on the black hole in IRAS 13224-3809 for 17 days straight, revealing the extremely variable nature of the winds.
“We often only have one observation of a particular object, then several months or even years later we observe it again and see if there’s been a change. Thanks to this long observation campaign, we observed changes in the winds on a timescale of less than an hour for the first time,” Dr. Parker said.
The changes were seen in the increasing temperature of the winds (millions of degrees Fahrenheit), a signature of their response to greater X-ray emission from the disc right next to the black hole.
The observations also revealed changes to the chemical fingerprints of the outflowing gas: as the X-ray emission increased, it stripped electrons in the wind from their atoms, erasing the wind signatures seen in the data.
“The chemical fingerprints of the wind changed with the strength of the X-rays in less than an hour, hundreds of times faster than ever seen before,” said co-author Dr. Andrew Fabian, also from Cambridge’s Institute of Astronomy.
“It allows us to link the X-ray emission arising from the infalling material into the black hole, to the variability of the outflowing wind farther away.”
“Finding such variability, and finding evidence for this link, is a key step in understanding how black hole winds are launched and accelerated, which in turn is an essential part of understanding their ability to moderate star formation in the host galaxy,” said XMM-Newton project scientist Dr. Norbert Schartel.
“This is the first time we have seen that winds are interacting with the black hole’s radiation,” Dr. Parker said.
“Further study of this source is likely to have wide-ranging implications for our knowledge of how these winds form and are powered, where they are located, how dense they are, and how long they last — all of which will add to our understanding of the interaction between black holes and their galaxies.”
The research is published in the March 2 issue of the journal Nature.
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Michael L. Parker et al. 2017. The response of relativistic outflowing gas to the inner accretion disk of a black hole. Nature 543, 83-86; doi: 10.1038/nature21385
