xml:space="preserve">

When scientists first theorized about black holes, the idea was relatively simple: Their gravitational pull is so strong, nothing can escape them — not even light.

But over the past decade, astrophysicists have wondered whether the full picture isn't more complicated. They found an apparent and peculiar relationship between the mass of a black hole and the size of the galaxy that surrounds it, possibly suggesting that one had an influence on the other.

Advertisement

Recent observations of a black hole 2 billion light years from Earth show that something is actually flowing out of the darkness — a sort of wind that blows out as the black hole sucks in matter. A study authored by several scientists with ties to the University of Maryland, Baltimore County last month suggests that the wind is sweeping through the galaxy, named PDS 456, pushing out material that could otherwise form new stars.

The findings, published in in February the journal Science, serve as evidence that black holes may have an influence that reaches far beyond their gravitational pull.

"The wind has been found in previous data, but these new data allowed a much more robust characterization of its properties," said Christopher Reynolds, an astronomy professor at the University of Maryland, College Park, who was not involved in the research. "It now seems clear that the wind carries tremendous energy, easily enough to have a strong effect on the properties of the galaxy."

Every large galaxy contains at its center what is known as a supermassive black hole, with a mass millions or billions of times greater than that of our sun. While some smaller black holes may have formed when the universe began, many of the large ones are made when stars collapse on themselves.

About a decade ago, scientists began exploring why there seems to be a correlation between the sizes of black holes and of the galaxies that surround them. But the answer didn't appear to relate to a black hole's gravity, according to Emanuele Nardini, a researcher at Keele University in the United Kingdom, who was the lead author of the study.

"Black holes are powerful objects, but their gravitational influence does not extend much beyond the very inner parts of a galaxy," Nardini wrote in a post about the study on the European Space Agency's website. "If black holes are really to influence the star-forming activity of an entire galaxy, there must be a feedback mechanism connecting the two on a global scale."

Though they cannot see black holes directly because the massive bodies don't reflect light, astrophysicists have studied them by observing the way stars and gas behave around them.

To observe the winds emanating from the black hole in PDS 456, astronomers used two satellites: the European Space Agency's XMM-Newton and NASA's Nuclear Spectroscopic Telescope Array, or NuSTAR. Both satellites observe X-rays, which allowed the scientists to see evidence of the winds flowing from the black hole because such radiation is produced as matter flows into the black hole and pushes skimmed-off material back out into space.

The NuSTAR mission launched in 2012, so it has only recently begun providing new views and insights for scientists.

The scientists studied segments of data recorded in late 2013 and early 2014. The black hole at the center of PDS 456 has the mass of 12 billion suns.

What the data showed was a sphere of gas flowing out, like "a shell surrounding the whole of the black hole," said Tracey Jane Turner, a UMBC physics professor who was a co-author of the study. Before, she said, the scientists didn't know if the winds were flowing in all directions around the black hole.

In addition to being able to detect the shape of the flow of gas for the first time, they were able to measure its intensity — material amounting to 10 times the mass of the sun each year. Earlier observations suggested it moved at one-third the speed of light.

Those findings are key in exploring what the relationship between the black holes and their galaxies might be.

The study's authors suggest it's that the winds limit the growth of the black hole itself and also disrupt the formation of stars, pushing out the molecular gas that fuels the formation of new stars and grows the galaxy.

Advertisement

"This tells us there's a direct link between the black hole and this wind it's creating and the growth of the host galaxy," Turner said.

Next, the scientists look to study the phenomenon in greater detail and in other galaxies. Several of the other scientists who worked on the February paper have been visiting professors at UMBC and continue to collaborate with Turner, she said.

They suspect that in PDS 456, their observations may be from a relatively early stage in a feedback loop between the galaxy and the black hole. But in other galaxies, they could observe it at different points.

"We're looking for more examples of this," Turner said. "This is the best case so far."

twitter.com/ssdance

Advertisement
Advertisement
Advertisement