Winds a quarter of the speed of light spotted flowing around binary black holes

Scientists have identified two black holes in regional galaxies consuming their companion stars at an unusually high rate, and spewing out matter at one-fourth the speed of light, according to a new report in the journal Nature.

To reach its conclusion, the study team used information from the European Space Agency’s (ESA) XMM-Newton space observatory, showing for the first time powerful winds gusting at extreme speeds from two strange sources of x-ray radiation. The study team was able to confirm these sources mask a compact object attracting matter at very high rates.

When monitoring the Universe in the X-ray part of spectrum, scientists plainly see the sky is covered with two kinds of astronomical items: supermassive black holes, sitting at the middle of large galaxies and consuming the material around them, and binary systems, which includes the remains of a star feeding on gas from a neighboring star. In each case, the gas creates a whirling disc around the dense central object. Friction in the disc warms the interstellar gas, causing it to emit light at various wavelengths, with an emphasis in X-rays.

Another moderate class of items was uncovered in the 1980s and is still not well comprehended. Ten to a hundred times more brilliant than ordinary X-ray binaries, these sources are too weak to be associated with supermassive black holes. They are also usually discovered far from the middle of their host galaxy.

“We think these so-called ‘ultra-luminous X-ray sources’ are special binary systems, sucking up gas at a much higher rate than an ordinary X-ray binary,” study author Ciro Pinto, an astronomer from the University Cambridge, said in a news release. “Some of these sources host highly magnetized neutron stars, while others might conceal the long-sought-after intermediate-mass black holes, which have masses around one thousand times the mass of the Sun. But in the majority of cases, the reason for their extreme behavior is still unclear.”

Strange sightings in distant galaxies

The study team collected data on three ultra-luminous X-ray sources; all situated in nearby galaxies situated less than 22 million light-years from the Milky Way. The information was acquired over many years with the Reflection Grating Spectrometer on XMM-Newton, which permitted the scientists to identify simple X-ray features.

In all three sources, the researchers could identify x-ray emission from gas in the outer parts of the disc all around the central compact object, slowly streaming towards it.

But two of the three sources – referred to as NGC 1313 X-1 and NGC 5408 X-1 – also showed indications of x-rays being soaked up by gas that is flowing out of the central source at 70,000 kilometers per second, nearly a quarter of the speed of light.

“This is the first time we’ve seen winds streaming away from ultra-luminous x-ray sources,” Pinto said. “And the very high speed of these outflows is telling us something about the nature of the compact objects in these sources, which are frantically devouring matter.”

The sources studied the team are potentially being supplied through a disc which has been swollen as a result of internal pressures from the incredible speeds of material passing through it. As the fat disc moves material farther from the black hole’s gravitational clutches it also engenders very high-speed winds like the ones detected by the Cambridge scientists.

“With a broader sample of sources and multi-wavelength observations, we hope to finally uncover the physical nature of these powerful, peculiar objects,” Pinto said.

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Image credit: ESA – C. Carreau

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