Black holes are voracious eaters, but they don't have the nicest table manners. As they rip into a star, they tend to produce a bright flash of light that astronomers call a tidal disruption flare, the celestial equivalent of all the applesauce that fails to quite make it down a baby's throat.
And now, according to a paper being published in the Astrophysical Journal this week, scientists have realized that all that expulsion can reveal just how much material the black hole is consuming in the first place.
The study looks at an event first detected on November 11, 2014. At that time, scientists realized they had picked up bursts of light from a tidal disruption flare about 300 million light years away. The pair of scientists behind the new paper decided to look more broadly at data from that part of the sky.
They realized that almost two weeks after the x-ray burst scientists had originally seen, there was a second large burst. This second burst consisted of radio waves, a longer form of light than x-rays. Although the radio waves came from a much larger portion of the sky than the x-rays, the two bursts displayed similar patterns. The researchers concluded that the radio burst somehow followed from the x-ray burst.
To fill the gap, they argue that because the radio "echoes" come from highly charged particles (scientists knew that bit already), the time lag and the greatly expanded footprint of the signal reflect a jet of material coming out of the black hole. Within the jet itself, these light bursts are absorbed by the rest of the jet—it takes a while for the particles releasing the light to have enough space that their fireworks actually shine.
The connection means that scientists can use the radio observations to understand what the black hole itself is doing. “This is telling us the black hole feeding rate is controlling the strength of the jet it produces,” Pasham said. “A well-fed black hole produces a strong jet, while a malnourished black hole produces a weak jet or no jet at all.”
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