Some young galaxies with black holes in their centre change their emissions of radio waves far faster than astronomers thought possible. This means it might be easier to spot a type of galaxy known as a blazar.
at the International Centre for Radio Astronomy Research in Perth, Australia, and her colleagues surveyed more than 21,000 radio-emitting galaxies under 100,000 years old with a black hole at their core. They found 123 that she calls “bouncy baby black holes”, because their emissions are more variable than the rest.
This variability, found at the lower end of the radio spectrum, is puzzling, says Ross, who presented the findings on 29 June at the virtual conference of the .
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At these low frequencies, the radio waves from galaxies mostly come from enormous mushroom-shaped structures called lobes created by the jets of material shot out by the black hole. These jets stretch enormous distances, up to 2 million light years from the galaxy, meaning that a physical process affecting the radio emission, even if it was propagated at the speed of light, would take tens of thousands to millions of years to cause observable changes. And yet Ross and her team saw changes happening within a year.
The team has come up with a number of tentative explanations. The first is that some of the galaxies aren’t actually changing, but just appear to be from our perspective because of intervening matter in our Milky Way galaxy.
For others, it could be that the black hole is temporarily shining brightly in radio waves as a result of ingesting a clump of matter, outshining the lobes.
Finally, it could be that some of the galaxies are aligned so that the jets are pointing towards and away from Earth, meaning radio telescopes are seeing the immediate environment of the black hole rather than the lobes. “We are looking down the barrel of the gun,” says Ross.
Such lined-up galaxies have previously been spotted as bright X-ray and gamma-ray sources, and are known as blazars. If follow-up observations confirm her hunch, Ross says, astronomers could hunt for blazars in low frequency surveys done from Earth, instead of searching for them with much more expensive orbiting X-ray or gamma ray telescopes.
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