Categories: AstronomyQuasars

Quasars can twinkle?

This illustration depicts a gas halo surrounding a quasar in the early Universe. The quasar, in orange, has two powerful jets and a supermassive black hole at its centre, which is surrounded by a dusty disc. The gas halo of glowing hydrogen gas is represented in blue. A team of astronomers surveyed 31 distant quasars, seeing them as they were more than 12.5 billion years ago, at a time when the Universe was still an infant, only about 870 million years old. They found that 12 quasars were surrounded by enormous gas reservoirs: halos of cool, dense hydrogen gas extending 100 000 light years from the central black holes and with billions of times the mass of the Sun. These gas stashes provide the perfect food source to sustain the growth of supermassive black holes in the early Universe.

It turns out you can teach an old dog new tricks. With a recent upgrade to a 50-year-old radio telescope, astronomers have spotted nearly a dozen of a rare class of quasars, ones capable of flickering in less than an hour.

Quasars are among the most powerful sources of radiation in the universe. Powered by a giant black hole in the center of a galaxy gobbling down material as quickly as it can, quasars emit more light than millions of galaxies combined. But because of their extreme distance, they only appear to us as spots of intense radio emission on the sky.

Among the quasars, one kind is very peculiar: the so-called intra-hour variable, or IHV, quasars. These quasars appear to twinkle in less than an hour, which shouldn’t be possible given the vast bulk of the quasar itself.

Instead, the culprit behind the rapid variability appears to be intervening gas clouds. On their way through the billions of light-years to Earth, the radio waves encounter random blobs of plasma, and turbulent motions in the plasma can cause the quasars to twinkle, just like the wiggling atmosphere of the Earth causes distant starlight to twinkle.

Radio waves emitted from a quasar first pass through an intervening gas cloud before reaching the Apertif telescope on Earth. (credit: ASTRON/Studio Eigen Merk)

Despite knowing about IHV’s for decades, until now astronomers have spotted only a scant handful. But the first science result from the newly-installed Apertif (APERture Tile In Focus) instrument on the 50-year-old Westerbork Synthesis Radio Telescope is the revelation of ten new IHV’s, including one with a plasma blob surprisingly close to home.

It’s possible that one of the turbulent clouds is near our own solar system, possibly even within the Oort cloud, according to the project scientists. Understanding this plasma cloud could provide clues to the origins and evolution of our solar system, and this is the first evidence of its possible existence.