NASA Telescope Reveals Different Types of Black Hole 'Batteries' Powering Blazars (VIDEO)
NASA's Fermi Gamma-ray Telescope has uncovered some new information about two classes of black-hole-powered galaxies. Scientists have discovered that these black holes may actually represent different sides of the same cosmic coin, and that apparently distinctive properties defining each class probably reflect a change in the way the galaxies themselves extract energy from their central black holes.
Active galaxies possess luminous cores that are powered by black holes containing millions or even billions of times the mass of the sun. As gas falls toward these supermassive black holes, it settles in an accretion disk and heats up. Then, some of the gas blasts out of the disk in jets that move in opposite directions at nearly the speed of light.
Blazars in particular are the highest-energy type of active galaxy. They emit light across the spectrum, from radio to gamma rays, and make up more than half of the discrete gamma-ray sources catalogued by Fermi's Large Array Telescope. To be considered a blazar, an active galaxy needs to either show rapid changes in visible light on timescales as short as a few days, strong optical polarization, or glow brightly at radio wavelengths with a "flat spectrum."
Yet there are two different types of blazars. One is known as flat-spectrum radio quasars (FSRQs), which show strong emission from an active accretion disk, much higher luminosities, smaller black hole masses and lower particle acceleration in jets, and the other is known as BL Lacs, which are dominated by the jet emission, with the jet particles reaching much higher energy and the accretion disk emission either weak or absent.
In order to learn a bit more about these blazars, the researchers examined the distribution of BL Lacs. They then compared their distribution across cosmic time with a similar sample of FSRQs. In the end, they found that starting around 5.6 billion years ago, FSRQs began to decline while BL Lacs underwent a steady increase in numbers.
"What we think we're seeing here is a changeover from one style of extracting energy from the central black hole to another," said Roger Romani, one of the researchers, in a news release.
The new findings reveal a bit more about these black holes. As the universe expands and the density of galaxies decreases, so do galaxy collisions and the fresh supply of gas they provide to the black hole. This means that the galaxies need new ways to draw power.
The findings are published in The Astrophysical Journal.
Want to see more? Check out the video below, courtesy of YouTube.