Black holes from small galaxies might emit gamma rays

As a general rule of thumb, if there is a puzzling phenomenon occurring somewhere deep in outer space, a black hole is often the culprit behind it.

This is according to postdoctoral researcher Vaidehi Paliya in the department of physics and astronomy, whose January 2018 publication in The Astrophysical Journal Letters details the discovery of seven galaxies that could potentially shake up what astrophysicists thought they knew about how the size of a galaxy - and the black hole at its center - can affect its behavior.

It has been widely believed that only massive galaxies contain enough energy to become blazars, which are stupendous jets of radiation powerful enough to stretch thousands of light years. But Paliya's latest research might indicate that smaller galaxies can also do this, if the conditions are right.

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Credit: Wikimedia Commons

Blazars launch jets from the black holes at their centers.

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The Fermi Space Telescope detectors often spots supermassive black holes whose polar jets are pointed in our direction. These active galactic nuclei appear as bright gamma ray emissions. About a 1000 of these powerful objects have been detected.

 

What we call "light" is actually just a tiny fraction of the broad range of radiation on the electromagnetic radiation spectrum. The entire span stretches from very-low-energy radio waves through microwaves, infrared light, visible light, ultraviolet light, X rays, and finally to very-high-energy gamma rays.

In fact, gamma rays are so energetic that they are harmful to life on Earth. Luckily, Earth's atmosphere absorbs gamma rays, preventing them from affecting life on the ground. But this poses a problem if you want to observe the Universe in gamma-ray light. The very atmosphere that protects us from gamma rays prevents us from directly observing them from the ground. Astronomical observations of gamma-ray sources are therefore done with high-altitude balloons or satellites, above the protective blanket of Earth's atmosphere.

The high energy of gamma rays poses another problem: they can pass right through any lens or mirror, making it very difficult to focus them in a telescope. Astronomical observations, therefore, must rely on a different technology to view the gamma-ray universe. Scientists must make use of methods developed by particle physicists, who have long understood techniques for measuring high-energy particles. The Fermi Gamma-ray Space Telescope's specialized astronomical instruments employ detectors used and perfected by physicists interested in the interactions of subatomic particles.

 

NASA's Fermi Gamma-ray Space Telescope has identified the farthest gamma-ray blazars, a type of galaxy whose intense emissions are powered by supersized black holes. Light from the most distant object began its journey to us when the universe was 1.4 billion years old, or nearly 10 percent of its present age.

Despite their youth, these far-flung blazars host some of the most massive black holes known. That they developed so early in cosmic history challenges current ideas of how supermassive black holes form and grow. Blazars constitute roughly half of the gamma-ray sources detected by Fermis Large Area Telescope (LAT). Astronomers think their high-energy emissions are powered by matter heated and torn apart as it falls from a storage, or accretion, disk toward a supermassive black hole with a million or more times the sun’s mass. A small part of this infalling material becomes redirected into a pair of particle jets, which blast outward in opposite directions at nearly the speed of light.

Blazars appear bright in all forms of light, including gamma rays, the highest-energy light, when one of the jets happens to point almost directly toward us. Previously, the most distant blazars detected by Fermi emitted their light when the universe was about 2.1 billion years old. Earlier observations showed that the most distant blazars produce most of their light at energies right in between the range detected by the LAT and current X-ray satellites, which made finding them extremely difficult.