Teen quasars observed by the Hubble Space Telescope

Galaxies containing quasars observed using the Hubble Space Telescope: in the top row the quasars are visible, in the bottom row the quasars' light is subtracted (Image NASA/ESA)
Galaxies containing quasars observed using the Hubble Space Telescope: in the top row the quasars are visible, in the bottom row the quasars’ light is subtracted (Image NASA/ESA)

An article in the journal “Astrophysical Journal” describes a research conducted on quasars using the Hubble Space Telescope. These objects that are incredibly bright were observed in their formation phase, when they were in a sense teen-agers. The observations confirm the hypothesis that quasars are generated by galactic collisions that feed the supermassive black hole at their center.

Quasars have been known for about 50 years but since they’re located in other galaxies often distant billions of light years we’re still discovering their secrets. The energy source that generates the extraordinary brightness of quasars has been identified in the black hole at the center of these galaxies but it was still to be understood what could feed them so as to reach these levels.

According to one theory, the merger of two galaxies may be the cause that “turn on” a quasar. A team of researchers used the Wide Field Camera 3 of the Hubble Space Telescope to examine a sample of 11 quasars at infrareds, so they could examine the galaxy that hosts them.

The extremely intense brightness of quasars is a problem because it covers the rest of the host galaxy but there are cases where the quasar is surrounded by an enormous amount of dust. The consequence is that it weakens its light and the galaxy can be observed at the infrareds.

The result is that the brightest quasars were found to be in galaxies that were merging. The researchers were able to observe these quasars in a time when they were growing rapidly. It’s a chaotic period and Eilat Glikman of Middlebury College in Vermont, lead author of this study, compared it to humans’ teenage years.

When two galaxies collide and start merging, the gravitational balance within them is disrupted. The consequence is that the gravitational forces make at least part of the disk of gas around the supermassive black hole at the center of a galaxy fall towards it. The effect is a substantial increase in the emission of electromagnetic radiation to reach the exceptional levels of quasars.

The observed quasar existed at the time of the peak of star formation, about 12 billion years ago. The universe was small so collisions between galaxies were much more common. Those galaxies were young so they contained higher quantities of dust and gas that, in addition to forming stars, could feed the supermassive black hole at their center.

In April 2015, another research on quasars observed, again with the Hubble Space Telescope, the remnants of ancient quasars now exhausted. In that research clues were also found that suggested that at least in some cases there were galactic mergers. Gradually, scientists are putting together information about these phenomena that greatly influence the evolution of galaxies.

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