Astronomers Discover Rare Triple Quasar System


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Telescopes at European Southern Observatory’s La Silla site, which includes the New Technology Telescope Image Credit: Iztok Boncina/ESO Creative Commons License.

Astronomers have discovered a rare triple quasar system. What are the implications of this astronomical find?

In a paper published in the Monthly Notices of the Royal Astronomical Society, a team of astronomers announce the discovery of only the second system of three physically associated quasars. The team led by E. P. Farina also included C. Montuori, R. Decarli, and M. Fumagalli discovered the system of quasars, QQQ J1519+0627, using European Southern Observatory’s New Technology Telescope at La Silla Observatory and the Centro Astrónmico Hispano Alemán 3.5 meter telescope at Calar Alto Observatory.

Discovering QQQ J1519+0627

To discover this triple quasar system, the team of astronomers searched the Sloan Digital Sky Survey for candidate systems of quasars. Quasars can be near the same position in the sky, but not physically associated because they are at different distances from Earth. The team next measured the spectra of the quasars in candidate systems with the New Technology Telescope.


Astronomers measure distances to quasars from the Doppler red shifts in their spectra. If the quasars in a candidate system all have nearly the same red shift, they are at nearly the same distance and therefore physically associated. The team next imaged the system with the Calar Alto telescope to measure the brightness of the quasars. The team also eliminated the possibility that the quasars are multiple images of the same quasar caused by the gravitational lens effect from an intervening galaxy.

The three individual components of this quasar system are called QQQ1519A, QQQ1519B, and QQQ1519C. The quasar system’s redshift (z=1.51) corresponds to a light travel time distance of a little over 9 billion light years, meaning that we are seeing this system as it was approximately 9 billion years ago. The exact distance depends on the specific cosmological model of the universe used in the calculation. In any case, studying quasars at this distance gives astronomers clues to the early development of galaxies, like our Milky Way galaxy.

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