3.02.2018

The quiescent galaxy eMACSJ1341-QG-1as seen by the Hubble Space Telescope. The yellow dotted line traces the boundaries of the galaxy’s gravitationally lensed image. The inset on the upper left shows what eMACSJ1341-QG-1 would look like if we observed it directly, without the cluster lens. The dramatic amplification and distortion caused by the intervening, massive galaxy cluster (of which only a few galaxies are seen in this zoomed-in view) is apparent.
Credit: Harald Ebeling, UH IfA

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Extremely distant galaxies are usually too faint to be seen, even by the largest telescopes. But nature has a solution: gravitational lensing, predicted by Albert Einstein and observed many times by astronomers. Now, an international team of astronomers, led by Harald Ebeling of the Institute for Astronomy at the University of Hawaiʻi at Mānoa, has discovered one of the most extreme instances of magnification by gravitational lensing.

Using the Hubble Space Telescope to survey a sample of huge clusters of galaxies, the team found a distant galaxy, eMACSJ1341-QG-1, that is magnified 30 times thanks to the distortion of space-time created by the massive galaxy cluster dubbed eMACSJ1341.9-2441.

The underlying physical effect of gravitational lensing was first confirmed during the solar eclipse of 1919, and can dramatically magnify images of distant celestial sources if a sufficiently massive object lies between the background source and observers.

Galaxy clusters, enormous concentrations of dark matter and hot gas surrounding hundreds or thousands of individual galaxies, all bound by the force of gravity, are valued by astronomers as powerful “gravitational lenses.” By magnifying the galaxies situated behind them, massive clusters act as natural telescopes that allow scientists to study faint and distant sources that would otherwise be beyond the reach of even the most powerful man-made telescopes.

“The very high magnification of this image provides us with a rare opportunity to investigate the stellar populations of this distant object and, ultimately, to reconstruct its undistorted shape and properties,” said team member Johan Richard of the University of Lyon, who performed the lensing calculations.

Although similarly extreme magnifications have been observed before, the discovery sets a record for the magnification of a rare “quiescent” background galaxy—one that, unlike our Milky Way, does not form new stars in giant clouds of cool gas.

Explained UH team leader Ebeling, “We specialize in finding extremely massive clusters that act as natural telescopes and have already discovered many exciting cases of gravitational lensing. This discovery stands out, though, as the huge magnification provided by eMACSJ1341 allows us to study in detail a very rare type of galaxy.”

Details of the discovery are published in Astrophysical Journal Letters.