Gravitational lens reveals hiding dwarf dark galaxy

CHARLOTTESVILLE, Va., April 14 (UPI) -- Originally, scientists were simply trying to capture an image of the gravitational lens SDP.81 using the Atacama Large Millimeter Array. Their efforts were part of a 2014 survey aimed at testing ALMA's new, high-resolution capabilities.

More than a year later, however, the image revealed a surprise -- a dwarf dark galaxy hiding in the halo of a larger galaxy, positioned some 4 billion light-years from Earth.

A gravitational lens, or gravitational lensing, is a phenomenon whereby the gravity of a closer galaxy bends the light of a more distant galaxy, creating a magnifying lens-like effect. The phenomenon is often used to study galaxies that would otherwise be too far away to see.

Astronomers initially assumed SDP.81 revealed the light of two galaxies -- that of a more distant galaxy, 12 billion light-years away, and that of the a closer galaxy, 4 billion light-years away.

But new analysis of the image by researchers at Stanford University has revealed evidence of a dwarf dark galaxy.

"We can find these invisible objects in the same way that you can see rain droplets on a window. You know they are there because they distort the image of the background objects," astronomer Yashar Hezaveh explained in a news release.

The gravitational influence of dark matter distorted the light bending through the gravitational lens.

Hezaveh and his colleagues recruited the power of several supercomputers to scan the radio telescope data for anomalies within the halo of SDP.81. They succeeded in identifying a unique clump of distortion, less than one-thousandth the mass of the Milky Way.

The work may pave the way for the discovery of more collections of dark matter and also solve a discrepency that's long plagued cosmologists and astronomers.

Galactic models predict many more satellite objects than satellites and astronomers can find. If many of theses satellites are dwarf dark galaxies, it may explain why they're so difficult to find.

"Our current measurements agree with the predictions of cold dark matter," said fellow researcher Gilbert Holder, an astronomer at McGill University in Montreal, Canada. "In order to increase our confidence we will need to look at many more lenses."