Composite image of the gravitational lens SDP.81 showing the distorted ALMA image of the more distant galaxy (red arcs) and the Hubble optical image of the nearby lensing galaxy (blue center object). 
Y. Hezaveh, Stanford Univ.; ALMA (NRAO/ESO/NAOJ); NASA/ESA Hubble Space Telescope

Week in Geek - Hiding in the light edition

This may look like the a poor recreation of the Eye of Sauron, but it’s actually a gravitational lens of one galaxy warping the light from another.

Back in 2014, astronomers using the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile discovered this lensing system, dubbed SDP.81. Gravitational lenses are a prediction of Einstein’s theory of general relativity that describes gravity as a space-time continuum - light traveling through space from a distant galaxy can be “bent” if it passes too close to a massive galaxy or galaxy cluster. When this happens along our line of sight, we see the closer galaxy surrounding by false imaged of the more distant galaxy. The shape and distribution of the false images depends on the mass of the closer galaxy (or galaxies).

A schematic representing how light from a distant galaxy is distorted by the gravitational effects of a nearer foreground galaxy, which acts like a lens and makes the distant source appear distorted, but brighter, forming characteristic rings of light.

The blue glow in the center of the image above is a relatively close galaxy around 3.5 billion light years away (as observed by the Hubble Space Telescope). The red arcs in the image are the false images of a more distant galaxy over 12 billion light years away (as observed by ALMA). Now, new analysis of how the light from this more distant galaxy was warped to make the arcs we see has revealed that there is a dark dwarf galaxy hiding just to the lower left of the center (as marked by a small white dot). But the white dot isn’t actually there in the Hubble images, so what’s going on?

Astronomers led by Yashar Hezaveh at Stanford University deduced that something massive enough to affect the shape of the red arcs has to be there. They think it could be a small, faint, dark-matter dominated galaxy in orbit around the visible blue galaxy, which is not uncommon at all since most galaxies should be surrounded by a collection of smaller ones. The biggest problem seems to be detecting them.

As Neal Dalal, another member of the team, states in the ALMA press release:

“This discrepancy between observed satellites and predicted abundances has been a major problem in cosmology for nearly two decades, even called a ‘crisis’ by some researchers… If these dwarf objects are dominated by dark matter, this could explain the discrepancy while offering new insights into the true nature of dark matter.”

Here’s some more geek from the week:

Keep on geeking!

@Summer_Ash, In-house Astrophysicist


Rachel Maddow Show Geek

Week in Geek - Hiding in the light edition