Skip to main content

Mystery of a strange, mirrored double galaxy solved using Hubble data

When telescopes like Hubble peer out into the cosmos, they can sometimes sneak a view of very distant objects using a phenomenon called gravitational lensing. This is where a massive object like a galaxy passes between a distant object and Earth, and the gravity of this intermediate object warps spacetime and acts as a magnifying glass. This allows astronomers to glimpse objects which would otherwise be too faint and far away to be visible.

But sometimes these phenomena result in strange outcomes, like an oddity spotted by Hubble in 2013 which appeared to be two objects that were perfect mirror images of each other.

This Hubble Space Telescope snapshot shows three magnified images of a distant galaxy embedded in a cluster of galaxies.
This Hubble Space Telescope snapshot shows three magnified images of a distant galaxy embedded in a cluster of galaxies. LEAD AUTHOR: NASA, ESA, Richard E. Griffiths (UH Hilo) CO-AUTHOR: Jenny Wagner (ZAH) IMAGE PROCESSING: Joseph DePasquale (STScI)

Astronomers are used to seeing galaxies that appear to be stretched into odd shapes due to gravitational lensing, but this mirroring effect was baffling. “We were really stumped,” said astronomer Timothy Hamilton of Shawnee State University, who first spotted the object, in a statement.

Recommended Videos

Since then, Hamilton and others have been studying the strange object and have finally figured out its puzzling nature. They found that there was a massive cluster of galaxies that was previously uncataloged between Earth and the object, aligned in such a way that it produced two twin images of the distant galaxy. The background galaxy stretches across a ripple in space created by dark matter — and this ripple creates not only the two mirrored images but also a third image of the galaxy positioned to one side.

“Think of the rippled surface of a swimming pool on a sunny day, showing patterns of bright light on the bottom of the pool,” explained another of the researchers, Richard Griffiths of the University of Hawaii in Hilo. “These bright patterns on the bottom are caused by a similar kind of effect as gravitational lensing. The ripples on the surface act as partial lenses and focus sunlight into bright squiggly patterns on the bottom.”

This very rare finding doesn’t only let astronomers sneak a peek at a distant galaxy — it can also help them learn about the dark matter which makes up a large percentage of our universe, by showing how “clumpy” or “smooth” it is. That’s important as there’s a lot we are yet to understand about this mysterious matter.

“We know it’s some form of matter, but we have no idea what the constituent particle is,” Griffiths said. “So we don’t know how it behaves at all. We just know that it has mass and is subject to gravity. The significance of the limits of size on the clumping or smoothness is that it gives us some clues as to what the particle might be. The smaller the dark matter clumps, the more massive the particles must be.”

The research is published in the journal The Monthly Notices of the Royal Astronomical Society.

Georgina Torbet
Georgina has been the space writer at Digital Trends space writer for six years, covering human space exploration, planetary…
Hubble images a pair of galaxies caught in the process of merging
This NASA/ESA Hubble Space Telescope image features Arp 122, a peculiar galaxy that in fact comprises two galaxies – NGC 6040, the tilted, warped spiral galaxy and LEDA 59642, the round, face-on spiral – that are in the midst of a collision.

After last week's image of the week from the Hubble Space Telescope showed a cluster of galaxies that appeared to be very close to each other but actually weren't, this week's image shows two images that are practically on top of each other. The two galaxies shown in the image below, NGC 6040 and LEDA 59642, are so close that they are interacting and have a shared name as a pair, Arp 122.

This NASA/ESA Hubble Space Telescope image features Arp 122, a peculiar galaxy that in fact comprises two galaxies – NGC 6040, the tilted, warped spiral galaxy and LEDA 59642, the round, face-on spiral – that are in the midst of a collision. ESA/Hubble & NASA, J. Dalcanton, Dark Energy Survey/DOE/FNAL/DECam/CTIO/NOIRLab/NSF/AURA Acknowledgement: L. Shatz

Read more
Hubble captures a busy frame of four overlapping spiral galaxies
This image from the NASA/ESA Hubble Space Telescope features a richness of spiral galaxies.

This week's image from the Hubble Space Telescope shows a host of galaxies overlapping in a complex swirl. Four main galaxies are shown in the image, three of which look like they are practically on top of each other, but all is not as it appears in this case.

The largest galaxy in the image, located on the right, is NGC 1356, an elegant barred spiral galaxy similar to our Milky Way. It is also known as the Great Barred Spiral Galaxy due to the prominent nature of its bar, which is a bright structure at the center of the galaxy which is rich with stars. Near this galaxy appear two smaller spiral galaxies, LEDA 467699 and LEDA 95415, and off on the left side of the image is IC 1947.

Read more
Hubble captures a formation of galaxies neatly lined up
An interacting galaxy system known as Arp-Madore 2105-332, that lies about 200 million light-years from Earth in the constellation Microscopium.

Sometimes, Hubble or other telescopes will capture two or more galaxies that are in the process of merging -- called interacting galaxies. These huge collisions can warp one or both of the galaxies, twisting them into strange shapes. The results of such collisions can be catastrophic, with one of the galaxies being destroyed. Or they can be creative, with one larger galaxy being formed from the two merging galaxies.

However, sometimes galaxies that appear very close in images are not actually interacting. Sometimes, they merely appear to be close when seen from Earth, but they can actually be thousands of light-years apart. That's the case with a previous Hubble image showing two overlapping galaxies.

Read more