Space: Mystery in a ring of light
Back in 1936, Albert Einstein remarked on a phenomenon he himself predicted was so unlikely to occur that we would never see it. It’s a consequence of his General Theory of Relativity, which says that any massive object distorts the space around it, bending passing light rays and producing something we call a gravitational lens. his effect has been validated many times during the past century.
But Einstein’s 1936 prediction concerns a particular gravitational lens scenario – when the massive object sits directly between ourselves and a much more distant light source, such as a star or galaxy.
Intuitively, you would imagine that the intervening massive object would block our view of the distant source, but it does the reverse by virtue of the gravitational lens. It magnifies the light, making the distant source much brighter than the nearer object. hen the alignment is exact, it turns our view of the distant object into a perfect ring. Not surprisingly, this is called an Einstein ring, and the first complete specimen was discovered in 1998.
Fast-forward to today.We now have an extraordinary example of how the study of Einstein rings has progressed. A very remote galaxy with the unmemorable name of SPT0418-47 has been observed, not in visible light but in microwave radiation, by the Atacama Large Millimeter-Submillimeter Array (ALMA), operated in northern
Chile by the European Southern Observatory in partnership with other agencies. SPT0418-47 appears as a bright ring due to the gravitational lens of an invisible intervening galaxy, but with structure that lets us tease out what it would look like if we could see it directly in close-up.
Using the fine details of its blotchy appearance, the ring has been deconstructed into an accurate image of SPT0418-47 by a team of German and Dutch astronomers.They have revealed something that looks remarkably like a galaxy in today’s Universe, with a rotating disc and central bulge.That’s surprising, since the distance of this galaxy means we see it as it was more than 12 billion years ago, when the Universe was just 1.4 billion years old.
Most galaxies we can observe from this early epoch are unstructured and chaotic, compared with those in the modern Universe.Why is this one so neat and tidy? And are there others like it? Those questions are now the subject of further study.