The Great American Pastime orbits around a minor miracle: The fact that a batter can swipe at a 3-inch ball, going some 90 mph, and actually hit it.
Perhaps my wonder betrays my own athletic deficiencies; I’ve never been any good at ball sports. But putting bat to ball with the split-second timing required to make contact, getting everything to line up in the right place at the right time, seems almost superhuman.
Astronomy is a science that depends on such lucky alignments. We can only spot planets around other stars when they happen to reside in systems that roughly line up with our own; we can only see a pulsar if its beam happens to point our way; many key discoveries in astronomy and physics have been furnished by eclipses, our solar system’s homegrown alignment.
Last year, astronomers caught an alignment so rare that is has only been recorded once before. They captured a special type of supernova, called a Type Ia, being gravitationally “lensed” by galaxy some 2 billion light years from Earth.
That’s a lot of lucky breaks, so let’s break them down, starting with gravitational lensing.
In his theory of general relativity, Einstein argued that mass distorts the fabric of space itself, acting as a “lens” that warps the path light takes through space. That can result in funhouse-style optical oddities. It’s a weird trick, and a useful one, too: Astronomers can use gravitational lensing effects to learn more about dark matter, dark energy and even, in its “micro” form, exoplanets.
Gravitational lensing only works when the distant object, the lens, and Earth happen to line up just right, though. That’s rare enough. Now imagine trying to hit the perfect alignment with a distant source like a supernova explosion, which shines bright for a few months and then fades back into the background.
That’s what makes this new discovery so remarkable: Astrophysicists caught a Type Ia supernova just as it was being lensed by a galaxy located about 2 billion light years from Earth.
A Type Ia supernova explosion happens when a white dwarf star steals so much matter from a neighboring star that it goes into catastrophic gravitational overload. These supernovae are particularly coveted by astronomers because, intrinsically, they are all equally bright, so their received brightness at Earth tells you how far away they are.
Getting a fix on astronomical distances is tough, so “standard candles” like these are critical scientific tools.
The lensing made the supernova, which is about 4 billion light years from Earth, look 50 times brighter than normal, which was what first caught astronomers’ attention. Follow-up observations showed that the supernova actually appeared as four separate bright spots on the sky, its image cloned by one of those gravitational funhouse-mirror tricks.
Astronomers were able to train a flock of powerful telescopes on the images, making it possible to pick out fine details in both the supernova’s home galaxy and the lensing galaxy.
Astronomers hope this won’t be the last time they catch a Type Ia supernova as it is being gravitationally lensed. Thanks to this event, they now have template with which to refine future searches.
The odds may be long — astrophysicist Peter Nugent, an author on two papers describing the phenomenon, put them at about one in every 50,000 observed supernovae — but they’re not superhuman.
After all, the stars have aligned once: they just might do it again.
Kate Becker is a science writer living in Boston. Contact her at spacecrafty.com, or connect via facebook.com/katembecker or twitter.com/kmbecker.
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