Astro Hobo

Having just spent four days at the largest Astronomy conference ever, I suddenly feel like trying out a new line of work. So, here it is, my first blog. This is shameless promotion of a cool result that I was near, but not a part of.

The result: The fastest spinning pulsar yet found. Why is this cool?

Well, pulsars are just cool in general, but the history of this discovery is as well. Pulsars are what's left over after a very big star goes supernova. They're weird little objects. You can think of them as an atomic nucleus 20 kilometers across with a magnetic field a billon to a quadrillion times as strong as the Earth's magnetic field. They are born spinning, and, just like one of those hand-crank generators you see at science fairs, they produce an electrical force which accelerates electrons. Unlike a hand-crank generator, these electrons get accelerated to energies which experimental physicists can only dream of. Particle accelerators are still trying to reach TeV energies. Pulsar accelerated electrons can reach 10s, maybe 100s of TeV energies. All these electrons produce light, from radio waves to gamma-rays, beamed in various directions (exactly how this happens and in what directions the light is beamed is still under hot debate...it turns out to be a surprisingly difficult problem). This power generation comes at the cost of slowing down the pulsar's spin, and eventually (after a few million years) it slows down so much that you can't see it anymore.

But you can read all about the details elsewhere. Here, I just want to talk about what it took to break the record for the fastest pulsar. Pulsars were first discovered in the 60s by a grad student named Jocelyn Bell (whose thesis advisor won the nobel prize for her discovery, not her!). Shortly afterwards, the pulsar powering the Crab nebula was discovered spinning 30 times a second. The Crab pulsar was born in a supernova explosion that just about everybody but the Europeans saw in the sky in 1054 AD (detailed records of it were found in China and in various other places around the world, but not in Europe. It was, just, like, you know, one of the brightest things in the sky for months, so why would anybody in Europe bother noting it down somewhere....weird, eh?). It is pretty much the youngest pulsar known, and since pulsars slow down with time, then you might expect the Crab's pulsar to be the fastest one around. And for a long time it was.

But that didn't stop Don Backer and friends from looking for a really fast pulsar, and in 1982, using the biggest radio telescope ever built (in fact, the biggest telescope of any type ever built) they found one spinning 642 times a second. Dubbed the millisecond pulsar, it heralded an entire new class of pulsars. These are actually very old pulsars that stole material and angular momentum from a companion star in order to spin faster and faster. How fast can they spin? Well, you'd think that all that was necessary was to find some more of these "recycled" pulsars and find the one with the fastest spin.

And so people started looking, and more were found. Some just by looking randomly in the sky, some by looking at giant conglomerations of millions of stars packed together in globular clusters. In fact, in 23 years, over 100 more have been found, spinning typically about 300 times a second.

But, the millisecond pulsar remained the fastest spinning one. This was ridiculous. How could the very first one of these things found be the fastest as well? A frustrated generation of pulsar searchers were kept up late trying to be the ones to break the record. Sure, they found lots of interesting other pulsars, but why couldn't they break the record?

Well, Scott Ransom, fresh out the army and with too much free time at Harvard started on a decade long quest. First, create the sweetest pulse search software ever, which he called Presto. By the end of his PhD, it was ready. Then off to McGill University to be a postdoc with Vicky Kaspi. She had lots of data coming in from that same biggest telecope in the world which had recently been spiffed up (its called Arecibo, its in Puerto Rico, and has been featured in the movie Contact and a James Bond movie). She also had a big cluster of computers ready for Presto to search all that data. Three years later, with the help of native Albertan grad student Jason Hessels, a dozen or so new recycled pulsars were found. But the record remained unbroken.

But then comes Senator Robert C. Byrd to the rescue.

In the Blue Ridge Mountains of West Virginia, a behemoth was taking shape. The largest steerable structure ever built, the Green Bank Telescope (named after the Senator, whose political skills brought the project to West Virginia) rose up among the peaks. A 110 meter by 100 meter oval, it has a special surface which allows it to observe at high radio frequencies. To go with this telescope, a special pulsar instrument called the Spigot was built out of which pours 25 Megabytes of data every second. At low radio frequencies, a pulsar's signal gets smeared out by all the free electrons running around in the galaxy. Hidden behind our Galaxy was a special cluster called Terzan 5 which was predicted to have the largest number of pulsars in any cluster. The GBT (as astronomers call the telescope) and Spigot were the perfect combination to peer through the Galactic muck at that cluster.

Scott went "that's my baby".

And he was right. He pointed the GBT at Terzan 5 for hours, and Presto almost immediately started picking pulsars out of the data pouring from the Spigot. Many observations and a year of searching the terabytes of data later, 33 pulsars have been found. And one of them, modestly called Terzan 5ad, spins 716 times a second. Don Backer's millisecond pulsar, after 23 years, is now in second place.

But is this really the fastest one out there? Scott and Jason don't think so. And there are dozens of other pulsar searchers searching for the next record-breaker. Any bets on when?