The universe, it turns out, has its own cosmic clocks
July 6, 2010 Leave a comment
Clocks are finicky devices. No matter how carefully you calibrate a clock — whether it be an old-fashioned pendulum, wristwatch, digital, atomic, or (my personal strategy) a cell phone — sooner or later, tiny discrepancies occur, which get larger the longer they go uncorrected, until suddenly you find yourself running very late for your best friend’s wedding, or that critical business meeting that could make or break your career.
Heck, if it weren’t for the theory of general relativity helping scientists correct for tiny discrepancies, our Global Positioning System would quickly go off kilter.
The universe, it turns out, has its own cosmic clocks: the spinning collapsed stars known as pulsars. These unusual objects were first discovered in 1967, when Jocelyn Bell, then a graduate student in astronomy, noticed a strange “bit of scruff” in the data coming from her radio telescope.
Could it be a transmission from extraterrestrial life? She and her advisor, Anthony Hewish, jokingly called the radio source LGM-1, for “Little Green Men.” But of course, it wasn’t E.T., after all: they had discovered the first pulsar.
Pulsars are often described as “cosmic flywheels,” since because of their rotation, they produce periodic bursts of radio waves that sweep across the expanse of space like the beam from a lighthouse. And those periodic bursts are extremely precise — millisecond pulsars which spin the fastest, are accurate within a millionth of a second over the course of a year — which makes them excellent “timekeeping” devices for astrophysical phenomena, especially the search for gravitational waves: those telltale ripples in the fabric of space-time caused by gravitational effects, according to general relativity.
At least that’s the conclusion (announced last week in Science) of scientists at the University of Manchester’s historic Jodrell Bank Observatory in the UK (known to Dr. Who and Douglas Adams fans the world over), who have developed a method to offset the teensy variations in rotation that have hindered efforts to date in the search for gravitational waves. Scientists have yet to directly observe gravitational waves, although several major experiments around the world are on the hunt.
Millisecond pulsars are of particular interest, because of their highly stable rotation. The hypothesis is that those tiny ripples would ever-so-slightly alter the pulsars’ time-keeping as they washed over them. But even millisecond pulsars show very slight irregularities, sufficient to hamper efforts to detect the even weaker gravitational waves. And if you think adjusting your wristwatch or digital alarm clock is a pain, imagine if you had to figure out how to adjust an ultra-dense collapsed star in the far reaches of the universe. Read more.
Source: Discovery News