Pulsars are some of the strangest objects in the universe.
They are the dense, rapidly spinning remains of dead stars, and they send out beams of radio waves like cosmic lighthouses.
As they spin, these beams sweep across space, and when one points toward Earth, astronomers detect a pulse.
Some pulsars, known as millisecond pulsars, spin incredibly fast—hundreds of times per second—and are so regular that they are often compared to precise clocks.
For many years, scientists believed that the radio signals from pulsars were produced close to the star’s surface, near its magnetic poles. But a new study suggests that this long-held idea may not tell the full story.
The research, published in Monthly Notices of the Royal Astronomical Society, was carried out by scientists from Germany and Australia.
They examined radio observations from nearly 200 millisecond pulsars and compared them with gamma-ray data collected by NASA’s Fermi space telescope.
What they found was surprising. About one-third of these fast-spinning pulsars showed radio signals coming from two or more separate regions, with gaps in between where no signal was detected. This unusual pattern is rare in slower pulsars, appearing in only about 3% of them.
Even more intriguing, many of these radio signals lined up exactly with bursts of gamma rays. This suggests that both types of radiation may be coming from the same place in space, rather than from different regions as previously thought.
To explain this, the researchers propose that millisecond pulsars can produce radio waves in two distinct locations.
One is near the magnetic poles, as scientists have long assumed. The other is much farther away, in a region called the “current sheet.” This area lies just beyond the “light cylinder,” an invisible boundary where the pulsar’s magnetic field would need to move faster than light to keep up with the star’s rotation.
Depending on how we view a pulsar from Earth, we may see signals from the surface, from this outer region, or from both. This can create the broken and complex radio patterns that have puzzled astronomers for years.
This discovery could have important consequences. It suggests that more pulsars may be detectable than previously thought, because their radio signals are not limited to a narrow beam near the surface. It may also explain why the orientation, or polarization, of their radio waves has been so difficult to understand.
In addition, the findings hint that nearly all millisecond pulsars that emit gamma rays may also produce radio waves, even if those signals are faint.
However, the study also raises new questions. Scientists now need to understand how stable radio signals can form so far from the star, in a region that is highly energetic and chaotic.
Overall, the results show that these tiny, fast-spinning stars are even more complex than expected, sending signals not just from their surfaces, but from the far reaches of their powerful magnetic fields.
Source: Max Planck Society.
