Some of the most precise clocks in the universe are not clocks at all – they are fastly-rotating pulsars, which can be more accurate than atomic clocks. They are so precise that they can be used to test the most sophisticated physics theories to a staggering precision, so astronomers are always looking for more of them.
And last week, using the Fermi Large Area Telescopes (LAT), an international team of astronomers was able to discover six brand new millisecond pulsars. The discovery was possible by following up the Fermi detection with radio observations at the Arecibo telescope in Puerto Rico.
Millisecond pulsars (MSP) are neutron stars that spin on their axis at an extremely high velocity. Sometimes, pulsars have companion stars, and during their orbits the pulsar starts absorbing material from the companion, quite literally sucking the life out of them. Due to the conservation of angular momentum, the infalling material can give a boost to the pulsar that speeds it up, and it can end up rotating hundreds of times per second.
In a paper published online on Arxiv, the researchers detailed the rotational period of these objects, with the fastest spinning every 1.99 milliseconds and the slowest every 4.66 milliseconds. Although they’re all fast, there is much variation among the six objects. So the researchers divided them into three groups.
There were three MSPs categorized as “black widows”, where the pulsar has stolen almost all the mass from the companion, which is now just a degenerate mass object weighing less than 10 percent of the Sun’s mass. Two pulsars were “redback,” a term that describes pulsars eclipsed by the large outflows from the companion star. The last object has a more classical white dwarf companion.
Fermi has detected over 1,000 unidentified sources of gamma-rays, and the researchers think that some of those sources could be more MSPs. “Of the 230 millisecond pulsars (MSPs) currently known in the Galactic disk, 30% have been discovered in previously unidentified sources of gamma rays detected by the Fermi LAT instrument” the team noted in the paper.
“While only around 10% of all known pulsars rotate at millisecond rates, MSPs make up half of all pulsars observed to emit gamma rays”