Earlier, I took part in a Reddit AMA, where I asked some NASA scientists and collaborators about the new NICER system for finding and studying pulsars. A pulsar is a star that collapsed in on itself, and spins about at incomprehensibly fast speeds while emitting high levels of radiation. While some pulsars rotate as “slowly” as once per second, according to Space.com, the fastest ones “can rotate more than 700 times per second.” In the discussion, the NICER Science Lead said that a “dead” pulsar can rotate thousands of times per second — the entire collapsed star rotates that much.
Because they’re spinning so fast, these pulsars appear to be blinking rapidly when viewed from Earth.
Below are my questions and the answers from the AMA. For the full discussion, click here:
Modern Cereal Box: Are slower spinning pulsars necessarily older/younger than faster spinning pulsars? Or does the spinning have less to do with age and more to do with the size/type of the original star?
Thanks for your question!
Generally speaking, pulsars gradually spin down if they’re in isolation — that is, if they’re not interacting with other stars. That’s because the energy they radiate away (in the form of light and particles) ultimately derives from their spin. So, yes, a slower-spinning pulsar is likely older than a faster-spinning one, but there are important exceptions. Certainly the size and magnetic field strength of the progenitor star has something to do with the spin rate when the pulsar is born (presumably in a supernova explosion), but there are also random events called “glitches” that cause a pulsar to temporarily speed up its spin before resuming the gradual slow-down. More dramatically, a “dead” pulsar can be spun up to super-high rates (thousands of revolutions per second) and brighten again by drawing matter from a companion star, in a process we call “accretion”. The pulsar landscape is very rich, and part of the fun for us is to try to understand how spin rate, magnetic field strength, age, progenitor properties, and many other known and unknown characteristics, relate to each other and give us the collection of neutron stars and pulsars we see today. (–Zaven)
MCB: Now that NICER is active, how much more can we learn about pulsars than we could before?
NICER provides an order of magnitude improvement in sensitivity, energy resolution, and timing resolution than the last major X-ray timing observatory. With NICER we expect to be able to predict the radius of a Neutron star to a precision of 5%- an order of magnitude improvement. This allows is to rule out or allow various models about the composition of the very cores of Neutron stars. -Keith G
MCB: How far away would a pulsar have to be before NICER could no longer detect it?
The brightest pulsar observed at X-ray energies is situated in a distant galaxy 40-50 million light years away. NICER may discover even more distant ultra-luminous sources like this pulsar. -Slavko B
MCB: With the amount of pulsars that are currently being discovered, would it be possible for NICER to witness one collapsing into a black hole? If not, why not?
Most pulsars are expected to simply spin down and cool off. They don’t become black holes. They will become too dim to be detected, and float through our galaxy as cold relics of past star formation. Some pulsars (or neutron stars) are in orbit around a companion, which can provide additional mass transfer. I.e. “feed” the neutron star with more matter. That can be enough to push a neutron star over the edge of stability and cause it to become a black hole. This happens on the stellar evolutionary time scale of hundreds of millions to billions of years. So, unfortunately, the occurrence is so rare that it is unlikely we will detect a pulsar transforming into a black hole. (–Craig)
The scientists who answered our questions were:
Dr. Zaven Arzoumanian – NICER Science Lead, NASA’s Goddard Space Flight Center
Dr. Keith Gendreau – NICER Principal Investigator, NASA’s Goddard Space Flight Center
Dr. Slavko Bogdanov – Pulsar/Neutron star Scientist, Columbia University
Dr. Craig Markwardt – NICER Calibration Lead & Neutron Star Scientist, NASA’s Goddard Space Flight Center