Pulsars are particularly mysterious stars. They are neutron stars that spin on their axis so quickly that they create light pulses. They are a potential end product of stars going supernova, one of the most extreme phenomena in the universe. We are always learning more about them and Hubble has now spotted a pulsar with features that we've never seen before.
As reported in the Astrophysical Journal, RX J0806.4-4123 has an unusual infrared emission suggesting that a peculiar feature surrounds it. It is the first neutron star with an extended emission detected only in infrared light.
“This particular neutron star belongs to a group of seven nearby X-ray pulsars – nicknamed ‘the Magnificent Seven’ – that are hotter than they ought to be considering their ages and available energy reservoir provided by the loss of rotation energy,” lead author Professor Bettina Posselt, from the Pennsylvania State University, said in a statement. “We observed an extended area of infrared emissions around this neutron star the total size of which translates into about 200 astronomical units (or 2.5 times the orbit of Pluto around the Sun) at the assumed distance of the pulsar.”
The team has two potential explanations for the remarkable signal. The first is that the material is a fallback disk. The supernova would have thrown out a lot of debris into space and it might have coalesced to form a disk. This disk would have interacted with the pulsar slowing its rotation and heating it up, which would also help to explain the pulsar's other properties.
“If confirmed as a supernova fallback disk, this result could change our general understanding of neutron star evolution,” Posselt explained.
The other hypothesis suggests that the material emitted in infrared comes from interstellar space. Pulsars have very strong magnetic fields, and these can accelerate particles. If the pulsar is moving faster than the speed of sound in the interstellar medium, it could shock gas and create a pulsar wind nebula.
“Typically, pulsar wind nebulae are seen in X-rays and an infrared-only pulsar wind nebula would be very unusual and exciting,” added Posselt.
These observations open up a new way to potentially study pulsars, which are mostly observed using radio and X-ray telescopes. Upcoming observatories like the James Webb Space Telescope, due to launch in 2021, might reveal a lot more.
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