Cosmic Oddity Challenges What We Know About Pulsars
Somewhere out in space, a pulsar is acting strangely. It's emitting infrared radiation-and nothing else-in a way that's making scientists reconsider what they known about these cosmic phenomena.
After a large star goes supernova, the leftover material is typically a neutron star. These are usually around 12.4 to 14.9 miles (20 to 24 km) in diameter, but contain tremendous amounts of mass. The only known phenomena with a higher density than a neutron star is a black hole.
Pulsars are neutron stars with magnetic fields, and typically those magnetic fields are hundreds of millions of times stronger than the Earth's. Like the stars they once were, pulsars also give off light. But these lights are like the lighthouses of the universe, spinning in circles since they are not aligned with the pulsar's axis. And while pulsars can emit light across numerous wavelengths, this one specific pulsar is emitting in a way never quite seen before.
Bettina Posselt, associate research professor of astronomy and astrophysics at Penn State and the lead author of a paper describing the phenomena, says in a press statement:
“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. We observed an extended area of infrared emissions around this neutron star-named RX J0806.4-4123- 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.”
That means that this member of the Magnificent Seven, which was spotted by the Hubble Telescope, was shooting out infrared emissions at a distance never before seen. No other neutron star has sent out emissions only in the infrared at that distance. The finding means that one of the universe's most well-known phenomena might not be as well-known as previously thought.
Posselt says there are two main theories about the pulsar's emissions, both of which would challenge current scientific thinking.
“One theory is that there could be what is known as a ‘fallback disk’ of material that coalesced around the neutron star after the supernova. Such a disk would be composed of matter from the progenitor massive star. Its subsequent interaction with the neutron star could have heated the pulsar and slowed its rotation. If confirmed as a supernova fallback disk, this result could change our general understanding of neutron star evolution.”
The other theory involves the interstellar clouds of dust known as nebulas. Specifically, the emissions might be a new variety of pulsar wind nebula, which are typically found in supernova remnants and are powered by pulsar winds.
Posselt explains:
“A pulsar wind nebula would require that the neutron star exhibits a pulsar wind. A pulsar wind can be produced when particles are accelerated in the electric field that is produced by the fast rotation of a neutron star with a strong magnetic field. As the neutron star travels through the interstellar medium at greater than the speed of sound, a shock can form where the interstellar medium and the pulsar wind interact. The shocked particles would then radiate synchrotron emission, causing the extended infrared emission that we see. Typically, pulsar wind nebulae are seen in X-rays and an infrared-only pulsar wind nebula would be very unusual and exciting.”
Either possibility pushes forward what is known about stars and their aftermath. It's something that scientists are hopeful to further investigate with frequently delayed but still-promised James Webb Space Telescope.
Source: Penn State
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