The challenges of cosmic curiosity What we know about pulsars

Somewhere in space, a pulsar acts strangely. It emits infrared radiation, and nothing else, so that scientists reconsider what they knew about these cosmic phenomena.

After a large star has become supernova, the remaining material is usually a neutron star. These usually have a diameter of 20 to 24 km, but contain huge amounts of mass. The only known phenomenon with a higher density than a neutron star is a black hole.

Pulsars are neutron stars with magnetic fields, and these magnetic fields are typically hundreds of millions of times more powerful than those of the Earth. Like the stars, pulsars emit light. But these lights are like the lighthouses of the universe, rotating in circles because they are not aligned with the axis of the pulsar. And while pulsars can emit light over many wavelengths, this specific pulsar emits in a way never seen before.

Bettina Posselt, associate professor of astronomy and astrophysics research at Penn State and lead author of an article describing the phenomena, states in a press release:

"This neutron star belongs to a group of seven nearby X-ray pulsars – nicknamed" the seven gorgeous "- which are warmer than they should be given their age and the available energy reservoir provided by the loss of rotational energy. We observed an extended infrared emission zone around this neutron star – called RX J0806.4-4123 – whose total size translates to about 200 astronomical units (or 2.5 times the orbit of Pluto around the Sun) at the supposed distance of pulsar. "

This means that this Magnificent Seven member, who was spotted by the Hubble telescope, was emitting infrared emissions at a distance never seen before. No other neutron star has emitted emissions only in the infrared at this distance. The discovery means that one of the most well-known phenomena of the universe might not be as known as expected.

Posselt says that there are two main theories on pulsar emissions, both of which would challenge current scientific thinking.

"One theory is that there might be what's called a" fallback disk "of material that has fused around the neutron star after the supernova. Such a disc would be composed of material from the massive star of the ancestor. Its subsequent interaction with the neutron star could have heated the pulsar and slowed its rotation. If confirmed as a supernova backup disk, this result could change our general understanding of the evolution of neutron stars. "

The other theory concerns interstellar dust clouds known as nebulae. Specifically, the emissions could be a new variety of pulsar nebulae, typically present in supernova remnants and powered by pulsar-like winds.

Posselt explains:

"A pulsating wind nebula would require the neutron star to have a pulsar wind. A pulsar wind can be produced when the particles are accelerated in the electric field produced by the rapid rotation of a neutron star with a strong magnetic field. As the neutron star passes through the interstellar medium at a speed greater than that of the sound, a shock can occur where the interstellar medium and the pulsar wind interact. The shocked particles would then emit a synchrotron emission, causing the prolonged infrared emission we see. As a general rule, pulsar wind nebulae are seen in X-rays and an all-infrared pulsar wind nebula would be very unusual and exciting.

The one or the other possibility advances what we know about the stars and their consequences. This is something that scientists hope to deepen with the James Webb Space Telescope, often delayed but still promised.

Source: Penn State