Watching twinkling pulsars help understand the mystery of interstellar plasma

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(ORDO NEWS) — Pulsars are rapidly spinning remnants of stars that glow like beacons. Sometimes they show sharp changes in brightness.

Scientists predict that these short bursts of brightness are due to dense regions of interstellar plasma (hot gas between stars) scattering the radio waves emitted by the pulsar.

However, we still do not know where the energy sources necessary for the formation and maintenance of these regions of dense plasma come from.

To better understand these interstellar formations, we need more detailed observations of their small-scale structure, and pulsar scintillation or “scintillation” is a promising way to do this.

When a pulsar’s radio waves are scattered by interstellar plasma, the individual waves interfere and create an interference pattern on Earth.

As the Earth, pulsar and plasma move relative to each other, this pattern is seen as a change in brightness over time and frequency: a dynamic spectrum. This is called scintillation.

Due to the point nature of pulsar signals, scattering and scintillation occur in small regions of the plasma.

After specialized processing of the dynamic spectrum signal, we can observe striking parabolic features, known as scintillation arcs, which are associated with the image of scattered pulsar radiation in the sky.

One particular pulsar, named J1603-7202, underwent strong scattering in 2006, making it an interesting target for visualizing these regions of dense plasma.

However, the pulsar’s trajectory has not yet been determined, as it orbits another compact star called a white dwarf in a complex orbit, and scientists have no alternative methods to measure it in this situation.

Fortunately, scintillation arcs serve a dual purpose: their curves are related to the speed of the pulsar, as well as to the distance to the pulsar and plasma.

The change in the speed of a pulsar along its orbit depends on the orientation of the orbit in space.

Therefore, in the case of the J1603-7202 pulsar, in our recent study we calculated the changes in the arc curve over time to determine the orientation.

The measurements we obtained for the J1603-7202 orbit are a significant improvement over the previous analysis. This demonstrates the viability of the scintillation method in addition to alternative methods.

We measured the distance to the plasma and showed that it is about three-quarters of the distance to the pulsar from the Earth.

This does not seem to match the positions of any known stars or interstellar gas clouds. Studies of pulsar scintillations often look at structures that are otherwise invisible.

Therefore, the question remains open: what is the source of the plasma that scatters the radiation of a pulsar?

Finally, using our orbit measurement, we can estimate the mass of J1603-7202’s orbital companion, which is about half the mass of the Sun.

Considered in conjunction with J160-7202’s extremely circular orbit, this means that the companion is likely a carbon-oxygen stellar remnant a rarer find around the pulsar than the more common helium-based remnants.

Since we have an almost complete orbit model, we can now convert J1603-7202 scintillation observations into sky-scattered images and map interstellar plasma at the scale of the solar system.

Imaging the physical structures that cause extreme radio scattering could help us better understand how such dense regions form and the role interstellar plasma plays in galaxy evolution.


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