PSU: Pulsars' Tails Offer Geometry Lessons to Astronomers

[bystander]

A tale of two pulsars' tails: Plumes offer geometry lessons to astronomers
Pennsylvania State University | 2017 Jan 17

An artist’s representation of what the three unusual tails of the pulsar Geminga may look like close up. NASA's Chandra X-ray Observatory is giving astronomers a better look at pulsars and their associated pulsar wind nebulae, enabling new constraints on the geometry of pulsars and why they look the way they do from Earth. Illustration: Nahks TrEhnl

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Like cosmic lighthouses sweeping the universe with bursts of energy, pulsars have fascinated and baffled astronomers since they were first discovered 50 years ago. In two studies, international teams of astronomers suggest that recent images from NASA's Chandra X-ray Observatory of two pulsars — Geminga and B0355+54 — may help shine a light on the distinctive emission signatures of pulsars, as well as their often perplexing geometry.

Pulsars are a type of neutron star that are born in supernova explosions when massive stars collapse. Discovered initially by lighthouse-like beams of radio emission, more recent research has found that energetic pulsars also produce beams of high energy gamma rays.

Interestingly, the beams rarely match up, said Bettina Posselt, senior research associate in astronomy and astrophysics, Penn State. The shapes of observed radio and gamma-ray pulses are often quite different and some of the objects show only one type of pulse or the other. These differences have generated debate about the pulsar model. ...

Chandra Images Show That Geometry Solves a Pulsar Puzzle
NASA | Chandra X-ray Obervatory | 2017 Jan 18

Deep Chandra Observations of the Pulsar Wind Nebula Created by PSR B0355+54 - Noel Klingler et al

• Astrophysical Journal 833(2):253 (2016 Dec 20) DOI: 10.3847/1538-4357/833/2/253
  arXiv.org > astro-ph > arXiv:1610.06167 > 19 Oct 2016

Geminga’s Puzzling Pulsar Wind Nebula - B. Posselt et al

• Astrophysical Journal 835(1):66 (2017 Jan 20) DOI: 10.3847/1538-4357/835/1/66
  arXiv.org > astro-ph > arXiv:1611.03496 > 10 Nov 2016

[neufer]

Geminga moves 3 arc-minutes per millenium

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<<Geminga is a neutron star approximately 250 parsecs (around 800 light years) from the Sun in the constellation Gemini. Its name is both a contraction of "Gemini gamma-ray source", and a transcription of the words gh'è minga "it's not there" in the Lombard dialect of Milan (pronounced [ɡɛˈmiŋɡa]). The proper motion of Geminga is 178.2 mas/year which corresponds to a projected velocity of 205 kilometers per second. This is very fast for a star, comparable to Barnard's star.

The nature of Geminga was quite unknown for 20 years after its discovery by NASA's Second Small Astronomy Satellite (SAS-2). Finally, in March 1991 the ROSAT satellite detected a periodicity of 0.237 seconds in soft x-ray emission. Thus, it is supposed that Geminga is a sort of neutron star: the decaying core of a massive star that exploded as a supernova about 300,000 years ago.

It was once thought that this nearby explosion was responsible for the low density of the interstellar medium in the immediate vicinity of the Solar System. This low-density area is known as the Local Bubble. Possible evidence for this includes findings by the Arecibo Observatory that local micrometre-sized interstellar meteor particles appear to originate from its direction. More recently, however, it has been suggested that multiple supernovae in subgroup B1 of the Pleiades moving group were more likely responsible, becoming a remnant supershell.>>