Manly: 'Pompom' Stars May Solve Quasar Puzzle

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'Pompom' Stars May Solve Quasar Puzzle
Manly Astrophysics | 2017 Jun 27

[img3="Schematic graphic of quasar twinkling. Credit: M. Walker (artwork), CSIRO (photo)"]http://www.manlyastrophysics.org/Images ... llSize.jpg[/img3][hr][/hr]

Gas filaments surrounding stars like the strands of a pompom may be the answer to a 30-year old mystery: why quasars twinkle. ...

Walker's team was studying quasars – powerful, distant galaxies – when they saw one called PKS 1322–110 start to dim and brighten wildly at radio wavelengths over just a few hours.

"This quasar was twinkling violently," Walker said.

Quasar radio twinkling was recognized in the 1980s. Most often it is gentle – small, slow changes in radio brightness. Violent twinkling is rare and unpredictable.

Stars in the night sky twinkle when currents of air in our atmosphere focus and defocus their light. In the same way, quasars twinkle when streams of warm gas in interstellar space focus and defocus their radio signals.

But until now it was a mystery what those streams were and where they lay.

The first sign that stars are involved came when the team prepared to look at their twinkling quasar, PKS 1322–110, with one of the 10-m Keck optical telescopes in Hawai'i.

"At that point we realised this quasar is very close on the sky to the hot star Spica," co-author Dr Vikram Ravi (Caltech) said.

Walker remembered that another violently twinkling quasar, J1819+3845, is close on the sky to the hot star Vega – something previously noted by other researchers. Two hot stars, two twinkling quasars: is this just a coincidence?

Further work suggested it's not.

Walker's team re-examined earlier data on J1819+3845 and another violent twinkler, PKS 1257–326. They found that this second quasar lies close on the sky to a hot star called Alhakim.

The chance of having both twinkling quasars near hot stars is one in ten million, the researchers calculated. ...

Extreme Radio-Wave Scattering Associated with Hot Stars - Mark Walker et al

• Astrophysical Journal 843(1):15 (01 Jul 2017) DOI: 10.3847/1538-4357/aa705c
  arXiv.org > astro-ph > arXiv:1705.00964 > 02 May 2017

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Click to play embedded YouTube video.

<<Spica, also designated Alpha Virginis, is the brightest star in the constellation of Virgo and the 16th brightest star in the night sky. Spica derives from Latin spīca virginis "the virgin's ear of [wheat] grain". Spica is a spectroscopic binary and rotating ellipsoidal variable; a system whose two main stars are so close together they are egg-shaped rather than spherical, and can only be separated by their spectra. The primary is a blue giant and a variable star of the Beta Cephei type. Both stars rotate faster than their mutual orbital period. This lack of synchronization and the high ellipticity of their orbit may indicate that this is a young star system.

Spica is believed to be the star that gave Hipparchus the data that led him to discover the precession of the equinoxes. A temple to Menat (an early Hathor) at Thebes was oriented with reference to Spica when it was built in 3200 BC, and, over time, precession slowly but noticeably changed Spica's location relative to the temple. Nicolaus Copernicus made many observations of Spica with his home-made triquetrum for his researches on precession.

Spica is a close binary star whose components orbit about each other every four days. The primary star has a stellar classification of B1 III–IV. The luminosity class matches the spectrum of a star that is midway between a subgiant and a giant star, and it is no longer a B-type main-sequence star. This is a massive star with more than 10 times the mass of the Sun and seven times the Sun's radius. The total luminosity of this star is about 12,100 times that of the Sun, and eight times the luminosity of its companion. The primary is one of the nearest stars to the Sun that has enough mass to end its life in a Type II supernova explosion.

The primary is classified as a Beta Cephei-type variable star that varies in brightness over a 0.1738-day period. The spectrum shows a radial velocity variation with the same period, indicating that the surface of the star is regularly pulsating outward and then contracting. This star is rotating rapidly, with a rotational velocity of 199 km/s along the equator.

The secondary member of this system is one of the few stars whose spectrum is affected by the Struve–Sahade effect. This is an anomalous change in the strength of the spectral lines over the course of an orbit, where the lines become weaker as the star is moving away from the observer. It may be caused by a strong stellar wind from the primary scattering the light from secondary when it is receding. This star is smaller than the primary, with about 7 times the mass of the Sun and 3.6 times the Sun's radius. Its stellar classification is B2 V, making this a main-sequence star.>>