News

In a new paper Sagiv Shiber, Amit Kashi, and I, presented the first simulations of the grazing envelope evolution (GEE).  In the GEE jets launched by the secondary star efficiently remove the outer part of the giant envelope, while the secondary star grazes the surface of the primary giant star and spirals-in. 

Simulations: A secondary main sequence star enters the envelope of an asymptotic giant branch star of 3.4 solar mass. We assume that the secondary star launches two opposite jets perpendicular to the orbital plane.  There are three segments, each 1.5 years: (i) Density in the orbital plane; (ii) 3D image of jet material (blue) and ejected gas from the envelope of the giant primary star (red); (iii) Temperature in the equatorial plane.   

Ealeal Bear and I listed planetary nebulae with `messy’ morphologies, such as the four in the figure. We propose that the progenitor of such planetary nebulae are triple-stellar systems. (paper  posted on the arXiv.) 

I posted a review paper on the operation of jets in a negative feedback mechanism in stars, galaxies, and clusters of galaxies. I argue that jets are more common that what is usually thought, and that they play an important role in powering many different kind of astrophysical objects.  (paper posted to the arXiv.)

 

Ealeal Bear and I suggested that in the rare case of an Intermediate-Luminosity Optical Transient (ILOTs) event, evaporation of extra-solar Kuiper belt objects at distances of d~500 – 10000AU from the ILOT can be detected.  (paper posted on the arXiv.)

Ron Schreier and I proposed that sub-Keplerian accretion belts around stars might launch jets. Our speculative belt-launched jets model has implications to a rich variety of astrophysical objects, from the removal of common envelopes to the explosion of core collapse supernovae by jittering jets. (paper posted to the arXiv)

I suggest that stars introduce mass and density scales that lead to `naturalness’ in the Universe (paper posted to the arXiv).  The combination of the stellar mass scale with the Planck mass and the Chandrasekhar mass leads to a ratio of order unity.  In the pure fundamental particles domain there is no naturalness; either naturalness does not exist or there is a need for a new physics or new particles. The `Astrophysical Naturalness’ offers a third possibility: stars introduce the combinations of, or relations among, known fundamental quantities that lead to naturalness.

 In a superb  course in astronomy, Phil Plait lectures in a series of tens of 12-minutes long episodes on all topics of astronomy. In episode #30, White Dwarfs & Planetary Nebulae: Crash Course Astronomy #30, he mentions (7:20 minutes) my idea that many planetary nebulae might be shaped by planets.  

Phil Plait was my master student (University of Virginia, 1990), and we studied the planetary nebula NGC 6826 seen here. 

I propose that some irregular `messy’ planetary nebulae (PNe) owe their morphologies to triple-stellar evolution where tight binary systems are tidally and frictionally destroyed inside the envelope of asymptotic giant branch (AGB) stars. I estimate that about one in six non-spherical PNe is shaped by one of these triple-stellar evolutionary routes. See paper. 

Such is the PN on the right NGC 6210 taken from the HST site. 

Amit Kashi and I posted a new paper where we add the group of ILOTs as a new member  of a large family of astrophysical objects whose activity is regulated by the operation of the negative jet-feedback mechanism (JFM).

Using 2D numerical hydrodynamical simulations of type Ia supernova remnants (SNR Ia), PhD student Danny Tsebrenko (Portman) and I show in a new paper that iron clumps few times denser than the rest of the SN ejecta might form protrusions in an otherwise spherical SNR. Such protrusions exist in some SNR Ia, e.g., SNR 1885 and Tycho. Iron clumps are expected to form in the deflagration to detonation explosion model of white dwarfs. For a possible alternative explanation, see news item from November 2014.

 See news item in New Scientist.