The jet feedback mechanism (May 2016)

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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.)


Launching jets from accretion belts (January 2016a)

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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)

Astrophysical Naturalness (October 2015)

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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.

From the media: Shaping planetary nebulae with planets (September 2015)

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 In a superb  course in astronoThe elliptical planetary nebulae NGC 6826 (the colors are not real)my, 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. 

Shaping planetary nebulae by triple-stellar systems (August 2015)

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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 asymNGC 6210 is an example of a `messy' planetary nebula that has no symmetry at allptotic 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

Type Ia Supernova Remnants: Shaping by Iron Bullets (June 2015)

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Using 2D numerical hydrodynamical simulations of type Ia supernova remnants (SNR Ia), PhD student Danny TsebrenkoSoker2015Tsebrenko (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.


Rescuing the intracluster medium of NGC 5813 (May 2015b)

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Shlomi HizShlomi2015llel (PhD Student), Assaf Sternberg and I argue that the intracluster medium  (ICM) of the cooling flow galaxy group NGC 5813 is more likely to be heated by mixing of post-shock jets’ gas residing in hot bubbles with the ICM, than by shocks or turbulent-heating. Heating by mixing rescues the outer ICM of NGC 5813 from its predestined fate according to cooling flow feedback scenarios that are based on heating by shocks.  See Paper.



Massive disk outflows mediated by extreme magnetic fields (May 2015a)

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Sagiv Shiber (a master student), Ron Schreier, and I  argue that magnetic fields amplified within a very high accretion-rate disk around main sequence stars can lead to the formation of massive bipolar outflows that can remove most of the disk’s mass and energy. Such energetic outflows can account for the powering of some eruptive objects, such as merging main sequence stars, major eruptions of luminous blue variables, such as the Great Eruption of Eta Carinae, and other Intermediate Luminosity Optical Transients (ILOTs: see the ILOT site). Such powerful outflows can also supply the extra energy required in the common envelope process and in the grazing envelope evolution of binary systems where the companion is a main sequence star. Paper was posted on astro-ph.