arXiv subjects

Noam Soker

Publications and source records attributed to Noam Soker.

At least 289 records · Page 16Linked to original sources

arXiv2013

Suppressing hot gas accretion to supermassive black holes by stellar winds

We argue that one of the basic assumptions of the Bondi accretion process, that the accreting object has zero pressure, might not hold in many galaxies because of the pressure exerted by stellar winds of star orbiting the central super massive black hole (SMBH). Hence, the Bondi accretion cannot be used in these cases, such as in the galaxy NGC 3115. The winds of these high-velocity stars are shocked to temperatures above the virial temperature of the galaxy, leading to the formation of a hot bubble of size ~0.1-10 pc near the center. This hot bubble can substantially reduce the mass accretion rate by the SMBH. If the density of the hot bubble is lower than that of the interstellar medium (ISM), a density-inversion layer is formed. As the gas loses energy by X-ray radiation, eventually more mass of the cooling shocked stellar winds will be accreted to the SMBH. This accretion will be of cold clumps. After a period of millions of years of low AGN activity, therefore, a stronger AGN activity will occur that will heat and expel gas, much as in cooling flow clusters. Adding to other problems of the Bondi process, our results render the Bondi accretion irrelevant for AGN feedback in cooling flow in galaxies and small groups of galaxies and during galaxy formation.

astro-ph.CO↗

arXiv2013

Multi-jets structure rather than rotation of the NGC 1333 IRAS 4A2 protostellar jets

We analyze the velocity gradient across the jets of the young stellar object (YSO) NGC 1333 IRAS 4A2 and explain it by decomposing the two opposite jets to two opposite sub-jets. The two sub-jets have the same radial velocity and the angle between them is only several degrees. Each of the two sub-jets is composed of two components. We also show that the alternative interpretation of jets' rotation is unlikely to account for the velocity gradient. The two sub-jets directions are constant, and there is no indication for precession. The line connecting the centers of the sub-jets defines a preferred direction in a plane parallel to the accretion disk launching the jets. We suggest that the preferred constant direction in the accretion disk is determined by the semi-major axis of a highly eccentric orbit of a brown dwarf or a massive planet companion. At each periastron passage the companion perturbs the accretion disk with a quadrupole mode, e.g., two spiral arms, that lead to the launching of the two sub-jets. We predict that a careful monitoring of the system will reveal a periodic activity with a period of few months to several years.

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arXiv2013

Steady Twin-Jets Orientation: Implications For Their Formation Mechanism

We compare the structures of the jets of the pre-planetary nebulae (PN) CRL618 and the young stellar object (YSO) NGC 1333 IRAS4A2 and propose that in both cases the jets are launched near periastron passages of a highly eccentric binary system. The pre-PN CRL618 has two `twin-jets' on each side, where by `twin-jets' we refer to a structure where one side is composed of two very close and narrow jets that were launched at the same time. We analyze the position-velocity diagram of NGC 1333 IRAS4A2, and find that it also has the twin-jets structure. In both systems the orientation of the two twin-jets does not change with time. By comparing these two seemingly different objects, we speculate that the constant relative direction of the two twin-jets is fixed by the direction of a highly eccentric orbit of a binary star. For example, a double-arm spiral structure in the accretion disk induced by the companion might lead to the launching of the twin-jets. We predict the presence of a low-mass stelar companion in CRL618 that accretes mass and launches the jets, and a substellar (a planet of a brown dwarf) companion to the YSO NGC 1333 IRAS4A2 that perturbed the accretion disk. In both cases the orbit has a high eccentricity.

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arXiv2013

Type Ia Supernovae inside Planetary Nebulae: Shaping by Jets

Using 3D numerical hydrodynamical simulations we show that jets launched prior to type Ia supernova (SN Ia) explosion in the core-degenerate scenario can account for the appearance of two opposite lobes ('Ears') along the symmetry axis of the SN remnant (SNR). In the double-degenerate and core-degenerate scenarios the merger of the two degenerate compact objects is very likely to lead to the formation of an accretion disk, that might launch two opposite jets. In the CD scenario these jets interact with the envelope ejected during the preceding common envelope phase. If explosion occurs shortly after the merger process, the exploding gas and the jets will collide with the ejected nebula, leading to SNR with axisymmetric components including 'Ears'. We also explore the possibility that the jets are launched by the companion white dwarf prior to its merger with the core. This last process is similar to the one where jets are launched in some pre-planetary nebulae. The SNR 'Ears' in this case are formed by a spherical SN Ia explosion inside an elliptical planetary nebula-like object. We compare our numerical results with two SNRs - Kepler and G299.2-2.9.

astro-ph.SR↗

arXiv2013

A binary scenario for the pre-explosion outburst of the supernova 2010mc

I raise the possibility that the pre-explosion outburst (PEO) of the type IIn supernova 2010mc (PTF 10tel) was energized by mass accretion onto an O main-sequence stellar companion. According to this suggestion the SN progenitor suffered a rapid expansion within months before explosion. The expansion was driven by leakage of energy from the core where vigorous oxygen nuclear burning takes place within a year prior to explosion. This expansion triggered mass transfer onto the secondary star. Most of the extra energy of the outburst comes from the accretion of ~0.1Mo onto the secondary star. As well, the gas outflowing at v~2000 km/s was launched from the accreting secondary star, most likely in a bipolar outflow. The binary model can account for the slower circumstellar medium that was ejected at earlier times, and explain the red-shifted peak of the Halpha emission at 5.8 days past explosion. I compare some properties of the PEO of SN 2010mc to those of other stellar eruptions, such as the stellar merger event V838 Monocerotis and the nineteenth century Great Eruption of the massive stellar binary system Eta Carinae. I speculate that all Type IIn supernovae owe their dense circumstellar gas to binary interaction.

astro-ph.HE↗

arXiv2013

Explaining the type Ia supernova PTF 11kx with a violent-prompt merger scenario

We argue that the multiple shells of circumstellar material (CSM) and the supernovae (SN) ejecta interaction with the CSM starting 59 days after the explosion of the Type Ia SN (SN Ia) PTF 11kx, are best described by a violent prompt merger. In this prompt merger scenario the common envelope (CE) phase is terminated by a merger of a WD companion with the hot core of a massive asymptotic giant (AGB) star. In most cases the WD is disrupted and accreted onto the more massive core. However, in the rare cases where the merger takes place when the WD is denser than the core, the core will be disrupted and accreted onto the cooler WD. In such cases the explosion might occur with no appreciable delay, i.e., months to years after the termination of the CE phase. This, we propose, might be the evolutionary route that could lead to the explosion of PTF 11kx. This scenario can account for the very massive CSM within ~1000 AU of the exploding PTF 11kx star, for the presence of hydrogen, and for the presence of shells in the CSM.

astro-ph.SR↗

arXiv2013

Explaining the supernova impostor sn 2009ip as mergerburst

We propose that the energetic major outburst of the supernova (SN) impostor SN 2009ip in September 2012 (outburst 2012b) was a mergerburst event, where two massive stars merged. The previous outbursts of 2009 and 2011 might have occurred near periastron passages of the binary system prior to the merger, in a similar manner to the luminosity peaks in the nineteenth century Great Eruption of the massive binary system Eta Carinae. The major 2012b outburst and the 2012a pre-outburst, resemble the light curve of the mergerburst event V838 Mon. A merger of an evolved star with a mass of M1~60-100Mo and a secondary main sequence star of M2~0.2-0.5M1 can account for the energy of SN 2009ip and for the high velocities of the ejected gas. The ejected nebula is expected to have a non-spherical structure, e.g. bipolar or even a more complicated morphology.

astro-ph.HE↗

arXiv2012

Numerical simulations of wind-equatorial gas interaction in eta Carinae

We perform three-dimensional gas-dynamical simulations and show that the asymmetric morphology of the blue and red-shifted components of the outflow at hundreds of astronomical units (AU) from the massive binary system eta Carinae can be accounted for from the collision of the free primary stellar wind with the slowly expanding dense equatorial gas. Owing to the very complicated structure of the century-old equatorial ejecta, that is not fully spatially resolved by observations, we limit ourselves to modelling the equatorial dense gas by one or two dense spherical clouds. Because of that we reproduce the general qualitative properties of the velocity maps, but not the fine details. The fine details of the velocity maps can be matched by simply structuring the dense ejecta in an appropriate way. The blue and red-shifted components are formed in the post-shock flow of the primary wind, on the two sides of the equatorial plane, respectively. The fast wind from the secondary star plays no role in our model, as for most of the orbital period in our model the primary star is closer to us. The dense clouds are observed to be closer to us than the binary system is, and so in our model the primary star faces the dense equatorial ejecta for the majority of the orbital period.

astro-ph.SR↗

arXiv2012

Heating the intra-cluster medium perpendicular to the jets axis

By simulating jet-inflated bubbles in cooling flows with the PLUTO hydrodynamic code we show that mixing of high entropy shocked jet's material with the intra-cluster medium (ICM) is the major heating process perpendicular to the jets' axis. Heating by the forward shock is not significant. The mixing is very efficient in heating the ICM in all directions, to distances of ~10kpc and more. Although the jets are active for a time period of only 20 Myr, the mixing and heating near the equatorial plane, as well as along the symmetry axis, continues to counter radiative cooling for times of >10^8 yr after the jets have ceased to exist. We discuss some possible implications of the results. (i) The vigorous mixing is expected to entangle magnetic field lines, hence to suppress any global heat conduction in the ICM near the center. (ii) The vigorous mixing forms multi-phase ICM in the inner cluster regions, where the coolest parcels of gas will eventually cool first, flow inward, and feed the active galactic nucleus to set the next jet-activity episode. This further supports the cold feedback mechanism. (iii) In cases where the medium outside the region of r~10kpc is not as dense as in groups and clusters of galaxies, like during the process of galaxy formation, the forward shock and the high pressure of the shocked jets' material might expel gas from the system.

astro-ph.CO↗

arXiv2012

The number of progenitors in the core - degenerate scenario for type Ia supernovae

We calculate the expected number of type Ia supernovae (SN Ia) in the core-degenerate (CD) scenario and find it to match observations within the uncertainties of the code. In the CD scenario the super-Chandrasekhar mass white dwarf (WD) is formed at the termination of the common envelope phase from a merger of a WD companion with the hot core of a massive asymptotic giant branch (AGB) star. We use a simple population synthesis code that avoids the large uncertainties involved in estimating the final orbital separation of the common envelope evolution. Instead, we assume that systems where the core of the secondary AGB star is more massive than the WD remnant of the primary star merge at the termination of the common envelope phase. We also use a simple prescription to count systems that have strong interaction during the AGB phase, but not during the earlier red giant branch (RGB) phase. That a very simple population synthesis code that uses the basics of stellar evolution ingredients can match the observed rate of SN Ia might suggest that the CD-scenario plays a major role in forming SN Ia.

astro-ph.SR↗

arXiv2012

The jet feedback mechanism (JFM): from supernovae to clusters of galaxies

We study the similarities of jet-medium interactions in several quite different astrophysical systems using 2D and 3D hydrodynamical numerical simulations, and find many similarities. The systems include cooling flow (CF) clusters of galaxies, core-collapse supernovae (CCSNe), planetary nebulae (PNe), and common envelope (CE) evolution. The similarities include hot bubbles inflated by jets in a bipolar structure, vortices on the sides of the jets, vortices inside the inflated bubbles, fragmentation of bubbles to two and more bubbles, and buoyancy of bubbles. The activity in many cases is regulated by a negative feedback mechanism. Namely, higher accretion rate leads to stronger jet activity that in turn suppresses the accretion process. After the jets power decreases the accretion resumes, and the cycle restarts. In the case of CF in galaxies and clusters of galaxies we also study the accretion process, which is most likely by cold clumps, i.e., the cold feedback mechanism. In CF clusters we find that heating of the intra-cluster medium (ICM) is done by mixing hot shocked jet gas with the ICM, and not by shocks. Our results strengthen the jet feedback mechanism (JFM) as a common process in many astrophysical objects.

astro-ph.SR↗

arXiv2012

Transient outburst events from tidally disrupted asteroids near white dwarfs

We discuss the possibility of observing the transient formation event of an accretion disk from the tidal destruction process of an asteroid near a white dwarf (WD). This scenario is commonly proposed as the explanation for dusty disks around WDs. We find that the initial formation phase lasts for about a month and material that ends in a close orbit near the WD forms a gaseous disk rather than a dusty disk. The mass and size of this gaseous accretion disk is very similar to that of Dwarf Novae (DNe) in quiescence. The bolometric luminosity of the event at maximum is estimated to be 0.001-0.1Lsun. Based on the similarity with DNe we expect that transient outburst events such as discussed here will be observed at wavelengths ranging from visible to the X-ray, and be detected by present and future surveys.

astro-ph.SR↗

arXiv2012

Inflating a chain of x-ray deficient bubbles by a single jet activity episode

We show that a continuous jet with time-independent launching properties can inflate a chain of close and overlapping X-ray deficient bubbles. Using the numerical code PLUTO we run 2.5D (i.e. spherical coordinate system with cylindrical symmetry) hydrodynamic simulations and study the interaction of the jets with the intra-cluster medium (ICM). A key process is vortex fragmentation due to several mechanisms, including vortex-shedding and Kelvin-Helmholtz (KH) instabilities. Our results can account for the structure of two opposite chains of close bubbles as observed in the galaxy cluster Hydra A. Our results imply that the presence of multiple pairs of bubbles does not necessarily imply several jet-launching episodes. This finding might have implications to feedback mechanisms operating by jets.

astro-ph.CO↗

arXiv2012

Accretion of Dense Clumps in the Periastron Passage of Eta Carinae

We perform 3D hydrodynamical numerical simulations of the winds interaction process in the massive binary system $η$ Carinae, and find the secondary star to accrete mass from the dense primary wind close to periastron passage. This accretion is thought to result in the spectroscopic event and X-ray minimum observed in the system every revolution. In this study we limit ourselves to explore the role of clumps in the primary wind in triggering the accretion process. We include the gravity of the secondary star and the orbital motion starting 19 days (90 degrees) before periastron passage. The accretion process is triggered by dense clumps that cannot be decelerated by the ram pressure of the secondary wind. The dense clumps are formed by instabilities in the thin dense shell formed by the shocked primary wind gas. We explore the role of the numerical viscosity and some physical parameters on the initiation of the accretion process, and explain the unique properties of $η$ Car that allow for the periastron accretion process to occur. The accretion starts about a week before periastron passage, as is required to explain the several weeks long X-ray minimum.

astro-ph.SR↗

arXiv2012

Merger by Migration at the Final Phase of Common Envelope Evolution

I find the common envelope (CE) energy formalism, the CE α-prescription, to be inadequate to predict the final orbital separation of the CE evolution in massive envelopes. I find that when the orbital separation decreases to ~10 times the final orbital separation predicted by the CE α-prescription, the companion has not enough mass in its vicinity to carry away its angular momentum. The core-secondary binary system must get rid of its angular momentum by interacting with mass further out. The binary system interacts gravitationally with a rapidly-rotating flat envelope, in a situation that resembles planet-migration in protoplanetary disks. The envelope convection of the giant carries energy and angular momentum outward. The basic assumption of the CE α-prescription, that the binary system's gravitational energy goes to unbind the envelope, breaks down. Based on that, I claim that merger is a common outcome of the CE evolution of AGB and red super-giants stars with an envelope to secondary mass ratio of (M_env/M_2)>~5. I discuss some other puzzling observations that might be explained by the migration and merger processes.

astro-ph.SR↗

arXiv2012

Exploding SNe with jets: time-scales

We perform hydrodynamical simulations of core collapse supernovae (CCSNe) with a cylindrically-symmetrical numerical code (FLASH) to study the inflation of bubbles and the initiation of the explosion within the frame of the jittering-jets model. We study the typical time- scale of the model and compare it to the typical time-scale of the delayed neutrino mechanism. Our analysis shows that the explosion energy of the delayed neutrino mechanism is an order of magnitude less than the required 10^51 erg.

astro-ph.HE↗

arXiv2012

The limited role of mergers in the black hole to bulge mass relation

We examine the intrinsic scatter in the correlation between black hole masses and their host bulge masses, and find that it cannot be accounted for by mergers alone. A simple merger scenario of small galaxies leads to a proportionality relation between the late-time black hole and bulge masses, with intrinsic scatter (in linear scale) increasing along the ridge line of the relation as the square root of the mass. By examining a sample of 86 galaxies with well measured black hole masses, we find that the intrinsic scatter increases with mass more rapidly than expected from the merger-only scenario. We discuss the possibility that the feedback mechanism that operated during galaxy formation involved the presence of a cooling flow.

astro-ph.CO↗

arXiv2012

The Interaction of the Eta Carinae Primary Wind with a Century Old Slow Equatorial Ejecta

We argue that the asymmetric morphology of the blue and red shifted components of the outflow at hundreds of AU from the massive binary system Eta Carinae can be understood from the collision of the primary stellar wind with the slowly expanding dense equatorial gas. Recent high spatial observations of some forbidden lines, e.g. [Fe III] lambda4659, reveal the outflowing gas within about one arcsecond (2300 AU) from Eta Car. The distribution of the blue and red shifted components are not symmetric about the center, and they are quite different from each other. The morphologies of the blue and red shifted components correlate with the location of dense slowly moving equatorial gas (termed the Weigelt blob environment; WBE), that is thought to have been ejected during the 1887 - 1895 Lesser Eruption. In our model the division to the blue and red shifted components is caused by the postshock flow of the primary wind on the two sides of the equatorial plane after it collides with the WBE. The fast wind from the secondary star plays no role in our model for these components, and it is the freely expanding primary wind that collides with the WBE. Because the line of sight is inclined to the binary axis, the two components are not symmetric. We show that the postshock gas can also account for the observed intensity in the [Fe III] lambda4659 line.

astro-ph.SR↗