scholarly journals Conversion of gas into stars in the Galactic center

2013 ◽  
Vol 9 (S303) ◽  
pp. 132-138
Author(s):  
S. N. Longmore
Keyword(s):  
Black Hole ◽  
Star Formation ◽  
Galactic Center ◽  
High Redshift ◽  
Formation Rate ◽  
Extreme Environment ◽  
Time Interval ◽  
Supermassive Black Hole ◽  
Mass Assembly ◽  
Sgr A

AbstractThe star formation rate in the central 500 pc of the Milky Way is lower by a factor of > 10 than expected for the substantial amount of dense gas it contains, which challenges current star formation theories. I discuss which physical mechanisms could be causing this observation and put forward a self-consistent cycle of star formation in the Galactic center, in which the plausible star formation inhibitors are combined. Their ubiquity suggests that the perception of a lowered central SFR should be a common phenomenon in other galaxies with direct implications for galactic star formation and also potentially supermassive black hole growth. I then describe a scenario to explain the presence of super star clusters in the Galactic center environment, in which their formation is triggered by gas streams passing close to the minimum of the global Galactic gravitational potential at the location of the central supermassive black hole, Sgr A*. If this triggering mechanism can be verified, we can use the known time interval since closest approach to Sgr A* to study the physics of stellar mass assembly in an extreme environment as a function of absolute time. I outline the first results from detailed numerical simulations testing this scenario. Finally, I describe a study showing that in terms of the baryonic composition, kinematics, and densities, the gas in the Galactic center is indistinguishable from high-redshift clouds and galaxies. As such, the Galactic center clouds may be used as a template to understand the evolution (and possibly the life cycle) of high-redshift clouds and galaxies.

scholarly journals A new MIR bow shock source in the Galactic center

2013 ◽  
Vol 9 (S303) ◽  
pp. 150-152 ◽  
Author(s):  
N. Sabha ◽  
M. Zamaninasab ◽  
A. Eckart ◽  
L. Moser
Keyword(s):  
Black Hole ◽  
Symmetry Axis ◽  
Galactic Center ◽  
Bow Shock ◽  
Shock Source ◽  
Stellar Cluster ◽  
Supermassive Black Hole ◽  
Sgr A ◽  
Central Parsec

AbstractWe find a convex-like feature at a distance of 0.68 pc (17″) from the position of the supermassive black hole, Sgr A*, at the center of the nuclear stellar cluster. This feature resembles a stellar bow shock with a symmetry axis pointing to the center. We discuss the possible nature of the feature and the implications of its alignment with other dusty comet-like objects inside the central parsec.

scholarly journals Mini-spiral as source of material for Sgr A* in bright state

2012 ◽  
Vol 8 (S290) ◽  
pp. 199-200 ◽  
Author(s):  
Bozena Czerny ◽  
Vladimír Karas ◽  
Devaky Kunneriath ◽  
Tapas K. Das
Keyword(s):  
Black Hole ◽  
Angular Momentum ◽  
Molecular Clouds ◽  
Galactic Center ◽  
Supermassive Black Hole ◽  
The Past ◽  
Accretion Process ◽  
Ring Mode ◽  
Sgr A ◽  
Bright Phase

AbstractThe question of the origin of the gas supplying the accretion process is pertinent especially in the context of enhanced activity of Galactic Center during the past few hundred years, seen now as echo from the surrounding molecular clouds, and the currently observed new cloud approaching Sgr A*. We discuss the so-called Galactic Center mini-spiral as a possible source of material feeding the supermassive black hole on a 0.1 parsec scale. The collisions between individual clumps reduce their angular momentum. and set some of the clumps on a plunging trajectory.We conclude that the amount of material contained in the mini-spiral is sufficient to sustain the luminosity of Sgr A* at the required level. The accretion episodes of relatively dense gas from the mini-spiral passing through a transient ring mode at ~ 104 Rg provide a viable scenario for the bright phase of Galactic Center.

scholarly journals Cosmic rates of black hole mergers and pair-instability supernovae from chemically homogeneous binary evolution

2020 ◽  
Vol 499 (4) ◽  
pp. 5941-5959
Author(s):  
L du Buisson ◽  
P Marchant ◽  
Ph Podsiadlowski ◽  
C Kobayashi ◽  
F B Abdalla ◽  
...  
Keyword(s):  
Black Hole ◽  
Star Formation ◽  
Star Formation Rate ◽  
High Redshift ◽  
Formation Rate ◽  
Star Formation History ◽  
Close Binaries ◽  
Detection Rates ◽  
Binary Evolution ◽  
Merger Rate

ABSTRACT During the first three observing runs of the Advanced gravitational-wave detector network, the LIGO/Virgo collaboration detected several black hole binary (BHBH) mergers. As the population of detected BHBH mergers grows, it will become possible to constrain different channels for their formation. Here we consider the chemically homogeneous evolution (CHE) channel in close binaries, by performing population synthesis simulations that combine realistic binary models with detailed cosmological calculations of the chemical and star-formation history of the Universe. This allows us to constrain population properties, as well as cosmological and aLIGO/aVirgo detection rates of BHBH mergers formed through this pathway. We predict a BHBH merger rate at redshift zero of $5.8 \textrm {Gpc}^{-3} \textrm {yr}^{-1}$ through the CHE channel, to be compared with aLIGO/aVirgo’s measured rate of ${53.2}_{-28.2}^{+55.8} \text{Gpc}^{-3}\text{yr}^{-1}$, and find that eventual merger systems have BH masses in the range $17{-}43 \,\textrm {M}_{\odot }$ below the pair-instability supernova (PISN) gap, and ${\gt}124 \textrm {M}_{\odot }$ above the PISN gap. We investigate effects of momentum kicks during black hole formation, and calculate cosmological and magnitude limited PISN rates. We also study the effects of high-redshift deviations in the star formation rate. We find that momentum kicks tend to increase delay times of BHBH systems, and our magnitude limited PISN rate estimates indicate that current deep surveys should be able to detect such events. Lastly, we find that our cosmological merger rate estimates change by at most ${\sim}8{{\ \rm per\ cent}}$ for mild deviations of the star formation rate in the early Universe, and by up to ${\sim}40\,\text{per cent}$ for extreme deviations.

scholarly journals The Herschel view of the Galactic center

2013 ◽  
Vol 9 (S303) ◽  
pp. 1-14
Author(s):  
John Bally ◽  
Keyword(s):  
Star Formation ◽  
Massive Star ◽  
Galactic Center ◽  
Galactic Plane ◽  
Formation Rate ◽  
Asymmetric Distribution ◽  
The Galaxy ◽  
Sgr A ◽  
Almost All

AbstractThe 3.5 meter diameter Herschel Space Observatory conducted a ∼720 square-degree survey of the Galactic plane, the Herschel Galactic plane survey (Hi-GAL). These data provide the most sensitive and highest resolution observations of the far-IR to sub-mm continuum from the central molecular zone (CMZ) at λ = 70, 160, 250, 350, and 500 μm obtained to date. Hi-GAL can be used to map the distributions of temperature and column density of dust in CMZ clouds, warm dust in Hii regions, and identify highly embedded massive protostars and clusters and the dusty shells ejected by supergiant stars. These data enable classification of sources and re-evaluation of the current and recent star-formation rate in the CMZ. The outer CMZ beyond |l| = 0.9 degrees (Rgal > 130 pc) contains most of the dense (n > 104 cm−3 gas in the Galaxy but supports very little star formation. The Hi-GAL and Spitzer data show that almost all star formation occurs in clouds moving on x2 orbits at Rgal < 100 pc. While the 106 M⊙ Sgr B2 complex, the 50 km s−1 cloud near Sgr A, and the Sgr C region are forming clusters of massive stars, other clouds are relatively inactive star formers, despite their high densities, large masses, and compact sizes. The asymmetric distribution of dense gas about Sgr A* on degree scales (most dense CMZ gas and dust is at positive Galactic longitudes and positive VLSR) and compact 24 μm sources (most are at negative longitudes) may indicate that eposidic mini-starbursts occasionally ‘blow-out’ a portion of the gas on these x2 orbits. The resulting massive-star feedback may fuel the compact 30 pc scale Galactic center bubble associated with the Arches and Quintuplet clusters, the several hundred pc scale Sofue-Handa lobe, and the kpc-scale Fermi/LAT bubble, making it the largest ‘superbubble’ in the Galaxy. A consequence of this model is that in our Galaxy, instead of the supermassive black hole (SMBH) limiting star formation, star formation may limit the growth of the SMBH.

scholarly journals Feeding and feedback in nearby AGN – comparison with the Milky Way center

2013 ◽  
Vol 9 (S303) ◽  
pp. 354-363 ◽  
Author(s):  
T. Storchi-Bergmann
Keyword(s):  
Star Formation ◽  
Milky Way ◽  
Galactic Center ◽  
Formation Rate ◽  
Activity Cycle ◽  
Nuclear Region ◽  
Nuclear Activity ◽  
The Galaxy ◽  
Mass Outflow ◽  
Sgr A

AbstractI discuss feeding and feedback processes observed in the inner few hundred parsecs of nearby active galaxies using integral field spectroscopy at spatial resolutions of a few to tens of parsecs. Signatures of feedback include outflows from the nucleus with velocities ranging from 200 to 1000 km s−1, with mass outflow rates between 0.5 and a few M⊙ yr−1. Signatures of feeding include the observation of gas inflows along nuclear spirals and filaments, with velocities ranging from 50 to 100 km s−1 and mass flow rates from 0.1 to ∼1 M⊙ yr−1. These rates are 2–3 orders of magnitude larger than the mass accretion rate to the supermassive black hole (SMBH). These inflows can thus lead, during less than one activity cycle, to the accumulation of enough gas in the inner few hundred parsecs, to trigger the formation of new stars, leading to the growth of the galaxy bulge. Young to intermediate age stars have indeed been found in circumnuclear rings around a number of Active Galactic Nuclei (AGN). In particular, one of these rings, with radius of ≈ 100 pc is observed in the Seyfert 2 galaxy NGC 1068, and is associated to an off-centered molecular ring, very similar to that observed in the Milky Way (MW). On the basis of an evolutionary scenario in which gas falling into the nuclear region triggers star formation followed by the triggering of nuclear activity, we speculate that, in the case of the MW, molecular gas has already accumulated within the inner ≈ 100 pc to trigger the formation of new stars, as supported by the presence of blue stars close to the galactic center. A possible increase in the star-formation rate in the nuclear region will then be followed, probably tens of millions of years later, by the triggering of nuclear activity in Sgr A*.

scholarly journals Extreme submillimetre starburst galaxies

2018 ◽  
Vol 619 ◽  
pp. A169 ◽  
Author(s):  
M. Rowan-Robinson ◽  
Lingyu Wang ◽  
Duncan Farrah ◽  
Dimitra Rigopoulou ◽  
Carlotta Gruppioni ◽  
...  
Keyword(s):  
Black Hole ◽  
Star Formation ◽  
High Redshift ◽  
Spectral Energy Distribution ◽  
Formation Rate ◽  
Optical Emission ◽  
Spectral Energy ◽  
Black Hole Growth ◽  
Show Evidence ◽  
Universal Ratio

We have used two catalogues, a Herschel catalogue selected at 500 μm (HerMES) and an IRAS catalogue selected at 60 μm (RIFSCz), to contrast the sky at these two wavelengths. Both surveys demonstrate the existence of “extreme” starbursts, with star-formation rates (SFRs) > 5000 M⊙ yr−1. The maximum intrinsic star-formation rate appears to be ~30 000 M⊙ yr−1. The sources with apparent SFR estimates higher than this are in all cases either lensed systems, blazars, or erroneous photometric redshifts. At redshifts between three and five, the time-scale for the Herschel galaxies to make their current mass of stars at their present rate of star formation is ~108 yr, so these galaxies are making a significant fraction of their stars in the current star-formation episode. Using dust mass as a proxy for gas mass, the Herschel galaxies at redshift three to five have gas masses comparable to their mass in stars. Of the 38 extreme starbursts in our Herschel survey for which we have more complete spectral energy distribution (SED) information, 50% show evidence for QSO-like optical emission, or exhibit AGN dust tori in the mid-infrared SEDs. In all cases however the infrared luminosity is dominated by a starburst component. We derive a mean covering factor for AGN dust as a function of redshift and derive black hole masses and black hole accretion rates. There is a universal ratio of black-hole mass to stellar mass in these high redshift systems of ~10−3, driven by the strong period of star-formation and black-hole growth at z = 1−5.

scholarly journals Sgr A West in the light of molecules: cold and dense gas east of the circumnuclear disk

2013 ◽  
Vol 9 (S303) ◽  
pp. 86-88 ◽  
Author(s):  
Lydia Moser ◽  
A. Eckart ◽  
A. Borkar ◽  
M. García-Marin ◽  
D. Kunneriath ◽  
...  
Keyword(s):  
Black Hole ◽  
Star Formation ◽  
Molecular Clouds ◽  
Near Infrared ◽  
Line Emission ◽  
Dense Gas ◽  
Dark Clouds ◽  
Supermassive Black Hole ◽  
Circumnuclear Disk ◽  
Sgr A

AbstractWe present the very first detection of N2H+J = (1 – 0) and CH3OH(2k−1k) line emission on 5″ scales in the circumnuclear disk (CND) around Sgr A*. The emission matches the position and shape of the dark clouds in the near-infrared. Our findings suggest that these molecular clouds in the eastern CND are significantly colder and denser than the rest of the CND, and partially shocked. The research on these dark clouds will contribute to understanding the processes of star formation close to a supermassive black hole.

scholarly journals Masers and Galactic structure: Micro-arcsecond astrometry with the VLBA

2007 ◽  
Vol 3 (S242) ◽  
pp. 348-355 ◽  
Author(s):  
M. J. Reid ◽  
A. Brunthaler ◽  
K. M. Menten ◽  
Xu Ye ◽  
Zheng Xing-Wu ◽  
...  
Keyword(s):  
Black Hole ◽  
Galactic Center ◽  
Galactic Plane ◽  
Infrared Images ◽  
Star Forming ◽  
Supermassive Black Hole ◽  
Star Forming Regions ◽  
The Galaxy ◽  
Trigonometric Parallaxes ◽  
Sgr A

AbstractAstrometric observations with the VLBA with accuracies approaching ~ 10 μas are being conducted in order to better understand the Galaxy. The location of Sgr A* on infrared images can be determined with an accuracy of a few mas, using stars with SiO maser emission as a calibration grid for infrared images. The apparent proper motion of Sgr A*, which is dominated by the effects of the orbit of the Sun around the Galactic center, has been measured with high accuracy. This measurement strongly constrains Θ0R0 and offers a dynamical definition of the Galactic plane with Sgr A* at its origin. The intrinsic motion of Sgr A* is very small and comparable to that expected for a supermassive black hole. When combined with infrared results, this provides overwhelming evidence that Sgr A* is a supermassive black hole. Finally, we are engaged in a large project to map the spiral structure and kinematics of the Galaxy. Preliminary trigonometric parallaxes, obtained with the VLBA, to eight massive star forming regions are presented.

Sgr A* as Source of the Positrons Observed in the Galactic Center Region

2016 ◽  
Vol 11 (S322) ◽  
pp. 172-175
Author(s):  
Pierre Jean ◽  
Nidhal Guessoum ◽  
Katia Ferrière
Keyword(s):  
Black Hole ◽  
Spatial Distribution ◽  
Galactic Center ◽  
Substantial Fraction ◽  
Physical Conditions ◽  
Supermassive Black Hole ◽  
Emission Time ◽  
Physical Interactions ◽  
Sgr A ◽  
Positron Production

AbstractWe explore the possibility that a substantial fraction of the positrons observed to annihilate in the central region of our Galaxy come from the supermassive black hole Sgr A* that lies at the center. This idea was proposed by several authors, but the propagation of the emitted positrons into the bulge and beyond remained a serious problem for models of the origin of GC positrons.We assume models of positron production with different energies. The propagation of positrons from their production site is followed in detail with Monte-Carlo simulations, taking into account the physical conditions of the propagation regions as well as various physical interactions. Using the known physics of positron annihilation in astrophysical environments, we calculate the properties of the annihilation emission (time evolution and spatial distribution) for the different models under consideration.We present the results of these simulations and the conclusions/constraints that can be inferred from them.

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