56 research outputs found
Neutralino dark matter vs galaxy formation
Neutralino dark matter may be incompatible with current cold dark matter
models with cuspy dark halos, because excessive synchrotron radiation may
originate from neutralino annihilations close to the black hole at the galactic
center.Comment: 6 pages, 3 figures, talk given at "Sources and detection of dark
matter in the Universe", Marina del Rey, CA, February 23-25, 200
A direct image of the obscuring disk surrounding an active galactic nucleus
Active galactic nuclei (AGN) are generally accepted to be powered by the
release of gravitational energy in a compact accretion disk surrounding a
massive black hole. Such disks are also necessary to collimate powerful radio
jets seen in some AGN. The unifying classification schemes for AGN further
propose that differences in their appearance can be attributed to the opacity
of the accreting material, which may obstruct our view of the central region of
some systems. The popular model for the obscuring medium is a parsec-scale disk
of dense molecular gas, although evidence for such disks has been mostly
indirect, as their angular size is much smaller than the resolution of
conventional telescopes. Here we report the first direct images of a pc-scale
disk of ionised gas within the nucleus of NGC 1068, the archetype of obscured
AGN. The disk is viewed nearly edge-on, and individual clouds within the
ionised disk are opaque to high-energy radiation, consistent with the unifying
classification scheme. In projection, the disk and AGN axes align, from which
we infer that the ionised gas disk traces the outer regions of the long-sought
inner accretion disk.Comment: 14 pages, LaTeX, PSfig, to appear in Nature. also available at
http://hethp.mpe-garching.mpg.de/Preprint
The central image of a gravitationally lensed quasar
A galaxy can act as a gravitational lens, producing multiple images of a
background object. Theory predicts there should be an odd number of images but,
paradoxically, almost all observed lenses have 2 or 4 images. The missing image
should be faint and appear near the galaxy's center. These ``central images''
have long been sought as probes of galactic cores too distant to resolve with
ordinary observations. There are five candidates, but in one case the third
image is not necessarily a central image, and in the others, the central
component might be a foreground source rather than a lensed image. Here we
report the most secure identification of a central image, based on radio
observations of PMN J1632-0033, one of the latter candidates. Lens models
incorporating the central image show that the mass of the lens galaxy's central
black hole is less than 2 x 10^8 M_sun, and the galaxy's surface density at the
location of the central image is more than 20,000 M_sun per square parsec, in
agreement with expectations based on observations of galaxies hundreds of times
closer to the Earth.Comment: Nature, in press [7 pp, 2 figs]. Standard media embargo applies
before publicatio
The Supermassive Black Hole at the Galactic Center
The inner few parsecs at the Galactic Center have come under intense scrutiny
in recent years, in part due to the exciting broad-band observations of this
region, but also because of the growing interest from theorists motivated to
study the physics of black hole accretion, magnetized gas dynamics and unusual
star formation. The Galactic Center is now known to contain arguably the most
compelling supermassive black hole candidate, weighing in at a little over 2.6
million suns. Its interaction with the nearby environment, comprised of
clusters of evolved and young stars, a molecular dusty ring, ionized gas
streamers, diffuse hot gas, and a hypernova remnant, is providing a wealth of
accretion phenomenology and high-energy processes for detailed modeling. In
this review, we summarize the latest observational results, and focus on the
physical interpretation of the most intriguing object in this region---the
compact radio source Sgr A*, thought to be the radiative manifestation of the
supermassive black hole.Comment: Annual Review of Astronomy & Astrophysics, Vol. 39 (2001), in press,
48 pages, 20 figures (partially in reduced quality), also available at
http://www.mpifr-bonn.mpg.de/staff/hfalcke/publications.html#gcrevie
Oocyte–Targeted Deletion Reveals That Hsp90b1 Is Needed for the Completion of First Mitosis in Mouse Zygotes
Hsp90b1 is an endoplasmic reticulum (ER) chaperone (also named Grp94, ERp99, gp96,Targ2, Tra-1, Tra1, Hspc4) (MGI:98817) contributing with Hspa5 (also named Grp78, BIP) (MGI:95835) to protein folding in ER compartment. Besides its high protein expression in mouse oocytes, little is known about Hsp90b1 during the transition from oocyte-to-embryo. Because the constitutive knockout of Hsp90b1 is responsible for peri-implantation embryonic lethality, it was not yet known whether Hsp90b1 is a functionally important maternal factor.To circumvent embryonic lethality, we established an oocyte-specific conditional knockout line taking advantage of the more recently created floxed Hsp90b1 line (Hsp90b1(flox), MGI:3700023) in combination with the transgenic mouse line expressing the cre recombinase under the control of zona pellucida 3 (ZP3) promoter (Zp3-cre, MGI:2176187). Altered expression of Hsp90b1 in growing oocytes provoked a limited, albeit significant reduction of the zona pellucida thickness but no obvious anomalies in follicular growth, meiotic maturation or fertilization. Interestingly, mutant zygotes obtained from oocytes lacking Hsp90b1 were unable to reach the 2-cell stage. They exhibited either a G2/M block or, more frequently an abnormal mitotic spindle leading to developmental arrest. Despite the fact that Hspa5 displayed a similar profile of expression as Hsp90b1, we found that HSPA5 and HSP90B1 did not fully colocalize in zygotes suggesting distinct function for the two chaperones. Consequently, even if HSPA5 was overexpressed in Hsp90b1 mutant embryos, it did not compensate for HSP90B1 deficiency. Finally, further characterization of ER compartment and cytoskeleton revealed a defective organization of the cytoplasmic region surrounding the mutant zygotic spindle.Our findings demonstrate that the maternal contribution of Hsp90b1 is critical for the development of murine zygotes. All together our data indicate that Hsp90b1 is involved in unique and specific aspects of the first mitosis, which brings together the maternal and paternal genomes on a single spindle
The disruption of proteostasis in neurodegenerative diseases
Cells count on surveillance systems to monitor and protect the cellular proteome which, besides being highly heterogeneous, is constantly being challenged by intrinsic and environmental factors. In this context, the proteostasis network (PN) is essential to achieve a stable and functional proteome. Disruption of the PN is associated with aging and can lead to and/or potentiate the occurrence of many neurodegenerative diseases (ND). This not only emphasizes the importance of the PN in health span and aging but also how its modulation can be a potential target for intervention and treatment of human diseases.info:eu-repo/semantics/publishedVersio
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