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A binary supermassive black hole leaves an imprint on a galactic nucleus in the form of a "mass deficit," a decrease in the mass of the nucleus due to ejection of stars by the binary. The magnitude of the mass deficit is in principle related to the galaxy's merger history, but the relation has never been quantified. Here, high-accuracy N-body simulations are used to calibrate this relation. Mass deficits are shown to be approximately 0.5M_{12}, with M_{12} the total mass of the binary; the coefficient in this relation depends only weakly on the binary mass ratio or on the galaxy's pre-existing density profile. Hence, after N mergers, the mass deficit is ~0.5 N M_h with M_h the final (current) black hole mass. When compared with observed mass deficits, this result implies between 1 and 3 mergers for most galaxies, in accord with hierarchical galaxy formation models. Implications for binary stalling radii, the origin of hyper-velocity stars, and the distribution of dark matter at the centers of galaxies are discussed., Comment: 11 pages, uses emulateapj.sty

In a relativistic model of a neutron star, the star's mass is less than the mass of the individual component baryons. This is due to the fact that the star's negative binding energy makes a contribution to the star's total energy and its mass. A consequence of this relativistic mass deficit is that a neutron star that is accreting matter increases its mass at a rate which is slower than the mass of a baryon times the rate that baryons are accreted. This difference in the rate of change of the masses has a simple relation with the star's gravitational redshift. We show that this effect has the potential to be observed in binaries where the mass transfer is driven by angular momentum losses from the gravitational radiation emitted by the binary motion.

We investigate a hierarchical structure formation scenario in which galaxy stellar cores are created from the binding energy liberated by shrinking supermassive black hole (SMBH) binaries. The binary orbital decay heats the surrounding stars, eroding a preexisting 1/r^2 stellar cusp. We follow the merger history of dark matter halos and associated SMBHs via cosmological Monte Carlo realizations of the merger hierarchy from early times to the present in a LCDM cosmology. Massive black holes get incorporated through a series of mergers into larger and larger halos, sink to the center owing to dynamical friction, accrete a fraction of the gas in the merger remnant to become supermassive, and form a binary system. Stellar dynamical processes drive the binary to harden and eventually coalesce. A simple scheme is applied in which the loss cone is constantly refilled and a constant density core forms due to the ejection of stellar mass. We find that a model in which the effect of the hierarchy of SMBH interactions is cumulative and cores are preserved during galaxy mergers produces at the present epoch a correlation between the `mass deficit' (the mass needed to bring a flat inner density profile to a 1/r^2 cusp) and the mass of the nuclear SMBH, with a normalization and slope comparable to the observed relation. Models in which the mass displaced by the SMBH binary is replenished after every major galaxy merger appear instead to underestimate the mass deficit observed in `core' galaxies., emulateapj, 6 pages, 4 figures, revised version to appear in ApJ August 20, 2003 issue

The severity of the mass discrepancy in spiral galaxies is strongly correlated with the central surface brightness of the disk. Progressively lower surface brightness galaxies have ever larger mass discrepancies. No other parameter (luminosity, size, velocity, morphology) is so well correlated with the magnitude of the mass deficit. The rotation curves of low surface brightness disks thus provide a unique data set with which to probe the dark matter distribution in galaxies. The mass discrepancy is apparent from $R = 0$ giving a nearly direct map of the halo mass distribution. The luminous mass is insignificant. Interpreting the data in terms of dark matter leads to troublesome fine-tuning problems. Different observations require contradictory amounts of dark matter. Structure formation theories are as yet far from able to explain the observations., Comment: Accepted for publication in the Astrophysical Journal. 49 pages AAStex + 16 figures

A sudden depletion or intensity "dimming" of the X-ray corona sometimes accompanies a solar eruptive flare or coronal mass ejection (CME). We have identified a dimming that occurred just prior to a "halo" CME, observed on 1997 April 7 using the Soft X-ray Telescope (SXT) on Yohkoh. Halo CMEs are prime candidates for "space weather" effects. The dimming occurred in compact regions near a flare of 14 UT on April 7, over a projected area of about 1020 cm-2, and indicate that a mass of a few times 1014 g was ejected. This is a lower limit imposed by the obscuration of the dimming volume by the brightness of the accompanying flare and other factors. Most of the mass deficit comes from two regions close to the ends of a preflare S-shaped active-region structure, and the resulting dimmings in these regions persisted for more than three days following the flare. A cusp-shaped loop—not apparent prior to the flare—dominates the emission in the flare decay phase, and has a mass comparable to that lost in the dimming regions. Our findings are consistent with the source of the CME being a flux rope that erupted, leaving behind the dimming regions. The cusp-shaped loop probably represents magnetic fields reconfigured or reconnected by the eruption. We do not see an X-ray analog of the wavelike disturbance evident in SOHO EUV images.

We report the first detection of a gap and a ring in 336 GHz dust continuum emission from the protoplanetary disk around TW Hya, using the Atacama Large Millimeter/Submillimeter Array (ALMA). The gap and ring are located at around 25 and 41 au from the central star, respectively, and are associated with the CO snow line at ~30 au. The gap has a radial width of less than 15 au and a mass deficit of more than 23%, taking into account that the observations are limited to an angular resolution of ~15 au. In addition, the 13CO and C18O J = 3 - 2 lines show a decrement in CO line emission throughout the disk, down to ~10 au, indicating a freeze-out of gas-phase CO onto grain surfaces and possible subsequent surface reactions to form larger molecules. The observed gap could be caused by gravitational interaction between the disk gas and a planet with a mass less than super-Neptune (2M_{Neptune}), or could be the result of the destruction of large dust aggregates due to the sintering of CO ice., Comment: 6 pages, 5 figures