Light bending and X-ray echoes from behind a supermassive black hole.

The innermost regions of accretion disks around black holes are strongly irradiated by X-rays that are emitted from a highly variable, compact corona, in the immediate vicinity of the black hole1-3. The X-rays that are seen reflected from the disk4, and the time delays, as variations in the X-ray emission echo or 'reverberate' off the disk5,6, provide a view of the environment just outside the event horizon. I Zwicky 1 (I Zw 1) is a nearby narrow-line Seyfert 1 galaxy7,8. Previous studies of the reverberation of X-rays from its accretion disk revealed that the corona is composed of two components: an extended, slowly varying component extending over the surface of the inner accretion disk, and a collimated core, with luminosity fluctuations propagating upwards from its base, which dominates the more rapid variability9,10. Here we report observations of X-ray flares emitted from around the supermassive black hole in I Zw 1. X-ray reflection from the accretion disk is detected through a relativistically broadened iron K line and Compton hump in the X-ray emission spectrum. Analysis of the X-ray flares reveals short flashes of photons consistent with the re-emergence of emission from behind the black hole. The energy shifts of these photons identify their origins from different parts of the disk11,12. These are photons that reverberate off the far side of the disk, and are bent around the black hole and magnified by the strong gravitational field. Observing photons bent around the black hole confirms a key prediction of general relativity.

Effects of nicotine cycling on weight loss and regain in male rats.

Over successive periods of weight loss and regain caused by deprivation and refeeding, weight loss becomes slower during deprivation and weight is regained quicker during refeeding. One period of nicotine administration and termination results in changes in intake and weight gain comparable to that caused by one period of food deprivation and refeeding. However, no study has examined the effect of multiple periods of nicotine administration and cessation on weight loss and regain. The present study examined the effect of repeated cycles of nicotine administration and cessation on growth rate. Thirty-two male Sprague-Dawley rats underwent three nicotine administration cycles. Cycles consisted of 2 weeks of nicotine or saline followed by 2 weeks of no drug. Nicotine administration decreased growth and food consumption, and cessation resulted in a resumption of normal growth and intake. However, changes in food consumption and body weight were similar across cycles. Thus, although nicotine administration and cessation produced reliable changes in food consumption and body weight similar to those caused by diet cycling, there were no comparable cumulative effects of nicotine cycling on growth rate.

Use of phenylpropanolamine to reduce nicotine cessation induced weight gain in rats.

The present study was conducted to determine if phenylpropanolamine (PPA) administered during the first week of nicotine termination could reduce or eliminate the body weight rebound which accompanies nicotine cessation. Sprague-Dawley rats were administered nicotine for 2 weeks after which they received either PPA or saline for 1 week. Control animals received saline during both drug periods. Body weight, food consumption, and water consumption were measured daily before drug, during nicotine and PPA administration, and for 14 days after PPA administration. In contrast to animals receiving saline upon termination of nicotine, animals receiving PPA did not gain weight at an accelerated rate. Termination of PPA did not result in a body weight rebound. To the extent that these results generalize to humans, they suggest that PPA could be used to reduce or eliminate postcessation weight gain in smokers who stop smoking.