Though fragile comet nuclei have been seen falling apart as they near the Sun, nothing like the slow breakup of an asteroid has ever before been observed in the asteroid belt. A series of Hubble Space Telescope images shows that the fragments are drifting away from each other at a leisurely one mile per hour. This makes it unlikely that the asteroid is disintegrating because of a collision with another asteroid. A plausible explanation is that the asteroid is crumbling due to a subtle effect of sunlight. This causes the rotation rate to slowly increase until centrifugal force pulls the asteroid apart. The asteroid's remnant debris, weighing in at 200,000 tons, will in the future provide a rich source of meteoroids.
Reflection from the strong gravity regime in a lensed quasar at redshift z = 0.658
Nature 507, 7491 (2014). doi:10.1038/nature13031
Authors: R. C. Reis, M. T. Reynolds, J. M. Miller & D. J. Walton
The co-evolution of a supermassive black hole with its host galaxy through cosmic time is encoded in its spin. At z > 2, supermassive black holes are thought to grow mostly by merger-driven accretion leading to high spin. It is not known, however, whether below z ≈ 1 these black holes continue to grow by coherent accretion or in a chaotic manner, though clear differences are predicted in their spin evolution. An established method of measuring the spin of black holes is through the study of relativistic reflection features from the inner accretion disk. Owing to their greater distances from Earth, there has hitherto been no significant detection of relativistic reflection features in a moderate-redshift quasar. Here we report an analysis of archival X-ray data together with a deep observation of a gravitationally lensed quasar at z = 0.658. The emission originates within three or fewer gravitational radii from the black hole, implying a spin parameter (a measure of how fast the black hole is rotating) of a = at the 3σ confidence level and a > 0.66 at the 5σ level. The high spin found here is indicative of growth by coherent accretion for this black hole, and suggests that black-hole growth at 0.5 ≤ z ≤ 1 occurs principally by coherent rather than chaotic accretion episodes.
Astrophysics: Cosmic lens reveals spinning black hole
Nature 507, 7491 (2014). doi:10.1038/nature13209
Authors: Guido Risaliti
The power of a cosmic lens to magnify and split the light from a distant, mass-accreting giant black hole into four components has allowed researchers to measure the black hole's spin. See Letter p.207
Our spiral-shaped Milky Way galaxy lives in a comparatively quiet backwater region of the universe. This is not the case for galaxies crammed together inside huge clusters. As they zip around within a cluster, gas can be pulled from their disks due to a process called ram pressure stripping. Galaxy ESO 137-001 is one example. The star-city looks like it is "leaking" as it plunges through the Norma galaxy cluster.
As part of the tests to try and diagnose the stray light issue noticed in the first month of instrument commissioning, the Gaia operations team is making a series of spacecraft orientation changes.
The spacecraft was first tilted from 45 to 42 degrees and then to 0 degrees, that is, facing its sunshield directly at the Sun. Then the spacecraft was returned to 45 degrees.
Gaia tilt seen from Earth
Astronomers Peter Veres and Bryce Bolin, who were following a call for Earth-bound observations to improve the prediction of Gaia’s brightness under different viewing conditions, used the 2.24m telescope on Mauna Kea in Hawaii to capture Gaia’s tilt from 0 to 45 degrees on 27 February.
The resulting movie nicely illustrates the change in brightness of the spacecraft over a period of around half an hour (12:14:52 UT to 12:42:06 UT), as Gaia’s sunshield tilted away from the Earth. Gaia is the bright object in the centre of the movie and moves downwards.
Dave Tholen, who processed the images, said: “We started with 10 second exposures for the first 30 exposures, then increased the exposure time to 20 seconds to get images 31 to 35, then increased again to 40 seconds for images 36 to 40. The last three exposures were 80 seconds each.”
The observations also captured a main belt asteroid (2002 RS34) moving from top centre to the right of the field of view in the movie.
As for the issue of stray light, the data are still being analysed. The tilting process will be repeated again, at a much slower rate, in order to gather more information from on-board systems during the transition period.