Kennelful of Pluto puppies


Pick of the Pics and Updating Magic Universe

A kennelful of Pluto puppies

Three successive images from the Hubble Space Telescope show two remote objects in the Solar System inching across the sky in front of a distant galaxy (bottom left of each image). The near-vertical streaks are due to the objects moving while Hubble was watching. They are small “trans-Neptunian” objects – comets or asteroids – orbiting the Sun at about 43 times farther out than the Earth. They appear to be companions, at about half the separation of the Earth and Moon. Credits: a negative version of part of Fig. 3 in Fuentes et al., Astrophysical Journal (see references); imagery from HST/ACS/WFC

Soon to be published is the discovery of 14 new members of the Solar System in the so-called Kuiper Belt beyond the most distant “real” planet, Neptune. They are 40-100 km leftover scraps from the building of the Sun’s family of planets. To find them, a team from the Harvard-Smithsonian Center for Astrophysics and Northern Arizona University, led by Carlos Fuentes, trawled through existing images from the Hubble Space Telescope.

As Halley’s Comet and 15 other regular visitors came from the trans-Neptunian Kuiper Belt, I suppose I should be updating my Comets book, but although it mentions “Halley-class” comets orbiting not far beyond Neptune, it doesn’t name the Kuiper Belt. That important feature figures in Magic Universe, which was written two decades later and is more receptive to updating on this point. Here’s the most relevant section in the story called “Comets and asteroids: snowy dirtballs and their rocky cousins”.

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Dark matter’s lens


Updating Magic Universe

Dark matter’s lens on the cosmic scenery

Since 1996 the efforts of the French astrophysicist Jean-Paul Kneib to exploit natural lenses in the sky, created by the dark matter that surrounds clusters of galaxies, have fascinated me. While other stargazers used the “gravitational lenses”, bending light in the Einsteinian manner, to see galaxies far beyond the range of unaided telescopes, Kneib’s aim was to chart the mysterious dark matter itself. He wanted to see how visible matter and the far weightier dark matter have interacted through cosmic time – to see “the whole history of the Universe from start to finish”, as Kneib remarked to me in 2002.

It’s been taxing work, but now Kneib is one of the team reporting in today’s Science magazine about the dark matter around one the richest known clusters of galaxies. Abell 1689 lies 2.2 billion light-years away in the Virgo constellation, and a couple of years ago its extraordinary lensing power revealed a very distant and early object in the sky, Galaxy A1689-zD1, 12.8 billion light-years away. But that’s by the way

The new report not only gauges the cluster’s dark matter but uses the galaxies beyond it to infer the overall nature of space-time itself, dominated by the even more massive dark energy that drives the accelerating expansion of the Universe.

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Stars rush about


Pick of the pics

Young stars rush about like naughty children

Flicking between images of a star cluster taken by the WFPC2 camera in the Hubble Space Telescope in 1997 and 2007 reveals individual stars moving, like those seen in the boxes. In two years of close examination, German astronomers have gauged the motions of more than 700 stars and found them to be faster than expected. Most of the cluster stars move by less than 1/10 of a pixel over the ten-year period, which is not discernible by eye. The object is the massive compact Young Cluster, NGC 3603, lying 20,000 light-years away in the Carina spiral arm of the Galaxy. Credit: NASA, ESA and Wolfgang Brandner (MPIA), Boyke Rochau (MPIA) and Andrea Stolte (University of Cologne)

Extracts from the Hubble press release

[If the flicking doesn’t work, go to this Hubble url to see it offered, on the right. NC]

With a mass of more than 10,000 suns packed into a volume with a diameter of a mere three light-years, the massive young star cluster in the nebula NGC 3603 is one of the most compact stellar clusters in the Milky Way and an ideal place to test theories for their formation.

A team of astronomers from the Max-Planck Institute for Astronomy in Heidelberg and the University of Cologne led by Wolfgang Brandner (MPIA) wanted to track the movement of the cluster’s many stars. Such a study could reveal whether the stars were in the process of drifting apart, or about to settle down.

The results for the motion of these cluster stars were surprising: this very massive star cluster has not yet settled down. Instead, the stars’ velocities were independent of their mass and thus still reflect conditions from the time the cluster was formed, approximately one million years ago.

In the long term such massive compact star clusters may lead to the development of the huge balls of stars known as globular clusters, whose tightly packed stars remain held together by gravity for billions of years.

Wolfgang Brandner (MPIA): This is the first time we have been able to measure precise stellar motions in such a compact young star cluster.

Andrea Stolte (Cologne): This is key information for astronomers trying to understand how such clusters are formed, and how they evolve.

Boyke Rochau (MPIA) Our measurements have a precision of 27 millionths of an arcsecond per year. This tiny angle corresponds to the apparent thickness of a human hair seen from a distance of 800 km.