Kategorie: Kosmologie

Astronomers generally assume that the dusty disks where planets form are found around young stars in stellar nurseries. Now, for the first time, a planet-forming disk has been found in the environment of a dying star. A team of astronomers is reporting at the meeting of the American Astronomical Society that material from the dying star Mira A is being captured into a disk around Mira B, its companion. Michael Ireland of the California Institute of Technology and his coauthors say that the finding implies that there should be many similar undiscovered systems in the solar neighborhood, providing a myriad of new places to look for young planets orbiting stars other than our Sun. Located 350 light years away in the constellation of Cetus, Mira first shook the foundations of the astronomy world 400 years ago with its changing brightness: visible to the naked eye for about 1 month at a time, becoming 1.000 times fainter and disappearing from view, only to re-appear again on an 11 month cycle. Although Mira was once a star very similar to the sun, it is now in its death throes as it loses its dusty outer layers at a rate of one Earth-mass every seven years. If Mira were a single star, all this material would travel into outer space. However, like two out of every three star systems, Mira has a companion star that orbits around it, in this case with a period of about 1.000 years. This companion, Mira B, has a gravitational field that catches nearly one percent of the material lost from Mira A. By using specialized high-contrast techniques at the 10-meter Keck I telescope in Hawaii and the 8-meter Gemini South telescope in Chile, Michael Ireland’s team discovered heat radiation coming not from Mira B itself, but also from a location offset from Mira B by a distance equivalent to Saturn’s orbit.
First Planet-Forming Disk Found in the Environment of a Dying Star

The distribution of dark matter has been mapped in 3D for the first time, revealing how the mysterious substance has evolved over the lifetime of the universe. The results confirm that dark matter provided the scaffolding that allowed ordinary matter to clump together to form galaxies and clusters of galaxies. Dark matter is an invisible substance that betrays its presence through the gravitational tug it exerts on ordinary matter. It is six times more abundant than ordinary matter and is thought to have seeded the first distinct structures in the universe, which began as a very uniform soup of matter. Computer simulations suggest that the formation of dark matter clumps attracted surrounding gas, which then condensed to form galaxies and galaxy clusters. But this dark matter clumping process had never been confirmed observationally. Now, astronomers have mapped the changing distribution of both dark matter and ordinary matter over time. Nick Scoville, of Caltech in Pasadena, US, led the Cosmic Evolution Survey (COSMOS), which combined data from the world’s leading observatories to produce the map. The key to determining the dark matter distribution is an effect called gravitational lensing, by which light rays from a distant object such as a galaxy are bent by the gravity of an intervening concentration of matter. Although dark matter cannot be seen directly, its presence can be inferred by the way its gravity distorts the images of galaxies behind it. The Hubble Space Telescope (HST) mapped out these distortions over a patch of sky equivalent to the width of four Full Moons in the largest survey it has ever performed. It devoted 10% of its time over two years to complete the survey. The Subaru telescope on Mauna Kea, Hawaii, and the Very Large Telescope in Paranal, Chile, measured the spectrum of light from galaxies seen by Hubble, which allowed the galaxies‘ distances to be calculated. The XMM-Newton X-ray satellite contributed by mapping gas within galaxies and galaxy clusters – the most abundant form of ordinary matter in those objects.
These results were presented on Sunday at a meeting of the American Astronomical Society in Seattle, Washington, US.
COSMOS

Hubble Maps the Cosmic Web of „Clumpy“ Dark Matter in 3-D

First 3D map of the Universe’s dark matter scaffolding

The discovery of several large, metal-poor stars located far from the center of the Andromeda galaxy suggests our nearest galactic neighbour might be up to five times larger than previously thought. The newfound stars are massive, bloated stars known as red giants. Although found far beyond the most visible portion of Andromeda’s swirling disk, the stars are still gravitationally bound to the galaxy and make up part of its extended „halo“. The finding, presented on Sunday at the 209th meeting of the American Astronomical Society, suggests Andromeda is at least one million light-years across and could help settle a discrepancy between Andromeda and the Milky Way that has long puzzled astronomers.
Astronomers discover an enormous halo of red giant stars around Andromeda

A team of scientists using Oak Ridge National Laboratory supercomputers has discovered the first plausible explanation for a pulsar’s spin that fits the observations made by astronomers. Anthony Mezzacappa of the Department of Energy lab’s Physics Division and John Blondin of North Carolina State University explain their results in the newest issue of the journal „Nature“.

http://www.ornl.gov/ornl/news/news-releases/2007/ornl-team-discovers-new-way-to-spin-up-pulsars

Stellar mass black holes have been discovered, and astronomers now believe that supermassive black holes exist at the centres of most galaxies. But now a black hole has been discovered inside a globular star cluster. This could be one of the elusive „intermediate-mass“ black holes. Globular clusters contain thousands, or even millions of stars, and astronomers never thought they could hold a black hole. Computer simulations predicted that a black hole that formed in the cluster would sink into the centre of the cluster, but then inevitably get slung out into space after gravitational interaction with the stars in the cluster. This new black hole was found by ESA’s XMM-Newton X-ray observatory, which was able to spot the tell-tale X-ray signature of a black hole. The black hole is located inside a globular cluster in the relatively nearby elliptical galaxy NGC 4472, located about 50 million light-years away in the Virgo Cluster. It’s possible that it gained mass by merging with other black holes, and consuming enough material that it could lock its position inside the middle of the galaxy. With enough mass, the stars in the cluster just wouldn’t be able to eject it.
Black hole boldly goes where no black hole has gone before

DEM L238 and DEM L249 are two supernova remnants in the Large Magellanic Cloud. X-ray data from NASA’s Chandra and ESA’s XMM-Newton observatories suggest that the stars responsible for these debris fields were unusually young when they were destroyed by thermonuclear explosions.
https://chandra.harvard.edu/photo/2007/deml238/

At the end of December 2006, a fascinating experiment was conducted over Antarctica by Canada and its partners, the U.S., the U.K., and Mexico. Attached to a huge helium balloon, a large aperture sub-millimetre telescope called BLAST peered deep into space to study the earliest stages of star and planet formation, and to make high-resolution maps of diffuse galactic emissions.
Canadian Space Agency: BLAST Mission 2006 – Antarctica

To see any distance in space, you need some kind of telescope. We’ve got some pretty powerful ones here on Earth, but nature has us beat with gravitational lenses. This is a phenomenon when a relatively nearby object passes directly between us and a more distant object. The gravity from the nearby object acts like a telescope lens to bend light and magnify the more distant object. Until now, these gravitational lenses have been single stars or distant galaxies, but now a new class of lenses is being called into service: entire groups of galaxies! The research is being done as part of the Canada-France-Hawaii Legacy Survey which will devote 500 nights of telescope time over the next 5 years.

R. A. Cabanac et al.: The CFHTLS strong lensing legacy survey (PDF)

New observations from NASA’s Spitzer Space Telescope strongly suggest that infrared light detected in a prior study originated from clumps of the very first objects of the universe. The recent data indicate this patchy light is splattered across the entire sky and comes from clusters of bright, monstrous objects more than 13 billion light-years away. Astronomers believe the objects are either the first stars – humongous stars more than 1.000 times the mass of our sun – or voracious black holes that are consuming gas and spilling out tons of energy. If the objects are stars, then the observed clusters might be the first mini-galaxies containing a mass of less than about one million suns.
https://www.spitzer.caltech.edu/news/ssc2006-22-nasa-telescope-picks-up-glow-of-universes-first-objects

The small open star cluster Pismis 24 lies in the core of the large emission nebula NGC 6357 in Sagittarius, about 8.000 light-years away from Earth. Some of the stars in this cluster are extremely massive and emit intense ultraviolet radiation. The brightest object in this cluster is designated Pismis 24-1. It was once thought to weigh as much as 200 to 300 solar masses. This would not only have made it by far the most massive known star in the galaxy, but would have put it considerably above the currently believed upper mass limit of about 150 solar masses for individual stars. Now, Hubble Space Telescope high-resolution images of the star show that it is really two stars orbiting one another. They are estimated to be 100 solar masses each.
HubbleSite: Images – Pismis 24 and NGC 6357