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Comment by Michel on March 23, 2011 at 2:42pm

Eye Candy: The Square Nebula

From APOD.


Explanation: What could cause a nebula to appear square? No one is quite sure. The hot star system known as MWC 922, however, appears to be embedded in a nebula with just such a shape. The above image combines infrared exposures from the Hale Telescope on Mt. Palomar in California, and the Keck-2 Telescope on Mauna Kea in Hawaii. A leading progenitor hypothesis for the square nebula is that the central star or stars somehow expelled cones of gas during a late developmental stage. For MWC 922, these cones happen to incorporate nearly right angles and be visible from the sides. Supporting evidence for the cone hypothesis includes radial spokes in the image that might run along the cone walls. Researchers speculate that the cones viewed from another angle would appear similar to the gigantic rings of supernova 1987A, possibly indicating that a star in MWC 922 might one day itself explode in a similar supernova.

Comment by Michel on March 23, 2011 at 2:23pm

DEEP SPACE - Brown dwarf could be coldest known star
CBC News Posted: Mar 23, 2011 10:23 AM ET

Astronomers say they've found a new candidate for the coldest known star — a brown dwarf with the temperature of a freshly made cup of tea.

While you might burn yourself drinking such a tea, at 100 degrees Celsius, the boiling point of water is actually extremely cold for the surface of a star. The temperature of Earth's sun, for example, is about 5,500 C.

Scientists liken brown dwarfs to failed stars because they aren't big enough for gravity to trigger the nuclear reactions that make stars shine. Astronomers say such discoveries are significent because a brown dwarf is not exactly a star and not exactly a planet, but instead something between the two, and hence can teach us about the physics of both.

Working with the European Southern Observatory's Very Large Telescope, astronomers say the newly-discovered brown dwarf is one of a pair in a double system 75 light-years from Earth. Astronomers describe the brown dwarfs, identified as CFBDSIR 1458+10B, in a paper in the current issue of The Astrophysical Journal.

"At such temperatures we expect the brown dwarf to have properties that are different from previously known brown dwarfs and much closer to those of giant exoplanets — it could even have water clouds in its atmosphere," the paper's lead author, Michael Liu of the University of Hawaii's Institute for Astronomy, said in a release.

The team of researchers, which included Etienne Artigau of the Université de Montréal, is not ready to say it has definitively found the coldest known star.

That's because another team working with NASA's infrared Spitzer Space Telescope recently identified two other very faint objects as other possible candidates, although their temperatures have not yet been measured so precisely.

 

This artist's impression shows the pair of brown dwarfs named CFBDSIR 1458+10. They are the coolest pair of brown dwarfs found so far. The colder of the two components (shown in the background) is a candidate for the brown dwarf with the lowest temperature ever found. (L. Calcada/ESO)

Comment by Michel on March 23, 2011 at 2:12pm



Testing gravity in gas-rich galaxies

Karen Masters & Kristine Spekkens

The rotation curve of a galaxy is the orbital speed of material as a function of distance from the center of the galaxy. In the 1970s, the astronomer Vera Rubin measured the rotation curves of several of the nearest spiral galaxies. To her astonishment, the curves remained flat beyond the edge of the galaxy’s stellar disc . Under the standard theory of gravity this implies that the mass in the outskirts of these systems far outweighs that of the detected gas and stars. Today, the flatness of spiral galaxy rotation curves remains key evidence for dark matter, which, broadly defined, is matter that obeys the law of gravity but does not emit any light.

Dark matter is an integral component of the currently favored cosmological model, in which over 90% of the matter in the Universe is made up of massive (“cold”) particles, which interact only via gravity. The model is named Lambda-Cold Dark Matter (ΛCDM), with Λ denoting a cosmological constant (sometimes called “dark energy”) that accelerates expansion at late cosmological times. An impressive array of observations fit this picture, from the spectrum of fluctuations in the cosmic microwave background (the first free-streaming photons in the Universe, e.g., Ref. [2]), to the luminosities of distant supernovae. The astrophysical community has adopted ΛCDM as the standard cosmological model, which makes the nature of dark matter one of the most important outstanding questions in the field.

But not all cosmologists are happy with this picture. Some are uneasy with the unknown components in the standard model, and worry that cosmology in the last 30 years has degraded into “naming the unknown” . In spiral galaxies at least, an alternative to invoking dark matter is to modify the theory of gravity in regions where there is a discrepancy between the mass inferred from dynamics (using standard gravity) and the baryonic mass (i.e., the census of normal material detected in stars and gas). The most successful of these ideas is MOND (Modified Newtonian Dynamics ), which modifies gravity at small accelerations to produce flat galactic rotation curves. For gravitational accelerations a less than some critical value a0, the usual Newtonian relation F=ma is modified to F=ma2/a0, and therefore the circular velocity around a mass M asymptotes to a constant value vf=(GMa0)1/4. Once the universal constant a0 is fixed observationally, MOND explains the rotation curve shapes of galaxies using their baryonic mass alone, while simultaneously accounting for the observed correlation between their rotation velocities and luminosities.

Read more here from Physics.
Via our Library/More... resource pages.

Comment by Doone on March 20, 2011 at 7:56pm

See Explanation. Clicking on the picture will download the highest resolution version available.

Parthenon Moon 
Image Credit & CopyrightAnthony Ayiomamitis (TWAN)

Explanation: Did you see the Full Moon last night? Near the horizon, the lunar orb may have seemed to loom large, swollen in appearance by the famous Moon illusion. But the Full Moon really was a large Full Moon last night, reaching its exact full phase within an hour of lunar perigee, the point in the Moon's elliptical orbit closest to planet Earth. A similar near perigee Full Moon last occured on December 12, 2008. The difference in the Moon's apparent size as it moves from perigee to apogee, its farthest point from Earth, is about 14 percent. Of course, a nearly Full Moon will rise again tonight, lighting the skies on the date of the Equinox or equal night. The Full Moon also looms large in this well-planned, telescopic lunar portrait. Captured earlier this year, the rising lunar orb is dramatically matched to the 2,500 year old Parthenon, in Athens, Greece.

Comment by Michel on March 19, 2011 at 6:12pm
This is now my new desktop wallpaper.
Comment by Doone on March 19, 2011 at 2:27pm

See Explanation. Clicking on the picture will download the highest resolution version available.

Messier 106 
Image Credit & CopyrightR Jay Gabany

Explanation: Close to the Great Bear (Ursa Major) and surrounded by the stars of the Hunting Dogs (Canes Venatici), this celestial wonder was discovered in 1781 by the metric French astronomer Pierre Mechain. Later, it was added to the catalog of his friend and colleague Charles Messier as M106. Modern deep telescopic views reveal it to be an island universe -- a spiral galaxy around 30 thousand light-years across located only about 21 million light-years beyond the stars of the Milky Way. Along with a bright central core, this colorful composite image highlights youthful blue star clusters and reddish stellar nurseries tracing the galaxy's spiral arms. It also shows off remarkable reddish jets of glowing hydrogen gas. In addition to small companion galaxy NGC 4248 (bottom right) background galaxies can be found scattered throughout the frame. M106 (aka NGC 4258) is a nearby example of the Seyfert classof active galaxies, seen across the spectrum from radio to x-rays. Active galaxies are believed to be powered by matter falling into a massive central black hole.

Comment by Michel on March 19, 2011 at 12:05pm

The Supermoon is this evening




Comment by Michel on March 19, 2011 at 10:59am

Black hole's burps may blow bubbles around Milky Way

 

STARS plunging into the giant black hole at the centre of our galaxy can explain two huge bubbles of gamma rays that NASA's Fermi space telescope discovered last year. The bubbles tower 25,000 light years above and below the Milky Way's disc of stars.

Read more in the discussion above.

 

Comment by Michel on March 17, 2011 at 8:39pm
Stunning animations. And amazing long-distance gymnastics.
Comment by Doone on March 16, 2011 at 9:13am

Hubble has taken this stunning close-up shot of part of the Tarantula Nebula. This star-forming region of ionised hydrogen gas is in the Large Magellanic Cloud, a small galaxy which neighbors the Milky Way. It is home to many extreme conditions including supernova remnants and the heaviest star ever found. The Tarantula Nebula is the most luminous nebula of its type in the local universe. (Credit: NASA, ESA  http://www.sciencedaily.com/releases/2011/03/110315093026.htm
 
 
 

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