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Brown dwarfs are failed stars.


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Brown dwarf.
brown dwarf ULAS J0034-00. Image credit: Gemini.

Brown dwarfs are failed stars that didn't have the mass to ignite fusion. But where do you draw the line between a large planet and a failed star? The Gemini observatory has helped discover the coolest brown dwarf ever seen. It's right in the middle between a star and planet.

The object is called ULAS J0034-00, and it weighs in around 15-30 times the mass of Jupiter. That sounds like a lot, but it's actually so small that it has the coolest surface temperature ever seen for a brown dwarf: 600-700 degrees Kelvin. It's only 50 light-years away, much closer than most of the stars you can see with the unaided eye. But it's so cool, only a powerful observatory can actually see it.

The finding was announced today at the American Astronomical Society meeting in Honolulu, Hawaii by an international team of astronomers. Their Discovery was first made using the United Kingdom Infrared Telescope (UKIRT), and then follow up observations with Gemini Observatory's Near Infrared Spectrograph (GNIRS) on Gemini South.

This Discovery opens up the possibility that even lower-mass objects are out there, further blurring the line between high-mass planets and the smallest brown dwarfs.

Original Source: http://www.gemini.edu/index.php?option=content&task=view&id=232

One of the Most Energetic Events Ever Seen in the Universe

X-ray image of 3C438. Image credit: Chandra.
May 30th, 2007: X-ray image of 3C438. Image credit: Chandra.

A new photograph taken by NASA's Chandra X-ray Observatory reveals one of the most energetic events ever seen in the universe. According to astronomers, two huge Galaxy clusters are currently undergoing a collision at a speed of 6.5 million km/h (4 million mph), releasing a tremendous amount of energy as their clouds of hot gas slam together. Or maybe it's a supermassive black hole consuming an incomprehensible amount of material.

In Chandra's vision, the gas heated to a temperature of 170 million degrees Celsius, glows brightly in the X-ray spectrum as bright arc, extending over two million light-years. If this was Galaxy clusters coming together, the arc is a shock front between them, were the clouds of hot gas are colliding.

Another theory, however, is that the disturbance is an outburst coming from a supermassive black hole that recently received a large infall of matter. The black hole can only consume so much before it starts to choke. The excess material is expelled outward into a pair of high-speed jets which can also glow brightly in the X-ray spectrum.

The black hole theory holds true, it would have to be consuming an implausible amount of mass; about 30 billion times the mass of the Sun over a period of 200 million years.

'These values have never been seen before and, truthfully, are hard to believe,' said Ralph Kraft of the Harvard-Smithsonian Center for Astrophysics (CfA).

Original Source: http://chandra.harvard.edu/press/07_releases/press_053007.html

Star Formation is Active in the Galactic Suburbs

Map of galaxy clusters. Image credit: Roy Gal/UH.
May 30th, 2007: Map of Galaxy clusters. Image credit: Roy Gal/UH.

Astronomers have always assumed that the most active star formation was happening in the largest Galaxy clusters, since they have the most activity. But a comprehensive new map of the universe shows that it's the Galaxy clusters in the outskirts which are the most active with new star formation.

This new comprehensive survey extends out, mapping Galaxy clusters between 6 and 9 billion light-years away. This included hundreds of clusters, and the massive superclusters, connected by webs of galaxies. They have even found the largest supercluster ever seen, which was present when the universe was half its current age.

The big surprise was how many of the outlying galaxies, not in the heart of the superclusters, are actually the most active with star formation. Many of these galaxies are producing more than 100 new suns per year, with actively feeding central black holes.

Original Source: http://www.news.ucdavis.edu/search/news_detail.lasso?id=8186

Blue moon on May 31st, 2007

The moon seen through a blue filter. Image credit: Kostian Iftica.
May 30th, 2007: The Moon seen through a blue filter. Image credit: Kostian Iftica.

On Thursday, May 31st, 2007, the Moon will be full again, like it does every 29 days. But according to some traditions, it'll be a special blue Moon, since it's full for the second time in May. The first full Moon occurred on May 2nd, and now, still in May, there's time for another full Moon.

The concept of a blue Moon has been around for hundreds of years, but the modern definition appeared in the last century. There was a reference to it in books like the Maine Farmer's Almanac, and an issue of Sky and Telescope in 1946 entitled 'Once in a blue Moon'.

Sky and Telescope has a detailed analysis here. And here's more information from NASA.

Does anything special happen to the Moon? Nope, it's just a quirk of the dates, since 29 days can fit inside the 30/31 days we have in a month.

To complicate the matter, though, there are times when the Moon can look blue. If there are tiny droplets of water in the air, they strongly scatter red and green light while allowing other colours to pass through. A moonbeam passing through a wispy cloud will turn a beautiful shade of blue.

So, tomorrow's a blue Moon, but it won't actually be blue. And the Moon can turn blue, but it doesn't have to be a full Moon, or a blue Moon. The blue Moon isn't anything special, it's just a trick of the dates. Did that make any sense?

Original Source: http://science.nasa.gov/headlines/y2007/30may_bluemoon.htm

Astrosphere for May 30, 2007

Mars Science Laboratory. Image credit: NASA/JPL/MAAS Digital.
May 30th, 2007: Mars Science Laboratory. Image credit: NASA/JPL/MAAS Digital.

Here's what's going around the astrosphere.

First, I'd like to remind you that the 5th Carnival of Space is happening tomorrow. Get your entries in!

The astronomy Blog has some interesting details on India's plans to send a mission to the Moon.

The Astroprof spoke with Mars Society's Bob Zubrin about going directly to Mars.

Pamela Gay is still at the American Astronomical Society meeting in Hawaii. She's finding that scientists are surprised at how much we're all following their research.

Space Politics has an analysis of Paul Spudis' speech at ISDC about how the Vision for Space Exploration is progressing.

Wandering Space has some cool links to new animations of the Mars Science Laboratory.

Supermassive Black Holes Spin at the Limits of Relativity

Artist impression of a supermassive black hole. Image credit: NASA.
May 29th, 2007: Artist impression of a supermassive black hole. Image credit: NASA.

You know the saying: nothing, not even light can escape a black hole. That makes them invisible. Amazingly, researchers from the University of Maryland have determined how fast a supermassive black hole is spinning. You won't be surprised to know it's spinning insanely fast, at the limits predicted by relativity.

The researchers used ESA's XMM-Newton X-ray telescope to examine the quantity of iron in an accretion disk around a supermassive black hole at the centre of Galaxy MCG-06-30-15. Because the disk is spinning so rapidly, the light from the disk is warped relativistically. According to their calculation, the black hole must be spinning at least 98.7% of the maximum spin rate allowable by Einstein's theory of General Relativity.

This result helps Astronomers understand how black holes grow over time. If supermassive black holes formed by slowly pulling in surrounding matter, they would be expected to spin faster and faster, until they reach this relativistic limit. If the supermassive black holes were instead formed by colliding smaller black holes, they'd be spinning much more slowly.

Original Source: http://www.newsdesk.umd.edu/scitech/release.cfm?ArticleID=1447

Dark Matter Annihilation at the Centre of the Milky Way

Centre of the Milky Way. Image credit: NASA.
May 29th, 2007: Centre of the Milky Way. Image credit: NASA.

Most of the universe is a complete and total mystery. And one of these mysteries is dark matter. It's out there, and Astronomers are slowly teasing out its characteristics, but it's not giving up its secrets easily. The problem is, Dark matter only interacts with regular matter through gravity (and maybe through the weak nuclear force). It doesn't shine, it doesn't give off heat or radio waves, and it passes through regular matter like it isn't there. But when Dark matter is destroyed, it might give Astronomers the clues they're looking for.

Researchers have theorized that one productive way to search for Dark matter might not be to search for it directly, but to look for the resulting particles and energy which are emitted when it's destroyed. In the environment around the centre of our galaxy, Dark matter might be dense enough that particles regularly collide, releasing a cascade of energy and additional particles; which could be detected.

And this theory could help account for a strange result gathered by the Wilkinson Microwave Anisotropy Probe (WMAP), a NASA spacecraft which is mapping the temperature of the cosmic microwave background radiation (CMBR). This background radiation was supposed to be roughly even across the entire sky. But for some reason, the satellite turned up an excess of microwave emission around the centre of our galaxy.

Perhaps this microwave radiation is the glow of all that Dark matter getting annihilated.

This conclusion was reached by a team of US astronomers: Dan Hooper, Douglas P. Finkbeiner and Gregory Dobler. Their work is published in a new research paper called Evidence Of Dark matter Annihilations In The WMAP Haze.

The excess microwave radiation around our galactic centre is known as the WMAP Haze, and was originally thought to be the emissions from hot gas. Astronomers set about trying to confirm this theory, but observations in other wavelengths failed to turn up any evidence.

According to the researchers, the microwave haze could be explained by annihilating particles of dark matter, like the interaction between matter and antimatter. As Dark matter particles collide they could give off any number of detectable particles and radiation, including gamma-rays, electrons, positrons, protons, antiprotons and neutrinos.

The size, shape and distribution of the haze matches the central region of our Galaxy which should also have a high concentration of dark matter. And if the Dark matter particles are within a certain range of mass - 100 to 1000s of times the mass of a Proton - they could release a torrent of electrons and positrons that nicely match the microwave haze.

In fact, their calculations precisely match one of the most attractive Dark matter particle candidates: the hypothetical neutralino which is predicted in supersymmetry models. When annihilated, these would produce heavy quarks, gauge bosons or the Higgs boson, and would have the right mass and particle size to produce the microwave haze observed by WMAP.

One of the predictions made in this paper is for the upcoming Gamma Ray large Area Space Telescope (GLAST), due to launch in December, 2007. If they're correct, GLAST will be able to detect a glow of gamma rays coming from the Galactic Centre, matching the microwave haze, and even put an upper limit of the mass of Dark matter particles. The upcoming ESA Planck mission will give an even more precise look at the microwave haze, providing better data.

It might still be mysterious, but Dark matter is revealing its secrets slowly but surely.

Original Source: http://arxiv.org/PS_cache/arxiv/pdf/0705/0705.3655v1.pdf

Dwarf Galaxy is Falling Into our Local Group for the First Time

Andromeda XII dwarf galaxy. Image credit: Scott Chapman/University of Cambridge.
May 29th, 2007: Andromeda XII dwarf galaxy. Image credit: Scott Chapman/University of Cambridge.

Life isn't easy for a dwarf Galaxy in our local group. They're passed from Galaxy to galaxy, harassed by gravity, and eventually torn up and consumed when they get to close to a large Galaxy like our own Milky Way. But Astronomers have turned up an example of a new class of dwarf galaxy, ones which formed very far away, and just arrived at the party.

The new dwarf Galaxy is called Andromeda XII, and it was discovered during a wide-field survey taken with the Canada-France Hawaii Telescope's 'MegaCam' instrument. It's one of the faintest dwarf galaxies ever discovered near the Andromeda Galaxy (M31), and it probably has the lowest mass ever measured.

Instead of being one of these dwarf galaxies that's suffered billions of years of galactic harassment, Andromeda XII is on a fast moving, highly eccentric orbit, which means it's falling into the Local Group of galaxies for the first time. And since it lived its life apart from these galactic interactions, it's a pristine object to study. Its rate of star formation, the size and shape of its Dark matter Halo and evolution weren't influenced by other galaxies.

Andromeda XII is moving so quickly that it probably won't even be captured by the Local Group, passing right through to destinations unknown.

Original Source: http://www.keckobservatory.org/article.php?id=107

Massive Binary System Discovered

Artist impression of twin massive stars. Image credit: NASA/Casey Reed.
May 29th, 2007: Artist impression of twin massive stars. Image credit: NASA/Casey Reed.

Many of the stars in the universe are located in binary or multiple star system, where several stars orbit a common centre of gravity. But Astronomers have discovered an extreme binary system, where two of the largest possible stars orbit one another.

The Discovery was made using NASA's Far Ultraviolet Spectroscopic Explorer (FUSE) satellite, as well as ground-based observatories. FUSE turned up a system called LS54-425 in the Large Magellanic Cloud, a satellite Galaxy of the Milky Way. This system contains two stars: one with 37 times the mass of the Sun, and the other is 62 solar masses.

Although they're extremely massive, these two type-O stars only orbit one another at 1/6th the distance between the Earth and the Sun, completing an orbit within 2.25 days. Both stars are generating massive solar winds, which collide, giving off X-rays and ultraviolet radiation. And this is how FUSE was able to spot them.

The more massive star is shedding material about 400 times as fast as our Sun, and the smaller star gives off about 40 times as much material. As they age and grow, the two stars will transfer a tremendous amount of material to each other, and eventually they will merge, creating a single star of 100 times the mass of the Sun.

And then, within just a few million years, this super star will detonate as a very energetic supernova.

Original Source: http://www.nasa.gov/centers/goddard/news/topstory/2007/fuse_titans.html

Snow Melt is on the Rise in Greenland

Satellite imagery of Greenland. Image credit: NASA.
May 29th, 2007: Satellite imagery of Greenland. Image credit: NASA.

The island of Greenland experienced more days of melting during 2006 on average than in the last 18 years, according to new NASA-funded research.

The data were gathered by the Special Sensor Microwave Imaging radiometer (SSM/I) flying aboard the Defense Meteorological Satellite Program spacecraft. It can peer through the clouds, and measure the rates of melting every day. During 2006, researchers estimated that portions of Greenland melted for an additional 10 days beyond averages.

Melting water on Greenland will impact global water levels. But the water can also slip down through cracks in glaciers, and lubricate the ice sheet. This can speed up the movement of glaciers, which eject ice into the ocean, and further accelerate sea level rise.

Original Source: http://www.nasa.gov/centers/goddard/news/topstory/2007/snowmelt_greenland.html



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