galaxy news: Clusters

‏إظهار الرسائل ذات التسميات Clusters. إظهار كافة الرسائل

الأربعاء، 29 أغسطس 2012

Black-Hole Incubators Discovered --In Huge Star Clusters at Center of Milky Way

Black-Hole Incubators Discovered --In Huge Star Clusters at Center of Milky Way
Black-Hole Incubators Discovered --In Huge Star Clusters at Center of Milky WayThe Daily Galaxy --Great Discoveries Channel: Sci, Space, TechFollow the Daily Galaxy Add Daily Galaxy to igoogle page

« Is the Biological, Darwinian Phase of Human Evolution Over? Hawking Says "Yes" (Today's Most Popular) |Main| Mar's Curiosity Mission Gale Crater Landing Site Named in Honor of Ray Bradbury »

August 23, 2012 Black-Hole Incubators Discovered --In Huge Star Clusters at Center of Milky Way

New-large-star-cluster

Japanese astronomers using two radio telescopes have produced a map of carbon monoxide distribution in the central region of our Galaxy. While mapping the region, they identified three huge gas clumps and a number of intermediate-mass black hole candidates. While previously there had been no certain evidence of the existence of intermediate-mass black holes, a team at the CSIRO radio telescope in Australia announced on 9 July 2012 that it had discovered the first intermediate-mass black hole.

From 2005 to 2010, the team using the Atacama Submillimeter Telescope Experiment in Chile and the Nobeyama Radio Observatory (NRO) 45-m telescope observed emission lines at wavelengths of 0.87 and 2.6 mm, emitted from carbon monoxide molecules in an area of several degrees that includes the center of the Milky Way Galaxy.

By comparing intensity values of emission lines at different wavelengths, the astronomers were able to estimate temperature and density of molecular gas. In this way, they succeeded in drawing detailed distribution maps of ‘warm, dense’ molecular gas at the center of the Milky Way Galaxy for the first time ever.

“The results are astonishing,” said Dr Tomoharu Oka of Keio University, lead author of a paper reporting the results in the Astrophysical Journal Supplement Series. “The ‘warm, dense’ molecular gas in that area is concentrated in four clumps. Moreover, it turns out that these four gas clumps are all moving at a very fast speed of more than 100 km/s. Sgr A – one of the four gas clumps – contains ‘Sagittarius A*,’ the nucleus of the Milky Way Galaxy.”

“The remaining three gas clumps are objects we discovered for the very first time. It is thought that ‘Sagittarius A*’ is the location of a supermassive black hole that is approximately 4 million times the mass of the Sun. It can be inferred that the gas clump ‘Sgr A’ has a disk-shaped structure with radius of 25 light-years and revolves around the supermassive black hole at a very fast speed,” Dr Oka added.

On the other hand, the team found signs of expansion other than rotation in the remaining three gas clumps. This means that the gas clumps, L=+1.3°, L=–0.4°and L=–1.2°, have structures that were formed by supernova explosions that occurred within the gas clumps. The gas clump “L=+1.3°” has the largest amount of expansion energy, equivalent to 200 supernova explosions. The age of the gas masses is estimated at about 60,000 years.

The researchers used the NRO 45-m Telescope again to further examine the molecular gas’s distribution, motion and composition to determine whether supernova explosions caused the expansion.

“Observation clearly showed that the energy source of L=+1.3° is multiple supernova explosions. We detected multiple expansion structures and molecules attributed to shock waves,” Dr Oka said. “Based on the observation of L=+1.3°, it is also natural to think that the expanding gas clumps L=–0.4° and L=–1.2° derived energy from multiple supernova explosions.”

A supernova is a massive explosion that occurs when a star with more massive than eight to ten times the mass of the Sun ends its life. Such a high occurrence of supernova explosions – once per 300 years – indicates that many young, massive stars are concentrated in the gas clumps. In other words, this means that there is a massive ‘star cluster’ in each gas clump. Based on the frequency of the supernova explosions, the team estimated the mass of the star cluster buried in L=+1.3°as more than 100,000 times the mass of the Sun, which is equivalent to that of the largest star cluster found in the Milky Way.

“The Solar System is located at the edge of the Milky Way Galaxy’s disk, and is about 30,000 light-years away from the center of the Milky Way Galaxy. The huge amount of gas and dust lying between the Solar System and the center of the Milky Way Galaxy prevent not only visible light, but also infrared light, from reaching the Earth. Moreover, innumerable stars in the bulge and disc of the Milky Way Galaxy lie in the line of sight. Therefore, no matter how large the star cluster is, it is very difficult to directly see the star cluster at the center of the Milky Way Galaxy,” Dr Oka explained.

“Huge star clusters at the center of the Milky Way Galaxy have an important role related to formation and growth of the Milky Way Galaxy’s nucleus,” he said.

According to theoretical calculations, when the density of stars at the center of star clusters increases, the stars are merged together, one after another. Then, it is expected that intermediate-mass black holes (IMBHs) with several hundred times the mass of the Sun are formed. Eventually, these IMBHs and star clusters sink into the nucleus of the Milky Way Galaxy. It can be thought that the IMBHs and star clusters are then merged further, and form a massive black hole at the Milky Way Galaxy’s nucleus. Alternatively, the IMBHs and star clusters could help expand an existing massive black hole.

While previously there had been no certain evidence of the existence of intermediate-mass black holes, a team at the CSIRO radio telescope in Australia announced on 9 July 2012 that it had discovered the first intermediate-mass black hole.*It can be thought that the supermassive black hole at Sagittarius A*, the nucleus of our Galaxy, has also been grown up through these processes. In summary, the new discovery is the finding of ‘cradles’ of IMBHs that become ‘seeds’ of the supermassive black hole at the nucleus.

“We would like to observe IMBHs in the star cluster. Actually, our observation data have already indicated traces of IMBHs,” Dr Oka said. One of the newly discovered gas masses, ‘L=–0.4°,’ contains two small gas clumps moving at a very fast speeds. If it is confirmed that these small gas clumps are rotating, it can be inferred that there are ‘invisible huge masses’ at the center of the gas clumps.

The image below is Globular cluster Mayall II (M31 G1), a strong candidate for hosting an intermediate-mass black hole at its core.

451px-HST_G1_(Mayall_II) (1)

The Daily Galaxy via National Astronomical Observatory of Japan

Posted at 11:00 AM | Permalink

Comments

Whoa, did i just get thrown down a wormhole???

Posted by:Payner |August 23, 2012 at 09:25 PM

السبت، 25 أغسطس 2012

Image of the Day: Spectacular Colliding Clusters of Massive Stars (Weekend Feature)

Image of the Day: Spectacular Colliding Clusters of Massive Stars (Weekend Feature)
Image of the Day: Spectacular Colliding Clusters of Massive Stars (Weekend Feature)The Daily Galaxy --Great Discoveries Channel: Sci, Space, TechFollow the Daily Galaxy Add Daily Galaxy to igoogle page

« 'Curiosity' Fires Up Its Laser Beam on 1st Mars Target (Weekend Feature) |Main| "Dwarfing Mount Everest" --Mars' Olympus Mons »

August 18, 2012 Image of the Day: Spectacular Colliding Clusters of Massive Stars (Weekend Feature)

676795main_cluster-collision-670

Astronomers using data from NASA's Hubble Space Telescope have caught two clusters full of massive stars that may be in the early stages of merging. The clusters are 170,000 light-years away in the Large Magellanic Cloud, a small satellite galaxy to our Milky Way.

What at first was thought to be only one cluster in the core of the massive star-forming region 30 Doradus (also known as the Tarantula Nebula) has been found to be a composite of two clusters that differ in age by about one million years.The entire 30 Doradus complex has been an active star-forming region for 25 million years, and it is currently unknown how much longer this region can continue creating new stars. Smaller systems that merge into larger ones could help to explain the origin of some of the largest known star clusters.

The Hubble image above shows the clusters in the gigantic 30 Doradus nebula, which is 170,000 light-years from Earth. The Hubble observations, made with the Wide Field Camera 3, were taken Oct. 20-27, 2009. The blue color is light from the hottest, most massive stars; the green from the glow of oxygen; and the red from fluorescing hydrogen.

Lead scientist Elena Sabbi of the Space Telescope Science Institute in Baltimore, Md., and her team began looking at the area while searching for runaway stars, fast-moving stars that have been kicked out of their stellar nurseries where they first formed.

"Stars are supposed to form in clusters, but there are many young stars outside 30 Doradus that could not have formed where they are; they may have been ejected at very high velocity from 30 Doradus itself," Sabbi said.

She then noticed something unusual about the cluster when looking at the distribution of the low-mass stars detected by Hubble. It is not spherical, as was expected, but has features somewhat similar to the shape of two merging galaxies where their shapes are elongated by the tidal pull of gravity. Hubble’s circumstantial evidence for the impending merger comes from seeing an elongated structure in one of the clusters, and from measuring a different age between the two clusters.

According to some models, the giant gas clouds out of which star clusters form may fragment into smaller pieces. Once these small pieces precipitate stars, they might then interact and merge to become a bigger system. This interaction is what Sabbi and her team think they are observing in 30 Doradus.

There are an unusually large number of high-velocity stars around 30 Doradus. Astronomers believe that these stars, often called "runaway stars" were expelled from the core of 30 Doradus as the result of dynamical interactions. These interactions are very common during a process called core collapse, in which more-massive stars sink to the center of a cluster by dynamical interactions with lower-mass stars. When many massive stars have reached the core, the core becomes unstable and these massive stars start ejecting each other from the cluster.

The big cluster R136 in the center of the 30 Doradus region is too young to have already experienced a core collapse. However, since in smaller systems the core collapse is much faster, the large number of runaway stars that has been found in the 30 Doradus region can be better explained if a small cluster has merged into R136.

Follow-up studies will look at the area in more detail and on a larger scale to see if any more clusters might be interacting with the ones observed. In particular, the infrared sensitivity of NASA’s planned James Webb Space Telescope (JWST) will allow astronomers to look deep into the regions of the Tarantula Nebula that are obscured in visible-light photographs. In these areas cooler and dimmer stars are hidden from view inside cocoons of dust. Webb will better reveal the underlying population of stars in the nebula.

The 30 Doradus Nebula is particularly interesting to astronomers because it is a good example of how star-forming regions in the young universe may have looked. This discovery could help scientists understand the details of cluster formation and how stars formed in the early universe.

The Daily Galaxy via NASA, ESA, R. O'Connell (University of Virginia), and the Wide Field Camera 3 Science Oversight Committee

Posted at 08:21 AM | Permalink

Comments

The picture is beautiful but the story kind of gives me a problem.

The story seems like a lot of guess work and supposition. And with statements like "She then noticed something unusual about the cluster" directly followed by "It is not spherical, as was expected,". She expects the unusual! And things like "think they are observing" and "they might then interact" gives it a just not sure feeling. So the problem it gives me is I always HATE when storys are reported as facts when there are so many different possibilities. But now I can see what happens when just the opposite happens and I am not sure its any better. Maybe its the way its written, I dont know.

Posted by:smartypants |August 19, 2012 at 07:02 AM

The elongated shape instead of the expected spherical shape for gravity is not explained by their guesswork and interpretations. See the better electromagnetic interpretation of these connecting plasma filaments and this new feature story at my blog http://HOLOGRAPHICGALAXY.BLOGSPOT.com

Posted by:Holo |August 19, 2012 at 09:12 AM

Ditto, Smartypants. What's ironic is that because they continually present suppositions and guesses as facts, no one ever seems to agree with anyone else. It's as though good science is whatever one wants it to be. Still, I'm glad to know what they're thinking, and if I want to know more, I do a little investigating of my own...keeps me in touch with what's happening in the cosmos.

Posted by:Tosca Zraikat |August 19, 2012 at 06:07 PM