Posts Tagged ‘galaxies’

A Theoretical Link Found Between Radio Jets and Gamma Rays

Wednesday, May 6th, 2009 by Bellatrix

Scientists from the Max Plank Institute for Radio Astronomy in Bonn Germany using NASA’s Fermi Gamma Ray Space Telescope and the world’s largest radio telescope array have solidified a theoretical link between radio jets coming from the center of active galaxies and gamma ray bursts. This is a fine demonstration and use of new technology combined with an innovative use of existing technology.

Active galaxies are extremely bright galaxies which emitted oppositely directed jets of charged particles from their centers traveling near the speed of light.  Some, called Blazars, are especially bright because their jets are orientated along our line of sight.  These jets glow brightly in the radio part of the spectrum and in the 90’s it was hinted with the Chandra X-ray Observatory that they might emit in the higher energy parts of the spectrum as well. Astronomers believe these jets arise from matter that is falling into the central massive black holes of the galaxies, but the exact processes behind them is not well understood; which makes them the object of much study.

Now the Fermi telescope uses it’s Large Area Telescope, LAT, to scan the entire sky every 3 hours getting snapshots of the gamma ray bursts throughout the sky and monitor flares. Gamma ray bursts are the highest energy form of light below cosmic rays, and the origins of these gamma ray bursts is still undetermined; the objective of Fermi is to help clarify these origins. 

The new study was part of the MOJAVE program, which is a long-term study of the jets form active galaxies using primarily the VLBA. The VLBA is the National Science Foundation’s Very Long Baseline Array, a set of 10 radio telescopes located from Hawaii to the Virgin Islands and operated by the National Radio Astronomy Observatory in New Mexico.  Signals from these 10 different telescopes are combined and the array acts like a single enormous radio dish more than 8,500 kilometers across. The VLBA can resolve details about a million times smaller than Fermi and50 times smaller than any optical telescope.

Astronomers combined data from the VLBA and LAT. Active galaxies detected in the LAT’s first few months of operations generally possess brighter and more compact radio jets than galaxies the LAT did not see. Moreover, an active galaxy’s radio jets tend to be brighter in the months following any gamma-ray flares observed by the LAT.  A correlation was also found between active galaxies with the brightest gamma ray emission and those with the fastest jets.

The scientists were also able to use this data to study a phenomenon known as Doppler boosting. Doppler boosting makes radio-emitting blobs look brighter and appear to move faster than the speed of light due to the angle at which it is viewed and the fact the speed of the particles is close to the speed of light.  The VLBA data shows that the bigger the Doppler boost seen in a radio jet, the more likely it is that Fermi recorded it as a gamma ray source. Also, many objects found by Fermi to be extreme in gamma rays are broadcasting strong bursts of radio emission at the same time. 

All of this data points to the conclusion that the portion of an active galaxy’s radio jet closest to the galaxy’s center is also the source of the gamma rays.  These findings show us a very interesting and before unknown link between two “sides” of one object and possibly one process. This may bring astronomers one-step closer to solving two very large mysteries: the processes behind the jets and the exact processes or origins of gamma ray bursts. It could turn out to be quite nice and convenient if both questions could have the same answer, or an answer that comes from the same place. This new finding is also a demonstration of the use of the new technology of Fermi the space telescope that was designed just to study gamma ray bursts, a first of its kind, and the technology behind the VLBA, using standard radio telescopes in a new way to improve their usefulness

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Herschel/Planck New Launch Date Scheduled

Wednesday, April 15th, 2009 by Bellatrix

The largest mirror ever to be launched into space now has a set launch date.  The European Space Agency’s Herschel Space Observatory and Planck Satellite are set to launch into space May 6th. . Together these two pieces of equipment should be bringing in lots of new and exciting information about our own solar system and distant galaxies.

Sir Frederick William Herschel was a German born British astronomer from the 18th and 19th century. He was most famous for discovering the planet Uranus and discovering infrared radiation.  The Herschel Space Observatory will be the first to cover the full far infrared and sub-millimeter telescope.  The large mirror measures in at 3.5 meters; it’s a novel and advanced concept using 12 silicon carbide petals brazed together into a single piece. It is one of the major technological highlights of the mission.  Herschel will be investigating a large array of astronomical objects including: galaxy formation in the early universe and galaxy evolution, star formation and its interaction with the interstellar medium, chemical composition of atmospheres and surfaces of solar system bodies, and molecular chemistry across the universe.  Sounds like it has it work cut out.

The Planck Satellite will be going up with Herschel Observatory.  The satellite is named after the famous German physicist Max Planck who is considered the founder of quantum theory.  The satellite was designed to observe the anisotropies of the cosmic microwave background radiation, or CMB, over the entire sky using high angular resolution.  The mission is meant to improve upon the data collected from the well-known WMAP mission and will be used to test theories of the early universe and the origin of cosmic structure. 

Herschel and Planck will start their journey in space on board an Ariane 5 departing from Europe’s Spaceport in Kourou, French Guiana. Final preparations for the launch are now being made such as fueling the two satellites and filling Herschel’s cryostat (a vessel used to maintain cryogenic temperatures) with helium.  Once launched the two satellites will separate and be put into separate orbits around the second lagrangian point of the earth-sun system, a distance of about 1.5 million km’s from Earth.  Both satellites are part of the European Space Agency’s Horizons 2000 Scientific Programme, which consisted of about 15 satellite or telescope projects over the last 20 years including such other projects as Cluster, Huygens, XMM-Newton, and others.

The launch of these two satellites/observatories is exciting. They are new and advanced pieces of technology aimed at answering some large questions in astronomy today.  And are a fine example of astronomy goals and projects outside of the US.  So for now we just have to keep our fingers crossed and hold our breath for a successful launch and problem free start up. 

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Black Holes Hanging Out Together

Monday, March 30th, 2009 by Bellatrix

It has been observed for some time now that most large galaxies have super massive black holes at their center. It is generally believed that all galaxies have a central black, but some have thought for a while now that large galaxies may have more than one central black hole.  However, until very recently a binary black hole system had never been observed.  Astronomers from the National Optical Astronomy Observatory, NOAO, in Tucson AZ have found what they believe is the first binary system of two massive black holes.

The astronomers from NOAO used data from the Sloan Digital Sky Survey, SDSS, to look at quasars billions of light years away. More than 100,000 quasars are known while the astronomers for this study looked at 17,500 quasars from SDSS data.  A quasar is a quasi-stellar radio source; a powerfully energetic and distant galaxy with an active nuclei. They are hundreds of times brighter than our own galaxy and powered by matter falling into the black hole, or accreting, and as the matter falls in it heats up dramatically causing a luminous glow.

Astronomers are able to use “see” the central black hole by looking for a particular signature in the radiation coming from the in falling matter.  Now with two central black holes they would be too close together to actually distinguish their own accretion disks however there should be a characteristic dual signature in the emission lines.  It was this distinct signature that NOAO astronomers were looking for, and believe they have found.

Once the signature was detected the scientists had to rule out the possibility that it was coming from two separate galaxies in the same line of sight superimposed on each other. It took some work but they were able to determine that the emissions were coming form the same distance with only one possible host galaxies.  The double set of broad emission lines is pretty conclusive evidence that what was being seen is a binary black hole system. The smaller of the two black holes is estimated at about 20 million solar masses while the larger one is about 50 times bigger, as determined by their orbital velocities. 

This is an exciting discovery as it is the first of its kind. Further study can be used to research theories on galaxy mergers, super massive black hole evolution, and theories on gravity and relativity. It is theorized that galaxy mergers happen frequently and if each galaxy had a central black hole a merger would create a binary like this one. This theory also predicts that the two black holes will eventually merge themselves, evidence of which should, if theory is correct, be observable within the next few years. Also this is an ideal place to study theories of gravity and relativity, as the gravitational pull from a massive black hole binary system would be so strong gravitational effects not normally observable would be present.  It should be quite interesting to see what research and information comes from further study of this system. 

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Stellar Cannibalism Makes Massive Stars

Thursday, January 29th, 2009 by Bellatrix

Another mystery about stellar evolution may have an answer. A group of astronomers looking at globular clusters think they have figured out the origin of a particular type of star known as a blue straggler. The evidence is not concrete but definitely seems to present a plausible answer to a plaguing mystery.

Globular clusters are tightly bound groups of stars that live on the outskirts of galaxies. They make for interesting places of study since usually most of the stars within a particular cluster formed around the same age, so studying different clusters of different ages gives us information about star’s evolutionary paths. Most globular clusters are quite old though, as opposed to open clusters which are usually much younger, and globular clusters are not producing any new stars. Almost every star in a globular cluster is an older star, at least several billion years old. So herein lay the mystery.

In many globular clusters a certain type of star was observed, blue stragglers. Blue stragglers are very massive hot blue stars. Normally, hot massive blue stars are considered young when they are observed because if it is born that hot and massive it will burn out its fuel generally in several million to a few hundred million years. So the problem with finding them in these globular clusters is that since we know the clusters are much older than a few hundred million years these stars should not exist there. So how is it that these stars are where they are and look how they look??

There were two general theories about how these stars are formed. The first involved collisions between stars. You have two stars of medium mass colliding to make one massive star. The other theory was that of stellar cannibalism, in which one star in a binary system feeds of the mass of the other star. Binary systems are just those that contain two stars orbiting around and interacting with each other.

Researchers set out to answer this question by looking at 56 globular clusters. They found that the predicted number of collisions did not match that which was required to give the number of blue stragglers, thus dispelling that theory. They did, however, notice a correlation between the mass contained within the core of the cluster and the number of blue stragglers. It is known that the more massive the core is the higher numbers of binary systems exist within it. Thus they could infer a relationship between number of binary systems and the number of blue stragglers, seeming to support the second theory. This conclusion is also supported by direct observation of the number of binary systems in cluster cores. All of this points toward stellar cannibalism as the explanation. This would not be the only instance of stellar cannibalism in the galaxy. It has been seen many times in binary systems where one star is massive, usually a red giant, and the other is a white dwarf, or already dead star. The smaller white dwarf accretes matter from its larger partner until nuclear burning reignites on the star causing a nova explosion.

The next step for these researchers is to try and find out some information about the original two stars in the binary system, or the parents of the blue straggler. There must be something special about these binary systems that initiates the cannibalism. Are they mostly isolated, or could dynamical interactions between the system and nearby stars be a factor? It’s interesting that we do know a lot about stellar evolution and dynamics but there is always new and interesting ways in which the universe is trying to stump us.

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