Archive for the ‘Uncategorized’ Category

Exciting New Development in Observational Techniques

Tuesday, April 7th, 2009 by admin

Observational astronomers, engineers, and telescope experts are always working hard to better their observational equipment.  Even with all of our advanced technology when looking at things at such great astronomical distances we are still limited. However, recently astronomers in Germany made a break through with a new technique for improving resolution power of telescopes, allowing us to see previously unseen objects or resolve new details of known objects.

A team of astronomers, led by Stefan Kraus and Gerd Weigelt from the Max Planck Institute for Radio Astronomy (MPIfR) in Bonn, Germany, used European Southern Observatory’s (ESO) Very Large Telescope Interferometer (VLTI) to obtain the sharpest image of the young double star Theta 1 Orionis C in the Orion Trapezium Cluster.  The Theta 1 system is a massive binary system of young stars in the Orion star-forming region. In previous images of the system, even with the Hubble Space Telescope, the telescopes were not able to resolve the two separate stars in the system, which are only separated by a distance of about 20 milliarcseconds.  The team was also able to derive the properties of the system including the masses of the two stars, about 38 and 9 solar masses, and also an accurate measure of the distance to the system, about 1350 light years.

The increase in resolution power came from using the technique of interferometry.  This method allows one to combine light collected from several telescopes, making what is like a “virtual” telescope with a resolving power equal to that of a ground based telescope with a 200 meter mirror or a space based telescope with a 130 meter mirror.  The Very Large Telescope now allows European astronomers to reconstruct images from the interferometric infrared data with the use of its near infrared beam combination instrument AMBER.  This gives the astronomers a resolving power of about 2 milliarcseconds.

Early imaging interferometry was almost exclusively done with long wavelength radio telescopes because the longer the wavelength of incoming radiation the easier it is to measure the phase information of data. Examples of radio interferometers are the Very Large Array, or VLA, and The Multi-Element Radio Linked Interferometer Network, or MERLIN. As the speeds of correlators and associated technologies have improved, the minimum radiation wavelength observable by interferometry has decreased. Now this is the first time astronomers have been able to use this technique with the shorter wavelength of infrared.

So far this technique with the VLIT has only been used to study Theta 1 in the Orion region.  The results obtained will be important for studying the Orion region and for theoretical models of massive star formation, as Theta 1 is a particularly massive and young star in an active star forming region.  Beyond the Orion data this method for observing promises to yield new discoveries and information about many different objects and topics. It is quite exciting innovation bringing us closer to new information without the need for necessarily spending much more time and money on new equipment. 

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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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Everyone can be The Astronomer

Tuesday, March 3rd, 2009 by admin

The year 2009 is the international year of astronomy; it marks 400 years since Galileo used the telescope to first look up at space. As part of the celebration NASA and other astronomical societies having been doing things to celebrate.  NASA is doing its part this month by allowing the public to be the astronomers. They have put the public in control of the Hubble Space Telescope. NASA has picked six astronomical objects and is allowing the public to vote on which object Hubble will view and collect data on next. I decided to go over each of the six objects and describe what they are and why they might be of interest.

The first object is a star-forming region called NGC 6334 also known as the Cat’s Paw Nebula or the Bear Claw Nebula. It is located in the Scorpius constellation that is located in the southern hemisphere near the center of the galaxy.  It is located about 5,500 light years away. It glows with a deep red color that originates from a large amount of ionized hydrogen in the area. The nebula is usually obscured by large amounts of gas and dust sometimes making it difficult to observe from ground based telescopes.  The region is a very active star-forming region, which is the reason it is considered for observation. Observing these star forming regions tells us a lot about the birth and evolution of stars, and the interaction of a large number of young stars in close proximity to each other.

The second contestant is the planetary nebula NGC 6072, which is also located in the constellation Scorpius. There is not much information available on this object and it has not been viewed very often.  It is a remnant of a dead low mass star; a white dwarf with an envelope of gas and molecules surrounding it that were puffed off layers of the star as it was dying. Observing planetary nebulas is always useful, it gives us information about stars after they die and how the elements given off interacts with surrounding gas and dust. They also usually make for very pretty pictures.

The third object is planetary nebula NGC 40, otherwise known as the Bow-Tie Nebula. It is located about 3,500 light years form Earth in the constellation Cepheus. It is also composed of hot gas surrounding a dying/dead star. The white dwarf left behind radiates at about 50,000 degrees C and the gas envelope at about 30,000 degrees C.  This nebula has been imaged more than the other nebula, perhaps making it a less attractive candidate.

The fourth object in the contest is the spiral galaxy NGC 5172.  It is located at a distance of about 57 mega parsecs or about 150 million light years. It is a spiral type Sbc. IT has been a host to several well-documented supernovae. From what we can tell it is very similar in size and shape to our own Milky Way galaxy, which is the reason it may be a good candidate for study. Since we can not get an outside looking in view of our own galaxy studying ones similar to our own tell us information we could not otherwise get.

The next possible object is the edge on galaxy known as NGC 4289. It is located in the Virgo Constellation about 50 million light years away.  It is also a spiral galaxy but instead of being viewed face on it is seen completely edge on.  There are advantages to looking at the same types of things from different views; especially with astronomy. When looking at things so far away with things obstructing your view, light traveling so far, being bent around objects being able to see galaxies edge on can help with verifying measurements of brightness, velocity and other variables.

The last option for an object to choose is Arp 274, or NGC 5679, and is actually two (possibly three) galaxies interacting with each other.  It is also located in the Virgo constellation. Interacting galaxies are treasure-troves of data. By studying them we can information on formation and evolution or galaxies. We get information on how these interactions affect star formation, surrounding galaxies, central black holes, and more. I think this is a great candidate for further study. 

So those are the six objects open for voting. I encourage any readers to go check out NASA’s site and vote. I personally think this was a great idea on NASA’s part. Hubble has always been very popular and a great tool for creating public interest in astronomy, which can at times be hard to do.  I think it’s smart to give the general people the option to pick what they think is interesting and what they want to know more about. I encourage anything that the industry wants to do to try and rose public support, especially in times when funding is hard to come by NASA needs to keep the public in its corners.  I’m excited to see who the winner will be. 

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Far-Side of The Moon

Monday, March 2nd, 2009 by Evan Finnes

The Apollo missions of the 1970’s can be credited with many great discoveries–the most notable of which, were the six missions that sent twelve astronauts to the moon.  During these manned missions to the Moon, rock samples were collected and returned to the Earth.  The analysis of these samples led to the current hypothesis of lunar formation.  This hypothesis suggests that the Moon was formed by a catastrophic collision between Earth and Mars-sized planetesimal.  After this collision, the Moon would have been covered by a thick blanket of magma, which cooled to form a crust much different from the Earth’s crust.   Then 3.8 billion years ago, during the late heavy bombardment, the Moon’s surface was pounded by meteor impacts, leaving the surface deformed and heavily cratered.  New data gathered by the Japanese mission, SELENA, may offer new insights into the formation of the moon.

SELENA focused on the differences between the near and far side of the moon, such as: compositional, gravitational, topographical, and tectonic differences.   However, it is difficult for spacecrafts to relay information from the far side of the Moon, due to the fact that the Moon is tidally locked to the Earth.  SELENA was able to surmount this obstacle by using a companion satellite positioned in an elliptical orbit at a higher altitude.  This companion satellite was then able to relay information between Earth and SELENA. 

Because the Moon is a homogeneous body, there are several differences between the near (Earth facing) and far-side of the Moon.  The nearside of the Moon is covered by dark basaltic plains, (the very features that Galileo once mistook for seas).  The far side of the Moon is much more heavily cratered, and the higher elevations are composed of a bright material. These compositional differences are accompanied by differences which are intrinsic properties of the materials that make up each side of the Moon, such as crustal thickness and density.  Other differences between lunar faces include volcanic activity and surface age.

Another key difference between the lunar faces is the gravitational anomalies found on either side of the Moon.   These differences in gravitational anomalies can be used to deduce possible density differences of the interior.  Positive gravitational anomalies on the nearside of the Moon have been known about for several years and are associated with the large areas of basaltic planes.  These planes are referred to as mascons (mass concentrations).    These mascons could be the result of basaltic magma filling basins after basin formation, or they could be the result of mantle uplift that could have occurred during a large impact event.  SELENA was able to map the gravitational anomalies of the lunar far-side for the first time.  What SELENA discovered was that the far-side mascons have small central positive gravitational anomalies that are surrounded by a wide ring of negative anomalies.  These differences in gravitational anomalies observed on either side of the Moon could suggest that the far-side of the Moon may have had much cooler and rigid conditions in its early history.  

SELENA also used a Lunar Radar Sounder to map subsurface stratigraphy beneath the nearside basaltic basins.  The results of this experiment show that the thickness of the most recent volcanic flows may have been deformed compressive stresses that occurred during a period of global cooling, and not entirely because of the stresses which occurred during mascon formation.

The terrain camera onboard SELENA was able to photograph volcanic flows on the lunar far-side.  These photos were then used to estimate the age of the far-side basalts using cratering statistics. Based on the cratering statistics, the age of the lunar far side was found to be much younger than the lunar nearside, with volcanic activity continuing to make fresh surface until approximately 2.5 billion years ago.

Although the data gathered so far is not enough to paint a clear picture of lunar evolution, it has become clear that the mascons formed much differently on either side of the Moon during late heavy bombardment.  To help interpret these discoveries, new data will be on its way as China, India, and the United States all have orbiters slated for lunar observation in the next couple of years.  In the meantime we are left to wonder, are these differences due to external processes such as a giant impact, or are they due to internal processes such as core formation, and crustal differentiation?  One thing seems clear, the difference in surface age on either side of the Moon will be an important variable when devising a model for lunar evolution.


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