Archive for the ‘Event Horizon by Bellatrix’ Category

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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Fast As A Speeding Star

Monday, March 2nd, 2009 by Bellatrix

Using the Hubble Space Telescope, NASA scientists have discovered stars doing something very interesting: speeding around through the interstellar medium.  This came as quite a surprise especially since they were not even looking for them. This is not usual behavior for stars and brings up many new questions about what these stars are doing and why.

The scientists discovered 14 of these crazy runaway stars.  Because of their movement it was harder to gather information about them but scientists were able to deduce some facts about the stars. The stars appear to be young, maybe only about a million years old.  This was deduced from looking a their strong stellar winds. Most stars only have such winds when they are quite young or very old. The nebulae around the stars do not math that of those typically seen around old dying stars. And only very massive stars have winds throughout their lifespan, but these stars could not be that massive because they do not have glowing clouds of ionized gas around them. They are estimated to be about 2 to 8 solar masses.

These stars plow through regions of dense interstellar gas creating brilliant arrowhead shaped glowing bow shocks and trailing tails of glowing gas. These bow shocks are created when the strong winds coming from the stars slam into the surrounding dense gas. It’s difficult to tell their exact distance from Earth but depending on the distance these bow shocks could be 100 billion to a trillion miles wide. By studying these bow shocks we can tell that the stars are moving very quickly, about 180,000 km/hr.  All stars are moving as they are orbiting around the galaxy but not nearly at these speeds, the sun for comparison moves through the galaxy at only about 13,000 km/hr.  Assuming this “young” phase lasts only a million years the stars would have traveled about 160 light years.

The scientists have hypothesized that these stars were likely kicked out or ejected from massive star clusters.  There’s two possible ways this expulsion could have happened.  One way is if a binary system, consisting of two stars orbiting each other, had one star go supernova the explosion would eject the companion star.  The other possibility would be if two binary systems or a binary and a third star collided one of the stars could have used he energy from the interaction to escape the system.

Runaway stars have been observed before, the first being found in the late 80s. However, those stars produced much larger bow shocks meaning they were probably more massive with larger stellar winds.  Scientists think these new objects, the medium size stars, are probably more common since medium sized stars are more common in general and because they would be more susceptible to being ejected.  These objects are difficult to find and observe because one doesn’t know where to find them or where to look for them. 

Follow up studies are planned to look for more of these objects, called interlopers, and to study these recently discovered ones. Further studies will tell us more about the effects these speed demons have on the environments they pass by or interact with. Theorists and modelers will have to set to work on looking at the origins of the objects and the causes of their ejections. Pretty interesting to think about these stars being expelled from their homes now doomed to zoom around the galaxy alone. 

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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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Balloon Picking up Mysterious Radio Signals

Friday, January 16th, 2009 by Bellatrix

NASA’s most recent balloon trip has found something new and unexplained, don’t you just love when that happens. The ARCADE balloon mission has uncovered a new radio signal with unknown origin, which may be more of an interesting find than the balloons real mission.

The findings come from NASA’s balloon borne instrument known as Absolute Radiometer for Cosmology, Astrophysics, and Diffuse Emission, or ARCADE. ARCADE was launched in July of 2006 in Palestine Texas. It flew to an altitude of 37km, 120,000 ft, where the atmosphere thins and begins to give way to space. It took data for about 4 hours before parachuting back to Earth. Balloons like this one are used for this reason, they can get above the interference caused by our atmosphere but are much cheaper to launch and build then a full blown satellite.

ARCADE’s mission was to observe and collect radio data from some of the first stars born in our universe. Since these stars are so distance their light is only observable at radio wavelengths. For the instrument to be sensitive enough to pick up this information it had to be cooled, really cooled. It was sent up with 500 gallons of liquid helium to keep it at a frosty 2.5 degrees Celsius above absolute zero. So it was all poised and ready but the data it was sent to collect was lost in a powerful radio signal of unknown origin.

This background radio signal was about 6 times larger than what they had expected to find. It was too strong, or loud, to be coming from the distant stars, and even too loud to be coming from known radio sources like gas from the halo of our galaxy. All galaxies give off some radio noise, usually just a hiss, except for those which are radio loud, usually quasars. But even with all these radio loud galaxies there isn’t enough of them to account for this noise, for the noise to be coming from just galaxies there’d have to be so many radio galaxies they’d be packed in like sardines, one right next to another, which just isn’t the case.

So obviously there’s something that we are missing, something loud making this racket that we don’t even know about; and that’s exciting. This is a great example of why astronomy is so exciting. This routine type mission that was supposed to just give a few details on a particular type of star and then BAM! There’s a mystery with possible far reaching implications. Is this a new object all together? Is it an evolutionary stage of galaxies that we didn’t know about? NASA hasn’t yet mentioned any planned follow up to try and dig deeper into this mystery but I’m sure that it is coming, I mean everyone loves a good mystery.

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