Posts Tagged ‘star’

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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ExtraSolar CO2

Monday, December 1st, 2008 by Evan Finnes

For the first time carbon dioxide has been found in the atmosphere of a planet outside of our own solar system. This is an important discovery because carbon dioxide is one the chemicals we would expect to find on a planet that harbors life, the other chemicals include: oxygen, water, and methane. Water vapor, along with carbon monoxide has previously been detected in the planet’s atmosphere.

Unfortunately, the discovery of carbon dioxide on this planet cannot be correlated to life. This Jupiter sized planet, which is located 63 light years from Earth, is known as HD 189733b. It has an orbital period of about 2.2 days and has a scorching surface temperature of about 1117 K. The close proximity of the planet to its host star may be responsible for the formation of carbon dioxide in the planet’s atmosphere. As the planet orbits, relatively close to its sun, it receives a high dosage of ultraviolet radiation. This radiation may have stripped apart other chemicals in the planet’s atmosphere while creating new chemicals, such as carbon dioxide.

The carbon dioxide was detected by analyzing the infrared spectrum of the planet. Because HD 189733b lies so close to its host star, the combined spectrum of the star/planet system had to first be analyzed and recorded. Scientists then waited for the planet to disappear behind its host star, so that the suns individual spectrum could be recorded. To obtain the planets individual spectrum, the spectrum of the star was subtracted from the star/planet system.

French astronomers discovered HD 189733b, in the constellation Vulpecula, on Oct. 5, 2005 by observing the transit of the planet across its host star. Since its discovery, the planet has reached a number of milestones. It was the first extrasolar planet to be mapped, it was the first found to contain water vapor and methane (which probably react in the high temperatures to form the carbon monoxide), and now it is the first exosolar planet known to contain carbon dioxide.

This discovery confirms our ability to detect the chemical compositions of planets outside of our solar system. If, and hopefully when, an Earth-like is discovered, analyzing the spectral signatures will be more difficult due to the small sizes of terrestrial planets. As we continue to develop our techniques by recording the spectral signatures of Jupiter-like planets, and super Earths, there should be little doubt that we will be ready to analyze the atmosphere of an Earth or Mars sized planet when the discovery occurs, bringing us one step closer to eventually detecting life on another planet.

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Double Checking Our Data

Wednesday, November 26th, 2008 by Bellatrix

Scientists believe they have found the answer to a mystery about a thought to be nearby galaxy. The funny thing is this answer was found by rather serendipitously after finding out our current estimates for the distance of the galaxy were wrong.

The galaxy named NGC 1569 was a bit of a mystery. It is an irregular shaped dwarf galaxy, which isn’t in itself strange, but the galaxy was going through a burst of star formation with no discernable reason. The galaxy was forming stars much faster than any other galaxies in its nearby region. Well then we realized that the problem with that statement was not NGC 1569 itself but the galaxies we thought were nearby it.

Scientists recently pointed the Hubble Space telescope at NGC 1569 to scan for red giant stars. The astronomers were hoping to get an estimate of the galaxies age by looking for red giants, as red giants can be used as reliable standard candles for measuring distance since they all burn at the same known brightness. However, the astronomers were only able to see the brightest red giants, even using Hubble, the stars were too dim to be resolved. This fact lead astronomers to question the previous estimate for how far away the galaxy actually is. And now after looking at the data astronomers have realized the galaxy is actually about one and a half times farther away than previously thought, making it about 11 million light years away.

The problem was before this the galaxy had only been studied with ground based telescopes, which have much less resolving power than space based telescopes, which can make estimates less accurate. With this new information the galaxy’s star formation makes more sense. This distance puts the galaxy in the middle of a cluster of ten other galaxies. The gravitational interaction of the galaxies tugging on each other would be enough to explain the high rate of star formation we see in this galaxy.

So using Hubble we have answered yet another question, good ol’Hubble. However, this instance makes one wonder how many other numbers that we have for things like distance or mass etc might be inaccurate after only being studied by ground-based telescopes. How many things should we go back over with space-based telescopes to make sure? And how many mysteries or unexplainable phenomena might be answered by simply rechecking our data??

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Testing Magnetars

Tuesday, November 18th, 2008 by Bellatrix

Magnetars are a bizarre form of star, with mysteries that have eluded astronomers for a long time. Recently with the help of the European Space Agency’s XMM Newton and Integral Satellite astronomers have been able to test and explain one of the unknown aspects of what magnetars are really doing.

Magnetars are a special kind of neutron star. Neutron stars, for a quick reminder, are what is left after a massive star dies in a supernova. They are very small, maybe 20 km in diameter, but very dense, a teaspoon worth of neutron star would weigh about one hundred million tons. Magnetars form a special class of neutron stars that have incredibly strong magnetic fields, about a thousand times stronger than that of a normal neutron star, and they have incredibly fast rotation. Magnetars are also known to shine bright in X-rays, but scientists have been unable to test any theories because they are unable to reproduce the strong magnetic properties in a lab.

We have found about 15 magnetars. One type known as SGR, or soft gamma repeaters, sporadically release bursts of short gamma rays and hard x-rays. The other type is known as AXPs, or anomalous X-ray pulsars, pulse periodically with x-rays. While once thought to be two different objects we now know they share many of the same properties. Magnetars strong magnetic fields are thought to be so strong that they can twist the crust of the star. This twist would produce currents in the form of a cloud of electrons flowing around the star. Its thought that these currents interact with radiation coming from the stellar surface to produce x-rays.

Using data from XMM Newton and Integral astronomers have looked at all known magnetars and actually found evidence of these electron clouds. They found that the electron density around these magnetars is about a thousand times stronger than for a normal pulsar. They were also able to measure the velocity of the electron clouds going around the magnetars.

This data has provided scientists the chance to find a link between an observed phenomenon and the physical process behind it. The team is now working to try and develop more detailed models of what exactly is happening on the surface of the magnetar. These objects are very bizarre and are an example of a celestial object with extreme conditions. It is something that challenges current theories and provides us with examples of new and interesting phenomenon that we could never observe on earth. Studying the is an exciting and interesting challenge for astronomers and physicists.

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