Asteroids are more than just boring rocks
Asteroids that are very porous and smaller than about 10 kilometer can get spun up by the Sun. This spin is caused by regular Sun light and can be compared to propellers in the wind. At a certain point the asteroids spins so fast that it splits into two pieces. These pieces then form a so-called binary asteroid where both rocks are orbiting around each other, comparable to lots of stars that orbit other stars. During their rotation around each other, the smaller of the two takes energy away from the larger one. This means that the larger one starts to rotate slower and the smaller one uses this energy to move further away from his larger companion. If the smaller rock is less than 60 percent of the size of its companion it can eventually even escape from his big brother. This results in two asteroids orbiting solely through the solar system and perhaps even starting the whole cycle over again.A new study has led to this discovery. Astronomers tracked the movement of various pairs of asteroids for a long period. Calculating back, they discovered that the pairs often originated from the same point. This implies that the two rocks started off as one. Also, in every situation when the two asteroids started off from the same point, the smaller one was less than 60 percent the size of the larger one.
Asteroid research is actually a hot topic in astronomy recently. NASA has plans to land men on an asteroid as a build up for a future Mars mission. Also, an asteroid impact may be the source of life here on Earth. At least they are believed the set back the evolutionary clock when one impacted on Earth, destroying almost all (dinosaur) life. Therefore these results are a good step in the right direction in understanding what they are made of and how they evolve.
Source University of Colorado
Image credit: ESO/L. Calcada
Is our solar system 2 million years older?
Aging our solar systems happens by examining meteorites that have crashed here on Earth. Previous studies have shown that the age is quite accurately known. Astronomers are quite certain that the solar system is somewhere around 4.567 billion years old. However, especially the last number (the million years) is undergoing some debate. Recent measurements on a meteorite which was found in the Sahara Desert revealed the solar system to be about 1 to 2 million years older than this.
Where does this discrepancy come from? Well, there are different methods to measure the age, but all methods use meteorites. Each meteor consists of lots of different elements, some of which are stable and some of which change due to radioactive decay. The speed at which an element decays is quite accurately known. Now if you can determine how much of the elements have decayed, relative to another element, then you can calculate back how long this element has been decaying. The standard decay method has been the lead-decay method. However, the last few years some suggestions came that this method was not so precise after all. Using a method that examined magnesium and aluminum gave a age a bit older than the 'lead' age. The recent studies used the lead method again, but this time the age was comparable to that of the magnesium/aluminum method, thereby solving the debate. One question left answered, though, is why the previous lead measurement on a different meteor gave a younger age.
The new meteorite also revealed a higher fraction of so-called iron-60. This is just like regular iron, but with a few extra neutrons. This kind of iron is only produced in supernova explosions. In order for this amount of iron-60 to be present in the cloud from which our solar system formed, one or more supernova explosions had to take place in the cloud's vicinity. A few years ago it was still widely believed that the Sun formed from a cloud, surrounded only by some other Sun-like stars, but in relative isolation. Now, using these results and some others, it appears as if the solar cloud had some very fierce and massive brothers surrounding him.
Source: Nature
Image credit: NASA top and bottom
Crowded planetary system found
Today a big step is taken in the research on planets orbiting a star other than our Sun. While most systems discovered so far mainly consisted of just one planet and some of two or three, the new discovered system contains at least 5 and possible even 7 planets. This makes the system similar to our Solar system in term of the number of planets.
The planets are found around a Sun-like star named HD 10180. Using the HARPS spectrograph attached to the European Southern Observatory's 3.6 meter telescope in La Sille, Chile, tiny wobbles in the motion of the star were detected. Due to the attraction of the different planets on the star, the star has tiny back and forth motion which can be measured. The five strongest signals come from planets comparable to Neptune. These planets orbit their host star in 6 to 600 days. This means that the orbits of the planets are all smaller than that of Mars, so the system is much more crowded in its inner region than our Solar system. One of the two other possible planets is a Saturn-like planet which orbits around the star in about 6 years. Finally, the last planet could be the lowest-mass planet ever discovered with a mass of about 1.4 times that of the Earth. It is in a very close orbit around its host star. A 'year' for that planets would only last 1.18 Earth-days.
These last two planets are not confirmed yet, because their signals are very hard to detect from the tiny wobbles that the star makes. The motion the Earth-like planet causes on the star is only about 3km/hour, which is very hard to measure.
The system is very unique in many aspects. Next to the presence of at least 5 planets, no giant gas planet has been found. Also, the sizes of the planets' orbits follow a regular pattern, just like the planets in our Solar system. This discovery takes the research on exoplanets to a completely different level. Studying multi-planetary systems is going to be main event for astronomers in the coming years. The dynamics in such a system are still poorly understood, but this discovery is a great step in the right direction.
Source: ESO
Image credit: ESO top and bottom
Movie credit: ESO
A new way of studying anti-gravity
Anti-gravity is basically just a different name for the mysterious dark energy that makes up about 72 percent of our universe. Where gravity pulls matter toward each other, dark energy appears to push matter away from each other. Scientists still have no idea what this 'energy' really is, but a new method using giant clusters of galaxies can help to better map this anti-gravity.
Not only is dark energy mysterious because it works as some sort of anti-gravity, it also gets stronger the further matter gets apart. In very crowded regions gravity beats dark energy and the matter stays together. However, when matter moves further apart, dark energy is on the winning hand. If you look at different clusters of galaxies, these are too far apart for gravity to move them together. Therefore, in general these clusters are moving further and further apart due to the dark energy. Scientist believe that the separating is going faster and faster.The new method to study dark energy actually uses gravity. The scientists studied a cluster of galaxies, named Abel 1689. Due to the enormous amount of galaxies within the cluster, there is an extremely strong gravitational pull for matter toward this cluster. The pull is even strong enough to bend light toward the cluster. This fact causes galaxies that are located behind the cluster to have their lights distorted. They appear as various light arcs around the cluster as can be seen in the image on the right.
The scientist used the various arcs in order to figure out how light from the more distant galaxies got bend by the cluster. This bending depends on the nature of dark energy. Using this method astronomers should be able to get a better view on how dark energy works. The scientists managed to create a general method which can be used for different kinds of these cosmic lenses. Perhaps the future will shed some more light onto this darkness.
Source: HubbleSite
Image credit: HubbleSite top and bottom
Stellar birthplaces change in an aging universe
The galaxy cluster that has been observed is named J02182-05102 and it is formed only 4 billion years after the big bang. Studying this cluster means that astronomers are essentially looking 10 billion years back in time, making it possible to observe where star formation was taking place in these early clusters. And the results seem to be somewhat surprising.It is a hallmark in galaxy evolution that the closer you get to a galactic cluster's center, the less star formation is taking place. The new observations imply that this was not the case in the early days. Apparently there was some vigorous star formation in the center, before it died out. One possible explanation given by the scientists is that the centers of clusters are much more populated than the outskirts. Probably a lot of interactions took place between all the galaxies there, triggering star formation.
J02182-05102 is about to shift its star formation to its outskirts. Most stars found in nearby cluster centers are at least 8 to 10 billion years old. Since the cluster is observed about 10 billion years ago, this means that soon it will turn into a graveyard in its center. For future research it would be interesting to get a full overview of cluster evolution. Now, a cluster has been observed where stars are still being formed in its center, but a bit older cluster would be interesting as well. There, astronomers can actually observe the 'shift' taking place.
Source: Texas A&M University
Image credit: NASA/ JPL
What happens to massive stars?
2010-08-20 20:20:38
Yesterday, we reported about exotic, cosmic objects, the so-called neutron stars. These stars are the remnant of stars, about 10 to 20 times the mass of the Sun, that died in a supernova explosion. According to the leading theories, a star which is initially more massive than 20 times the mass of the Sun, will collapse all the way into a black hole. It is even too massive for a dense neutron star to form. However, recent observations on the closest super star cluster Westerlund 1 revealed a neutron star which must have had a progenitor about twice as massive than this.
Westerlund 1 is a cluster of stars about 16.000 light-years away. It is known to host hundreds of very massive stars, some a million times brighter than the Sun or a thousand times larger. Another thing that is known about star clusters is that all stars are more or less formed at the same time. Of course not exactly the same time. It takes about 10.000 to 100.000 years, but this is still negligible compared to the ages of stars which are over millions of years.
Yesterday, we reported about exotic, cosmic objects, the so-called neutron stars. These stars are the remnant of stars, about 10 to 20 times the mass of the Sun, that died in a supernova explosion. According to the leading theories, a star which is initially more massive than 20 times the mass of the Sun, will collapse all the way into a black hole. It is even too massive for a dense neutron star to form. However, recent observations on the closest super star cluster Westerlund 1 revealed a neutron star which must have had a progenitor about twice as massive than this.
Westerlund 1 is a cluster of stars about 16.000 light-years away. It is known to host hundreds of very massive stars, some a million times brighter than the Sun or a thousand times larger. Another thing that is known about star clusters is that all stars are more or less formed at the same time. Of course not exactly the same time. It takes about 10.000 to 100.000 years, but this is still negligible compared to the ages of stars which are over millions of years.The lifetime of a star is solely determined by its mass. The more massive a star, the shorter it lives. This means that if a star has died in a supernova explosion and formed a neutron star, it must have been more massive than its brothers and sisters which are still alive in the cluster. Observations on the one hand show that there are stars with masses over 40 times that of the Sun. On the other hand, a so-called magnetar, a neutron star with a very strong magnetic field, has been discovered. This implies that the star must have been more massive than 40 times the mass of the Sun before it died and formed a neutron star.
One of the leading theories on how a magnetar is formed, states that the progenitor needs a companion during its main life. The magnetar progenitor then loses a lot of mass to its companion, leaving a less massive star. This star then dies and forms a magnetar. This new discovery can help astronomers understand how important mass loss to companions is in a star's life and how often it takes place.
Just to end with an imaginary note. If we lived within Westerlund 1, the night sky would be filled with full moons. It is a shame we don't, or not?
Source: ESO
All humans stuffed in sugar cube
2010-08-19 20:34:58
This title may seem very odd, but it indicates the extotic objects astronomers observe when searching through the universe. There actually exist objects that are so dense, that if you would take a sugar cube of it, it would be as heavy as the combined mass of all humans on Earth. These objects are so-called neutron stars and recent observations can shed some more light on what these objects are made of.
A neutron star is what is left after a star of about 10 to 20 times the mass of the Sun dies in a supernova explosion. The remaining neutron star has a mass just over that of the Sun, but is only 10-15 kilometers big. Using the Rossi X-ray Timing Explorer astronomers observed one of these neutron stars, named J1749.
This title may seem very odd, but it indicates the extotic objects astronomers observe when searching through the universe. There actually exist objects that are so dense, that if you would take a sugar cube of it, it would be as heavy as the combined mass of all humans on Earth. These objects are so-called neutron stars and recent observations can shed some more light on what these objects are made of.A neutron star is what is left after a star of about 10 to 20 times the mass of the Sun dies in a supernova explosion. The remaining neutron star has a mass just over that of the Sun, but is only 10-15 kilometers big. Using the Rossi X-ray Timing Explorer astronomers observed one of these neutron stars, named J1749.The star was discovered because it pulsates. It has a companion star flying around it with a mass just under that of the Sun. This companion has gas flowing toward the neutron star. The magnetic field of the neutron star diverts the gas toward its poles. Here, a lot of gas falls directly onto the neutron star which causes it to emit x-rays. Because the neutron star is rotating around its own axis about 518 times per second, astronomers observe the x-rays in very short pulses.
This pulsating information is very important to astronomers. They need this in order to estimate the mass of the neutron star. Unfortunately, they do not have all the required information yet to determine its mass or its size. For that, more detailed observations of the orbit of the companion star are needed. However, in the foreseeable future this information should be available. This could help astronomers understand what these objects are made of and what the hell is going on there.
Source: NASA
Solar cycle problem solved?
The important aspect of the solution is so-called plasma flows. A plasma basically is a hot gas, but it is so hot that the atoms have lost their electrons. Normally, electrons swirl around the core of an atom, but when the temperature gets too high, the electrons move so fast that they can escape from their core. At this point you are left with a hot gas of atomic cores and electrons, this is a so-called plasma. During a solar cycle this plasma flows from the equator towards the poles. At the poles the plasma flows inward and then in the Solar interior, it moves back to the equator. The scientist think that the closer the plasma gets to the poles, the longer a cycle lasts. The laws of physics say that when the cycle gets closer to the poles, i.e. it is longer, the plasma moves slower. This explains why the cycle then lasts longer.
The scientist already predicted back in 2004 that this cycle would last longer and it seems they were right. Apparently, every once in a while the plasma flow reaches closer to the poles. Therefore astronomers should try to monitor the way the solar plasma behaves and thereby improve their knowledge on this behavior. Perhaps then, astronomers are able to fully understand what is going during a Solar cycle and why some last longer than others.
Source: UCAR
Image credit: NASA and UCAR