The Young Astronomers
From the monthly archives: November 2011
ESO astronomers using the Atacama Pathfinder Experiment telescope (mercifully reduced to APEX), have snapped a stunning new image of the Carina nebula.
The Carina Nebula as seen by APEX Credit: ESO/APEX/T. Preibisch et al. (Submillimetre); N. Smith, University of Minnesota/NOAO/AURA/NSF (Optical)
The LABOCA (Large APEX Bolometer Camera) captured the nebula in submillimetre light - better known as microwaves (through the true range of microwaves extends over a wider range of wavelengths) – which is displayed as an orange overlay to an optical image captured by the Curtis Schmidt telescope at the Cerro Tololo Interamerican Observatory in Chile.
This wavelength (specifically 870 micrometers) picks out the feeble glow from cool gas and dust – the material from which stars are formed. The data is revealing more of the secrets of star formation, an area that has stubbornly held its own against the prying eyes of astronomers.
The nebula itself contains about 25,000 times the mass of the sun in the form of stars with another 140,000 solar masses in the form of these cool dust clouds.
The Carina nebula is located about 7500 light years away in the direction of, you guessed it, Carina – The Keel.
Despite it being much more distant that the Orion nebula, as viewed in the sky from Earth the two appear similar in size as the Carina nebula is several times larger, compensating for the increased distance. In the same way the moon and the sun have the same apparent size as viewed from Earth.
You can read more here
Black holes have always been some of the most enigmatic objects in the universe since their first mention in modern physics in the early days of General Relativity.
The models of Black Holes all predict that when it is ‘feeding’ – that is absorbing matter from the surrounding space – material will spiral round its equator in an accretion disk.
The Hubble Space Telescope has recently collected precise data on the accretion disk of a black hole at the centre of an extremely energetic galaxy far across the universe – a Quasar (QSO).
HE 1104-1805 Credit: NASA, ESA and J.A. Muñoz (University of Valencia)
The faint smudge in the centre of the image is a galaxy that sits between Earth and the QSO. The light from the QSO is primarily produced by material in the accretion disk of its central supermassive black hole – such black holes can be several million times the mass of the sun but could fit inside our Solar System. The mass of this foreground galaxy causes the light from the QSO behind to lens - magnifying and distorting the image. Such gravitational lensing can produce multiple images as in this case two bright images of the QSO have been generated some distance apart – the two bright starlike objects in the image.
It is by carefully observing how these images vary overtime and comparing the data from each image, that fine detail of the central accretion disk has been collected.
The variation is due to the lensing of the QSO altering slightly as the foreground galaxy moves relative to Earth and the QSO. Specifically a star in the foreground galaxy can move across the accretion disk image and alter the light that is beamed towards Hubble over the course of several days. This manifests itself in the data as slight colour changes in the light from the QSO being detected. As colour is related to temperature, and the star crosses the entire accretion disk astronomers have been able to study the temperature, colour and scale of the accretion disk to an accuracy comparable to studying individual grains of sand on the moon from the surface of the Earth.
The measurements show that the disk is between 4 and 11 light days across – that is a range of between 100 billion and 300 billion kilometres - whilst in normal everyday measurements this uncertainty seems ridiculously large we must remember that the QSO is billions of light years away and so the accuracy is phenomenally high. What’s more the technique shows lots of room for refinements in the future and so it is inevitable that the accuracy of such measurements will improve as well.
You can see a video and explanation of how the data was collected here
and can read more about the discovery here
The first stars coalesced from the primordial hydrogen and helium synthesised in the first few minutes after the birth of our Universe just a few hundred million years after the Universe burst into existence.
All stars are born when a cool clump of hydrogen and helium gas condenses under its own gravity. As it does so the central regions of the clump heat up eventually to the millions of Kelvin required for nuclear fusion to occur. Once this critical point is reached the star fuses hydrogen to helium and begins to shine brightly. Stars grow by absorbing more material onto their surfaces from the surrounding nebula and hence they grow in mass. Eventually their increased energy output disperses the surrounding cocoon to the point where the star’s gravity is insufficient to attract anymore material and the star ceases growing.
In the current era of the universe this process is aided by heavier elements such as carbon and oxygen, these aid the cooling of the surrounding gas which allows for it to fall onto the star – if the gas was too hot it would have too much energy and escape off into space. The first generation of stars did not have any heavy elements to aid their formation as they had yet to be produced as such elements are only produced in the final stages of a massive star’s life. Thus they would have had a much shorter time to absorb matter from their surroundings before it escaped their clutches.
This may suggest that the first stars should be much smaller than those currently populating the Universe, though this is not the case. As the density of material in the early Universe would have been much higher they would have more material with their grasp to begin with and so all predictions produce stars that are much more massive than the current average – which is only a fraction of the mass of Sol.
It had previously been though that the first generation of stars would have been the most massive of all, with material equating to several hundred solar masses, similar to the most massive stars currently known – such as those within the Large Magelanic Cloud’s R136 open cluster. This new study casts doubt on this view on the first stellar newborns.
Simulations conducted at NASA’s Jet Propulsion Laboratory in California by a team of researchers lead by Takashi Hosokawa have indicated that such first generation stars would be ‘only’ a few tens of times a massive as Sol.
Whilst they are still significantly more massive than the vast majority of stars in today’s Universe this discovery removes a significant problem for Cosmology.
If the first generation of stars were as massive as previously predicted they would have produced a particular chemical signature of elements during their lives that would be detectably different from those of conventional mass stars – the higher mass equates to a higher core temperature – combine this with the unique blend of elements available to produce the first stars (~75 Hydrogen, ~25% Helium with tiny traces of Lithium, Deuterium and Beryllium) there should be a ‘bar code’ of the particular abundances of various heavy elements (as fusion reaction rates are easily altered by starting conditions) in the oldest of today’s stars that could only be attributed to the existence of such monstrous precursor stars. As of yet this has not been detected.
Whilst this proves to be a problem for the old model of 1st generation stars, the revised masses produced by this study removes it all together – with no such high mass stars the elemental fingerprint would have never have existed easily explaining the lack of detection – there is nothing to detect!
This fingerprint of elements would have been generated by the stars ending their lives as a yet undetected variety of Supernova. The new mass predictions would cause the 1st stars to detonate in a manner akin to their more recent brethren, allowing for the lack of unusual supernova detections to be explained satisfactorily as well.
As we have seen the masses of the 1st stars are now thought to be much lower than first expected but why would they be less massive than previously predicted?
The answer lies in the surroundings of the stars. The new simulations indicate that the region directly around a forming first generation star was heated to temperatures of up to 50,000 Kelvin or 8 ½ times the surface temperature of Sol. This extremely high temperature would have allowed the surrounding gas to disperse much more quickly than previously thought, thus the growing star has less time to absorb material leading to a lower final mass.
The region around one of the first stars as it was forming Image credit: NASA/JPL-Caltech/Kyoto Univ.
The simulation produced a star of just 43 solar masses, a far call from the 1000 solar mass superstars of early predictions (though I should add as predictions became more advanced the mass of the 1st generational stars has been falling continually and this is the latest study in a long line to reduce the value further).
You can read more here
We are all familiar with the general layout of our Solar System, four inner rocky planets and four outer gas giants with an asteroid belt separating the two groups.
The Solar System that we now inhabit is, and has been stable for a considerable period of time (for at least a few billion years) though a new study has concluded that the early Solar System may have had at least one other inhabitant.
It has long been known that the early Solar System was a very changeable and violent region of space. It would have taken many millions of years for the gravitational tugs and pulls of the developing planets to allow our current planets to settle into stable orbits. During this time, many planetesimals (small bodies larger than asteroids that over time collided to form the planets that we see today via accretion) would have had their orbits destabilised. Some would have crashed into the sun or the developing gas giants or even, in at least a few cases but perhaps quite commonly, they could be thrown out of the Solar System entirely. However, what about the planets we know today? Could they have suffered similar events?
Uranus for one carries a scar of such an occurrence. Its axial tilt is so extreme it orbits the sun ‘on its back’ at nearly 90o to the plane of the ecliptic. This can be explained if a planetoid roughly the mass of Mars collided with Uranus in the early Solar System, so clearly such collisions can and did occur, but what about orbital disruptions?
New simulations conducted at the Southwest Research Institute inColoradoby David Nesvorny may provide an answer.
He conducted over 6000 simulations of this phase of the Solar System’s history with various different configurations of planets and orbits to try to determine which was most likely to produce a Solar System resembling the one we inhabit today. The results are quite surprising.
Using a four gas giant system at the start of the simulation, only 2.5% of simulations will produce a system with four at the end point, with the vast majority loosing at least one giant to gravitational distortions that would eject such it from the Solar System like is possible with the smaller planetesimals. Such a small percentage of ‘successful’ simulations indicates that it is highly unlikely for our Solar System to have a four gas giant starting scenario. Such systems appear too unstable for all planets to remain undisturbed as they develop.
However, other versions of the simulations produce much more favorable results. A situation where the Solar System formed with five giants is roughly 10 times as likely to have an end point similar to the current layout of our cosmic backyard.
This world would have been similar to the icy giants Uranus and Neptune and comparable to them in terms of mass. During the violent settling period of the early Solar System it would have suffered several gravitational encounters with other bodies leading to a final encounter with Jupiter around 600 million years after the birth of the Solar System that threw it into interstellar space never to return.
An artist's Impression of what the ejected planet may have looked like Credit: Southwest Research Institute
Such a scenario may seem outlandish to some, though it does carry weight. The recent detection of many times the expected number of free planets drifting the stars indicates that events such as this may indeed be commonplace in the Universe as a whole.
Though this research does pose more questions. If gas giants seem to be rather easily ejected in the early days of Solar Systems’, what about smaller earthlike worlds, and those similar to Mars?
Generally these are ignored in most research as their gravitational influences a much smaller than those of the much more massive gas giants, and thus have much smaller effects of Solar System evolution. However, research is now shifting to how the effect and are effected by the changing nature of forming Solar Systems.
David Nesvorny admits that he is as of yet not fully convinced that this lost world actually existed and further research will be needed to fully understand the development of the early Solar System though we are definitely getting closer.
You can read more here.
NASA’s Chandra Space Telescope has acquired a stunning image of 30 Doradus better known as the Tarantula Nebula.
Chandra's new view of the Tarantula Nebula Credit: X-ray: NASA/CXC/PSU/L.Townsley et al.; Infrared: NASA/JPL/PSU/L.Townsley et al.
It is one of the largest star forming regions close to the Milky Way and is the most recognisable feature of the Milky Way’s satellite galaxy the Large Magellanic Cloud.
Located just 160,000 light years away it is a cosmic stone’s through from the Earth and spanning a massive 1100 light years it is an excellent place to study star formation and evolution.
The red regions of this image show warm dust detected in the infra-red region of the electromagnetic spectrum by the Spitzer Space Telescope. It shows that the dust and gas have been blown into huge bubbles by the hot and bright stars within the nebula, 2400 of which can be found in the central R136 cluster that is just a few million years old. The data from Chandra is shown in blue and shows the presence of ionised hydrogen (HII) – hydrogen gas that has been heated to extreme temperatures, so much so that it is emitting highly energetic X-rays.
These observations may help to settle a debate as to what is causing the Tarantula nebula to expand. One group of researchers suggests that it is the hot X-ray emitting gas and dust which is causing the whole structure to billow outwards. Whilst another study indicates that it is the energy and particle winds from the hot young stars that are driving this expansion. The answer to this debate could be found in the near future as perhaps the new data will suggest that one of the two ideas is accurate or perhaps it is a combination of both.
You can read more about this image here
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